JOURNALOF GEOPHYSICALRESEARCH,VOL. 101,NO. B3,PAGES6021-6036,
MARCH 10,1996
Acomparison
of historicalandpaleoseismicity
in a newlyformed
faultzoneand a maturefault zone,NorthCanterbury,New
Zealand
Hugh
Cowan
1and
Andrew
Nicol
2
Department
ofGeology,
University
of Canterbury,
Christchurch,
NewZealand
PhillipTonkin
Department
of SoilScience,
Lincoln
University,
Lincoln,
NewZealand
Abstract.The timingof largeHoloceneprehistoric
earthquakes
is determined
by dated
surface
rupturesandlandslides
at theedgeof theAustralia-Pacific
plateboundary
zonein
NorthCanterb•, New Zealand.Collectively,thesedataindicatetwo large(M > 7)
earthquakes
duringthe last circa2500 years,withina newlyformedzoneof hybridstrikeslipandthrustfaultinghereindescribed
asthePorter'sPass-to-Amberley
FaultZone
(PPAFZ).Two earliereventsduringtheHolocenearealsorecognized,
butthedatapriorto
2500yearsarepresumedto be incomplete.A returnperiodof 1300-2000yearsbetween
largeearthquakes
in the PPAFZ is consistent
with a late Ho!ocenesliprateof 3-4 mm/yr if
eachdisplacement
is in therange4-8 m. Historicalseismicityin thePPAFZ ischaracterized
byfrequentsmall andmoderatemagnitudeearthquakes
anda seismicityratethatis
identical
to a region surroundingthe stmcturallymatureHope fault of the Marlborough
FaultSystemfarthernorth.This is despitean order-of-magnitude
differencein sliprate
between
the respectivefault zonesandconsiderable
dffœerences
in therecurrence
rateof
largeearthquakes.
The magnitude-frequency
distribution
in theHopefaultregionis in
accord
with the characteristic
earthquake
model,whereastherateof largeearthquakes
in
thePPAFZis approximated
(but overpredicted)by the Gutenberg-Richter
model.The
comparison
of thesetwo œault
zonesdemonstrates
theimportance
of the structural
maturity
ofthefault zone in relationto seismicityratesinferredfrom recent,historical,and
palcoseismic
data.
earthquakes
in thePorter'sPass-to-Amberley
FaultZone(PPAFZ),
a regionof newly formed strike-slipfaultingthat definesthe
Earthquake
hazardassessment
traditionally
incorporates
the deformationfront at the edge of the Australia-Pacific
plate
analysis
of historicandcontemporary
seismicity,
supplementedboundaryzonein northeastern
SouthIsland.
where
possible
bygeological
information
aboutaverage
sliprates,
North Canterburystraddlesthe edgeof the Australia-Pacific
rupture
lengths
andslipperevent.Thetimingandmagnitude
of plate boundaryzone betweenthe HikurangiTrough and the
prehistoric
earthquakes
resulting
in surface
rupture
aredeterminedSouthernAlps (inset,Figurel a). Dextralstrike-slipfaultsof the
Introduction
bydating
features
offsetbythefaultandbyexamining
thegeometry Marlborough
FaultSystem(MFS), farthernorth,transfer
oblique
ofthefaulttrace.However,thesedataaloneoftendo notprovide platemotionbetweentheAlpinefaultandtheHikurangisubduction
sufficient
informationto characterizelarge palcoseismic
events zone. These faults have smaller cumulative offsets toward the
[e.g.Ward,1994].
southeastbut higher slip rates that reflecta southwardrelative
InNorthCanterbury,
NewZealand,
wehavesupplemented
data migrationof thelocusof deformation
across
theregionduringthe
fromfaulttraceswith datafrom landslides
distributed
throughout lateQuaternary[e.g.,YeatsandBerryman,1987;H. Andersonet al.,
theeastern
foothillsof the Southern
Alps.Thesedataareused 1993].The mostsoutherly
elementof theMFS is the Hopefault
collective!y
to assess
the late Holocene
chronology
of large (Figurel a). Sixty kilometerssouthof the Hope fault, a zoneof
disseminated
shearis evolvingalonga similartrend(Figurela)
[Rynnand Scholz, 1978; Carter and Carter, !982; t!emer and
--l Now
atNorwegian
Seismic
Array,
Kjeller,
Norway.
1985].Elements
of thiszonecomprise
anastomosing
2Now
atFault
Analysis
Group,
Departmeat
ofEarth
Sciences,
Univer-Bradshaw,
sity
ofLiverpool,
Liverpool,
England.
strike-slipand thrustfaults that extend east-northeast
from the
Copyright
! 996bytheAmerican
Geophysical
Union.
Southern
Alpsalongthenorthern
marginof theCanterbury
Plains
andpassinto a fold andthrustbeltnearthe townof AmberIcy
Paper
Number
95JB01588.
0148-0227/96/95JB.0!
588$05.00
Fault Zone (PPAFZ)to describethe strikeand approximate
(Figures
la and2). We usethenamePorter's
Pass-to-Amber!ey
6021
6022
COWANET AL.:PALEOSEISMICITY
IN A NEWLYFORMEDFAULTZONE
!
i
!
i,
•
I
I
/./"
J
1170E
Figure la. Major structuralelementsof thenortheastern
SouthIsland,andthe locationsandyearsof selectedhistorical earthquakes.The onshorestructureis modifiedfrom Gregg[1964], Cowan[1992] and unpublisheddataof the
Active TectonicsResearchGroup,Universityof Canterbury.
Offshorestructureis simplifiedfrom Barnes [1994].
The numbered
rectangles
delineatetwo regionsselectedfor analysisof historicalseismicity.AbbreviationsareMFS,
MarlboroughFault System;HPF, Hope fault;HRS, HopeRiver segment;KPF, Kakapofault; PPAFZ, Porter'sPassto-AmberleyFaultZone;PBF, PegasusBay fault;PP,Porter'sPass;and AY, AmberIcy.Inset showslocationof Figures la and lb in relationto the Alpine Fault (Air) and Hikurangi Trough (HT), the main elementsof the New
Zealandplateboundary.The arrowindicatesthe directionand magnitude(42 mm/yr) of the plate motaonvector
[DeMets et al., 1990].
geographic
end-points
of thezone,whichhasonlyrecentlybeen
HistoricSeismicity
of the North CanterburyRegion
mappedcomprehensively
[Cowan,1992].
The region betweenthe Hope fault and PPAFZ is one of
Earthquakes
withinandadjoiningtheNorthCanterbury
region
transition
fromsubduction
tocollision[Reyners
andCowan,1993], duringtheperiod1942-1994areshownin Figurelb, withthose
wherethegeological
structure
of theuppercrustis dominated
by greaterthanmagnitude
6.5 since1888indicated
onFigurela. The
northeast
strikingreverse
andthrustfaultsthatdipsoutheast
andare focaldepths
formostevents
in thecatalogue
areuncertain
duetothe
closelyassociated
withgrowingfolds[Yousif,1987;Nicolet al., widespacing
of national
networkseismographs
(typically
>50kin),
1994]. This region has accommodated
~12-15% northwest- butlocalstudies
of microseismicity,
recorded
onportable,
smallsoutheast
shortening
duringthePleistocene,
andratesofshorteningapertureseismograph
arrays,haveindicatedthatmostearthquakes
doseto thePacificcoastareabout1%/100kyr [Nicoletal., 1994]. inthisregionarerestricted
totheupper10-15kmofthecrust
[Rynn
Detailed
studies
alongtheedgeof theplateboundary
zoneinNorth andScholz,1978;Cowan,1992;Reyners
andCowan,1993].
Canterbury
indicate
thatdeformation
probably
commenced
within
TheHopeRiversegment
of theHopefault(Figurela) andan
thelast0.5-1m.y.,disrupting
a volume
of crustnotsignificantlyadjacent
splay(Kakapo
fault)haveeachruptured
during
historic
deformed
sincetheCretaceous
[Cowan,1992;Nicoletal., 1994]. earthquakes
of magnitude
M---7.3andM~7.0,respectively
[Eiby,
Thepurposeof thispaperis to evaluatethelateHolocenerecord 1968;Cowan,1991;Yang,1991, 1992].Two moreevents
of
of large earthquakesin the PPAFZ, in order to understandthe magnitude
6.5.-6.9haveoccurred
in the eastern
partof North
frequency-magnitude
distribution
ofearthquakes
inanewlyformed Canterbury,
in 1901and1922,andanother
eventofM•,6.7occurred
faultzone.We compare
historical
andpalcoseismic
datafromthe in June 1994, to the west of the PPAFZ. The 1994 earthquake
PPAFZwithdatafromtheadjacent
structurally
mature
Hopefault occurredin the upper crust, and the 1901 and 1922 eventsare
zone, and use thesedata to evaluate differencesin fault behavior presumed
tohavealsobeenshallow,
based
onrelatively
limited
felt
betweenstmcturallymatureandnewlyformedfaultzones.
areas[McKay,1902;Skey,1925].Manymorefaultsin North
COWAN
ETAL.-PALEOSEISMI••IN A NEWLYFORMED
FAULT
ZONE
6023
o
ß
O0 o
Figurelb. ShaLlow
seismicity
(<40km)fortheregion
of Figurela during
theperiod1942-1994
(May30) [New
Zealand
Seismological
Observatory,
1994].Symbols
arescaled
withmagnitude,
andthecatalogue
iscomplete
above
M 3.0since1988;M 4.0since1964;M 5.0since
1942.Thedense
clusters
of seismicity,
northof theHopefaultand
westof thePPAFZ,areassociated
withearthquakes
ofMw5.9andMw6.7,in 1990and1994,respectively
[Andersonetal.,1993;
,•rnad6ttir
etal.,inpress].
Canterbury
exhibitevidence
of Holocene
displacement
[Gregg, Oligocene
andlowerMiocenetimestone
bedsacross
theMount
1964],
andsince1964,theNewZealand
national
seismograph
Greyblock
andvector
analysis
ofslipacross
Mount
Oxford
(Figure
network
haslocatedfrequentearthquakes
of smallto moderate 2) (H.A. Cowanet al.,manuscript
in preparation
1995).
magnitude
(M<5.4)alongthePPAFZ,makingthisoneof thebetter
ThePorter's
Passfattitformstheprincipalwestern
element
of
defined
surface
faultzones
in NewZealand
[Reyners,
1989].Data thePPAFZandis associated
withHolocene
offsets
nearPorter's
from
theinstrumental
catalogue
areutilized
laterin thispaper
for 'Pass
[Speight,
1938;Wellman,
1953;Berryman,
1979;Coyle,
1988;
comparisons
of recurrence
parmetersforlargeearthquakes
within Knuepfer,1992].New dataonlateHolocenefaultingfromthisarea
and
between
theHopefaultandPPAF'Z
regions.
are presentedhere. Farthereast,the Porter'sPassfault bifurcates
aroundMountOxford,andsplaysextendnortheast
andeastto Lees
ValleyandthenorthernCanterbury
Plains,respectively
(Figure2).
