bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-Frequency Tsunami Signals of the Great Indonesian Earthquakes of 26 December 2004 and 28 March 2005
Authors: Hanson Jeffrey A. , Reasoner Colin L. , Bowman J. Roger 
Published: January 2007

Abstract
Tsunamis generated by the great Indonesian earthquakes of 26 December 2004 (Mw 9.3) and 28 March 2005 (Mw 8.6) produced high-frequency (&gt;5 mHz) dispersed signals recorded by hydrophone stations offshore from Diego Garcia and Cape Leeuwin, Australia, and by many seismic stations in the Indian Ocean and on the coast of Antarctica. For the first and greater earthquake, the dispersed energy is commonly observed to 30 mHz and, in one case, to 60 mHz. The high-frequency signals are consistent with being generated at pointlike sources. The earliest arriving tsunami signals originate from a point near 4.3° N, 93.8° E, determined using event- to-station distances estimated by matching predicted dispersion to observations. The location is further constrained with azimuth estimates from an array of hydrophones. Fine structure in the tsunami signal indicates a second high-frequency source just south of Great Nicobar Island near 6.5° N, 93.6° E. The point sources are located close to the maximum slip area determined in several other seismic and tsunami studies. The dispersion of much later-arriving energy is consistent with travel over longer paths, and matches predictions for reflections of the tsunami from bathymetric features in the Indian Ocean basin. For the 28 March 2005 tsunami, the high- frequency dispersion is observed at the Diego Garcia hydrophone station and the AIS seismic station, and tsunami signals without apparent dispersion are seen at four other seismic stations. Phase velocities estimated at hydroacoustic stations agree with linear dispersion theory at frequencies above 12 mHz.
Simulated Strong Ground Motions for the GreatM9.3 Sumatra–Andaman Earthquake of 26 December 2004
Authors: Sørensen M. B. , Atakan K. , Pulido N. 
Published: January 2007

AbstractOn 26 December 2004, a devastating earthquake of M 9.3 occurred offshore northern Sumatra. Due to the size of this earthquake and the accompanying tsunami wave, disastrous consequences have been observed in several countries around the Indian Ocean. The tectonics in the region are characterized by the oblique, north-northeast-oriented subduction of the Indian–Australian plate under the Sunda microplate with a rate of 6–6.5 cm/yr. This oblique convergence results in strain partitioning, where the trench-perpendicular thrust faulting along the subducting slab accommodates the east–west component of the motion, whereas the north–south component of the motion is probably accommodated by the right-lateral strike-slip faulting along the Great Sumatran fault and the Mentawi fault. Source parameters of the 26 December 2004 event have been used for modeling the resulting ground motions in the nearby affected regions. Results give an insight on the importance of ground shaking in the total destruction of places like Banda Aceh, northern Sumatra, Indonesia. The modeling is performed for a multiasperity finite fault using a hybrid procedure combining deterministic modeling at low frequencies and semistochastic modeling at high frequencies. Results show that strong shaking was distributed over a large area including northwestern Sumatra and its offshore islands. In Banda Aceh, which experienced significant damage, bedrock velocities reached 60 cm/sec with duration of the shaking of ca. 150 sec. The largest ground motions occurred near the strongest asperities of the fault plane, where velocities of 200 cm/sec are modeled for bedrock conditions.
Coseismic Slip Distributions of the 26 December 2004 Sumatra–Andaman and 28 March 2005 Nias Earthquakes from gps Static Offsets
Authors: Banerjee Paramesh , Pollitz Fred , Nagarajan B. , Bürgmann Roland 
Published: January 2007

