Coseismic Deformation Research Articles

Earthquake Education Through the Use of Documentary Movies

Unscientific, false, inaccurate and/or exaggerated reporting about anything in media or other platforms is a serious concern that needs a solution. This is particularly important when reporting about disasters (e.g. earthquakes). The lack of authentic scientific input into science news reporting may lead to news disasters, which may prove to be much more critical and dangerous than say -earthquake disasters. Therefore, this paper explores such a problem in a portion of NW Borneo and offers solution to improve the existing norms on the earthquake science, education and awareness programs in SE Asia. The explored field location is Sabah, Malaysia, which is targeted to map the level of earthquake science education and awareness of local people, and to examine the co-seismic deformation associated with the 5th June, 2015 earthquake. This event has surprised the local communities because the region is geographically located away from the active tectonic plate boundaries, and has traditionally been considered a low earthquake risk region. This is in contrast to the existence of high earthquake hazard and risk regions in the neighboring Indonesia and the Philippines. Therefore, not surprisingly, the residents of Borneo where puzzled, surprised and worried when a medium magnitude earthquake occurred and caused significant loss of life and property. The lack of scientific education on the causes, and remedies of earthquake hazards in most of the South and Southeast Asian regions is a reality, which needs a real solution. Therefore, through this work a small initiative has been started in Sabah, Malaysia where stories from the earthquake victims were recorded after the devastation caused by the June 2015 earthquake. Their real time experiences were blended with the updated scientific data on the occurrence of earthquakes in Borneo, which are mostly gathered from previously published works and the work presented here. The entire work is converted into a small documentary movie that highlights the causes of earthquake and how it impacts human life.

From regional to local SPTHA: efficient computation of probabilistic tsunami inundation maps addressing near-field sources

Abstract. Site-specific seismic probabilistic tsunami hazard analysis (SPTHA) is a computationally demanding task, as it requires, in principle, a huge number of high-resolution numerical simulations for producing probabilistic inundation maps. We implemented an efficient and robust methodology using a filtering procedure to reduce the number of numerical simulations needed while still allowing for a full treatment of aleatory and epistemic uncertainty. Moreover, to avoid biases in tsunami hazard assessment, we developed a strategy to identify and separately treat tsunamis generated by near-field earthquakes. Indeed, the coseismic deformation produced by local earthquakes necessarily affects tsunami intensity, depending on the scenario size, mechanism and position, as coastal uplift or subsidence tends to diminish or increase the tsunami hazard, respectively. Therefore, we proposed two parallel filtering schemes in the far- and the near-field, based on the similarity of offshore tsunamis and hazard curves and on the similarity of the coseismic fields, respectively. This becomes mandatory as offshore tsunami amplitudes can not represent a proxy for the coastal inundation in the case of near-field sources. We applied the method to an illustrative use case at the Milazzo oil refinery (Sicily, Italy). We demonstrate that a blind filtering procedure can not properly account for local sources and would lead to a nonrepresentative selection of important scenarios. For the specific source–target configuration, this results in an overestimation of the tsunami hazard, which turns out to be correlated to dominant coastal uplift. Different settings could produce either the opposite or a mixed behavior along the coastline. However, we show that the effects of the coseismic deformation due to local sources can not be neglected and a suitable correction has to be employed when assessing local-scale SPTHA, irrespective of the specific signs of coastal displacement.

Time-dependent stress increase along the major faults in eastern Turkey

The co-seismic, and post-seismic effects of 18 earthquakes that occurred since 1822 were modelled in conjunction with a regionally variable secular inter-seismic effect in order to investigate how the Coulomb stress field in the eastern part of the North Anatolian and the East Anatolian Fault Zones, have evolved over the past two centuries. Results show that viscoelastic post-seismic relaxations caused by the 1939 Ms 7.9 Erzincan earthquake is still strong and influencing the seismic activity in the region. Post-seismic effects have increased the stress on the Yedisu segment as much as 5.3 bars, whereas supressed stress on the Kahramanmaras-Malatya segment. In general, increases in stress due to viscous-elastic effects are comparable, or in certain cases even larger than the increases in stress caused by co-seismic deformations. This indicates that the additional stress changes derived from viscoelastic deformations could be significant and should be taken into consideration when assessing seismic hazard along the active seismic zones. Two regions are identified as having high positive Coulomb stress changes therefore high seismic hazard; a segment close to Bingol Province in the East Anatolian Fault Zone and the Yedisu segment of the North Anatolian Fault Zone.