A surfacetracein LeesValleyis associated
with scarpsup to 6 m
ThePPAF-Z
extends
east-northeast
fromtheSouthern
Alpsand highon Holocenealluvialfans[Gregg,1964;Garlick, 1992],and
passes
into a fold and thrustbelt near the townof Amberleyand along the southernflank of the Ashley Range,major zonesof
(Figure2). The east
offshore
(Figuresla and2) [Barnes,
1994;Nicolet al., 1994]. crushedrockdivergeto theeastandsoutheast
striking
zone
extends
into
a
region
dominated
by
thrustfaultingand
Principal
elements
of thePPAFZbound
thenorthern
margin
of the
strikingzone
Canterbury
Plainswherethefoothills
of theSouthern
Alpsriseto foldingcentredon MountGrey,whereasthesoutheast
2000
m. ThePPAF'Z
is defined
by zones
of crushed
Torlessepassesbeneaththe CanterburyPlainsto the Cust anticlineand
Bayfaultzone
greywacke
that strike east and northeast,at a tugh angleto the Ashleyfaultandmayextendoffshoreto thePegasus
farther
east
[Kirkaldy
and
Thomas,
1963;
Herzer
and
Bradshaw,
regional
NW-SEgrainofMesozoic
deformation
[Gregg,
1964],and
1985;Barnes,1994](Figurela). DataonlateHolocenefaultingand
locally
cutthrough
thelateCretaceous-Cenozoic
cover
sequence,
in theeastern
partof thePPAFZhavebeencollected
from
disrupting
latePleistocene
andHolocene
landforms.
A totaloffset landslides
of<2kmacross
thePPAFZisinferred
fromthestrikeseparation
of Custanticline,Ashleyfault,andMount Grey.
Porter's
Pass-to-Amberley
FaultZone
COWAN
ETAL.:PALEOSEIS•CITY
IN A NEWLYFORMED
FAULTZONE
6024
Lees
Valley
'""
I
Oxford I
Ashley
fault'
t
...
I
I
Fig.4
L
LANDSLIDES
FOLDS
FAULTS
inferred
strike-slip
thrust
surface
•--
anticline
•
•
trace
syncline
•
xxxxxx
Dated
I
Canterbury Plains
Undated
© o.•--•o-•
.•o%3
© o-oo_1
___•_ _ i.i:•urban
aroa
•........ Basement
I
I Cover
sediments
highway ß 2195olovation(m)
N
1Okra
I
I
i
Figure 2. Structuralelementsof the Porter'sPass-to-Amberley
Fault Zone (PPAFZ) in North Canterbury,
New
Zealand,showingthe locationsof main faults,folds,andprehistoric
landslides.
Faultsthat are depictedwithout
sense-of-movement
indicators
represent
mapped
zonesof crushed
rock.Numbered
landslides
correspond
to datain
Table2 andFigure6. Thindashed
linesdenotethemargins
of activefoldson theCanterbury
Plains.Abbreviations
areKA, Kowai anticline;CA, Custanticline;MO, MountOxford,andMG, Mount Grey. The locationsof Figures3,
4, and 5 are indicated.
Holocene Faulting in the PPAFZ
Porter's
Pass Fault
heightof 150m on thenorthern
flankof Custanticline.
A steep
north-to-south
gradient
of Bouguer
gravityanomalies
across
the
anticlinehas beenattributedto the presence
of a faultwith
significant
throw[Kirkaldy
andThomas,
1963].Weinferthat
this
faultisconnected
tothesoutheast
striking
extension
ofthePorter's
indicatea Holoceneslip rateof ,--4mm/yr[Berryman,1979]and Passfault at GlentuiRiver,whichappears
to controlthefl0w
2.7-3.8mm/yr[Knuepfer,
1992].A few hundredmetersnorthof direction
of theAshleyRiverin the areaimmediately
tothe
Highway
73 atPorter's
Pass(Figure2), a radiocarbon
datefromthe northwestof Custanticline(Figure4).
lowerpartof a peatcolumnaccumulated
behindthesurface
trace
LateQuaternary
upliftof Custanticline
isevident
fromdrainage
indicates
thatthesurface
traceprobablyformed2000-2500years features
preserved
across
thecrestof thefold,whichiscapped
by
B.P. (Table 1).
two late Pleistocene
loesssheets[Trangmar,
1987].Ancestral
In a highwayembankment
on thesouthsideof thepass,two channels
of the AshleyRiverare incisedinto the loesssheets
buriedsofts,eachcontainingcharcoal,are offsetacrossthe fault (Figure
4), sothediversion
ofAshley
Rivertoitspresent
course
has
(Figure 3). The crosscutting
relationships
togetherwith the presumably
accompanied
upliftat the western
margin
of the
stratigraphy
indicatepossiblytwo ruptures
duringthe Holocene anticline,possibly
duringthe earlyHolocenesincetheyoungest
(Table1). The olderof the two soils,offsetacrossfault 1, may ancestral
channel
hasno loesscover.Theupliftwasprobabl5
reflecta rupture
between
7000and9000yearsago.Faults2 and3 caused
byrupture
ona faultthatisassociated
witha 1.5-kin-long
havedisplaced
bothsoilsatleastoncesince7000yearsago.
surfacetrace(Figure4) anda large(-500 m) offsetin basement
Studiesnear Porter'sPass,where the PPAFZ is relatively narrow,
Cust Anticline
[Kirkaldyand Thomas,1963].
Probable
lateHolocene
ruptures
in thisareaareinferred
from
TheCust
anticline
and
Ashley
fault,
located
onamajor
southeast
dated
landslides
andthetiming
ofAshley
River
downcutting
along
splay
of thePPAF-Z,
areimportant
sites
forpalcoseismic
the
northern
flank
ofthe
anticline.
Wood
collected
from
the
base0f
investigation
(Figures
2,4).The
recent
nature
ofthe
deformation
in gravel
deposits
overlying
thestrath
ofaterrace
13+ 12mabove
this
region
isindicated
bythe
presence
ofconsolidated
PliocenetheAshley
River
was
dated
atbetween
2100
and
2500
calibrated
early
Quaternary
siltstone
andconglomerate
which
crops
outtoa radiocarbon
years
old(Table
1and
Figure
4),implying
anaverage
,
COWANET AL.: PALEOS•-•SMI•
•N A NEWLYFORMEDFAULTZONE
6025
6026
COWANET AL.: PALEOSEISMICITY
IN A NEWLYFORMEDFAULTZONF_,
ß.'.'.'.'.'
'
........
Nothofaguscharcoa!'.'.' ß
500-700•,ea½s
B.'P.'.'-'- '.:
'•..'.',
,'-'.'.'-'.'.',
.
16900
:L--90
I
ß '- ! ' ";' "';"'''";"'I(NZ 7053)1
ß's0il'.'
.'
ß
''];:
'
' i' i' ib•ri•d
'
,.t-11o
.
ß
ß
....
.
.SOil.'.'.'
ß
'.' .'.'.'
ß.-.'.'.-.......................................................................................................
ß
........................................................
............
...........
ß
............
.-..
'-'-'-.-'.IF
AuLT2I--•.':
-:-:-:-
Figure 3. Age relationsbetweenfaultsandburiedsoilsexposedin a roadembankmentwithin the Porter'sPassfault
zoneat Porter'sPass.SeeFigure2 andTable1 for sitelocationanddescription,respectively.
downcuttingrate of 5.7 _+ 1.4 m/kyr. The heightof the terrace
strathabovethe presentfloodplainpresumablyreflectsan element
of tectonicuplift andfold growth,because
upstream
thefiveris in
equilibrium,whereasdownstream
it is aggrading[Cowan,1992],
Whether or not the downcuttingby Ashley River reflects
continuousor episodicuplift is unclear,but additionaldata from
landslides
at thislocality(Figure4) suggest
thatthefirstincrement
of uplift was inducedby coseismicrupturein this sectorof the
River is similar to the Ashley River, then the unfaultedterrace
formed'-'600-900yearsago.The availabledatathusimplythatthe
lastruptureof the Ashleyfaultpostdated2500 yearsB.P.andcould
have accompanied
the growthof Cust anticlinepriorto 600-900
yearsB.P.
Mount Grey Fault
TheMountGreyfaultcomprises
a northdippingthrustalong
the
southsideof MountGrey (931 m) in theeasternpartof thePPAFZ
(Figure2). The fault loopsaroundtheeasternflankof MountGrey
Ashley Fault
andbifurcates,
forminganoblique,left-lateraltearfaultthatstrikes
The Ashley fault offsetsPleistoceneandHoloceneterracesof the northand dips to the west, and againstwhich the Tertiarycover
OkukuRivereastof Custanticlineandhasa surfacetracelengthof sequence
hasbeenoverturned
[Wilson,1963].Thefaultisexposed
4.5 km [Brown, 1973; Bero'man, 1979] (Figure4). The fault is in a number
of streams
andformsa prominent
surface
trace
and
PPAFZ.
downthrown to the south, with throws of 1-4 m on a late Pleistocene
hillside bench hollow, behind which scree and bouldershave
aggradationsurfaceand 0.5-1.5 m on a Holocenestrathterrace
accumulated.
[Cowan, 1992]. Differencesin the throw of the fault on thesetwo
Radiocarbon
andweathering-find
datesdelineate
twosurface
surfacessuggestat leasttwo rupturessincethe formationof thelate rupture
events
withinthelast2500years(Table1).Evidence
forthe
Pleistocene aggradation surface. Variations in throw which oldestrecognized
eventwasobtainedfroma streambankexposure
accompanyslightchangesin the strikeof the fault, areconsistent of thefault(Figure2, 5), wherewoodandpeatwerepreserved
on
with a minor fight-lateral componentof displacement,but no thesurfaceof a debrisflow, offsetacrossa faultscarpthatisnow
unequivocaloffsetshavebeendocumented.
buried
3 m belowthepresent
ground
surface.
Thewood
wasnotin
The height of the Holocenestrathterraceoffsetby the Ashley growth
position
andwasburied
beneath
younger
colluvium,
which
fault is similar to the dated (i.e., 13 m) strathaboveAshley River, in turnwasoffset
bythefault.A soil,developed
onthedebris
fl0w
so the terracesmay be of approximatelyequal age.The fault trace andcontaining
a traceof charcoal
of unknown
agedefined
an
acrossthe Okuku River strathis not significantlydegraded,so the apparent
vertical
offset(downthrown
to thewest)across
thefault.
fiver presumablyabandonedthe surfaceprior to, or at the time of, Wecould
notdiscern
fromthefieldrelationships
whether
ornotthis
faulting.The oldestOkukuRiver terracenotoffsetby thefault(its buried
soilwasdeformed
orhadmerely
developed
onanexposed
riser truncatesthe surface trace) is about 4 m above the active fault
scarp
atalater
date.
