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1 Earth and Environmental Science
Department
New Mexico Tech
Socorro, New Mexico
87801
(S.L.B.)
2 Geological Survey of
Japan/AIST
Tsukuba, Japan
(K. Satake)
3 Tectonics
Observatory
Caltech
Pasadena, California 91125
(K.
Sieh)
The great Sumatra–Andaman earthquake of 26 December 2004 (UTC 00:58:53) was a momentous event, whether measured by scientific or human standards. Sadly, what is currently regarded as the third largest earthquake in recorded history led to the worst tsunami disaster in recorded history, with the loss of more than 200,000 lives and devastation throughout the Bay of Bengal. About three months later, on 28 March 2005, the Nias–Simeulue earthquake, near the southern end of the 2004 rupture, shocked the region again. Fortunately, this Mw 8.7 earthquake, the second largest earthquake in the past decade, was less destructive. These earthquakes and resulting tsunamis have been a sobering reminder to many in the community of earthquake scientists that the subject of our professional lives can have enormous impact on humanity. Hopefully, the legacy of the science presented in this volume will be a greater understanding of earthquake and tsunami processes that will be useful in advancing the resilience of our communities to Nature’s violence.
The 2004 and 2005 earthquakes and tsunami revealed much that we did not know about great subduction zone events. Both the length of the 2004 rupture (perhaps as great as 1600 km) and its duration (upward of 600 sec) exceeded any previously recorded. Although the issue of whether the 2005 earthquake was an aftershock or triggered by the 2004 earthquake is currently debated, the 2005 earthquake was a significant event that may rank as one of the largest aftershocks ever recorded. The 2004 rupture extended through sections of the Sunda megathrust that had ruptured separately in earlier large earthquakes. The limited historical records and tectonic characteristics of this section of the megathrust had led many of us to believe that it was incapable of producing a giant earthquake. Nonetheless, such unanticipated natural events often lead to unanticipated advances in human knowledge. Fortunately, advances in geophysical instrumentation and field techniques made these the best- recorded great earthquakes and tsunami in history and set the stage for the work represented here.
The articles in this volume embody key aspects of the current state of knowledge about earthquakes and tsunamis. Topics include determinations of the spatial extent and evolution of the 2004 and 2005 ruptures from seismographic, geodetic, tsunami, and field observations, catalogs of previous and subsequent regional seismic activity, and evidence for previous tsunamis and deformation. Although the 2004 Sumatra–Andaman earthquake is the best-recorded great earthquake in history, its analysis posed many challenges, as many standard techniques proved inadequate to deal with such a giant event. Hence, this issue contains articles that present new techniques and unique datasets used and developed for this particular earthquake.
 |
Earthquake Size and Energy |
|---|
For many earthquakes, estimates of radiated energy can be difficult to make. For the 2004 Sumatra–Andaman earthquake, the long duration and overlap of interfering arrivals in the commonly used calculation window make the task especially difficult. Because the duration of the P wave is long enough to include later arrivals, some standard methods for energy calculations will fail to produce an accurate estimate. Choy and Boatwright (2007) demonstrate that an extension of the empirical Green’s function method can be used to estimate the radiated energy for a great earthquake such as this one. The authors correct for the later-phase arrivals by using a modified empirical approach that produces a value of radiated energy (Es) of 1.4 x 1017 J. Comparisons of the corrected source spectra of various analysis window durations also suggest that the second half of the rupture radiated less high-frequency energy than the first half of the rupture.
|
Seismicity Catalogs |
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Dewey et al. (2007) present the USGS/NEIC seismicity catalog and ancillary data for the events following the 2004 Sumatra–Andaman earthquake. The catalog includes hypocenters, magnitudes, moment tensors, radiated energy, and apparent stress values routinely calculated for regional earthquakes during the 36 weeks following December 2004. They also interpret subsets of the catalog, such as the lack of moderate-magnitude aftershocks on the deeper portion of the seismogenic thrust fault as possibly related to the complete elastic strain release during the 2004 event. In contrast, their catalog contains numerous interplate thrust aftershocks along the 2005 Nias earthquake rupture zone, possibly reflecting a difference in strain release between these two closely spaced events.
