Large earthquakes nucleate at tectonic plate boundaries, and their occurrence within a plate's interior remains rare and poorly documented, especially offshore. The two large earthquakes that struck the northeastern Indian Ocean on 11 April 2012 are an exception: they are the largest strike-slip events reported in historical times and triggered large aftershocks worldwide. Yet they occurred within an intra-oceanic setting along the fossil fabric of the extinct Wharton basin, rather than on a discrete plate boundary. Here we show that the 11 April 2012 twin earthquakes are part of a continuing boost of the intraplate deformation between India and Australia that followed the Aceh 2004 and Nias 2005 megathrust earthquakes, subsequent to a stress transfer process recognized at other subduction zones. Using Coulomb stress change calculations, we show that the coseismic slips of the Aceh and Nias earthquakes can promote oceanic left-lateral strike-slip earthquakes on pre-existing meridian-aligned fault planes. We further show that persistent viscous relaxation in the asthenospheric mantle several years after the Aceh megathrust explains the time lag between the 2004 megathrust and the 2012 intraplate events. On a short timescale, the 2012 events provide new evidence for the interplay between megathrusts at the subduction interface and intraplate deformation offshore. On a longer geological timescale, the Australian plate, driven by slab-pull forces at the Sunda trench, is detaching from the Indian plate, which is subjected to resisting forces at the Himalayan front.
... Further underscoring the region's seismic vulnerability, April 11, 2012, marked a historic moment with the occurrence of the largest recorded strike-slip earthquake (8.6 Mw and 8.2 Mw) in history. With only a 2-hour interval between the two events, this unprecedented seismic activity (Delescluse et al. 2012;Duputel et al. 2012;Lay et al. 2005;Wang et al. 2012;Yue et al. 2012). Geodetic and geomorphic studies assessing the distribution of slip/locking on the Sumatra fault, as conducted by Tabei et al. (2017), suggest that the potential for significant earthquakes in Aceh remains considerable. ...
... This magnitude is based on the last tsunami threat in the southwest waters of Aceh on April 11, 2012. On the same day, two major earthquakes occurred, with the first one measuring 8.6 Mw (330 km southwest of the 2004 event's epicenter) and the second one occurring two hours later with a magnitude of 8.2 Mw, located approximately 180 km south of the first location (Delescluse et al. 2012). This scenario is referred to by Tursina et al. (2021), projecting tsunami inundation and sea level rise in the Banda Aceh region, which is located east of this study location. ...
This paper reflects on the progress of tsunami preparedness in a coastal community in Aceh, Indonesia, nearly two decades after the catastrophic 2004 Indian Ocean Tsunami. The research employs a comprehensive approach to thoroughly evaluate and comprehend the community’s preparedness, its correlation with local perceptions of tsunami risk, and delves into the prevalence of tsunamis in the area, with a specific emphasis on the significant impact of the 2004 Indian Ocean Tsunami on the coastal community of Aceh. To investigate the community’s readiness and the potential impacts of tsunamis at the study site, tsunami simulations were performed using the shallow water equation within the COMCOT (Cornell Multi-grid Coupled Tsunami) model. These simulations assessed run-up and inundation scenarios, thereby providing justification for the potential tsunami impact in the area. Modelling the scenario of tsunami in the region is important to measure the potential impact and estimation time for community to prepare the evacuation plan. In addition to the numerical modeling, a mixed-method approach was employed, involving the distribution of questionnaires and conducting in-depth interviews with 150 respondents directly on-site. These assessments yielded valuable insights into community perspectives on tsunami risk and their preparedness measures. The findings contribute to the development of effective strategies for disaster management by integrating local knowledge, experiences, and socialization programs. The study emphasizes the significance of ongoing endeavors to enhance community preparedness and mitigate the consequences of tsunamis.
... CCP stacking of receiver functions will give more knowledge about the seismicity of the area (Table 6.1). (Kagan & Jackson, 1999;Delescluse et al., 2012). The USGS refers to the M w 8.6 earthquake as the Indian Ocean earthquake, and from this point forward, we will use the same terminology. ...