Thesoilwasburied
beneath
another
debris
by a younger
soilprofilecontaining
a treestump
floodplain(Figure4). If the averagedowncutting
rateof theOkuku flow,alsocapped
COWANET AL.:PALEOSEISMICITY
IN A NEWLYFORMEDFAULTZONE
6027
KOWAI
ANT/CLINE
-"-"
/
..."*
I
.......
•
--
- -•
, ,
.
/
•%
•.•
,
_,
,
-'_
ß
"
k
',
I
I•//,1',;•%¾
•
•----
l •½
......
)
•
•"'•1
__
......
-
,-
/
•
,
,,eQuat.
sediments
'•
Cret-early
Ouat
ß
' sediment•
:'.:•
Torlessegre•ackebasement
Fold• •11
,,
"
--
)
__
•1 ' I•72-•
:•
'•
•
% ;
....
Figure4. Map of thenorthernCanterbury
Plainsshowing
therelationships
betweentheCustanticline,Ashleyfault,
andrange-boundingelementsof the PPAFZ. LSa andLSb indicatelocationsof the radiocarbondatesfrom landslide
8 (Table2 and Figure6). Topographic
contoursare reproduced
at 20-m and 10-m intervals(thin solidand thin
dashed
lines,respectively)
from NZMS 270, sheets
L35 andM35, by permission
of theDepartmentof Surveyand
Land Information, New Zealand.
derived
fromoutcrops
of
ingrowth
position.
A radiocarbon
dateof 182 + 60 yearsB.E (0.2-10x 106m3) rockavalanches,
obtained
fromanouterportion
of thetreestump
(Table1)indicated Tofiesse
basement
(Figure2). Thedataindicate
a clustering
of ages
aminimum
agefor the buffedsoil andthelastsurface
rupture betweenabout500 and700 yearsB.P.,withothersscattered
backto
recognized
at this site.
morethan7000 yearsB.P.(Table2 andFigure6).
Landslidesin the range 500-700 yearsB.P. are relatively
cobbles
exposed
attheground
surface
alongthefaulttracenorthof uniformlydistributedalongthe PPAFZ and are well preserved.
thestream
banklocality,
andweathering-rind
agesforthese
were However,thereare insufficientdata to confirma similarspatial
calculated
usingthemethod
of Chinn[1981]andcalibration
curve patternof landslidesat 2300 yearsor older,which presumably
ofMcSaveney
[1992]toevaluate
thetiming
ofsitedisturbance.
Two reflectstheremovalof landslidedebrisby erosion.A largelandslide
modal
rindthicknesses
wereobtained
andtheages(Table1) arein identifiedon the north limb of Cust anticline(Figure 4), which
good
agreement
with thetimeintervals
forwhichsurface
rupture
is containedwhole treesand an articulatedskeletonof the largest
inferred
fromtheradiocarbon
ages.
Theavailable
datacollectively
speciesof extinct moa, Diornis giganteus[Cowan, 1992], was
datedat circa2300yearsB.P.(Table2). Thisageis the
imply
surface
rupture
ontheMount
Greyfault,between
2300-2400radiocarbon
sameasthenearbystrathterraceof AshleyRiver(Figure4), andwe
years
B.P.and300450 yearsB.E
surmise
thatboththelandslideandtheonsetof fiver downcutting
accompanied
coseismicuplift of Custanticline.
Pre!fistoric
Landslidesof the PPAFZ
To assess
whethertheeffectsof thiseventextended
beyondthe
geographic
limitsof ourstudy,theagesof rockavalanches
fromthe
Landslides
provideadditional
datawithwhichto assess
the central SouthernAlps [Whitehouseand Griffiths, 1983] were
recurrence
intervalof largeprehistoric
earthquakes
in thePPAFZ. recalculatedusing the weathering-rindcalibration curve of
Twenty
landslides
havebeenidentified
withinthePPAb-Z,
andthe McSaveney[1992]. Two modal ageswere obtainedfor Southern
ages
for 10 of thesehave beendeterminedfrom radiocarbon
and Alps landslides(circa 1050-1400yearsB.P. andckca 1700-2100
weathering-rind
dating(Table2). Thelandslides
aremostly
large yearsB.P.),andthesedonotcoincidewithmodalagesforlandslides
Chipswere collectedfrom Torlessesandstone
bouldersand
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0
'"[Stream
channel
i -•
1
.
IMt
]
Grey
Fault
2330
+_40
yrs
B.P
(NZ 7852)
metres
Figure5. Stratigraphy
andconventional
radiocarbon
agesassociated
withsamples
fromanexposure
of theMount
Greyfaultin a streambankon theeastern
flankof MountGrey.SeeFigure2 andTable[ for sitelocation
and
description,respectively.
documented
in thePPAFZ(Figure6). The agesfor threelandsfides periodof 3 monthsandwerefollowed39 yearslaterby theM,7.4,
etal.,
fromthecentralSouthern
Alpsdo overlapwith thoseof thePPAFZ, Mw 7.1 Inangahuaearthquake[Adamset al., 1968;Anderson
in therange~2200-2450yearsB.P.,butfaultdataindicateprobable 1994]. It is doubtful whether each of these events couldbe
ruptureof thePPAFZduringthatperiod(Table1).
differentiated
from thegeologicalrecordusingradiocarbon
dating
Six landslideswith agesbetween500 and 700 yearsB.P. are had they occurred during prehistoric time, although
locatedwithin 1 km of themajorfaultsof thePPAFZ,andtwo of dendrochronology
andlichenometrycouldpotentiallydiscriminate
theseburythe traceof the Porter'sPassfault nearPorter'sPass the 1929 and 1968 events[e.g.,Bull et at., 1994]. Second,asthe
sotoodoes
(Figure2, landslides
1 and2 ). By contrast,
onlytwo landslides elapsedtime sincethe creationof a landformincreases,
withinthisagerangeweredatedbyWhitehouse
andGriffiths
[1983] the likelihood that it will be destroyed,modified,or buriedby
processes.
Furthermore,
periodsof nondeposition
may
in the SouthernAlps farther west. Collectively,the spatial subsequent
distributionof thesedata suggeststhat if the landslideswere concealthe occurrenceof ruptureeventsat a given site,and
of continuoussedimentation
aredifficultto testandare
seismically
triggered,
theyaremorelikelyrelatedtolocalrupture
of assumptions
thePPAFZratherthanto a regionaleventon theAlpineFault,an rarelyproven[e.g.Doig, 1990;CowanandMcGlone,1991].We
cannotrule out periodsof non depositionat any of thesites
interpretation
favoredby W.B. Bull (personal
communication,
in thisstudy,butthetemporal
clustering
of landslides
in
1994)basedon recent1ichenometric
datingof landslides
in the described
therange500-700yearsB.P.andtheircloseproximity
tothePPAFZ
suggest
thatthemostrecentrupture
of thiszoneprobably
occurred
Theinterpretation
of landslide
distributions
in paleoseismology
thatperiod.
Thelandslides
attributed
toearlierevents
(2000involvestwo assumptions:
(1) that landslides
were triggered during
coseismically;
and(2) that all landslides
of a similaragewere 2500yearsB.P.and7000-9000yearsB.P.)aremuchlessabundant,
coseismicwith the sameevent.Landslideshavebeentriggeredby indicating
thatin New Zealand's
mountainous
terrain,landslide
paleoseismicity
forupto
all large(M >7) historic
earthquakes
in New Zealand,
butmany datamayonlybeusefulfor characterising
SouthernAlps.
largelandslides
in seismically
activeregions,including
the 2000-3000years
B.P.
Southern
Alps, havenot beentriggered
by earthquakes
[e.g.,
PlafkerandEricksen,
1978;McSaveney
et al., 1992;McSaveney,Magnitude Estimates
1978,1993].In theabsence
of independent
evidence,
thecoseismic
Thedatingof surface
faultruptures
provides
a check
onthe
likelihood
that a givengroupof landslides
wastriggered
For both fault tracesand landslidesthere are at least two reasons coseismically,
buttheestimation
ofmagnitude
isproblematic
inthe
of datathatdefinethe rupturedimensions,
andthese
whyevidence
forlargepalcoearthquakes
couldbesparse.
First,it absence
mustbe remembered
thatfew datingtechniques
candiscriminate parameters
arepoorlyconstrained
forthePPAb-Z.
Relationships
landslide
distributions
andearthquake
magnitudes
have
events
separated
bya fewyearsordecades,
apointexemplified
by between
interpretation
of prehistoric
landslides
musttherefore
beregarded
astentative[Whitehouse
andGriffiths,1983].
proposed
based
onglobal
compilations
ofdatafrom
historic
threehistoric
earthquakes
in northern
South
Island.BoththeMs7.8 been
do notprovide
an
BulletandMs7.0Arthur's
Passearthquakes
of 1929[Henderson,events[Keefer,1984],but theseprobably
basis
for estimating
themagnitude
of prehistoric
1937;Speight,
1933;DowrickandSmith,1990]occurred
withina appropriate
COWANET AL.: PALEOSEISMICITY
IN A NEWLYFORMEDFAULTZONE
6029
Table
2.Description
ofDated
Landslides
From
thePorter's
Pass-Amberley
Fault
Zone
LocalityFrom
Figure2
Latitude,
Longitude
1, Ach
cron
Rivera
43.31,171.66
Landslide
Volume,
106m3
Age
a
6.0
500 +_69e
Method
b
43.28,171.78
2.0
A.D. 1290-1515
f
NZ 547
two slidese
2, KowaiRiver•
14C
AgeCalendar
Years
ø
560 + 90
WR
A.D. 1340-1520
60, 1988
3, KowaiRiver•
43.28,171.80
0.2
590 + 100
WR
A.D. 1300-1500
40, 1988
4, CoalCreek
43.40, 172.00
0.02
5600 + 62
•4C
4575-4335B.C.f
NZ 7918
5, AshleyGorge
43.19, 172.14
0.3
490 + 70
WR
A.D. 1430-1570
75, 1991
6, LeesValley
43.11,172.12
10.0
580 _+ 90
WR
A.D. 1320-1500
62,1991
7, GlentuiRiver
43.21,172.26
4.0
two slides
600 +_ 100
1210 +
190
WR
70, 1991
A.D. 1290-1490
A.D. 590-970
45, 1991
8a,Cust
Anticline
43.26,172.37
0.1
7400+ 90
i4C
6425-6000
B.C'f
NZ 7854
8b,Cust
Anticline
43.26,172.37
3.0
2300+ 60
2270 + 82
14C
NZ 7855
14C
mean
oftwodates
200-400B.C.f
NZ 7856
9, Mount
Thomas
43.15,
172.40
4.0
2467+ 66
I•*C
400-765
B.C'f
NZ 7895
10,MountGrey
43.09,172.55
0.2
3430 _+470
WR
970-1400B.C.
bimodal
99, 1991
1930-3250 B.C.
