February 25, 2010
Robert Muir-Wood
Chief Research Officer, RMS
CC
Miami
Feb 16th 2009
Larry Ruff and
Hiroo Kanamori
(1980)
Seismicity and
Subduction
Physics of the Earth
and Planetary
Interiors, 23, pp240252
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Mw 9.1 earthquake 1200km fault rupture
Displacement up to 20m
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Halobanon Tuangku Islands
12% of land in Banda Acheh has subsided and is
now at increased risk of surge and flood
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 After Dec 26th 2004 the old ‘M9 earthquake theory’ was clearly
wrong
 If the medical community had a theory – and then 300,000 people
died in an event that the theory said could not happen – would
they:
– Apologize?
– Immediately ensure this could not happen again
 & initiate a research project to determine where else such events
could occur.
 Such as NE Japan?
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 In 869 AD earthquake and tsunami was known to have struck the area
around Sendai, Sanriku Coast, Japan
– At the time of the earthquake, the Imperial Court of Japan battled with an
indigenous people of the Tohoku region. According to Nihon Sandai Jitsuroku,
around 1000 people were killed by the tsunami.
– The tsunami caused extensive flooding of the Sendai plain, destroying the town of
Tagajo.
 By 2001 archaeological investigations had identified the remains of 8th and
9th century buildings beneath the town, covered by sediments dated to the
middle of the 10th century. Tsunami sand deposits were found up to
4 kilometres (2.5 mi) from the coast.
 Three tsunami deposits were identified within the Holocene sequence of the
Sendai plain, all formed within the last 3,000 years, suggesting an 800 to
1,100 year recurrence interval for large tsunamigenic earthquakes.
 In 2001 it was reckoned that, after more than 1100 years there was a high
likelihood of a large tsunami hitting the Sendai plain
 The projected source (Mw=8.1 to 8.3) was much larger than the anticipated
‘Miyagi-oki earthquak’e (M~~7.5) given ‘99% probability in the next 30
years’.
 http://adsabs.harvard.edu/abs/2007AGUFM.T31G..03S
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 ‘The Jogan Sanriku Earthquake of 869 may have been the strongest
seismic disturbance ever to strike Japan’, a joint research team of Osaka
City University, Tohoku University, Tokyo University and others reported.
 The finding, based on evidence that traces of the tsunami following the
quake impacted a wider area than previously thought, was revealed at a
meeting of the Japan Society of Engineering Geology being held in Osaka.
 The team began researching sediment left by past tsunamis in marshes
along the Pacific coast and inner bays between Miyako, Iwate Prefecture,
and Kesennuma, Miyagi Prefecture, in 2004.
 The researchers found evidence of tsunami impacts far inland in Iwate
Prefecture, leading them to believe the earthquake that caused the tsunami
‘might have measured around a magnitude of 9, stronger than the
magnitude 8.6 Hoei Earthquake of 1707, which was previously believed
to have been the country's strongest quake’.
 The finding ‘is expected to influence how damage is forecast for future
earthquakes expected to occur along the Japan Trench’.
 In 2008-9 as part of site relicensing at the Fukushima NPPs evidence
of the 869AD tsunami was raised - but dismissed by TEPCO as a
‘historic earthquake’. The safety agency also dropped the issue.
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 A bigger earthquake has longer duration and longer period motions
– However, for most buildings duration does not simply lead to greater damage
– And maximum impact at a site will principally reflect distance to the fault rupture
 However a larger coseismic deformation directly couples to a larger tsunami
 For M9 earthquakes it is the tsunami that contributes most to both
casualties and property damages.
 In particular at intermediate distances - only an M9 earthquake will create a
tsunami significantly higher than the natural range of extreme sea/wave
levels.
 In both the Japan and Indian Ocean earthquake > 95% of the casualties
were caused by the Tsunami
– Indian Ocean - 280,000 killed - 1.5 million homes lost
– Japan 20,000 killed and major nuclear contamination from 3 reactor
meltdowns at Fukushima triggered by the tsunami
 For any region experiencing an M9 earthquake there will not have been a
previous M9 event in the past 200 years of history
– And hence will overwhelm tsunami protection walls, previous flood zones etc.