The book presents earthquake source, wave propagation, site amplification, and other seismological studies including earthquake simulation, application of Artificial Neural Network (ANN) in seismology, earthquake early warning system, waveform inversion, moment tensor analysis, receiver function analysis, earthquake prediction, and earthquake early warning system applications. To minimize the losses due to an earthquake, it is better to understand the source properties, medium characteristics, site condition, and amplitude of a probable earthquake at a particular site. The evolutions of earthquake source models make it possible to understand the source dynamics. However, analysis of the source using a single-domain method does not provide a better understanding of the source dynamics. Therefore, this book combines methods from the earthquake spectrum to waveform inversion and joint inversion. The book also discusses earthquake prediction methods and their reliability around the globe, and techniques of simulation viz. stochastic, empirical, semi-empirical, and hybrid, along with their limitations and application. Seismology is an interdisciplinary subject. Therefore, the information presented in the book will appeal to a wider readership from students, teachers, researchers, planners engaged in developmental work, and people concerned with earthquake awareness.
... Great earthquakes (M w ≥ 8.0) are known to occur predominantly within the shallow layers of subduction zones (depth ≤70 km) and most of those, during the GRACE GRACE-Follow-On era (2002-present), ruptured as thrust events when the cumulative stress building up at the interface between colliding plates exceeded the friction threshold (see Figure 1 of Lay (2015)). Much less frequently, strike-slip earthquakes within the oceanic plate (e.g., Wharton Basin, Indian Ocean, 2012, M w = 8.6) as well as normal faulting events (e.g., Kuril Islands, 2007, M w = 8.1;nucleation phase of Samoa, 2009, M w = 8.0) were also recorded at comparable moment magnitudes (e.g., Beavan et al., 2010;Delescluse et al., 2012;Han et al., 2016). Finally, the deepest parts of subducting slabs can host truly great, if rare, earthquakes (e.g., Sea of Okhotsk, 2013, M w = 8.3; Fiji, 2018, M w = 8.1). ...
Earthquakes involve mass redistribution within the solid Earth and the ocean, and as a result, perturb the Earth's gravitational field. For most of the shallow (<60 km) earthquakes with Mw > 8.0, the GRACE satellite gravity measurements suggest considerable volumetric disturbance of rocks. At a spatial scale of hundreds of km, the effect of volumetric change exceeds gravity change by vertical deformation; for example, negative gravity anomalies associated with volumetric expansion are characteristic patterns after shallow thrust events. In this study, however, we report contrasting observations of gravity change from two intermediate‐depth (100–150 km) earthquakes of 2016 & 2017 Mw 8.0 (two combined) Papua New Guinea thrust faulting events and 2019 Mw 8.0 Peru normal faulting and highlight the importance of compressibility in earthquake deformation. The combined 2016/17 thrust events resulted in a positive gravity anomaly of 5–6 microGal around the epicenter, while the 2019 normal faulting produced a negative gravity anomaly of 3–4 microGal. Our modeling found that these gravity changes are manifestation of vertical deformation with limited volumetric change, distinct from gravity changes after the shallow earthquakes. The stronger resistance of rocks to volume change at intermediate‐depth results in largely incompressible deformation and thus in a gravity change dominated by vertical deformation. In addition, malleable rocks under high pressure and temperature at depth facilitated substantial afterslip and/or fast viscoelastic relaxation causing additional vertical deformation and gravity change equivalent to the coseismic change. For the Papua New Guinea events, this means that postseismic relaxation enhanced coseismic uplift and relative sea level decrease.
... The 2012 twin earthquakes (Mw8.6 and Mw8.2) that struck the northeastern Indian Ocean Wharton Basin are the largest recorded intraplate strike-slip events. Delescluse et al. (2012) reported that the two Wharton Basin earthquakes occurred in the region with positive Coulomb stress change resulting from the 2004 Mw9.2 Sumatra-Andaman and 2005 Mw8.7 Nias megathrust earthquakes, and concluded that they may have been promoted by the two megathrust earthquakes. On the contrary, the stress transfer process of the offshore earthquake on tectonic plate boundary where large earthquake nucleate may be more noteworthy. ...