4580
+_ 660
SeeTable1 footnotefor explanationof weathering-rind
datingerrors.
aYearsbeforeA.D. 1950,with modalweatheringrind agesrounded
to nearest5 years.
bSymbol
•4Cdenotes
conventional
radiocarbon
ageandsample
numbers;
WRisweathering
rinds,
followed
bynumber
ofrinds
andyear(A.D.)of
measurement.
14
e
ages
(,calendar
A.D./B.C.).
dSymbol
DatafromC
Burrows
[1975].years
eDatafrom W.B. Bull (writtencommunication,1994).
f Calibrated
radiocarbon
ages
(95%confidence
levels
unless
otherwise
stated)
based
oncompilation
by$tuiver
andReimer
[I986]of20-year
tree
ring
data
fortheperiod
7210B.C.toA.D.1950,
withoffset
of-30radiocarbon
years
asrecommended
by$tuiver
andPearson
[1986]
andPearson
and
$tuiver[1986].
•DatafromCoyle[1988].
earthquakes.
Onlythe largest
prehistoric
rockfallsmaybe
Thethreshold
magnitude
for surface
rupture
andcoseismic
recognized,
andvariations
in earthquake
source
mechanism
and landsliding
in thePPAPZ
isunclear.
However,
since
allhistoric
regional
geology
couldstrongly
influence
thedistribution
of eamhquakes
larger
thanmagnitude
M •-7innorthern
South
Island
by landslides[McKay,1902;Henderson,
landslides.
For example,the 1929 and 1994 Arthur'sPass havebeenaccompanied
earthquakes
eachtriggered
rockfailsoveranareacomparable
to 1937;Speight,1933;Adamset al., 1968] we infer that the late
many
global
events
of similarmagnitude
(M. McSaveney,
personalHolocenelandslidesin the PPAFZ were probablytriggeredby
communication,
1995),buttheareas
affected
bylargelandslides
of earthquakesof similar magnitude.More precise estimatesof
woulddependcriticallyon detailedknowledgeof the
the
1929Bullerand1968Inangahua
earthquakes
[Adams,
1981]are magnitude
sub-surface
fault dimensionsand segmentation[Wells and
smaller
thanmightbeexpected
fromKe•er'sglobal
catalogue.
The
Coppersmith,
19941,parameters
that are poorlydefinedin this
Bu!ler
andInangahua
earthquakes
occurred
in a region
composed
hybrid
strike-slip
and
thrust
fault
zone.
Indeed,
lateralvariations
in
largely
of crystalline
Paleozoic
rocks,
in contrast
totheweakly
mtamorphosed
greywackeof the SouthernAlps. These fault behaviorare to be expected,and historic earthquakes
'differences,
together
with variations
in focaldepth,ruptureelsewhere[e.g.,Arnaike,1987:Steinand Yeats,1989;Hull, 1990;
directivity,
and topographic
effectsillustrate
someof the Steinand Ekstrem,!992; SrnaIleyet aI., !993; Andersonet aI.,
1994;Jibsonet al., 1994]suggest
thatnotall Holoceneruptures
in
unities thatwouldaccompany
theestimation
of earthquake
magnitudes
from prehistoric
landslidedistributions.
The the PPAPZ would necessarilyproduce surface fault offsets
indicativeof earthquakemagnitudeor amenableto palcoseismic
uncertainties
naturally
wouldbe compounded
by incomplete
investigation.
Thisseems
especially
likelyin thefoldandthrustbelt
aamp!ing
ofthespatial
distribution
ofprehistoric
landslides.
6030
COWAN ET AL.- PALEOSEIS•CITY
..............
•
•
8•
0
o
d
<•
•
N
•
•. pPAFZ"
raPix,
re-,•:
•v
•-
N:34
CA+A
--MG
•
• •
IN A NEWLY FORMED FAULT ZONE
•
rag*
--
PP
•
' 'D
i•II
m
I I
-- G
•
I'2
o
•
•
I
•
I
0
•9
•
7
' • 8b
......
•
1000
..........
ß
10
10
I
2000
3000
4000
5000
Years B.P.
Figure
6.Temporal
distribution
oflandslides
and
fault
ruptures
inthePPAFZ,
andacomparison
withdated
land-
slides
from
theSouthern
Alps
[Whitehouse
and
Grifflths,
1983].
Weathering-rind
ages
from
theSouthern
Alps
have
been
recalibrated
using
thecalibration
curve
ofMcSaveney
[1992].
Landslide
numbers
correspond
tothose
inTable
2 and
arelocated
onFigure
2.Abbreviations
areA,Ashley
fault;
CA,Cust
anticline;
MG,Mount
Grey
fault;
PP,
Porter's
Pass
fault.Asterisks
denote
faultruptures
dated
byweathering
rinds.
Refer
toTables
1and2 fordetails
of
faultruptures
andlandslides,
respectively.
at the easternend of the PPAFZ and farthernorth,wherelate
Holocene
surface
traces
arepreserved,
butlocallydisplay
vertical
offsets
thatareanomalously
largewithrespect
tofaultlength
and
for whichno landslides
havebeencorrelated
[Cowan,1994;A.
Nicol et al., unpublisheddata, 1991]. Uncertaintiesin the
assessment
of fault dimensions
andthelikelihoodof hiddenfaults
inthisyoung
faultzonealsocomplicate
theestimation
ofsliprate
andpotential
slipperevent.Localvariations
in faultkinematics
are
evident
fromthedifferential
upliftatCustanticline
(thisstudy)
and
log N(M) = a - am
(1)
where N(M) is the cumulativenumber of earthquakes
of
magnitudeequal to or greaterthan (M); a definesthe rateof
occurrence,and b is the exponential decay with increasing
magnitude,implying self-similarity [e.g., King, 1983]. The
parameters
a andb areconstants
of the seismicitymodelandare
computed
from a catalogue
of historicalseismicity.
Equation
(1)
maybe integrated
to obtaina cumulativeexponential
distribution,
truncatedat a maximummagnitudefor a givensetof faultsor
inthefoldandthrust
beltfarther
east[NicoIetaI., 1994].Davisand
volume of crust, suchthat
Namson[1994]andShawandSuppe[1994]haveshownthat
deta•ed
structural
analysis
canreveal
thepresence
ofhidden
faults,
N= No[10
a(Mø'
•) - 10b(Mø'
Mmax)]
(2)
andsimilarworkin progress
in thePPAFZ(H.A. Cowanet al.,
manuscript
in preparation,
1995)mayprovide
further
insight
into
NOis thenumber
of earthquakes
of magnitude
Mo orgreater,
thekinematics
andsubsurface
structure
ofthezone,
especially
if whereMo is anarbitrary
threshold
magnitude
[e.g.,Youngs
and
combined
withrecent
observations
ofgeodetic
strain
(C.F.Pearson Coppersmith,
1985]. When combinedwith an appropdm
et al., Straindistribution
across
the Australian-Pacific
plate attenuation
expression,
theseismicity
modelmaybeused
toderive
boundary
inthecentral
South
Island,
New
Zealand,
from
1992
GPS return
periods
orprobabilities
ofexceedance
forspecified
levels
of
andearlierterrestrial
observations,
submitted
to Journal
of ground
motion.
This
classical
hazard
analysis,
advanced
byCornell
Geophysical
Research;
hereinafter
Pearson
et al.; submitted
[1968],
hasbeen
applied
widely
inseismic
hazard
assessment
[•
manuscript,1995). Here, we restrict our discussionto the J.G.Anderson
etaI.,1993]andin NewZealand
by,among
othem
implications
of available
historical
andpalcoseismic
datafor Peeketal. [!980]andSmithandBerryman
[1986].
analysis
of seismicity
ratesandfaultbehavior.
SeismicityRate Analysis
Studiesof individualfaultshaveshownthattherecurrence
r•
oflargeearthquakes
(M>7)maybeunder-predicted
bythe/•value
model[e.g.,Wesnousky
et al., 1983;Schwartz
andCoppersmith,
1984;Davison
andScholz,
1985].Rather,thefrequency
of these
Thetraditional
approach
toseismicity
rateanalysis
istoassumelargeevents
appears
to begoverned
by relations
between
f•ult
a uniform
spatial
distribution
of earthquakes
andanexponential
geometry,
segmentation,
andcumulative
geological
offset,
which
distribution
ofmagnitudes
oftheGutenberg-Richter
form:
influence
thedistribution
of strength
properties
along
faultzo•
COWANET AL.:PALEOSEISMICITY
IN A NEWLYFORMEDFAULTZONE
6031
[e.g.,
King
andNabelek,
1985;
Sibson,
1989;
Wesnousky,
1988,(~25mm/yr)
isequivalent
tomore
than
60%ofthetotal
rate
of
1990].
Therecognition
ofstructural
controls
onthepropagation,
relative
plate
motion
[DeMets
etal.,1990],
which
represents
the
•est,andsubsequent
slipdistribution
associated
withsomehighest
rateofslipintheMarlborough
Fault
System
[Van
Dissen
c0seismic
faultruptures
[e.g.,Sibson,
1985,1989]hasdrawnandYeats,
1991].
Thelastsurface
rupture
inzone
1occurred
onthe
attention
tothesignificance
offaultsegmentation
asa possible
Hope
River
segment
during
anM -7.3earthquake
in1888
(Figure
indicator
ofthesizeofearthquakes
associated
withagiven
fault. la) [McKay,
1890;Cowan,
1991].
TheHopeRiversegment
has
This
concept
isimplicit
inthemodel
of"characteristic"earthquake
ruptured
repeatedly
at intervals
of 80-200years
during
thelast
recurrencein
which
most
ofthedeformation
associated
withagiven millenium,
orapproximately
every140years
during
thelast3500
fault
orsegment
isreleased
coseismically
byearthquakes
thatoccur years,if thesliprateandlocaloffsetin the 1888eventareincluded
within
a relativelynarrowrecurrence
time and magnitude[CowanandMcGlone,1991](Table3).
distribution
[WorkingGroup on CaliforniaEarthquake Zone 2 is centered on the PPAFZ whose cumulative offset and
Probabilities,
1990].Othermodels
advanced
toexplain
geologicalsliprateis approximately
oneorderof magnitude
smallerthanthe
evidence
of time-variable
andslip-variable
faultbehavior
[e.g., Hope fault. Both zone 1 and zone 2 containadditionalfaults
Schwartz,
1989; Scholz, 1989] also imply the nonrandomassociated with Holocene surface traces, for which litfie or no
occurrence
of largeearthquakes.
palcoseismicdata are available[Woodet al., 1994; this study].