Engdahl et al. (2007) present locations for earthquakes in the Sumatra–Andaman region between 1918 and 2005 that have been relocated using the Engdahl–Hilst–Buland (EHB) technique (Engdahl et al., 1998). The smaller depth uncertainties in this dataset are a key improvement over previous work and provide an opportunity for tectonic interpretations. For instance, the authors use this dataset to show a sharp separation between aftershocks of the 2004 and 2005 great earthquakes as well as variations in the slab dip and downdip seismogenic width along strike in the subduction zone.
Bilek (2007) examines several tens of Mw >6 earthquakes that occurred between 1992 and 2005 along the Sumatra–Andaman subduction zone to find that shallower events have longer durations, similar to other subduction zones in the circum-Pacific. Along-strike variation does not show a slow character in the Nicobar and Andaman segments; hence, the possible slow rupture in these segments during the 2004 mainshock is not interpreted to be caused by frictional variations along strike in the subduction zone. Absence of temporal change in the depth dependence before and after the 2004 earthquake suggests that the rupturing process in 2004 did not alter the fault-zone frictional conditions either.
Mishra et al. (2007)
describe aftershock locations determined
by using data from a temporary network of six
three-component short-period seismometers deployed on the
Andaman and Nicobar Islands following the 26 December
2004 Sumatra–Andaman earthquake. The network recorded
18,000 aftershocks, and the authors present earthquake
statistics such as average b-value (0.77) for this dataset. Patterns
in the aftershock locations are also compared with regional
tectonic features.
|
Spatial and Temporal Rupture Characteristics |
|---|
Vallée (2007) provides an analysis of the 2004 Sumatra– Andaman earthquake rupture using the empirical Green’s function method, more commonly used for smaller-magnitude earthquakes. He demonstrates the usefulness of this technique for an earthquake of this size, even using an empirical Green’s function event that was significantly smaller at an Mw 7.2 and separated from the centroid of the 2004 earthquake by several hundred kilometers. This technique appears to be particularly useful for rapidly producing an estimate of the seismic moment for great earthquakes, as the author presents an estimate of M0 5.1 x 1022 N m for the 2004 earthquake, a value comparable to the moment determined using more time-intensive analysis methods.
In one of the many examples of techniques combining two or more datasets, Rhie et al. (2007) compute slip distributions for the 2004 Sumatra–Andaman earthquake based on joint inversion of teleseismic and regional geodetic datasets. They find that values of maximum slip near 4° N and high slip through to 10° N are the key controls on the fit to the seismic data, whereas inversion of the GPS data suggests significant slip in the northern segments. The detailed sensitivity analyses presented in this article clearly show the importance of each dataset on the slip-distribution patterns, bolstering the case for using both of these complementary datasets for a more complete view of the rupture process.
Using yet another dataset,
Lambotte et al. (2007)
use a
singlet-stripping technique to isolate parameters from the
gravest free oscillations recorded around the globe to describe
the spatiotemporal extent of the sources for both the
2004 Sumatra–Andaman and the 2005 Nias earthquakes. For
the 2004 earthquake, they find a rupture length and duration
of 1250 km and 550 sec, respectively, consistent with studies
using teleseismic or GPS datasets.
|
Ground Motions |
|---|
|
Coseismic and Postseismic Deformation |
|---|
6.7–7.0 x 1022 N
m
(Mw 9.15). The coseismic model is also used to predict
sea
surface heights during tsunami propagation, finding a good
fit with the satellite altimetry data. In addition, the model of
postseismic deformation suggests that slip continued on the
interface beyond the 500-sec seismic slip, with 2.5 x
1022 N m of postseismic geodetic moment release. Rajendran et al. (2007) provide the most comprehensive evidence to date from the field for uplift and subsidence on the Nicobar and Andaman islands. They use mangrove forests, corals, and anthropogenic features to document subsidence at all visited locations on the Nicobar islands and a complex pattern of subsidence and emergence on the coasts of the Andaman islands. Their results are consistent with analysis of satellite imagery (Meltzner et al., 2006), but provide additional constraints on the magnitude of the vertical deformation that are useful in modeling slip on the megathrust.
