How does the challenge differ between plate boundaries, plate

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TOPIC 2:
How does the challenge of predicting
hazards differ between earthquakes
- at plate boundaries
- In plate boundary zones
- within plates?
Earthquake locations map narrow plate
boundaries, broad plate boundary zones &
regions of intraplate deformation
DIFFUSE BOUNDARY
ZONES
INTRAPLATE
NARROW
BOUNDARIES
Stein & Wysession, 2003 5.1-4
PLATE
BOUNDARY
PLATE
BOUNDARY ZONE
INTRAPLATE
A. Newman
Mountain building by
continental collision
produced boundary
zone extending 1000’s of
km northward from the
nominal plate boundary
at the Himalayan
front.
COLLISION BETWEEN INDIAN AND EURASIAN
PLATES: SPACE GEODETIC MOTIONS.
Total plate convergence
taken up several ways.
About half occurs
across locked Himalayan
frontal faults such as the
Main Central Thrust
These faults are part of
the interface associated
with the underthrusting
Indian continental crust,
which thickens crust
under high Himalayas.
Larson et al., 1999
COLLISION BETWEEN INDIAN AND EURASIAN
PLATES: SPACE GEODETIC MOTIONS.
GPS data also show
along-strike motion
behind the convergent
zone, in the Tibetan
Plateau, presumably
because the uplifted and
thickened crust spreads
under its own weight.
Extension is part of
a large-scale process of
crustal "escape" or
"extrusion" in which large
fragments of continental
crust are displaced
eastward by the collision
along major strike-slip
faults.
Larson et al., 1999
NORTH
AMERICA
- PACIFIC
PLATE
MOTION
48 mm/yr
PLATE
BOUNDARY:
SAN
ANDREAS
30-45 mm/yr
1900-2002
NORTH AMERICA
PACIFIC
PLATE BOUNDARY
ZONE: 1-10 mm/yr
OFF MAIN
BOUNDARY
INTRAPLATE :
(< 1 mm/yr)
CONTINENTAL STRIKE SLIP BOUNDARY ZONE
Stein, 1993
PLATE BOUNDARY
Most of the plate motion occurs on narrow
(< 100 km wide) boundary
Earthquakes result primarily from plate motion
Earthquake recurrence directly reflects known
plate motion
Earthquake locations don’t change for long time
(Myr)
Past plate motion, present plate motion,
geological, seismological, and geodetic rates
are consistent and so give consistent estimates
of earthquake hazard
1906 SAN FRANCISCO
EARTHQUAKE
Average 4 m
of motion
West side
moved north
Motion along
hundreds of
miles of San
Andreas
Fault
USGS
ELASTIC REBOUND MODEL PROPOSED
Over many years, rocks on
opposite sides of the fault move,
but friction on the fault "locks" it
and prevents slip
Eventually strain stored is more
than fault rocks can withstand,
and the fault slips in earthquake
Before plate tectonics, no idea
why motion occurred
Even so, F. Omori used Japanese experience to
predict that a similar earthquake was at least 100
years away
SAN ANDREAS FAULT
GPS FAR FIELD SLIP RATE
35 mm/yr
GEOLOGIC SLIP RATE 3700 yr ~ 35 mm/yr
Locked strain will be
released in next
earthquake
Since last earthquake
in 1857 ~ 5 m slip
accumulated
Z.-K. Shen
Agreement between paleoseismology, plate
motion, & GPS shows that large earthquakes
take up most of the motion
mean 132 yr
s 105 yr
Although time
between
earthquakes is
variable
36 mm/yr * 132 yr
~ 5 m slip
~ magnitude 7.7
earthquake
Sieh et al., 1989
VARIATIONS IN RECURRENCE TIME MAY BE DUE
TO DIFFERENCES IN EARTHQUAKE SIZE AND
STRESS TRANSFER
R. Stein et al., 1997
NORTH
AMERICA
- PACIFIC
PLATE
MOTION
1900-2002
NORTH AMERICA
48 mm/yr
PACIFIC
PLATE BOUNDARY
ZONE:
1-10 mm/yr OFF
MAIN BOUNDARY
PLATE BOUNDARY ZONE (1-10 mm/yr)
Some of the plate motion occurs in broad
(< 1000 km wide) zone away from boundary
Earthquakes result from plate motion and local
effects (topography)
Earthquake recurrence does not reflect known
plate motion
Earthquake locations change on intermediate
time (10 - 100 Kyr)
Geological, seismological, and geodetic rates
are usually consistent and so give consistent
estimates of earthquake hazard
PACIFIC NORTH
AMERICA
PLATE
BOUNDARY
ZONE
Earthquakes
away from
San Andreas
San Andreas
Fault system
GPS site
velocities
relative to
North America
Bennett et al., 1999
Intermountain
seismic belt
Eastern
California
shear
zone
Colorado
Plateau
Wasatch fault,
Salt Lake City,
Utah
M~7
earthquakes in
past 6000
years
None in past 500 years
GPS shows strain
building up for future
earthquakes
WASATCH FAULT: GPS & EARTHQUAKES AGREE
1 mm/yr -> 1 m/ 1000 yrs -> M7
M 7 expected ~ 1000 yr from seismicity
GPS consistent - shows ~1-2 mm/yr
extension
Stein et al., 2005
Chang et