There
is considerable
debateasto howwidelyandoverwhat Uncertainties
in the locationof historicearthquakes
mailer than
timescale
the "characteristic
earthquake"and othermodelsof magnitude
M 4.0, precludethe selectionof smallerzonesadjacent
1994]. However, the depth
periodic
faultbehavior
mayapply[cf.Nishen'ko,
1991;Nishenkoto the major faults [cf. Wesnousll.7,
of seismicityrecordedduringmicroearthquake
surveys
and
Sykes,
1993;KaganandJackson,
1994,1995;Reelefts
and distribution
Langbein,
1994].Whilethebehavior
of somefaultsappears
to be in zone1 [ArabaszandRobinson,1976;Kieckhefer,1977] andzone
g0vemed
by characteristic
earthquakes
overseveralearthquake2 [Reynersand Cowan, !993] indicatesthat most seismicityis
cycles
[e.g.,Schwartzand Coppersmith,
1984]and othersby restrictedto the upperi0-15 km of the crust.By conservatively
choosing
50 km widezonesfor seismicityrateanalysis
in thisstudy,
temporE
clusters
of earthquakes
[e.g.,Wallace,
1987;Coppersmith,
with the
1988;
Siehet aI., 1989], comparisons
of seismicity
at thescaleof we are thereforeconfidentthat all seismicityassociated
faultshasbeensampled.
plate
boundary
segments
haveindicated
nonperiodic
faultbehavior majorseismogenic
[Kagan
andJackson,1995].
Recent
analysis
of historicseismicity
andgeological
fault-slip SeismicityDistributionand RecurrenceParameters
data
fromsouthernCalifornia[Wesnousky,
1994] indicatesthatthe
structurally
maturefaultsof the SanAndreasfault zonedo exhibit
Three time periods were selectedbased on the relative
completeness
of the seismicitycatalogue:for eventsM >5 since
characteristic
behavior,
at leastoverthetimeperiods
(102-1041942;M >4 since1964andM >3 since1988.Onlythoseevevtswith
years)
considered.
In NorthCanterbury,
onehistoricsurfacerupture
crustaldepths(i.e.,restricted
andfreedepthsshallowerthan 4 km)
oftheHopeRiver segmentof theHopefault(Figurela), together were sampled,so as to excludeeventslocatedin the subdueted
with
palcoseismic
dataandspatialvariationsin lateQuaternary
slip Pacificplate 100 km beneaththe Hope fault region [Robinson,
ratefrom the same segment, are also consistentwith the
1991].The cataloguewasalsotruncatedat May 30, !994, to avoid
characteristic
earthquakemodel [Cowan, 1990, 1991; Cowanand
sampling those aftershocksof the lune 1994 Arthur's Pass
McGlone,
1991].Elsewherein New Zealand,significant
variations
earthquakethat fall within the northwestern
comer of zone 2
infaultbehaviorhavebeendocumented
[Berryman
andBeanland,
(Figurelb).
!991],andtheproblemthere,asin mostpartsof theworld,is one
The instrumental
seismicitycataloguefor zone 1 containsa
ofreconciling
geological
andseismological
dataspanning
different
numberof eventsof magnitudeM 4.0-6.4. mainly in the east.
•e periods.
Theseismicity
catalogue
forNewZealand
spans
only Several of theseeventsare associatedwith two swarms,the first of
thelast150 yearsfor largeearthquakes,
and the instrumental
which occurredsouthof the Hope fault on May 22, 1948, and
catalogue
spans
a muchshorter
period.Thisproblem
isintractablecomprised
sixevents(Mz,=5.9, 6.4, 6.2,5.7, 5.7, and5.8) withinthe
andacknowledged
in seismicityrate analysisand hazard spaceof 2 hoursand24 min[Eiby,1982].The second
swarm(April
estimation.
However,thehistoric
catalogue
forNorthCanterbury
is 22-28,1973)consisted
of fourevents(Mz,--5.2,4.5,4.4, and5.0)in
sufficiently
long to illustratesignificant
discrepancies
betweenanareanortheast
of theHopefault[Reyners,
1989].Onlythelargest
recurrence
ratesforlargeearthquakes
extrapolated
fromthehistoric event of that swarm lies within the northeastern comer of zone 1.
catalogue
versus
recurrence
ratesimpliedbygeological
data.
Neither of the two swarms can be attributed to movement on known
faults,buttheSeismological
Observatory
Filelocations
suggest
that
theyareprobablyunrelatedto theHopefault.
Oneinteresting
featureof thecatalogue
for zone1 is theabsence
of eventsof any magnitudein thewesternpartof the regionand
fartherwest,wherethe 1888and1929 raptures
occurred(Figure
Seismicity
Zones
lb). This quiescence
wasalsoapparentduringan earlierstudyof
[ArabasxandRobinson,1976] andmay reflecta
For the purposeof comparing
historicseismicity
and microseismicity
Pa!eoseismic
data,two100x50krnzones
(Figures
la andlb) were significantreductionof stressin that regionfollowingthe large
lrrequency-Magnitude
Relations
for North
Canterbury
Seismicity
historicearthquakes.
selected,
based
onthecontrasting
structural
maturity
andgeological
• rates
oftheknown
faults.
Zone1encompasses
an~35-tan-ling The seismicitycataloguefor zone2 (Figurelb) clearlyshows
•easing
bend
intheHope
faultzone
across
which
about
half(~10- diminishingactivitysouthof thePPAFZ,butthestrikeof thatzone
well-defined
asnotedbyReyners
[1989],despite
all
14rnm/yr)
ofthetotalHope
faultsliprateislocalized
ontheHopeis remarkably
!•ver
segment,
withtheremainder
distributed
across
adjacent
butoneevent
(M•6.2)[Eiby,
1990],
being
smaller
than
M 5.5.A
splays,
notably
theKakapo
fault[Cowan,
!990;
Van
Dissen
and recent
study
ofmicroseismicity
inNoah
Canterbury
[Cowan,
1992;
l'eats,
1991;
Yang,
1991](Figure
la).TheHope
faulthasa Reyners
andCowan,
1993;
H.A.Cowan
etal.,manuscript
in
cumulative
offset
of~20km[Freund,
197!],anditstotal
sliprate preparation,
1995]
hasalso
shown
seismicity
clustered
along
the
COWAN
ETAL.:PALEOSEIS•• IN ANEWLY
FORMED
FAULT
ZONE
6032
Table
3.Magnitude-Frequency
Relations
Within
theHope
Fault
Region
(Zone
1)andPorter's
Pass-to-Amberley
Fault
Zone
(Zone
2)
Period
(Numberof
Threshold
Number
of
Recurrence
Parameters
Return
Periods
(years)
Events
,
Years) Magnitude
Regresseda
SE
b
SE
,
M6s
M7s
M>7r
HopeFaultRegion(Zone1)
1942-1994
M5
10
(52.5)
!964-1994
M4
4
3.76
0.47
0.87a
0.08
29
214
3.64
.0.47
0.85
0.08
29
204
3.3!
0.22
0.87a
0.05
8!
602
3.22
0.22
0.85
0.05
76
537
4.33
0.23
1.20a
0.06
-
-
3.14
0.43
0.87
0.12
120
891
0.60
0.13
59
234
1300-
2000d
80-200b
60-300 e
(30.5)
!988-1994
M3
32
(6.5)
PPAFZRegion(Zone2)
1942-1994
M5
6
(52.5)
1964-1994
M4
20
(30.5)
1988-1994
M3
48
1.83
0.75
3.33
0.88
0.87
0.16
78
575
3.01
0.35
0.81
0.07
71
457
3.29
0.36
0.87
0.08
85
631
3.81
0.13
0.97a
0.04
102
955
3.43
0.17
0.87
0.05
62
457
750-1000 e
1500-2000
f
(6.5)
Exceptasotherwise
noted,
b wasdetermined
through
aniterative
procedure
in whichonlya wasallowed
tovary.Twosetsofrecurrence
parameters
aregivenforeachofthethreetimeperiods
inorder
toevaluate
thesensitivity
ofa andbvalues.
Thestandard
errors
(SE)indicate
nosignificant
differences
in a fordifferera
valuesof b.Thesuperscript
S andP denotehistorical
returnperiods
impliedby seismicity
and
palcoseismicdata,respectively.
a The a andb caseswere determinedsimultaneously
by a linearleastsquaresfit.
t:CowanandMcGIone
[ 1991].
½Calculated
usingsliprateof 10-25m/kyrandslippereventof 1.5-3.0m. DataarefromCowanandMcGlone[1991]andVanDissen
and Yeats [1991].
dFromlandslide
andfaultrupture
data(thisstudy).
e Calculated
usinga sliprateof 3-4 m/kyrandslippereventof 3 m. SlipratesfromBerryman[ 1979]andKnuepfer[1992].
f Calculated
using
a sliprateof3-4m/kyrandslipperevent
of6 m.Sliprates
fromBerryman
[1979]andKnuepfer
[199o_].
PPAFZ,withmosteventsconf•edtotheupper8-15kmof thecrust. Gutenberg-Richter
model(Figure7), buttheclosestmatchbetween
The recurrence
parameters
a andb of the Gutenberg-Richterthe histories/andgeologicaldataand the smallesterrorsforthe
relationwerecomputed
for thePPAFZandHopefaultregions
using historical
recurrence
parameters
areobtained
fromthemagnitu•
ordinaryleastsquares
regression
andan iterativeapproach
to the frequency
distribution
of M >3 earthquakes
since1988(Table
3).
selection
of b values(Table3). Therecurrence
parameters
listedin Therecurrence
estimates
for largeearthquakes
derivedfromlonger
in zone2 are higherthanthose
Table3, and illustratedfor the period1964-1994in Figure7, periodsof historicalseismicity
data(Table3).
indicatenegligible
differences
in activityratesbetween
theselected impliedby thepalcoseismic
regions,despitean orderof magnitude
differencein sliprateand
cumulativeoffset.By contrast,the palcoseismic
data from each
regionimply significant
differences
in recurrence
intervalsforlarge Discussion
earthquakes
(Table3), yet neithercouldbe reliablypredictedfrom
Further
interpretation
of thehistorical
seismicity
datamay
be
thehistoricseismicitycatalogue.
giventhatthe seismicity
catalogue
is possibly
too
In zone1 thepresence
of manyadditional
faultswithpotential
to unwarranted
tosustain
arobust
"productivity"
analysis
atmagnitudes
less
generate
largeearthquakes
in theHopefaultregionemphasizes
the short
deceptivenessof contemporary seismicity. Moreover, the than
M4.Thehistorical
data
inthemagnitude
range
M <6.0straddle
discrepency
between
recurrence
ratesforlargeearthquakes
inferred aperiod
ofseismic
quiescence
intheHopefaultregion,
which
may
from historicaland geologicaldata would be accentuated
if the notberepresentative
ofthelonger-term
seismicity
rate.Similarly,
swarmearthquakes
mentionedabovewereto be excludedfrom the the
relatively
high
rateofseismicity
inthePPAP-Z
dur'mg
thelast
30
analysis;i.e., theseismicityrateabovemagnitude5 wouldbe even years
may
reflect
long-term
temporal
variations
indeformation
and
lower in zone 1 during the historicalperiod. The situationis clustering
ofearthquake
occurrence,
asforexample,
inferred
from
differentin zone2, wherethe discrepency
betweenhistoricand comparisons
oflowgeological
slipratebuthigher
geodetic
smi•
palcoseismic
data is in the oppositesense(Table 3). There, the andseismicity
rates,in thereverse
faultprovince
of northwestera
Island[H.Anderson
et al., 1993;Bearart
et al.,1994];
recurrencerate for large earthquakes
is approximated
by the South
COWANET AL.:PALEOSEISMI•• IN A NEWLYFORMEDFAULTZONE
lO
Hope
Fault
(Zone
1)
10
'7
6033
PPAFZ
(Zone
2)
1964-1994
lO o
-ii.'i "',
'' Geological
data
10-2
-
ii !