Abstract
Static offsets produced by the 26 December 2004 M ∼9 Sumatra– Andaman earthquake as measured by Global Positioning System (gps) reveal a large amount of slip along the entire ≳1300 km-long rupture. Most seismic slip inversions place little slip on the Andaman segment, whereas both near-field and far-field gps offsets demand large slip on the Andaman segment. We compile available datasets of the static offset to render a more detailed picture of the static-slip distribution. We construct geodetic offsets such that postearthquake positions of continuous gps sites are reckoned to a time 1 day after the earthquake and campaign gps sites are similarly corrected for postseismic motions. The newly revised slip distribution (Mw 9.22) reveals substantial segmentation of slip along the Andaman Islands, with the southern quarter slipping ∼15 m in unison with the adjacent Nicobar and northern Sumatran segments of length ∼700 km. We infer a small excess of geodetic moment relative to the seismic moment. A similar compilation of gps offsets from the 28 March 2005 Nias earthquake is well explained with dip slip averaging several meters (Mw = 8.66) distributed primarily at depths greater than 20 km.
Online material: Offset estimation procedure, comparison of results to other studies and simpler solutions, and tables of coseismic offsets can be found here: https://www.seismosoc.org/Publications/BSSA_html/bssa_97-1a/05609-esupp/#figS6
Numerical Modeling of the Great 2004 Indian Ocean Tsunami: Focus on the Mascarene Islands
Authors: Hébert H. , Sladen A. , Schindelé F. 
Published: January 2007

AbstractOn 26 December 2004, the Mw 9.2 Sumatra earthquake triggered the greatest tsunami ever observed in recent times. The unprecedented quality and variety of observations on modern instruments provide opportunities to refine modeling techniques as well as our perception of tsunami hazard in oceanic regions where historical events are not as frequent as in the Pacific Ocean. We present a numerical modeling of the 2004 tsunami on the Mascarene Islands with refined computations on La Réunion Island, where postevent survey observations and one tide gauge record are available. We use two different source models (models A and B) to account for the observations, and we also test an additional source model (model C) to study the effect of a tsunami originating in the 1833 epicentral area (southern Sumatra). A wave trapped on the edge of La Réunion may explain the greatest water heights reached in the western coastline of the island. The observed tide gauge data are reasonably well fit (models A and B). The run-up data can also be explained with our models. Late disturbances observed in La Pointe des Galets may be explained by a late tsunami reflection from Madagascar or by harbor resonances. Finally we also show that model C (1833-like) strikes La Réunion more heavily than models A and B.
Tsunami Source of the 2004 Sumatra–Andaman Earthquake Inferred from Tide Gauge and Satellite Data
Authors: Fujii Yushiro , Satake Kenji 
Published: January 2007

Abstract
Tsunami source of the 2004 Sumatra–Andaman earthquake was estimated from a joint inversion of tsunami waveforms recorded on tide gauges and sea surface heights captured by satellite altimetry measurements. The earthquake, the largest in the past 40 years, caused devastating tsunami damage to countries around the Indian Ocean, but the tsunami source, in particular, its northern end, was not well resolved. Although aftershocks and crustal deformation extended from off northwestern Sumatra Island through the Nicobar Islands to the Andaman Islands, some seismic-wave analyses indicated a shorter source length, several hundred kilometers. We used tsunami waveforms recorded at 12 tide gauge stations around the source and the sea surface heights measured by three satellites: Jason1, topex/Poseidon, and Envisat. We numerically computed tsunami propagation using realistic bathymetry; more than 66,000 depth points were digitized from nautical charts and combined with the ETOPO2 data. Inversion of satellite data indicates that the tsunami source extended to the Andaman Islands with a total length of 1,400 km, but such a model produces much larger tsunami waveforms than observed at Indian tide gauge stations. Inversion of tide gauge records and the joint inversion indicate that the tsunami source was about 900 km long. The largest slip, about 13 to 25 m, was located off Sumatra Island and the second largest slip, up to 7 m, near the Nicobar Islands. The slip distribution is similar for different rupture velocities and rise times, with a slow velocity of 1 km/sec and a rise time of 3 min yielding the largest variance reduction.
Teleseismic Relocation and Assessment of Seismicity (1918–2005) in the Region of the 2004Mw 9.0 Sumatra–Andaman and 2005Mw 8.6 Nias Island Great Earthquakes
Authors: Engdahl E. Robert , Villaseñor Antonio , DeShon Heather R. , Thurber Clifford H. 
Published: January 2007