Testing Different Tectonic Models for the Source of the Mw 6.5, 30 October 2016, Norcia Earthquake (Central Italy): A Youthful Normal Fault, or Negative Inversion of an Old Thrust?

AbstractWe adopted a multidisciplinary approach to investigate the seismotectonic scenario of the 30 October 2016, Mw 6.5, Norcia earthquake, the largest shock of the 2016–2017 central Italy earthquake sequence. First, we used seismological and geodetic data to infer the dip of the main slip patch of the seismogenic fault that turned out to be rather low‐angle (~37°). To evaluate whether this is an acceptable dip for the main seismogenic source, we modeled earthquake deformation using single‐ and multiple‐fault models deduced from aftershock pattern analyses. These models show that the coseismic deformation generated by the Norcia earthquake is coherent with slip along a rather shallow‐dipping plane. To understand the geological significance of this solution, we reconstructed the subsurface architecture of the epicentral area. As the available data are not robust enough to converge on a single fault model, we built three different models encompassing all major geological evidence and the associated uncertainties, including the tectonic style and the location of major décollement levels. In all models the structures derived from the contractional phase play a significant role: from controlling segmentation to partially reusing inherited faults, to fully reactivating in extension a regional thrust, geometrically compatible with the source of the Norcia earthquake. Based on our conclusions, some additional seismogenic sources falling in the eastern, external portions of the Apennines may coincide with inherited structures. This may be a common occurrence in this region of the chain, where the inception of extension is as recent as Middle‐Upper Pleistocene.

Source Parameter Estimation of the 2009 Ms6.0 Yao’an Earthquake, Southern China, Using InSAR Observations

On 9 July 2009, an Ms6.0 earthquake occurred in mountainous area of Yao’an in Yunnan province of Southern China. Although the magnitude of the earthquake was moderate, it attracted the attention of many Earth scientists because of its threat to the safety of the population and its harm to the local economy. However, the source parameters remain poorly understood due to the sparse distribution of seismic and GNSS (Global Navigation Satellite System) stations in this mountainous region. Therefore, in this study, the two L-band ALOS (Advanced Land Observing Satellite-1) PALSAR (Phased Array type L-band Synthetic Aperture Radar) images from an ascending track is used to investigate the coseismic deformation field, and further determine the location, fault geometry and slip distribution of the earthquake. The results show that the Yao’an earthquake was a strike-slip event with a down-dip slip component. The slip mainly occurred at depths of 3–8 km, with a maximum slip of approximately 70 cm at a depth of 6 km, which is shallower than the reported focal depth of ~10 km. An analysis of the seismic activity and tectonics of the Yao’an area reveals that the 9 July 2009 Yao’an earthquake was the result of regional stress accumulation, which eventually led to the rupture of the northwestern most part of the Maweijing fault.

An integrated study on the coseismic and post-seismic deformation of the 2010 Yushu earthquake based on InSAR analysis

We carry out an integrated study on coseismic and post-seismic deformation caused by 2010 Yushu earthquake sequence, including both mainshock and aftershocks, by using multi-scene ENVISAT/ASAR data on two adjacent tracks. We map the extended deformation region to the west of mainshock and show the westward extension of seismogenic fault of mainshock. Based on our whole deformation field derived from mosaic interferograms, the total length of seismogenic fault reaches \({\sim }103\,\hbox {km}\) longer than \({\sim }71\,\hbox {km}\) suggested by the previous report. Several coseismic interferograms with different time baselines have similar deformation patterns, which indicate that the influence of aftershocks and post-seismic slip on coseismic deformation field is limited. Also, we observe a clear and separate deformation area, \({\sim }38\,\hbox {km}\) to the west of the mainshock epicentre, with maximum displacement of \({\sim }9\,\hbox {cm}\). The localised deformation is composed of two patches with opposite motion directions, where an aftershock cluster with at least 47 events (\({>}\hbox {Ms}\,3.0\)) occurred. We infer that this localised deformation is caused by aftershocks ruptured on a blind active fault. While a weak post-seismic deformation band along main rupture zone near mainshock epicentre is likely attributable to short-term afterslip.