',,
10.-3
Geologicaldata
3
4
5
6
7
8
3
Magnitude
4
5
6
7
8
Magnitude
Figure7. Comparison
of frequency-magnitude
relations
for theHopefault(Zone1) andPPAFZ(Zone2) (Figure
lb) for theperiod1964-1994.The frequency
histograms
werecompiledat classintervals
of M 0.1. The solidline
represents
thecumulative
frequency,
whereas
thedashed
straightlinedenotes
thebestfit ( b value0.87)forthemagnituderangedefinedby verticalticks.The shadedboxesindicatetherecurrence
rateandpossiblemagnitude
for
largeearthquakes
inferredfrom geologicaldata.The magnitude-frequency
distribution
for the Hope fault is in
accord
with thecharacteristic
earthquake
model,whereas
thatof thePPAP-Z
is approximated
by theGutenberg-Richtermodel.Note in Table3, however,thatthe Gutenberg-Richter
relationship
overpredicts
therecurrence
rateof M
>7 earthquakesin the PPAFZ.
Temporal
variationsin seismicityrate may profoundlyaffectthe ---2500years is only sparselypreserved.Moreover, while the
frequency-magnitude
distributionand apparentrelationshipscombinedevidenceof faultingandlandslides
between2000 and
between
seismic productivityand fault slip rate, structural 2500yearsB.P.is quitecompelling,
thiscannotbesaidof the500complexity,
or maturity.Forexample,hadit beenpossible
tosample 700 yearB.P.event,for whichourinterpretation
restslargelyonthe
seismicity
in theHopefaultregionfor the50 yearsstraddling
the landslide
dataalone.
1888
earthquake,
theproductivity
couldhavebeenhigherandthe
If ourrecordoflateHolocene
rupture
of thePPAFZiscomplete,
frequency-magnitude
relationships
impliedbysuchdatamightnot theimplied
interval
of 1300-2000
yearsbetween
thelasttwoevents
have
underpredicted
therecurrence
rateforthelargest
events
onthe wouldrequke
4-8 m displacement
pereventtobeconsistent
with
Hope
faultto thesamedegree
asthecurrent
dataset(Table
3). theinferred
sliprateof 3-4 mm/yron thePorter's
Passfault.
Conversely,
lowseismicity
ratesmaytypifythebehavior
of the Displacements
perevent
of thisorderhavebeen
documented
for
Hope
fault,
since
it isclearthattheM--,7.3event
ofonecentury
ago numerous
Holocene
faults
throughout
NewZealand
[Bcrr3,'man
and
has
not
been
followed
byongoing
high
rates
ofactivity.
Beanland,
1991]
and
fi,rnad6ttir
etal.[1995]
have
modeled
upto5
Return
periods
forlarge
rareevents
areclearly
sensitive
toslight m of displacement
forthe1994Arthur's
Pass
earthquake
(Figure
changes
inrecurrence
parameters
whenregressions
areperformed
la). Thustheinferred
return
period,
displacement
perevent,
and
ondatadominated
by smaller
events,
or whenthecatalogue
is sliprateneed
notbeinconsistent.
Moreover,
itseems
reasonable
to
heterogeneous
with respect
to magnitude
[e.g.,Okal and conjecture
thatlarger
displacements
perevent
couldbeexpected
l•omanowicz,
1994;
Kagan
andJackson,
1995].
It isperhaps
ironicwithin
anewly
formed
faultzone
composed
ofnumerous
short
(<10
therefore
that the closestmatchbetweenthe historicaland km) segments
thatmightaccommodate
moreelasticstrainthana
geological
datafromthePPAFZshould
beobtained
fromonly6.5 mature
faultwhichhasundergone
strain
softening.
Thebehavior
of
years
(1988-1994)
of seismicity
data(Table3), giventhat thePPAFZ
atitspresent
stage
ofdevelopment
could
therefore
be
recurrence
estimates
based
onsuch
a short
timeperiod
would
be moreconsistent
withthatof intra-plate
faultzones,
i.e.,
assigned
alowweighting
inany
seismic
hazard
assessment
ofthatcharacterized
bylowsliprate,
more
interseismic
faulthealing
region.
processes,
andlarger
sliporstress
dropperevent
[Kanamori
and
The
available
palcoseismic
data
show
that
even
atthis
earlyAllen,
1986].
stage
ofdevelopment,
elements
ofthePPAFZ
areamenable
to Although
theavailable
recurrence
anddisplacement
estimates
in the PPAFZareconsistent
with theinferred
palcoseismic
investigation.
The apparent
absence
of large for largeearthquakes
geological
slip
rate
of
the
Porter's
Pass
fault,
we
cannot
discount
the
landslides
orsurface
ruptures
withages
between
oryounger
than
possibility
that
the
slip
per
event
is
less
than
that
required
to
account
500-700
and
2000-2500
years
B.P.
indicates
thatthedata
forthelate
Holocene
maybe complete.
However,
it is clearfromthe for the total strain, which recent studies have shown to be
distribution
of landslide
ages
thatevidence
forevents
olderthan geodeticallymeasurableat well over the 95% confidencelevel
6034
COWAN ET AL.: PALEOSRISMICITY IN A NEWLY FORMED FAULT ZONE
(Pearson
et al., submitted
manuscript,
1995).At present,sliprates
Stephenson,
Preliminary
reports
ontheInangahua
earthquake,
New
Zealand,May 1968,DSIR Bull. 193, 1968.
for faultsin the centraland easternpartsof the PPAPZare too
F.,Seismic
explorations
of theburied
faultassociated
with
the
poorly definedto permit momentrate summationfor direct .•rnaike,
1948 Fukui earthquake,J'.Phys.Earth, 35, 285-308, 1987.
comparison
withratesof geodeticstrain,butit ispossible
thatsome Anderson,
H.,T.Webb,
andJ.Jackson,
Focalmechanisms
oflarge
fraction of the slip across the PPAFZ is distributedamong
quakes
intheSouth
Island
ofNewZealand:
Implications
fortheaceore.
ofPacific-Australia
platemotion,
Geophys.
J.Int.,115,1032.
secondary
structures,
or accommodated
by smallerearthquakes modation
1054, 1993.
thanwepresentlyrecognize
in thegeological
record.Oneof several
H., S.Beanland,
G.Blick,D. Darby,
G.Downes,
I. Haines,
J.
explanationsadvancedto explain a historicdeficit of moment Anderson,
Jackson,
R.Robinson,
andT. Webb,
The1968May9_3
Inangahua,
New
releasein California[e.g.,Dolan et al., 1995]is thata largerfraction
Zealand,eaxthquake:
An integrated
geological,
geodetic,
andseisra0.
logicalsourcemodel,N•Z. J. Geol. Geophys.,37, 59-86, 1994.
of thetotalsliprateacrossthatregionis releasedby morefrequent
J.G.,M. Ellis,andC.DePolo,
Earthquake
rateanalysis,
TeetonG.
moderate(M~6-6.5) earthquakes
for whichthereis lessgeological Pmderson,
physics,218, 1-21, 1993.
evidence [Ward, 1994; Wesnousky,1994]. Alternatively, a
Arabasz,
W.J.,andR. Robinson,
Microseismicity
andgeological
strucl•
proportionof the strain may be accommodatedby relatively
inthenorthern
South
Island,
NewZealand,
N. Z.J. Geol.Geophys.,
I9,
569-601, 1976.
aseismicslip in numeroussmallearthquakes
[e.g.,Lin and Stein,
1989;Hill et at., 1990].In thePPAFZ,thehistoricalseismicityrates ,&rnad6ttir,
T.,J.Beavan,
andC.Pearson,
Deformation
associated
with
the
18 June,!994, Arthur'sPassearthquake,
New Zealand,N.Z.J.Geol.
may be "randomly"high for the sampledtime periodsand
Geopirys.,in press,1995.
magnituderange considered,but it is also plausiblethat the Barnes,P.M.,Structural
stylesandsedimentation
at thesouthern
terminafrequencyof largeearthquakes
maybequasi-periodic
andgoverned
tionoftheHikurangi
subduction
zone,offshore
NorthCanterbury,
byfactorsuniqueto a faultzonein theearlystages
of development. Zealand,
Ph.D.thesis,
Univ.ofCanterbury,
Christchurch,
NewZealand,
1994.
Conclusions
Dated surfacerupturesand landslidescorroborate
an inference
Beavan,
J.,D. Darby,
G.Blick,C.Pearson,
T •d'nad6ttir,
R.I.Walcott,
Parsons,and P. England,GPS measurements
at the transition
between
continental
collision
andsubduction
on thePacific-Australian
plate
boundary
inNewZealand,
EosTrans.
AGU,75(44),
FallMeet.
Suppl,
oftwolarge(M >7.0)earthquakes
withinthePPAFZduringthelast
669, 1994.
~2500 years.Two earliereventsduringthe Holoceneare also Berryman,
K., ActivefaultingandderivedPHS directions
in theSouth
Island,
NewZealand,
inTheOriginoftheSouthern
Alpsedited
byR.[
recognized,
but the dataprior to 2500 yearsarepresumed
to be
WalcottandM.M. Cresswell,
Bull.R. $oc.N.Z., 18, 29-34,1979.
incomplete.
A returnperiodof 1300-2000yearsfor ruptureof the Berryman,
K.R., andS. Beanland,
Variationin faultbehavior
in different
PPAFZwouldbeconsistent
with theinferredsliprate(3-4 rnm/yr)
tectonicprovinces
of New Zealand,J. Struct.Geol.,13, 177•189,1991.
ofitsprincipalelement,
thePorter'sPassfault,provided
thattheslip Brown,
LJ., Geological
mapofNewZealand,
sheet
S76"Kaiapoi",
1st
ed.
per eventis in the range4-8 m.
scale1:63,360,Dep.of Sci.Ind.Res.,Wellington,
NewZealand,
1973.