|
Tsunami Studies |
|---|
Fujii
and Satake (2007) perform one of the first joint
inversions of regional tide gauge data and satellite altimetry
measurements to produce a tsunami source model that extends
900 km to the north along the subduction zone. They
find a slip distribution, stable within a large range of rupture
velocities and rise times, with peak slip of 13–25 m offshore
Sumatra Island, with moderate slip of up to 7 m in the Nicobar
Island region. Although there are still some discrepancies
between results produced from either tide gauge or
satellite data alone, this article provides detailed descriptions
of the inversion results for individual datasets as well as the
joint inversion.
Hébert et al. (2007) present tsunami numerical simulation in the Indian Ocean with special focus on the Mascarene Islands and compared the results with tide gauge record and run-up measurements on La Réunion Island. Tsunamis computed from uniform and heterogeneous slip distributions show distinguishable differences in maximum water-height distribution on both basinwide (Indian Ocean) scale and local scale on harbors in the islands. An important conclusion is that a tsunami source off southern Sumatra, similar to the 1833 source, would produce larger tsunami impact on La Réunion than the 2004 models.
Piatanesi and Lorito (2007) invert tsunami waveforms recorded at 14 tide gauge stations around the Indian Ocean to estimate rupture velocity and the slip distribution on the fault. The largest slip is estimated to be 30 m on a deeper subfault off Aceh Province. Large slip (mean slip >10 m) is estimated on shallow subfaults beneath Great Nicobar to Little Andaman Islands. The slip was also large, about 20 m, on a deep subfault east of North Andaman Island. The mean rupture velocity is estimated as 2.0 km/sec.
Hanson et al. (2007) analyze tsunami signals recorded on hydrophones and seismic stations for the 2004 and 2005 events. The tsunami signals between 1 and 30 mHz show dispersive character expected for a gravity wave in the ocean; shallow-water wave at lowest and deep-water wave at highest frequency, respectively. The high-frequency tsunami signals in December originated west off Sumatra and near Great Nicobar Island, where large slips were inferred by other studies. They also show that islands or a submarine plateau acted as reflectors for high-frequency tsunami signals.
Geist et al. (2007) examine various tsunami forecast models and compare the results with the observed data from the 2004 tsunami. While an empirical method based on a scalar point source can successfully forecast the mean and maximum tsunami heights, a subfault dislocation model with real-time data dissemination is needed to reproduce the observed regional variation of tsunami heights. They test a stochastic source model as a tsunami hazard-assessment model and find that small average slip (9 m) with a long fault (1600 km) best reproduce the observed run-up values.
Nawa et al. (2007) use a set of geophysical instruments deployed off the coast of Antarctica in their analysis of the 2004 tsunami. They model observations from an ocean- bottom pressure gauge, a superconducting gravimeter, and a broadband seismometer. Although their predictions match the amplitudes and periods of the observed data well, the timing of the model signals differ from the data.
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Tectonic Comparisons |
|---|
Because of the large tsunami generated by the 2004
earthquake, there is a question as to whether the 2004 event
is a "tsunami earthquake" as defined by
Kanamori (1972).
These earthquakes, such as the 1992 Nicaragua earthquake,
typically have slow rupture within the shallowest portion of
the subduction zone fault and generate larger tsunami than
expected for the surface-wave magnitude.
Seno and Hirata
(2007) show that the 2004 earthquake had some components
of a "tsunami earthquake," especially a long duration and
some moment release in the very shallow, near-trench region.