al., 2006
PLATE INTERIOR (2< mm/yr)
Plate interior deforms slowly far away from
boundary
Don’t know what causes earthquakes, probably
indirect result from plate motion, mantle flow, and
local effects (topography, sediment, glacial)
Earthquake recurrence does not reflect known
plate motion
Earthquake locations change on short time scales
(100s - Kyr)
Geological, seismological, and geodetic rates can
differ and so give different estimates of
earthquake hazard
CONTINENTAL INTRAPLATE EARTHQUAKES
Complex regional system of interacting faults
Seismicity migrates between faults due to stress transfer
Seismicity varies in space and time
Earthquakes can occur on fault for a while, then move
Past can be poor predictor
A complex system whose behavior
depends on the
interactions between
components that can’t
be viewed in isolation
McKenna, Stein & Stein, 2007
CONTINENTAL INTRAPLATE EARTHQUAKES ARE
OFTEN EPISODIC, CLUSTERED & MIGRATING
“Large continental
interior earthquakes
reactivate ancient
faults … geological
studies indicate that
earthquakes on
these faults tend to
be temporally
clustered and that
recurrence intervals
are on the order of
tens of thousands of
years or more.”
(Crone et al., 2003)
Meers fault,
Oklahoma
Active 1000 years
ago, dead now
Liu, Stein & Wang 2011
during the period
prior to the period
instrumental events
Earthquakes in North China
Beijing
Bohai Bay
Ordos
Plateau
1303 Hongtong
M 8.0
Weihi rift
Large events often pop up where there was little seismicity!
Liu, Stein & Wang 2011
during the period
prior to the period
instrumental events
Earthquakes in North China
Beijing
Bohai Bay
Ordos
Plateau
Weihi rift
1556 Huaxian
M 8.3
Large events often pop up where there was little seismicity!
Liu, Stein & Wang 2011
during the period
prior to the period
instrumental events
Earthquakes in North China
Beijing
Bohai Bay
Ordos
Plateau
Weihi rift
1668 Tancheng
M 8.5
Large events often pop up where there was little seismicity!
Liu, Stein & Wang 2011
during the period
prior to the period
instrumental events
Earthquakes in North China
1679 Sanhe
M 8.0
Beijing
Bohai Bay
Ordos
Plateau
Weihi rift
Large events often pop up where there was little seismicity!
Liu, Stein & Wang 2011
during the period
prior to the period
instrumental events
Earthquakes in North China
1975 Haicheng
M 7.3
Beijing
1976 TangshanBohai Bay
M 7.8
Ordos
Plateau
1966 Xingtai
M 7.2
Weihi rift
Large events often pop up where there was little seismicity!
No large (M>7) events ruptured the same
fault segment twice in past 2000 years
Historical
Instrumental
Weihi rift
In past 200 years, quakes migrated from Shanxi Graben to N. China Plain
Maps are like ‘Whack-a-mole’ - you wait for
the mole to come up where it went down,
but it’s likely to pop up somewhere else.
NEW MADRID SEISMICITY: 1811-12 AFTERSHOCKS?
Stein & Newman, 2004
Ongoing seismicity looks
like aftershocks of 1811-12,
as suggested by the fact
that the rate & size are
decreasing. Moreover, the
largest are at the ends of
the presumed 1811-12
ruptures
Rate-state friction
predicts aftershock
duration
 1/loading rate
Plate boundary
faults quickly
reloaded by steady
plate motion after
large earthquake
Long aftershock sequences
in slowly deforming
continental interiors
Stein & Liu, 2009
Stein & Liu
2009
Faults in continents
reloaded much
more slowly, so
aftershocks
continue much
longer
Lots of seismicity may be aftershocks
Aftershock
sequence of
the 1976
Tangshan
earthquake
continues
today (M. Liu)
Effect of major (5 MPa) weak zones
Complex space-time variability due to fault interactions via
stress transfer
Seismicity extends beyond weak zones
Short-term seismicity does not fully reflect long-term
Variability results from steady platewide loading
without local or time-variable loading
We are just
beginning to study
how mid-continent
earthquakes work,
but it seems that
often
Hazard assessment based only on the recent
earthquake record overestimates the risks in
regions of recent large earthquakes and
underestimates them where seismicity has
been recently quiescent.
PLATE
BOUNDARY:
1900-2002
Hazard
assessment
is
reasonably
good (“B”)
NORTH AMERICA
PACIFIC
All should be
better in China
due to longer
earthquake
record
PLATE BOUNDARY
ZONE:
Hazard assessment
is adequate (“C”)
INTRAPLATE:
Hazard assessment
is probably poor
(“D”)
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