T Moutoux,
andW.M.Phillips,
Lichen
dating
Palcoseismic
datafrom the adjacentstmcturally
matureHope Bull,W.B.,J.King,E Kong,
of
coseismic
landslide
hazards
in
alpine
mountains,
Geomorphology,
fault zone farthernorthindicatesignificantdifferences
in fault
10, 253-264, 1994.
b•haviorwith respectto the PPAF'Z,with recurrence
intervalsfor Burrows,
CJ.,A 500-year
oldlandslide
in theAcheron
Rivervalley,
Caw
terbury,N.Z. J. Geol.Geophys.,
18, 357-360,1975.
largeearthquakes
apparently
differingby a factorof 5 or more.
at
Paradoxically,
thedifferences
in historical
seismicity
ratesfor the Carter,R.M., and L. Carter,The MotunauFault and otherstructures
southern
edgeof theAustralian-Pacific
plateboundary,
offshore
Marl-
Hope
fault
and
PPAFZ
( zones
i and
2,respectively,
Figure
lb)are borough,
New
Zealand,
Tectonophysics,
88,133-159,
1982.
negligible
despite
anorder
ofmagnitude
difference
insliprateand Chinn,
T.J.H.,
Useofrock
weathering-rind
thickness
forHolocene
absolu!e
in NewZealand,Arct.Alp.Res.,13, 33-45,1981.
cumulative
offsetassociated
withthemajorfaults.Themagnitude- age-dating
K.I.,Temporal
andspatial
clustering
ofearthquake
activity
frequency
distribution
fortheHopefaultregionisin accord
withthe Coppersmith,
centralandeasternUnitedStates,Seismol.Res.Lett.,59, 299-304,
characteristic
earthquake
model,whereas
themagnitude-frequency the
1988.
distributionin the PPAPZ is approximated,
but slightly Cornell,C.A.,Engineering
seismic
riskanalysis,
Bull.Seismol.
Soc.
overpredicted,
by theGutenberg-Richter
relationship
(Table3 and
58, 1583-1606, 1968.
Figure7). The comparisonof thesetwo fault zonesdemonstratesCowan,H.A., LateQuaternary
displacements
ontheHopefaultatGly•m
Wye,NorthCanterbury,
N.Z.J. Geol.Geophys.,
33,285-293,1990.
theimportance
of thestructural
maturityof thefaultzonein relation
H.A.,TheNorthCanterbury
earthquake
of September
1, 1888,
J.
toseismicity
ratesinferredfromrecent,
historical,
andpalcoseismicCowan,
R. Soc.N.Z.,21, !-12, 199!.
Cowan,H.A., Structure,
seismicityand tectonics
of the Porter's
AmberleyFaultZone, North Canterbury,
New Zealand.Ph.D.th•s,
Acknowledgments.This study was fundedby the New Zealand
Univ.of Canterbury,
Christchurch,
New Zealand,1992.
UniversityGrantsCommittee
andNewZealand'Earthquake
Commission,Cowan,H.A., (Compilor),Fieldguideto New Zealandactivetecto•esandformedpartof a Ph.D.programmewithintheActiveTectonicsResearch
Groupat the Universityof Canterbury.
BrianMolloy andNeville Moar
providedradiocarbon
agesand pollendatafrom sitesat Porter'sPass.We
IASPEI94,27thGeneralAssembly
of IASPEI,January
1994,Welllag.
ton, R. Soc.N.Z. Misc. Sen, 27, 1994.
H.A., andM.S.MeGlone,
LateHolocene
displacements
and
thankWarwickSmithandtheNewZealandSeismological
Observatory
for Cowan,
acteristicearthquakes
on the HopeRiver segment
of theHopefault,
seismicity
dataandConradLindholmfor helpwithdatareprocessing
at
New Zealand,J.R. Soc.N.Z., 21,373-384, 1991.
NORSAR.Reviewsby JohnAdams,KelvinBerryman,
Bill Bull,Hilmar
Coyle, S., The Porter'sPassFault, M.Sc. thesis,Univ. of Canterbury,
Bungum,
Jarg
Pettinga,
Maud
McSaveney,
Mark
Stirling,
and
Bob
Yeats Christchurch,
New
Zealand,
1988.
improved
thepaper
and
provided
impetus
toextend
some
aspects
ofthe Davis,
T.L.,andS.S.Namson,
A balanced
cross-section
oftheI994
work,
which
was
completed
while
the
first
author
worked
atthe
Norwegian
Northridge
earthquake,
southern
California,
Nature,
$72,167-169,
GeotechnicalInstituteand NorwegianSeismicArray (NORSAR),
1994.
supported
by a fellowship
fromtheResearch
Councilof Norway.
References
Adams,
J., ,--Earthquake-dammed
lakesin NewZealand,
Geology,
9, 215219, 1981.
Adams,
R.D.,G.A.Eiby,M.A.Lowry,G.J.Lensen,
R.P.Suggate,and
W.P.
Davison,
F.C.,andC.H.Scholz,
Frequency-moment
distribution
of
quakesin the AleutianAre: A test of the characteristic
earthq•
model,Bull. Seisrnol.Soc.Am., 75, 1349-1361,1985.
DeMets,C.,R.G.Gordon,
D.E Argus,andS. Stein,Current
platemoti0.•
Geophys.J. !nt., I01,425-478, 1990.
Doig,R.,2300yrhistory
of seismicity
fromsilting
events
inLake
Tadot•
sac,Charlevoix,
Quebec,Geology,
18, 820-89_.3,
1990.
COWAN ET AL.: PALEOSEISMICITY IN A NEWLY FORMED FAULT ZONE
6035
Dolan,
J.F.,K. Sieh,T.K.Rockwell,
R.S.Yeats,
J. Shaw,
J. Suppe,
G.H. NewZealand
Seismological
Observatory,
NewZealand
earthquakes:
1850I/u/tile,andE.M. Garb,Prospects
for largeror morefrequent
earth-
1994.Observatory
MasterFile,Inst.of Geol.andNuel.Sci.,Welling-
quakes
intheLosAngeles
metropolitan
region,
Science,
267,199-205,
ton, New Zealand, 1994.
1995.
Dowrick,
D.J.,andE.G.C.Smith,Surface
wavemagnitudes
of someNew
Zealand
earthquakes
1901-1988,
Bull.N. Z. Nat.Soc.Earthquake
Eng.,
23,198-219,1990.
Nicol,A., B.V.Alloway,andP.J.Tonkin,Ratesof deformation,
upliftand
landscape
development
associated
withactivefoldingin theWaipara
areaof NorthCanterbury,
New Zealand,Tectonics,
13, 1327-1344,
1994.
seismicpotential:1989-1999,PureAppI.
Eiby,
G.A.,An annotated
listof NewZealand
earthquakes,
1460-1965,Nishenko,S.P.,Circum-Pacifi½
N•.J. Geol.Geoœhys.,
11,630-64'7,1968.
Geoptrys.,135,169-259,1991.
S.P.,andL.R.Sykes,
Comment
on"Seismic
gaphypothesis:
Ten
Eiby,
G.A.,NewZealand
seismological
report1948-49~50,
Bull.E-164, Nishenko,
S•ismol.
Ohs.,W½11ington,
New Zealand,1982.
Eiby,
G.A.,TheLakeColeridge
earthquakes
of 1946,
Bull.N.Z.Nat.$oc.
yearsafter"by Y.Y. KaganandD.D. Jackson,
J. Geophys.
Res.,98,
9909-9916, 1993.
Okal,E.A.,andB.A.Romanowicz,
On thevariation
of b-valueswithearthEarthquake
Eng.,23, 150-158,1990.
quakesize,Phys.EarthPlanet.Inter.,87, 55-76,1994.
Fr•und,
R., TheHopeFault:A strike-slip
faultin NewZealand,
N.Z.Geol.
Pearson,
G.W.,andM. Stuiver,High-precision
calibration
of theradiocarbontimescale,500-2500BC,Radiocarbon,
28,839-862, 1986.
Peek,R., J.B. Benill, and R.O. Davis, A seismicitymodel iiar New
bury,
Christchurch,
NewZealand,
! 992.
Eng.,!3, 355-364,1980.
Crregg,
D.R.,Geological
mapof NewZealand
sheet18,"Hurunui"
scale Zealand,Bull.N.Z.Nat.$oc.Earthquake
Surv.Bull., 86, 1971.
6arlick,
R., LeesValleyFault.B.Sc.(Hons)dissertation,
Univ. of Canter1:250,000,
N.Z. Dep. of Sci. Ind. Res.,Wellington,New Zealand,1964.
Henderson,
J., WestNelsonearthquake
of 1929,N.Z.J. $ci. Technol.,
19.
66-144, 1937.
Plafker, G., and G.E. Ericksen, Nevados Huascaran avalanches, Peru, in
Rockslides
and Avalanches1, editedby B. Voight,pp. 277-314, Elsevier
Sci., New York, 1978.
N.Z.J.
ttcu'zer,
R.H., andJ.D. Bradshaw,
The MotunauFaultandotherstructures
at Reyners,M.E., New Zealandseismicity1964-87:An interpretation,
Geol. Geophys.,32, 307-315, 1989.
the southernedge of the Australian-Pacificplate boundary,offshore
Reyners,M.E. andH.A. Cowan,The transitionfrom subduction
to contiMarlborough,
New Zealand,Tectonophysics,
J15,161-166,1985.
nentalcollision:crustalstructurein the North Canterburyregion,New
Hill,D.P.,J.P.Eaton, and L.M. Jones,Seismicity!980-86, in The San
Zealand,Geopl•ys.
J. Int., 115, 119_4-1136,
1993.
Andreas
Fault System,California, U.S. Geol. Surv.Prof. Pap. 1515,
Robinson,R., Extentandgeometryof subduction
in the northernSouth
115-15!, 1990.
Islandand Wellingtonregions,New Zealand,Geol. Soc. N7.. Misc.
Hull,A.G., Tectonicsof the 1931 Hawk½'sBay earthquake,
N.Z.g. Geol.
PubI., 56, 44-46, 1991.
Geophys.,
33,309-320, 1990.
Jibson,
R.W., C.S. Prentice,B.A. Borisoff,E.A. Rogozhin,andC.J.Langer, Roelofts,E., and J. Langbein,The earthquakepredictionexperimentat
Parkfie!d,California,Rev.Geophys.,32, 315-336, 1994.
Someobservationsof landslidestriggeredby the 29 April, 1991, Racha
of the Arthur's Pass
earthquake,
Republicof Georgia,Bull. Seismol.Soc.Am..84,963-973, Rynn, J.M.W., and C.H. Scholz, Seismotectonics
I994.
region,southIsland,NewZealand,Geol.Soc.Am.Bull., 89, 1373-1388,
1978.
Kagan,
Y.Y., and D.D. Jackson,Long-termprobabilistic
forecasting
of
Scholz,C.H., Commentsonmodelsof earthquakerecurrence,in, Proceedearthquakes,
J. Geophys.
Res.,99, 13,685-13,700,1994.
ingsof Conference
XLV- Fault Segmentation
and Controlsof Rupture
Kagan,
Y.Y.,andD.D. Jackson,
New seismicgaphypothesis:
Fiveyears
Initiation and Terrnination,editedby D.P. Schwartzand R.H. Sibson,
after,
J. Geophys.
Res.,J00, 3943-3959,1995.
UJ. Geol.Surv.OpenFile Rep.,89-315, 350-360, I989.
Kanamori,
H., and C.R. Allen, Earthquakerepeattime andaveragestress
drop,
in Earttuluake
Source
Mecimnics,
Geophys.