Postseismic deformation at convergent margins is controlled mainly by continuous slip on the fault (afterslip) and relaxation of the earthquake‐induced stress in the viscoelastic upper mantle (viscoelastic relaxation). Study of these deformation processes provides insight into the rheological properties of upper mantle and slip behavior of the fault. We have constructed a three‐dimensional finite element model to investigate the postseismic deformation of the 2018 Mw 7.9 Kodiak earthquake. We derived the first 2‐year postseismic Global Positioning System observations to constrain afterslip and upper mantle rheology in the south‐central Alaska. The upper mantle is separated into the mantle wedge and oceanic upper mantle topped by an 80‐km thick asthenosphere layer by the subducting slab. Results show that afterslip generally occurred in areas adjacent to the rupture zone and has a small magnitude of a few tens of millimeters. The viscosities of the asthenosphere and mantle wedge are determined to be in a range of 1–4 × 10¹⁸ and 0.5–5 × 10¹⁹ Pa s with an optimal value of 2 × 10¹⁸ and 2 × 10¹⁹ Pa s, respectively. Model results reveal a localized weak mantle wedge of ∼10¹⁸ Pa s beneath Lower Cook Inlet that may be due to the fluids dehydrated from the slab. Coulomb stress changes show that the earthquake enhanced coseismic and postseismic stress loading of up to 0.9 and 0.1 bar, respectively, on the shallow subduction interface near Kodiak Island, but there is no obvious triggered seismicity, probably due to the low stress status already released by the 1964 Mw 9.2 Alaska earthquake.
... However, specific mechanisms and spatiotemporal distributions of the diverse nature of earthquake sequences are poorly understood. Various physical processes have been suggested to explain the spatio-temporal evolution and triggering potential of earthquake sequence, e.g., time-dependent static or dynamic stress perturbation (Dieterich 1994;Stein 1999;Felzer and Brodsky 2006;Hill and Prejean 2015;Parsons et al. 2017), co-seismic fluid pressurization (Mulargia and Bizzarri 2015;Nur and Booker 1972), aseismic afterslip (Perfettini and Avouac 2004), relaxation of co-seismic stress by poro-elastic effect (Freed and Lin 2002;Gahalaut et al. 2008;He and Peltzer 2010;Kundu et al. 2012;Yadav et al. 2018), thermal destressing (Im et al. 2021), viscoelastic relaxation effect (Wiseman and Bürgmann 2012; Delescluse et al. 2012), hydrothermal process driven by fluid diffusion (Ross et al. 2017), and magmatic intrusions (Sykes 1970;Nur 1974). Besides these inherent mechanisms for spatio-temporal evolution of earthquake sequence, earthquake sequence can also be modulated by periodic external loading phenomena, e.g., by solid earth and ocean tides generated by the gravitational pull of the sun and moon that induce periodic loading (Agnew 1996(Agnew , 1997Tanaka 2012;Bucholc and Steacy 2016). ...
We report solid-earth tidal modulation of early aftershocks of the July 2019 Ridgecrest earthquake sequence, which occurred close to the southeastern edge of the Coso geothermal field. We found that the frequency of early aftershocks in the northern part, close to the Coso geothermal field, was modulated by the solid earth tides as they exhibit a strong correlation with the peak shear stress and Coulomb stress imparted by the solid earth tides. However, aftershocks that occurred farther south of the Coso geothermal field in the same sequence exhibit a weak correlation with the solid earth tidal stress. Our analysis implies that the tidal modulation of the earthquake sequence in the northern part is due to its vicinity to the Coso geothermal fields in southern California, which contain high-pressure fluids and are well known for their susceptibility towards tidal triggering.
... Notwithstanding, positively buoyant continental India is also resisting continental subduction that may in turn induce stresses in the interior of the Indo-Australian plate, leading to its fragmentation (Wiens et al., 1985;Cloetingh and Wortel, 1986;Gordon and Houseman, 2015;Coudurier-Curveur et al., 2020). In fact, several oceanic fracture zones in the Indian Ocean seem to be reactivating as shown by the M W 8.6 and 8.2 Indian ocean earthquakes in 2012 (Delescluse et al., 2012;Yue et al., 2012) and in time the Indo-Australian plate may split in two. Indeed, as illustrated in Fig. 1b, the 2012 earthquakes form part of a swarm of earthquakes, mostly strikeslip, between India and Australia that point to the early stage of India-Australia plate break-up. ...