Co- and post-seismic Deformation Mechanisms of the MW 7.3 Iran Earthquake (2017) Revealed by Sentinel-1 InSAR Observations

The extraction of high-accuracy co- and post-seismic deformation fields and inversions of seismic slip distributions is significant in the comprehension of seismogenic mechanisms. On 12 November 2017, a MW 7.3 earthquake occurred on the border between Iran and Iraq. To construct the co-seismic deformation field, Sentinel-1A synthetic aperture radar (SAR) images from three tracks were used. Based on a prior knowledge, least-squares iterative approximation was employed to construct the three-dimensional (3D) co-seismic deformation field. to derive a time series of 2D post-seismic deformation, the multidimensional small baseline subset (MSBAS) technique was use. Co-seismic deformation fields were asymmetric; the maximum relative displacement was nearly 90cm in the radar line-of-sight between two centers of co-seismic deformation. The 3D co-seismic deformation field showed southwestward horizontal motion and continuous subsidence-to-uplift variation from northeast to southwest. The two-dimensional (2D) post-seismic deformation time series showed a gradual decaying trend and good correspondence with the aftershock distribution. The main mechanism of post-seismic deformation was an afterslip of the post-seismic faults. We used the elastic half-space model to invert co-seismic deformation fields and obtain source parameters of the slip model. The maximum and average slips were 2.5 and 0.72 m, respectively. The average slip angle was 126.38° and the moment magnitude was MW 7.34. The results of this study will contribute to research on regional tectonic activities.

Scaly fabric and slip within fault zones

Scaly fabric was first described early in the development of geology and has experienced a recent renaissance with the realization that it may play a key role in the shallow coseismic deformation of plate boundary faults, such as the M9 Tohoku-Oki megathrust event. The fabric itself is an anastomosing network of polished surfaces. It is often present in clay-rich sediments deformed by pure and/or simple shear. The faults where it is found typically have multiple modes of slip, from creep to tremor to seismic slip. It is a macroscopic, multi-scale structure that has, to date, been impossible to create under laboratory conditions. In this paper, I review the state of the art of our understanding of this fabric, its mechanical modes of deformation, and its capacity for both aseismic and seismic slip. I also summarize the challenges we face to understand its full importance in the evolution of plate boundary faults. The conclusion is that scaly fabric is linked to frictional-viscous shear zones where bulk viscous deformation is accompanied by localized shear—a condition typical of frictional transition zones in faults.

Impact of topography and three-dimensional heterogeneity on coseismic deformation

Knowledge of deformation at plate boundaries has been improved greatly by the development of observational techniques in space geodesy. However, most theoretical and numerical models of coseismic deformation have remained very simple and do not include realistic Earth structure. 3-D material heterogeneity and topography are often neglected because simple models are assumed to be sufficient and available tools cannot easily accommodate complex heterogeneity. In this study, we demonstrate the importance of 3-D heterogeneity using a spectral element method that incorporates topography and 3-D material properties. Using a parabolic hill model and a topographic model of the 2010 Maule earthquake, we show that topographic features can alter the shape of observed surface deformation patterns. We also estimate the coseismic surface deformation due to a model of the slip distribution of the 2015 Gorkha earthquake using realistic topography and 3-D elastic structure, and find that the presence of topography causes changes in the shape of observed surface displacement patterns, while material heterogeneities primarily affect the magnitude of observed displacements. Our results show that the inclusion of topography in particular can affect predictions of coseismic deformation modelling.

Coseismic and Postseismic Deformation of the 2016 Mw 6.6 Aketao Earthquake from InSAR Observations and Modelling

On November 25, 2016, the Mw 6.6 Aketao earthquake occurred in Xinjiang, western China. We used the combination of ascending Sentinel-1A, descending Sentinel-1B and ascending ALOS-2 PALSAR data to measure the coseismic deformation. The line-of-sight (LOS) coseismic deformation implies that the earthquake was dominated by right-lateral strike-slip. Ignoring the fault-perpendicular deformation, the fault-parallel and up–down deformation was extracted based on the combination of Sentinel-1A and 1B observations. Results show that the maximum fault-parallel deformation is ~ 13.7 cm at the north wall and the minimum is ~ −16.5 cm at the south wall of the Muji fault. Then, coseismic slip distribution was derived using the steepest descent method (SDM) based on a single-segment fault model using the three InSAR LOS observations as constraints. The slip distribution reveals two slip centers. The maximum slip of the eastern center is 0.5 m at a depth of 8.8 km, where the rake angle is ~ 181.2°. The maximum slip of the western center is 0.6 m at a depth of 10.8 km, where the rake angle is ~ 181.1°. The derived seismic moment obtained equals the Mw 6.6 earthquake. In this study, postseismic deformation time series in 1.5 years after the earthquake were retrieved from 26 multi-temporal Sentinel-1 descending scenes. The postseismic LOS deformation at the north and south walls of Muji fault both increases with time but in opposite directions. The cumulative deformation is 60–80 mm at the north wall, and –30 to −20 mm at the south wall. The postseismic deformation shows similar patterns with the coseismic deformation, and has the same mechanism. There is no obvious lock at the unbroken gap.