AbstractThe Mw 9.0 2004 Sumatra–Andaman Islands and Mw 8.6 Nias Island great earthquake sequences have generated over 5000 catalog-reported earthquakes along ∼1700 km of the Sumatra–Andaman and western Sunda regions. Studies of prior regional seismicity have been limited to global catalog locations that often have poorly constrained epicenters and depths. Approximately 3650 teleseismically well- recorded earthquakes occurring in this region during the period 1918–2005 are relocated with special attention to focal depth. Reduced uncertainties of epicenters and depths in the region (on the order of 15 and 10 km, respectively) foster interpretation of focal mechanism data and provide additional details about the subducting Indian and Australian plates. The revised earthquake dataset reveals a sharp delineation between aftershocks of the 2004 and 2005 earthquakes near Simeulue Island and a steepening in slab dip from south to north. The downdip width of the aftershock zone of the 2004 Mw 9.0 earthquake varies from ∼200 km at its northern end to ∼275 km at its southern end, and events located between 35 and 70 km focal depth occur more frequently in the southernmost section of this aftershock zone. Outer- rise and near-trench normal and strike-slip faulting earthquakes also increase in frequency following the 2004 and 2005 earthquakes. Earthquake swarms triggered along the Andaman backarc spreading center both north of Sumatra and near Siberut Island, 100 km south of the Nias Island aftershock sequence, illustrate the complex and variable nature of seismicity following these great earthquakes.
Did the 2004 Sumatra–Andaman Earthquake Involve a Component of Tsunami Earthquakes?
Authors: Seno Tetsuzo , Hirata Kenji 
Published: January 2007

Abstract
Tsunami earthquakes are characterized by (1) slow slip and (2) tsunamis larger than expected from seismic slip. We examine whether the 2004 Sumatra– Andaman earthquake had these features and thus involved a component of tsunami earthquakes. Fitting the effective moment versus frequency curve, we obtain characteristic times τ (Kanamori, 1972) of 70 and 290 sec. The former is on the scaling for normal earthquakes; the latter is longer. In the area off northern Sumatra, by back- projecting the wavefront recorded on the sea surface height (ssh) by the satellite altimetry, we estimate the seaward edge of the fault plane to be located at the deformation front. We then invert the ssh, assuming that the seaward edge of the fault is at this location, and obtain a maximum slip of 40 m, which was estimated to be 15 m previously. This amount of slip, approximately twice the slip estimated seismologically and geodetically, suggests that additional crustal deformation, such as inelastic uplift of the trench sediments, might have occurred near the deformation front. We propose that a similar, possibly slow, slip occurred in the shallow subduction boundary, extending from all over the rupture zone derived by the body-surface waves, with a smaller northward propagation velocity, corresponding to the longer τ. This rupture mode would solve the enigmatic features of this event seen in the seismological and tsunami data. The 2004 Sumatra–Andaman earthquake, having both features (1) and (2) that characterize tsunami eathquakes, likely had a component of tsunami earthquakes.
Implications of the 26 December 2004 Sumatra–Andaman Earthquake on Tsunami Forecast and Assessment Models for Great Subduction-Zone Earthquakes
Authors: Geist Eric L. , Titov Vasily V. , Arcas Diego , Pollitz Fred F. , Bilek Susan L. 
Published: January 2007

AbstractResults from different tsunami forecasting and hazard assessment models are compared with observed tsunami wave heights from the 26 December 2004 Indian Ocean tsunami. Forecast models are based on initial earthquake information and are used to estimate tsunami wave heights during propagation. An empirical forecast relationship based only on seismic moment provides a close estimate to the observed mean regional and maximum local tsunami runup heights for the 2004 Indian Ocean tsunami but underestimates mean regional tsunami heights at azimuths in line with the tsunami beaming pattern (e.g., Sri Lanka, Thailand). Standard forecast models developed from subfault discretization of earthquake rupture, in which deep- ocean sea level observations are used to constrain slip, are also tested. Forecast models of this type use tsunami time-series measurements at points in the deep ocean. As a proxy for the 2004 Indian Ocean tsunami, a transect of deep-ocean tsunami amplitudes recorded by satellite altimetry is used to constrain slip along four subfaults of the M &gt;9 Sumatra–Andaman earthquake. This proxy model performs well in comparison to observed tsunami wave heights, travel times, and inundation patterns at Banda Aceh. Hypothetical tsunami hazard assessments models based on end- member estimates for average slip and rupture length (Mw 9.0–9.3) are compared with tsunami observations. Using average slip (low end member) and rupture length (high end member) (Mw 9.14) consistent with many seismic, geodetic, and tsunami inversions adequately estimates tsunami runup in most regions, except the extreme runup in the western Aceh province. The high slip that occurred in the southern part of the rupture zone linked to runup in this location is a larger fluctuation than expected from standard stochastic slip models. In addition, excess moment release (∼9%) deduced from geodetic studies in comparison to seismic moment estimates may generate additional tsunami energy, if the exponential time constant of slip is less than approximately 1 hr. Overall, there is significant variation in assessed runup heights caused by quantifiable uncertainty in both first-order source parameters (e.g., rupture length, slip-length scaling) and spatiotemporal complexity of earthquake rupture.
Slip of the 2004 Sumatra–Andaman Earthquake from Joint Inversion of Long-Period Global Seismic Waveforms and gps Static Offsets
Authors: Rhie Junkee , Dreger Douglas , Bürgmann Roland , Romanowicz Barbara 
Published: January 2007