They infer that the seismogenic rupture propagated
north with a rupture velocity of 2.5 km/sec, but slowed to
0.7 km/sec along the near-trench region. This slow rupture
consisted of about a third of the total seismic moment. They
estimate that the durations of fast and slower slips were,
respectively, 500 sec and 2000 sec from seismic-
moment estimates at various frequencies, and the effective
slip for tsunami generation was as large as 40 m near the
deformation front off Sumatra.
|
28 March 2005 Nias–Simeulue Earthquake |
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Paleoseismic and Paleotsunami Evidence for Prior Events |
|---|
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Dedication |
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Manuscript received September 7, 2006
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References |
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Ammon, C.
J., C. Ji, H. K. Thio, D. Robinson, S. D. Ni, V. Hjorleifsdottir, H. Kanamori, T. Lay, S. Das, D. Helmberger, G. Ichinose, J. Polet, and D. Wald
(2005). Rupture process of the 2004 Sumatra-Andaman
earthquake, Science308
,1133
–1139.
Banerjee, P., F. Pollitz, B. Nagarajan, and R. Bürgmann
(2007). Coseismic
slip distributions of the 26 December 2004 Sumatra-Andaman and
28 March 2005 Nias earthquakes from GPS static offsets,
Bull. Seism.
Soc. Am. 97, no. 1A,S86
–S102.
Bilek, S. L. (2007). Using earthquake source durations
along the Sumatra–
Andaman subduction system to examine fault zone variations, Bull.
Seism. Soc. Am. 97, no. 1A,S62
–S70.
Braitenberg, C., and M. Zadro (2007). Comparative
analysis of the free
oscillations generated by the Sumatra–Andaman Islands 2004 and the
Chile 1960 earthquakes, Bull. Seism. Soc. Am.97
, no. 1A,S6
–S17.
Chlieh, M., J.-P. Avouac, V. Hjorleifsdottir, T.-R Song, C. Ji, K. Sieh, A. Sladen, H. Hebert, L. Prawirodirdjo, Y. Bock, and J. Galetzka (2007). Coseismic slip and afterslip of the great (Mw 9.15) Sumatra–Andaman earthquake of 2004, Bull. Seism. Soc. Am.97 , no. 1A,S152 –S173.
Choy, G. L., and J. Boatwright (2007). The energy
radiated by the December
26, 2004 Sumatra–Andaman earthquake estimated from 10-
minute P-wave windows, Bull. Seism. Soc. Am.97
, no. 1A,S18
–S24.
Dewey, J. W., G. Choy, B. Presgrave, S. Sipkin, A. C. Tarr, H. Benz, P. Earle, and D. Wald
(2007). Seismicity associated with the Sumatra–
Andaman Islands earthquake of December 26, 2004, Bull. Seism. Soc.
Am. 97, no. 1A,S25
–S42.
Engdahl, E. R., R. van der Hilst, and R. P. Buland (1998). Global teleseismic earthquake relocation with improved travel times and procedures for depth determinations, Bull. Seism. Soc. Am.88 ,3295 –3314.
Engdahl, E. R., A. Villaseñor, H. R. DeShon, and C. H. Thurber
(2007).
Teleseismic relocation and assessment of seismicity (1918–2005) in
the region of the 2004 Mw 9.0 Sumatra–Andaman and 2005
Mw 8.6
Nias Island great earthquakes, Bull. Seism. Soc. Am.97
, no. 1A,S43
–
S61.
Fujii, Y., and K. Satake (2007). Tsunami source of the
2004 Sumatra–
Andaman earthquake inferred from tide gauge and satellite data, Bull.
Seism. Soc. Am. 97, no. 1A,S192
–S207.
Geist, E. L., V. V. Titov, D. Arcas, F. F. Pollotz, and S. L. Bilek
(2007).
Implications of the 26 December 2004 Sumatra–Andaman earthquake
on tsunami forecast and assessment models for great subduction zone
earthquakes, Bull. Seism. Soc. Am.97
, no. 1A,S249
–S270.
Hanson, J. F., C. Reasoner, and J. R. Bowman (2007).
High frequency
tsunami signals of the great Indonesian earthquakes of 26 December
and 28 March 2005, Bull. Seism. Soc. Am.97
, no. 1A,S232
–S248.