Co-seismic grace gravity-based 11-layered 3-D thrust fault model for the Sumatra earthquake 2004

Our co-seismic Gravity Recovery and Climate Experiment gravity data (level 2 ‘RL_05’ data product ‘GX-OG-_2-GSM) for the Sumatra earthquake 2004 is obtained by differencing monthly gravity field average for November 2004 from that of January 2005 and band-pass filtering (\(17{-}30^{\circ }\) and orders) in the spectral domain. Here, we propose a 11-layered three-dimensional (3-D) thrust fault gravity model based on different co-seismic rupture models in the literature. It honours co-seismic deformation of the ocean surface, ocean bottom and subsurface earth medium, different earthquake parameters and hypocentre information (\({\sim }35\) km below mean sea level). Our forward gravity response matches well with the observed gravity (RMS error of \(0.06257\,\upmu \hbox {gal}\) (6.26%)) data and our model allowed an independent computation of rupture length, instantaneous velocity, average seismic moment and momentum, which are, respectively, 1560 km, 2.9 km/s, \(4.53\times 10^{22 }\,\hbox {N}\,\hbox {m}\) and \( 9.7\times 10^{17}\,\hbox {kg}\,\hbox {m/s}\). These parameters fairly agree with those in the literature. The computed momentum indeed corresponds to an area pulse (\(9.7\times 10^{17}\,\hbox {kg}\,\hbox {m/s}\)) at ocean bottom that led to a tsunami generation. Thus, the proposed multi-layered 3-D gravity model in traditional fashion fully accounts for co-seismic gravity signal of the Sumatra earthquake 2004.

The 2016 Mw 6.0 Hutubi earthquake: A blind thrust event along the northern Tian Shan front

The Tian Shan Range, which trends E-W along the southern margin of the Junggar Basin, is one of the longest and most active intracontinental orogenic belts in central Asia. On 8 December 2016 (05:15:04 UTC), a Mw 6.0 earthquake ruptured the northern Tian Shan front. Here, we use Sentinel-1 radar imagery to investigate the deformation and source parameters related to this event. The co-seismic surface deformation was predominated by uplift without surface rupture. Ascending and descending interferograms indicate that the event triggered small co-seismic deformations with maximum line-of-sight displacements of 22 mm and 24 mm, respectively. Although the north-dipping and south-dipping plane solutions can both fit the observations well, the north-dipping solution with a dip of 58° is preferred in consideration of the relocated aftershocks and regional geological structure. Significant slip is located between depths of 12 km and 17 km, suggesting that the event was caused by a completely blind thrust fault. This blind rupture is characterized largely by a compact thrusting patch with a peak slip of 56 cm at a depth of 13 km. The source model generates a geodetic moment of 6.678 × 1017 N m corresponding to a Mw 5.85 event. Both the interferometric synthetic aperture radar modeling and the aftershock locations indicate that the rupture plane is linked to the Huoerguosi-Manas-Tugulu fault at a depth of ∼16 km, a typical locking depth in the Tian Shan. We suggest that the 2016 Hutubi earthquake more likely occurred on a back-thrust of the Huoerguosi-Manas-Tugulu fault, and the back-thrust is interpreted to represent a preexisting normal fault beneath the Qigu anticline belt that was tectonically inverted during the Cenozoic.