Abstract
The 26 December 2004 Great Sumatra–Andaman earthquake opened a new era for seismologists to understand the complex source process of a great earthquake. This is the first event with moment magnitude greater than 9 since the deployment of high-dynamic-range broadband seismic and Global Positioning System (gps) sensors around the globe. This study presents an analysis of the ruptured fault- plane geometry and slip distribution using long-period teleseismic data and gps- measured static surface displacements near the fault plane. We employ a rupture geometry with six along-strike segments with and without a steeper down-dip extension. The fault segments are further subdivided into a total of 201 ∼30 × 30 km fault patches. Sensitivity tests of fault-plane geometry and the variation in rupture velocity indicate that the dip and curvature of the fault plane are not well resolved from the given data set and the rupture velocity is constrained to be between 1.8 and 2.6 km/sec. Error estimations of the slip distribution using a random selection of seismic and gps station subsets (50% of all stations) illustrate that slip is well resolved along the whole rupture and the mean slip uncertainty is less than 1.5 m (about 11%). Although it is possible that near-field gps data include contributions from additional postseismic transient deformation, our preferred model suggests that the Sumatra–Andaman earthquake had a magnitude of Mw 9.20 + 0.05/−0.06.
Online material: Comparison of slip models, gps modeling, waveform fit, fault geometry, and inversion parameters.
Constraining the Overall Kinematics of the 2004 Sumatra and the 2005 Nias Earthquakes Using the Earth’s Gravest Free Oscillations
Authors: Lambotte S. , Rivera L. , Hinderer J. 
Published: January 2007

AbstractThe giant Aceh–Sumatran 2004 earthquake is the largest earthquake recorded since the great Chilean 1960 and the Alaskan 1964 events. The Earth’s free oscillations were strongly excited and recorded by numerous stations with an extremely good signal-to-noise ratio, even for the gravest modes. These particular modes are interesting because phases of these well-separated split free oscillations carry information on the overall kinematics of the source of large earthquakes (Mw &gt;8) and, in particular, on the length, duration, and mean rupture velocity. Using the singlet-stripping technique, we study some of the Earth’s gravest free oscillations (0S2, 0S3, 0S4, 1S2, 0S0, and 1S0) recorded at several broadband permanent stations (Geoscope, Incorporated Research Institutions for Seismology [iris], Global Geodynamics Project [ggp]) to recover individual singlet parameters: phases, frequencies, and quality factors. We use these parameters to constrain the spatiotemporal extent of the source of the Sumatra earthquake of 26 December 2004 and the Nias earthquake of 28 March 2005. We mainly use vertical-component data from seismometers and superconducting gravimeters, because they are less noisy than the horizontal seismic data, but we also show that, for the 2004 event, horizontal components can also be used (1S2). On the basis of the initial phase measurements presented here, we obtain, for the 2004 event, a fault length of about 1250 km and a duration of about 550 sec. For the 2005 event, our measurements favor a model in which the southern segment breaks ≈40 sec later, but the bilateral nature of the rupture and its spatial dimension prevent us from properly constraining its spatial extent.
Comparative Analysis of the Free Oscillations Generated by the Sumatra– Andaman Islands 2004 and the Chile 1960 Earthquakes
Authors: Braitenberg Carla , Zadro Maria 
Published: January 2007