 M9 tsunamis have caused c30% of all earthquake casualties since 2000
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 Earth … shaking off, as a horse doth his rider, so many and such great
cities. …. of the Libyans all and every one. Prostrate lie the largest towns
of Sicily, prostrate all of Greece save one; (Libanius)
 ‘Crete was very much shaken, as was likewise the Peloponnese, and all
Greece, many places being destroyed; indeed almost all were
overturned, except Athens and the country of Attica.’ (Chronicler
Zosimus)
 ‘100 towns in Crete were completely destroyed’.(Chronicler Malalas)
 ‘there was destruction in Crete, Achaea, Boeotia, Epirus and Sicily and
many ships were thrown 100 stades on to mountainsides’. (Chronicler:
George the Monk)
 ‘ ‘the sea changed its familiar boundaries; for in some places the quaking
was so severe that places where previously people walked they could
now sail. In other places, the sea retreated so far that the bottom of the
sea was found to be dry. (5thC Socrates Scholasticus)
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 ‘In these times there occurred a great and very fearsome earthquake to the extent
that at Alexandria the sea disappeared for a long time and boats were found lying as
if on dry land. And a multitude of people ran to see the unexpected wonder, and
when the water turned around and came back further than its accustomed place,
50,000 people were drowned and some of the ships moored there were covered by
the waters, and others found in the River Nile were thrown inland up to 180 stades
(18km)’. (Byzantine chronicler George the Monk)
 ‘Slightly after daybreak, and heralded by a thick succession of fiercely shaken
thunderbolts, the solidity of the whole earth was made to shake and shudder, and the
sea was driven away, its waves were rolled back, and it disappeared….. For the
mass of waters returning when least expected killed many thousands by drowning,
and with the tides whipped up to a height as they rushed back. Other huge ships,
thrust out by the mad blasts, perched on the roofs of houses, as happened at
Alexandria, (Ammanius)
 Other (ships) were hurled nearly two miles from the shore, like the Laconian vessel
near the town of Methone (SW Pelopenese) which I saw when I passed by, yawning
apart from long decay.’
 “There was an earthquake throughout the world, and the sea flowed over the shore,
causing suffering to countless people in Sicily and many other islands”. Jerome
Alexandria at the western end of the Nile delta was the second largest city in the Empire
after Rome, with a population of more than 300,000.
Even two hundred years later Alexandrians held a yearly commemorative festival
'the birthday of the earthquake',
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 Crete
– Kissamos (W Crete) shortly after 355-361 (destruction so great the dead
were left unburied
– Eleutherna W Crete shortly after 355-361
– Gortyn I(Central Crete) 10-15 years before 383AD
 Libya
–
–
–
–
–
Leptis Magna, Tripolitis NW coast shortly after 364-367
Sabratha, Tripolitic NW coast shortly after 364-387 before 378
Balagrae (El Beida) Cyrenaica, NE Coast shortly after 364
Cyrene, Cyrenaica, NE Coast shortly after 364
Ptolemais, Cyrenaica, NE Coast shortly before 364-378
 Cyprus
– Kourion between late 364 and Sept 365
 Sicily/Italy
– Agrigento – shortly after 364-367
– Selinunte Temple C after 330AD
– Reggio Calabria before 374
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There were 4 Roman emperors
between 360-365AD
New emperor’s head coin stamps
were sent to each town
Coins in rubble constrain the
date of collapse
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‘ ‘the sea changed its familiar boundaries; for in
some places the quaking was so severe that plac
where previously people walked they could now
sail. In other places, the sea retreated so far that
the bottom of the sea was found to be dry. (5thC
Socrates Scholasticus)
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 The earthquake historian Emanuela Guidoboni argued that because Libanius wrote
about the places impacted by the earthquake in a funeral oration to the Emperor
Julian (who died in June 363AD) these must reflect otherwise unknown earthquakes
at least two years before 365AD
 The funeral oration references the supernatural troubles that had befallen the world
after Julian’s untimely death.