Soil liquefaction in seasonally frozen ground during the 2016 Mw6.6 Akto earthquake

Soil liquefaction is a type of coseismic hydrological change triggered by earthquakes, and its occurrence results in major property damage and casualties. The dynamics of coseismic hydrological changes are not fully understood. In order to address this, we studied coseismic deformations such as liquefaction and ground fissures that occurred as a result of strong seismic activity during the 2016 Mw6.6 Akto earthquake, which took place in the interior of the Pamir Plateau in northwestern China. This paper presents a systematic survey of the frozen soil liquefaction and ground fissures caused by this earthquake. The majority of liquefaction sites near the Karaat River are located on the T1 terrace, in Bulake village, and are adjacent to the alluvial fan of the Kungai Mountain. We find that the liquefaction was caused by the original spring and coseismic ground fissure during the earthquake. Approximately 80% of the liquefaction sites are formed along the original spring in the epicenter. The maximum height of sand boils is 15 cm. The remaining 20% of the liquefaction sites are formed along the coseismic ground fissure. Our results suggest that the frozen soil layer impedes liquefied material in the lower unfrozen soil layer from reaching the surface, and the material formed from liquefaction is consequentially channeled through the primary fault and coseismic ground fissures. Liquefaction associated with the Akto earthquake demonstrates the importance of accounting for the possibility of a series of coseismic geological disasters, such as soil liquefaction and ground fissures, in areas with similar geology, altitude, and temperature.

Coseismic Deformation of the Earth’s Surface in the Area of the Catastrophic 2008 Wenchuan Earthquake According to GPS Measurements

The occurrence time prediction of the strongest earthquakes is one of most topical tasks of seismology. Appearing in the recent years, new observation methods for precursors of different nature can open avenues to achieve success in the field of medium-term seismic forecast. One such method is to observe the Earth’s surface deformation using the Global Positioning System (GPS). Such a region is the territory of South-Western China, where in 2008 occurred the catastrophic Wenchuan earthquake, which caused very large destruction of infrastructure and huge human losses. This GPS system has been in operation since 1991 in the eastern part of the Qinghai–Tibet Plateau, the Sichuan Basin, and the Yunnan–Guizhou Plateau. The results of these observations have already been published and can be applied to study of the activity and segmentation of faults. Until 2004, the measurement network covering the Longmen Shan fault zone and the adjacent territory consisted of ten major points and some additional ones. The 1991–2001 data of GPS observations show that in the Longmen Shan fault zone was recorded offset to the northeast with a relatively low rate of 2.3 mm/year. As a result of studying the surface horizontal deformation using GPS observations, it was established that the focus area in 1999–2007 (prior to the strongest earthquake of 2008) was characterized by anomalously low rates of horizontal movements. This was probably related to the accumulation of stresses in the crust. It can be concluded retrospectively that the results of GPS observations could be considered as a medium-term precursor of the 2008 Wenchuan earthquake, which showed the location of the future seismic source position. The length of the zone of relatively weak horizontal displacements exceeded 250 km, which statistically correspond to a magnitude about 8 earthquake. The seismic rupture system (with a total length of ~240 km, originating during the 2008 Wenchuan earthquake) was confined to the NE-trending Longmen Shan fault zone, which occurs between the eastern margin of the Qinghai–Tibet Plateau and the northwestern part of the Sichuan Basin. Immediately after the Wenchuan event, the pattern of distribution of rates of horizontal movements has greatly changed. The horizontal deformations spanned most of the territory adjacent to the seismic fault zone, and the Longmen Shan Fault Zone exhibited the tectonic reduction of the surface at the expense of reversed movements of fault wings toward each other. The amplitudes of horizontal movements at equal distance on both sides of the branch of the Yingxiu–Beichuan main seismic rupture to the west are reduced slowly, and to the east – quickly. The vertical coseismic surface deformation, registered using satellite geodesy in the epicentral area of the seismic event, were mainly expressed in the submergence of the surface by different amounts in the southeastern wing of the Longmen Shan fault zone in the Sichuan Basin. It can be concluded on the basis of an analysis of the total seismic energy release during the earthquake that the period of 1991–2007 was an evident stage of seismic calm period prior to the strongest earthquake, whereas a period of seismic activity has been registered since 2008 (at the moment of the major shake) up to the present and may last several more years. The extremely low rate of horizontal displacements in the epicentral area of the preparing strongest earthquake can be considered as a middle-term precursor of its occurrence place.