Abstract
The Chile 1960 and Sumatra–Andaman Islands 2004 earthquakes are among the three greatest events that have occurred since the instrumental recording of seismic waves. The two events have similarities in hypocentral depth and focal mechanism but are very different when considering the extension of the fault plane. The recent event has close to 50% greater length than the Chile event, and although the moment magnitude of the Chile event is 0.2 to 0.5 points greater, the magnitude determination of the Sumatra–Andaman depends on the frequency range considered in the calculations (free oscillations with periods &gt; 1000 sec or seismic waves, with periods of 300–500 sec). For the Chile event only the seismic moment for periods of T &lt; 1000 sec is presently available, although the estimate of seismic moment at larger periods is crucial for a comparison of the two events. Our study makes a direct comparison of the free oscillation amplitudes of the two events by analyzing the records of the Grotta Gigante long-base tiltmeters, which have been recording tilt continuously since 1960. The particular mountings and physical dimension of the instruments make them particularly apt to record the torsional free oscillation waves, scarcely observed by standard long-period seismographs and not directly observable by the gravity meters. We determine the singlet frequencies for some of the lower spheroidal and torsional modes and a broad spectrum of multiplet frequencies for the higher modes. After correcting for the decay of the modes, we determine the amplitude ratios of the activated modes for the two events. The amplitude ratios vary between 1.5 and 3. Our results can be used directly for determining the ratios of the seismic moments of the two events over the frequency range 0.3–3 mHz, the only necessary correction being that of the site dependence of the free mode amplitudes.
Seismicity Associated with the Sumatra–Andaman Islands Earthquake of 26 December 2004
Authors: Dewey James W. , Choy George , Presgrave Bruce , Sipkin Stuart , Tarr Arthur C. , Benz Harley , Earle Paul , Wald David 
Published: January 2007

AbstractThe U.S. Geological Survey/National Earthquake Information Center (usgs/neic) had computed origins for 5000 earthquakes in the Sumatra–Andaman Islands region in the first 36 weeks after the Sumatra–Andaman Islands mainshock of 26 December 2004. The cataloging of earthquakes of mb (usgs) 5.1 and larger is essentially complete for the time period except for the first half-day following the 26 December mainshock, a period of about two hours following the Nias earthquake of 28 March 2005, and occasionally during the Andaman Sea swarm of 26–30 January 2005. Moderate and larger (mb ≥5.5) aftershocks are absent from most of the deep interplate thrust faults of the segments of the Sumatra–Andaman Islands subduction zone on which the 26 December mainshock occurred, which probably reflects nearly complete release of elastic strain on the seismogenic interplate-thrust during the mainshock. An exceptional thrust-fault source offshore of Banda Aceh may represent a segment of the interplate thrust that was bypassed during the mainshock. The 26 December mainshock triggered a high level of aftershock activity near the axis of the Sunda trench and the leading edge of the overthrust Burma plate. Much near-trench activity is intraplate activity within the subducting plate, but some shallow-focus, near-trench, reverse-fault earthquakes may represent an unusual seismogenic release of interplate compressional stress near the tip of the overriding plate. The interplate-thrust Nias earthquake of 28 March 2005, in contrast to the 26 December aftershock sequence, was followed by many interplate-thrust aftershocks along the length of its inferred rupture zone.
Rupture Process of the 2004 Sumatra–Andaman Earthquake from Tsunami Waveform Inversion
Authors: Piatanesi Alessio , Lorito Stefano 
Published: January 2007

Abstract
The aim of this work is to infer the slip distribution and rupture velocity along the rupture zone of the 26 December 2004 Sumatra–Andaman earthquake from available tide gage records of the tsunami. We selected waveforms from 14 stations, distributed along the coast of the Indian Ocean. Then we subdivided the fault plane into 16 subfaults (both along strike and downdip) following the geometry and mechanism proposed by Banerjee et al. (2005) and computed the corresponding Green’s functions by numerical solution of the shallow-water equations through a finite- difference method. The slip distribution and rupture velocity were determined simultaneously by means of a simulated annealing technique. We compared the recorded and synthetic waveforms in the time domain, using a cost function that is a trade-off between the L1 and L2 norms. Preliminary tests on a synthetic dataset, together with a posteriori statistical analysis of the model ensemble enabled us to assess the effectiveness of the method and to quantify the model uncertainty. The main finding is that the best source model features a nonuniform distribution of coseismic slip, with high slip values concentrated into three main patches: the first is located in the southern part of the fault, off the coast of the Aceh Province; the second between 6.5° N and 11° N; and the third at depth, between 11° N and 14° N. Furthermore, we estimated that the rupture propagated at an average speed of 2.0 km/sec.