– Earth truly has been fully sensible of her loss, and has honoured the hero by an
appropriate … shaking off, as a horse doth his rider, so many and such great
cities. In Palestine several; of the Libyans all and every one. Prostrate lie the
largest towns of Sicily, prostrate all of Greece save one; the fair Nicaea lies in
ruins…. These are the honours paid to him by Earth … just as though it were not
lawful for creatures upon earth to enjoy health now that he has departed! ‘
 The first on the list, the earthquake in Palestine, is well established to have occurred
on May 19th 363 AD, a month before the death of Julian
 However the destruction of Nicaea (modern Iznik on the Marmara Sea) occurred in
an earthquake in October 368AD
 Classical historian Peter Van Nuffelen (2007) has demonstrated that the oration, and
the list contained, was compiled after 368AD (at least 5 years after Julian’s death)
 The destruction in Libya, Greece and Sicily can therefore all be attributable to the
single 365AD mega-earthquake - as referenced by other contemporary
commentators
 No need to ‘invent’ additional and otherwise unknown earthquakes
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 Far field uplift in Crete of 1-2m (100-150km to
the east of culmination of uplift) not explained
by this single fault model
 20+m displacement on a 100km fault length of
the Shaw et al model is inconsistent with the
‘aspect ratio’ (shear strain) of any other
modern major earthquake fault rupture
 Does not explain impact of the earthquake in
Cyprus, Libya or Sicily
 Does not explain the first motion retreat of the
sea at Alexandria or the magnitude of the
tsunami at that city,
 Therefore – as with the 1964 M9.2 Alaska
earthquake - the fault displacement beneath
western Crete appears to be a steeper thrust
emerging off the low angle overthrust
subduction displacement
 20m displacement therefore minimum
displacement on the underlying subduction
zone fault
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Available fault
rupture = 150km x
1200km
Displacement >20m
Average 10-15m?
Mw = 9.3 - 9.6
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Contemporary
government surveys in
Portugal and Spain
provide detailed data
on felt effects
600km
There was no survey of the
impacts in Morocco and the
small number of
contemporary accounts
have some conflicts
??
• MMI VII in the north
• Accounts indicating
widespread damage (MMI
VIII) in the south (Sale, Safi,
Agadir & Marrakech?)
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 The most extraordinary feature of the 1755 earthquake remains the range and
intensity of farfield long period effects – most widespread and intense ever observed.
– In Alaska earthquake 1964 only four seiches observed in coterminous US >0.3m amplitude.




 At distances of a few hundred kilometers from the earthquake source, the tops of
some high buildings fell (as in Malaga, south Spain).
 At distances greater than 1000km, chandelier ‘branches’ hung from church and
cathedral roofs oscillated – E-W for up to an hour (in particular in N Germany and
Holland)
– In the same region many rivers and canals were also sent into spectacular
oscillation.
Across southern Britain almost every pond and small lake was set in motion
– at Pibley Pond, Derby in a 10 hectare body of water: the water rose 0.6m and
continued flowing backwards and forwards for 2 hours.
Further to the north most large lakes and fjords were sent into motion
– At Loch Lomond in west Scotland water levels rose and fell 0.8m with a period of
10 minutes, with the principal phase lasting for 45 minutes.
This far field long period signature, across a very wide range of resonant periods of
water bodies, indicates a high amplitude of long period energy, within a coherent
long lasting low frequency wave train.
This implies a single phase of rupture on a very large seismic source.
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For some realistic terrestrial physics:
• Rupture velocity 3km/sec,
• Radiating the strongest modes of surface wave vibration at a
group velocity of 4km/sec for the lower frequencies, reducing to
3km/sec for the higher frequencies.
• Meanwhile the fastest P waves travel at 6km/sec.
Duration of
felt shaking
50s
125s
300km Fault
200s
epicentre
N
W
E
S
Unilateral rupture
However vibrations may not be perceived radiated from far sections of the fault.
The Mw 9.2 1964 Alaska earthquake, involved 800km of fault rupture starting at Valdez
and ending beneath Kodiak Island 300 seconds later. However an observant geologist at
Valdez only felt vibrations for 210 seconds - implying that vibrations radiated from further
than about 300km down the fault rupture were too weak to be observed.
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Observations are generally
consistent at one location
7
8
Actual rupture duration
likely to be 3-4 minutes
implies 540-720km
6
Source
area
Fact that full duration
reported over a range of
azimuths could suggest
slower (or multiple) fault
rupture
6
7
8
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Extends with distance
reflecting the expansion of
the observed wave train
with distance
CONFIDENTIAL
Fault
Primary farfield
polarisation
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‘On the island of Saba it flowed 21 feet’.
‘At St Martin’s a sloop that rode
at anchor in 15 feet of water
was laid dry on her broadside’.