Monogr.
Set.,vol 37, Schwartz, D.P., Palcoseismicity,persistenceof segments,and temporal
clusteringof large earthquakes-Examples
from the San Andreas,
edited
by S. Das,J. Boawright,andC.H. Scholz,pp. 157-167,AGU,
Wasatch,andLostRiver fault zones,in, Proceedings
of ConferenceXL,V
Washington,
D.C., 1986.
- Fault Segmentation
and Controlsof RuptureInitiationand TerminaKeefer,
D.K., Landsfides
caused
by earthquakes,
Geol.$oc.Am.Bull.,95,
tion, editedby D.P. Schwartzand R.H. Sibson,U3'. Geol. Surv.Open
406-421, 1984.
File Rep.,89-315,361-375, 1989.
Kieckhefer,
R.M., Microseismicityin the vicinity of the Clarencefault,
Schwartz,D.P., and K.J. Coppersmith,Fault behaviorand characteristic
NewZealand,N.Z. J. Geol. Geophys.,20, 165-177,1977.
ExamplesfromWasatchandSanAndreasFaults,J. GeoKing,
G.C.P.,Theaccommodation
of largestrains
in theupperlithosphere earthquakes:
phys.Res.,89, 5681-5698,1984.
oftheearthandothersolidsby self-similar
faultsystems:
ThegeometriShaw,J., andJ. Suppe,Active faultingand growthfolding in the eastern
caloriginofb-value,
PureAppI.Geophys.,
121,762-815,
1983.
SantaBarbaraChannel,California,Geol. Soc.Am. Bull., 106, 607-626,
King,
G.C.P.,andJ. Nabelek,The roleof bendsin faultsin theinitiation
1994.
andtermination
of earthquake
rupture,
Science
228,984-987,1985.
Sibson,
R.H., Stoppingof earthquakerupturesat dilationalfault jogs,
Kirkaldy,
P.H.S.,andE.G.Thomas,
Finalreportona seismic
survey
in the
Canterbury
Plainsareaof NewZealand,
BPShellandToddPetroleum Nature, 316, 248-251, 1985.
Development
Ltd,N.Z.Geol.Surv.OpenFilePet.Rep.,328,1963.
Knuepfer,
P.L.K.,
Temporal
variations
inlatest
Quaternary
slipacross
the
Australian-Pacific
plateboundary,
northeastern
SouthIsland,New
Sibson,R.H., Earthquake
faultingas a structuralprocess,
J. Struct.Geol.,
!I, 1-14, 1989.
Sieh,K., M. Stuiver,andD. Brillinger,A more precisechronologyof earth-
quakesproduced
by the SanAndreasfaultin southern
California,J.
Geophys.
Res.,94, 603-623,1989.
earthquake
of 25thDecember,
1987source
mechanism
at WhittierNarrows,LosAngelesBasin,Cali- Skey,H.E, Reporton theNorthCanterbury
199,2,in RecordSurveyN.Z., Dept. of Landsand Surv., Wellington,
f0mia,
J.Geophys.
Res.,94,9614-9632,
1989.
New Zealand, 1925.
McKay,
A.,Ontheearthquakes
ofSeptember
1888,
intheAmuri
andMar- Sinalley,R., J.Pujol,M. Regnier,J.M. Chiu,J.L. Chatelain,B.L. Isacks,M.
lborough
districts
of theSouth
Island,
N•'. Geol.Surv.
Rep.Geol. Araujo,andN. Puebla,Basementseismicitybeneaththe AndeanPreZealand,Tectonics,11,449-464, 1992.
Lin,J.,andR.S.Stein,Coseismie
folding,earthquake
recurrence
andthe
ExpIor.,20, 1-16, 1890.
cordilleranthin-s'kinnedthrust belt and implicationsfor crustal and
McKay,
A., Report
ontherecent
seismic
disturbances
withinCheviot lithospheric
behavior,
Tectonics,
12, 63-76,!993.
County
innorthern
Canterbury
andtheAmudDistrict
ofNelson,
New Smith,W.D., and K.R. Berryman,Earthquakehazardin New Zealand:
Zealand,
Govt.Print.,Wellington,
NewZealand,
1902.
lnlErences
fromseismology
andgeology,Bull.Roy.Soc.N.Z., 24,223MeSaveney,
M.J.,Sherman
Glacier
rockavalanche,
Alaska,
U.S.A,,in
242, 1986.
Rockslides
andAvalanches
1,edited
byB.Voight,
pp.197-258,
ElsevierSpeight,
R., TheArthur'sPassearthquake
of 9thMarch,1929,N.Z.J. Sci.
Sei.,New York,1978.
Technol.,15, 173-182, 1933.
M½Saveney,
MJ.,A manual
ofweathering-rind
dating
forsandstone
ofthe Speight,R., Recentfaultingin theSouthern
Alps,N.Z.J. Sci.TechnoI.,
!9,
Torlesse
Supergroup,
Tech.
Rep.
92/4,N.Z.Inst.
ofGeol.
andNucl.
Sci., 701-708, 1938.
Wellington,
NewZealand,1992.
R.S., and G. EkstrOm,Seismicityand geometryof a 110 ima-long
McSaveney,
M.J.,Rockavalanches
of 2 Mayand16September
1992, Stein,
blind thrustfatdt, 2, Synthesisof the 1982-1985Californiaearthquake
Mount
Fleteher,
NewZealand,
Landslide
News,
7, 2-4,1993.
sequence,
J. Geophys.
Res.,97, 4865-4883,1992.
MeSaveney,
M.J.,T.J.Chinn,
andG.T.Hahcox,
MountCookrockava- Stein,
R.S., andR.S. Yeats,Hiddenearthquakes,
Sci. Am., 260 (6), 30-39,
lanche
of 14December
1991,NewZealand,
Landslide
News,
6,32-34,
1989.
1992.
6036
COWAN ET AL.: PALEOSEISMICITYIN A NEWLY FORMED FAULT ZONE
Stuiver,M., and G.W. Pearson,High-precisioncalibrationof the radiocarbon time scaleAD 1950-500 BC, Radiocarbon,28, 805-838, 1986.
Sruiver,M., andP.J'.Reimer,A computerprogramfor radiocarbon
agecalibration, Radiocarbon, 28, 1022-1030, 1986.
Tortkin,P.S.,andL.R. Basher,Soil-stratigraphic
techniques
in thestudyof
soil and landformevolutionacrossthe SouthernAlps, New Zealand,
Geomorphology,
3, 547-575, 1990.
Trangrnar,
B.B.,Overviewof Canterbury
loessdeposits:
Tourguideforgut.
Syrup.on Loess:February14-21,presented
at Third Meetingof West-
W'dson,
D.D.,Geology
oftheWaipara
subdivision,
N.Z.Geol.
Surv.
Bull.
64, 122pp., 1963.
Wood,
R.A.,
J.R.
Pettinga,
S.Bannister,
G.Lamarche,
and
T.$.
McMorraa,
Structure
oftheHahruer
strike-slip
basin,
Hope
fattit,
New
Zealand,
Geol. $oc. Am. Bull., 106, 1459-1473, 1994.
Working
Group
onCalifornia
Earthquake
Probabilities,
Probabilities
of
largeearthquakes
in theSanFransisco
BayRegion,
California,
Geol. $urv.Circ., 1053, 51 pp., 1990.
Yang,
J.S.,TheKakapo
Fault-A
major
active
dextral
faultinthecentral
NorthCanterbury-Buffer
regions
ofNewZealand,
N.Z.J.Geol.
ern Pacific, INQUA LoessComm., Christchurch,New Zealand, 1987.
VanDissen,R., andR.S. Yeats,HopeFault,Jordanthrust,andupliftof the
SeawardKaikouraRange,NewZealand,Geology,19, 393-396,1991.
Wallace,R.E., Groupingandmigrationof surfacefaultingandvariations
in
sliprateson faultsin the GreatBasinprovince,Bull. $eismol.$oc.Am.,
phys.,34, 137-143, 1991.
Yang,
J.S.,
Landslide
mapping
andmajor
earthquakes
ontheKakapo
SouthIsland,NewZealand,J. R.. Soc.N.Z.,22,205-212,199o_
Yeats,
R.S.,midK.R.Berryman,
South
Island,
NewZealand,
andTrans.
77, 868-876, 1987.
verse
Ranges,
California:
A seismotectonic
comparison,
Tectonics,
6,
363-376, 1987.
Whrd,S.N., A multidisciplinary
approachto seismichazardin southern
California,Bull. $eismol.$oc. Am., 84, 1293-1309, 1994.
Wellman,H.W., Datafor thestudyof RecentandlatePleistocene
faulting
in the southIslandof New Zealand,N.Z.J. $ci. Technol.B 34, 270-288,
Youngs,
R.R.,andK.J.Coppersmith,
Implications
of faultsllprates
earthquake
recurrence
models
toprobabilistic
seismic
hazard
estimale•
Bull. Seismol.5oc. Am., 75, 939-964, 1985.
1953.
Yousir,
H.S.,Theapplications
ofremote
sensing
togeomorphologieal
he0.
Wells,D.L., andK.J. Coppersmith,
New empiricalrelationships
among
tectonic
mapping
in NorthCanterbury,
NewZealand,
Ph.D.thesis,
magnitude,rupturelength,rupturewidth,rupturearea,andsurfacedis-
Univ. Canterbury,
Christchurch,
New Zealand,1987.
placement,Bull. $eismol.$oc. Am., 84, 974-1002, 1994.
Wesnousky,
S.G., Seismological
and structuralevolutionof strike-slip
faults,Nature, 335, 340-343, 1988.
H. Cowan,NorwegianSeismicArray, RO. Box 51, Kjeller,N-2007
norsar.no)
Wesnousky,
S.G.,Seismicity
asa function
of cumulative
geologic
offset: Norway.(e-mail:hugh@trane.
A. Nicol, FaultAnalysisGroup,Departmentof EarthSciences,
University of Liverpool,LiverpoolL69 3BX, England.
P.Tonkin,Departmentof Soil Science,LincolnUniversity,P.O.Box94,
Wesnousky,
S.G.,TheGutenburg-Riehter
or characterisle
earthquake
disLincoln, New Zealand.
tribution,whichis it?Bull. Seismol.Soc.Arn.,84, 1940-1959,1994.
someobservationsfrom southernCalifornia,Bull. Seismol.$oc. Am.,
80, !374-1381, 1990.
Wesnousky,
S.G.,C.H.Seholz,K. Shimazaki,
andT. Matsuda,
Earthquake
frequency
distribution
andthemechanics
of faulting,
J. Geophys.
Res.,
88, 9331-9340, 1983.
Whitehouse,
I.E., andG.A. Griffiths,
Frequency
andhazard
of largerock
23, 1994;revisedMay 15, 1995;
avalanches
in the centralSouthern
Alps,New Zealand,Geology,
11, (ReceivedSeptember
331-334, !983.
acceptedMay 23, 1995. )