Hébert, H., A. Sladen, and F. Schindelé
(2007). Numerical modeling of the
great 2004 Indian Ocean tsunami: focus on the Mascarene Islands,
Bull. Seism. Soc. Am.97
, no. 1A,S208
–S222.
Kanamori, H. (1972). Mechanism of tsunami earthquakes, Phys. Earth Planet. Int. 6,346 –359.[CrossRef]
Konca, A. O., V. Hjorleifsdottir, T.-R. Song, J.-P. Avouac, D. V. Helmberger, C. Ji, K. Sieh, R. Briggs, and A. Meltzner
(2007). Rupture
kinematics of the 2005 Mw 8.6 Nias-Simeulue earthquake from
the
joint inversion of seismic and geodetic data, Bull. Seism. Soc.
Am. 97,
no. 1A, S307–S322.
Lambotte, S., L. Rivera, and J. Hinderer (2007).
Constraining the overall
kinematics of the 2004 Sumatra and the 2005 Nias earthquakes using
the Earth’s gravest free oscillations, Bull. Seism. Soc.
Am. 97, no. 1A, S128
–S138.
Meltzner, A. J., K. Sieh, M. Abrams, D. C. Agnew, K. W. Hudnut, J.-P. Avouac, and D. H. Natawidjaja (2006). Uplift and subsidence associated with the great Aceh-Andaman earthquake of 2004, J. Geophys. Res. 111,B02407 , doi10.1029/2005JB003891 .[CrossRef]
Mishra, O. P., J. R. Kayal, G. K. Chakrabortty, O. P. Singh, and D. Ghosh
(2007). Aftershock investigations in the Andaman–Nicobar
Islands of
India and its seismotectonic implications, Bull. Seism. Soc.
Am. 97,
no. 1A, S71–S85.
Nawa, K., N. Suda, K. Satake, Y. Fujii, T. Sato, K. Doi, M. Kanao, and K. Shibuya
(2007). Loading and gravitational effects of the 2004 Indian
Ocean tsunami at Syowa Station, Antarctica, Bull. Seism. Soc.
Am. 97
, no. 1A,S271
–S278.
Piatanesi, A., and S. Lorito (2007). Rupture process of
the 2004 Sumatra–
Andaman earthquake from tsunami waveform inversion, Bull. Seism.
Soc. Am. 97, no. 1A,S223
–S231.
Rajendran, C. P., K. Rajendran, R. Anu, A. Earnest, T. Machado, P. M. Mohan, and J. Freymueller
(2007). Crustal deformation and seismic
history associated with the 2004 Indian Ocean earthquake: a perspective
from the Andaman–Nicobar Islands, Bull. Seism. Soc.
Am. 97,
no. 1A, S174–S191.
Rhie, J., D. Dreger, R. Bürgmann, and B. Romanowicz
(2007). Slip of the
2004 Sumatra–Andaman earthquake from joint inversion of long period
global seismic waveforms and GPS static offsets, Bull.
Seism.
Soc. Am. 97, no. 1A,S115
–S127.
Seno, T., and K. Hirata (2007). Did the 2004
Sumatra–Andaman earthquake
involve a component of tsunami earthquakes? Bull. Seism. Soc.
Am. 97
, no. 1A,S296
–S306.
Sorensen, M. B., K. Atakan, and N. Pulido (2007).
Simulated ground motions
for the great M 9.3 Sumatra–Andaman earthquake of 26 December
2004, Bull. Seism. Soc. Am.97
, no. 1A,S139
–S151.
Stein, S., and E. A. Okal (2007). Ultralong period
seismic study of the
December 2004 Indian Ocean earthquake and implications for regional
tectonics and the subduction process, Bull. Seism. Soc.
Am. 97,
no. 1A, S279–S295.
Vallée, M. (2007). Rupture properties of the
giant Sumatra earthquake imaged
by empirical Green function analysis, Bull. Seism. Soc.
Am. 97,
no. 1A, S103–S114.
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