‘Antigua rose twelve feet
perpendicular’.
‘Martinique overflowed the
low land and water also
retreated a mile and in
other places flowed
into the upper rooms of
houses’.
Inferred
principal
Megafault
orientation
Barbados five feet. Barbados ‘water ran
over the wharfs into the houses’.
Also see: Barkan et al., (2009)
Marine Geology 264 109–122
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Hellenic Arc
SW Iberia
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 The question as to where M9 earthquakes can occur is the critical
issue around life safety for coastal dwellers in many regions
 The principal question for global earthquake hazard?
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T
T
T
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 Major coseismic strain deficit
 Long term tectonic uplift of Barbados – evidence it may be intermittent
and coseismic?
 Kelletat et al. (2004) mapped coral reef boulders on Long Island and
Eleuthera (Bahamas) as tsunami deposits.
– Atlantic facing cliffs between about 10 to 20 m above sea level and at 150
m distance from the cliff edge.
– The weight of individual boulders may reach more than 300 tons
 Coarse tsunami deposits of the Younger Holocene have been
discovered on the Netherlands Antilles islands of Curaçao, Bonaire, and
Aruba.
– Rampart deposited on 5-6 m high Pleistocene reef terraces contains
several million tons of boulders and coarse fragments. Much material
originates from a fringing reef, but the largest boulders (max. 260 t) are
broken out of the Pleistocene cliff.
– The deposits reach up to 400 m inland
– There is a clear regional westward decrease in amount and size from the
east coast of Bonaire to the east coast of Aruba.
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E coast of St. Martin (500 BP) S coast of Anguilla (1,500 BP)
Curaçao (1,500 BP); 6 m asl
15m asl E coast of N
Eleuthera, (3,000 BP)
 Sander R. Scheffers, Jay Haviser, Tony Browne and Anja Scheffers, Tsunamis, hurricanes, the demise
of coral reefs and shifts in pre-historic human populations in the Caribbean, Quaternary International
(2008), doi:10.1016/j.quaint.2008.07.016
CONFIDENTIAL
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Tsunami
boulder
fields
• Plate boundary motion 6-8mm/yr
•<10% relieved by seismicity historically
•‘Incipient subduction’ zone identified along compressional
continental margin
•More likely location for megathrust than the source of the 1755
earthquake!
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 Earthquake
epicentres
– yellow: all
NEIC events
1973-2009;
– red: the same
but Ms>5;
 Main faults (black
lines:
 Main MTD (pink
areas:

Cattaneo et al., 2010
Submarine Landslides
Along the Algerian
Margin: A Review of
Their Occurrence and
Potential Link with
Tectonic Structures,
pp515-525 in D.C.
Mosher et al. (eds.),
Submarine Mass
Movements and Their
Consequences,
Advances in Natural
and Technological
Hazards Research, Vol
28, © Springer Science
(2010 p515-525
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RP for
20m
slip
250 yrs
500 yrs
Hellenic Arc
Caribbean?
SW Iberia
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W.Med??
1000 yrs
2000 yrs
4000 yrs
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 Regions totally unprepared for megatsunamis
– No warning systems
– No historical memory
– Significant exposure concentrations at 500-1000km distances (unlike Pacific) but
comparable to Sri Lanka and Thailand in 2004
 Potential for major tsunamis at moderate distances in places which would
not have felt the earthquake
 Enormous tourism and port infrastructures close to sea level
 Concentrations of exposure directly above the potential fault rupture
– Algiers, Oran, Blida etc
– Barbados
 Potential for massive tsunami life loss in western Mediterranean – Valencia,
Barcelona, Nice, Genoa etc
 What probability should be assigned to potential M9 events in Caribbean
and Mediterranean?
 Or is there too much vested interest (from NPPs and political authorities) in
not ‘rocking the boat’ – as was the case in Japan?
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Clustering of the largest Earthquakes
6xM>8.5
17 yrs
0xM>8.5
3xM>9.0
8xM>8.5
0xM>8.5
28 yrs
15 yrs
39 yrs
2xM>9.0
5xM>8.5
Data: USGS PAGERCAT 1900-2008, USGS-NEIC & gCMT 2008-present
Figure courtesy of Charles Ammon, after Ammon et al., SRL, 2010
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