Coseismic Deformation of the 6 February 2018 Mw 6.2 Hualien Earthquake Based on Strong‐Motion Recordings

Coseismic Deformation of the 6 February 2018 Mw 6.2 Hualien Earthquake Based on Strong‐Motion Recordings

Source parameters of the 2017Mw 6.2 Yukon earthquake doublet inferred from coseismic GPS and ALOS-2 deformation measurements

We investigated an M_w ∼ 6.2 earthquake doublet on the border of the USA and Canada using ALOS2 Light-of-Sight displacements and GPS measurements. We selected three L-band ALOS-2 interfergorams with temporal baselines of one yr to extract coseismic deformation maps, in which master and slave images were both acquired in July. A subpixel-based alignment and another range spectral splitting techniques under the GAMMA InSAR software framework were applied to improve the interferometric coherence and reduce the effects of phase anomalies in two of the three interferometric pairs due to either ionospheric delay or a potential focusing issues in the generation of the ALOS2 SLC data. The updated interferograms convincingly reveal deformation fringe patterns produced by the two earthquakes. We conducted a nonlinear geophysical inversion to estimate the geometric parameters of the earthquakes with the InSAR and GPS measurements. The best-fitting model shows that a thrust faulting on a reverse fault and left-lateral strike-slip faulting on a nearly vertical fault with the centroid depths of 9.3±0.6 and 8.4±0.7 km, respectively, are most likely responsible for the earthquake doublet. The eastern Denali fault (EDF) and Duke River fault are major active faults in the region and the earthquake doublet could be due to reactivation of the part of the two faults system.

First Field Evidence of Coseismic Land‐Level Change Associated with the 25 December 2016 Mw 7.6 Chiloé, Chile, Earthquake

Assessments of megathrust earthquake rupture patterns provide fundamental insights into the processes that control the seismic cycle along subduction zones. When large earthquakes occur in regions with sparse geodetic networks, as was the case for the magnitude (⁠ Mw ⁠) 7.6 Chiloe, Chile, earthquake of 25 December 2016, estimates of vertical coseismic deformation from fixed intertidal biotic indicators provide important evidence that help to constrain fault slip. Ten months after the Chiloe earthquake, we observed a white fringe of bleached coralline algae (Corallinaceae) along the southeastern coastline of Isla Quilan, south of Isla de Chiloe, killed by reduced tidal wetting resulting from coseismic land uplift. Our quantitative measurements of the vertical extent of algal mortality provide the first field‐based report of the effects of the 2016 earthquake. We infer Isla Quilan coseismically uplifted by 25.8±14.3 cm ⁠. The vertical extent of mortality (VEM) and the aspect (compass direction) of the bedrock surface are uncorrelated, but we find that exposure to waves and shielding from insolation may prevent or delay mortality. Focusing on sites sheltered from waves, we demonstrate that with a large number of measurements (⁠ >100 ⁠), land‐level changes as low as 25 cm may be quantitatively assessed. The absence of bleaching on Isla de Chiloe may reflect the smaller magnitude of coseismic uplift at this location or the lack of suitably sheltered bedrock surfaces. Previously published fault dislocation models are consistent with our field observations; however, the coralline algae data are on their own insufficient to discriminate between competing hypotheses over the amount of fault slip. By combining our field data with space geodetic data in a model that uses detailed fault geometry, we constrain peak slip to ∼3 m ⁠, approximately 80% of the maximum cumulative plate convergence since the last great earthquake in the region.

The Effect of the Earth’s Rotation on Tsunami Waves Triggered by the 2013 Deep-Focus Okhotsk Sea Earthquake

The features of the dynamics of weak tsunami waves caused by the deep-focus Okhotsk Sea earthquake on May 24, 2013, are studied with numerical modeling. It is found that the vast area of coseismic deformations along with the shallow depth of the Sea of Okhotsk and high latitudes were favorable for effects of the Earth’s rotation in the dynamics of the 2013 Okhotsk Sea tsunami. The comparison of calculations with and without the Coriolis force showed that the Earth’s rotation significantly affects the wave field, changing the wave forms and the distribution of the maximum amplitudes.

Late Holocene paleoseismology of Shuyak Island, Alaska

We report stratigraphic evidence of land-level changes along the eastern portion of the Alaska-Aleutian megathrust. Four marshes on Shuyak Island record variable amounts of coseismic deformation during four pre-20th century earthquakes. We combine these data with paleoseismic evidence from across the Kodiak, Kenai and Prince William Sound segments of the megathrust. These indicate that in the last 2000 years, AD 1964 was the only one to rupture all three segments simultaneously and generate a Mw 9.2 earthquake. The Kodiak segment ruptured independently on four further occasions with magnitudes > Mw 8.0; in AD 1788 and c.400 (440–320) BP, and independently but around the times of great earthquakes in the Prince William Sound segment c.850 and c.1500 BP.

Calculating coseismic deformation and stress changes in a heterogeneous ellipsoid earth model

Calculating coseismic deformation and stress changes in a heterogeneous ellipsoid earth model