The Himalaya and the Tibetan plateau, the highest mountain range on Earth, have been growing continuously for the last 55 Myr since India collided with Eurasia. The forces driving this protracted mountain building process are still not fully understood. Although subduction zones are considered the main driving force for plate tectonics, mantle flow and plate boundary migration, their role in driving the Indian indentation and the northward movement of the collisional plate boundary is yet to be tested with geodynamic models. Here, we use four-dimensional geodynamic physical models to show that active subduction of the Indo-Australian plate along the Sunda subduction zone is probably the main driver of the India-Asia convergence, Indian indentation, and the consequent growth of the Himalaya-Tibet mountains, and also the present-day eastward crustal displacement of southeast Asia. Our experiments show that at least 880 km of northward indentation of India would not have ensued in the absence of the lateral subduction zones. Our experiments with lateral subduction zones show that subduction of the Indian continental lithosphere is maximum close to the eastern and western syntaxes, which ranges between 450 and 500 km. Based on our model results we propose that the protracted growth of collisional mountains on Earth, like the Himalaya, is highly dependent on nearby active subduction zones.
... The Indo-Australian plate deforms in response to a wide range of processes, including Sumatran subduction, India-Eurasia collision, plate flexure, and oceanic plate fault reactivation. The latter includes fracture zone reactivation and a series of complex largemagnitude earthquakes that occurred in 2012 (e.g., Delescluse et al., 2012). ...
The 2012 Sumatra (Mw 8.6) earthquake, which falls into the largest and rarest group of the great intraplate earthquakes, continues to awe many brilliant minds. An enormous aftershock (Mw 8.2) was felt two hours after the Indian Ocean earthquake along the triple intersection of the Indian, Australian, and Sunda plates in the northwest. Over the past 20 years, there have been numerous earthquakes in the Sumatran subduction zone, including the 2004 earthquake (Mw 9.2) of Sumatra-Andaman, the 2005 earthquake (Mw 8.6) of Nias-Simeulue, the 2007 earthquake (Mw 8.4) of Bengkulu, the 2010 earthquake (Mw 7.8) of Mentawai tsunami, and a large number of other minor to moderate-sized events. It often takes a few seconds to a few minutes for the stress brought on by an earthquake to dissipate. This massive discharge disrupts the lithosphere and asthenosphere, which causes more earthquakes to occur nearby. A comprehensive comprehension of stress variations along a fault and its neighboring faults is essential for effectively predicting and mitigating seismic risks. Drawing inspiration from the earthquake finite fault model pioneered by Guangfu Shao, Xiangyu Li, and Chen Ji from UCSB, we have formulated Coulomb stress models tailored to the Sumatran subduction zone and the Sumatran fault. It was discovered that the primary shock’s related coulomb stress change exceeded the stress-triggering threshold. The aftershock struck a place where there was a lot of stress from the mainshock. Therefore, the Coulomb failure stress change brought on by the mainshock is likely what caused the Sumatra aftershock to occur.
[1] Pore pressure changes are rigorously included in Coulomb stress calculations for fault interaction studies. These are considered changes under undrained conditions for analyzing very short term postseismic response. The assumption that pore pressure is proportional to fault-normal stress leads to the widely used concept of an effective friction coefficient. We provide an exact expression for undrained fault zone pore pressure changes to evaluate the validity of that concept. A narrow fault zone is considered whose poroelastic parameters are different from those in the surrounding medium, which is assumed to be elastically isotropic. We use conditions for mechanical equilibrium of stress and geometric compatibility of strain to express the effective normal stress change within the fault as a weighted linear combination of mean stress and fault-normal stress changes in the surroundings. Pore pressure changes are determined by fault-normal stress changes when the shear modulus within the fault zone is significantly smaller than in the surroundings but by mean stress changes when the elastic mismatch is small. We also consider an anisotropic fault zone, introducing a Skempton tensor for pore pressure changes. If the anisotropy is extreme, such that fluid pressurization under constant stress would cause expansion only in the fault-normal direction, then the effective friction coefficient concept applies exactly. We finally consider moderately longer timescales than those for undrained response. A sufficiently permeable fault may come to local pressure equilibrium with its surroundings even while that surrounding region may still be undrained, leading to pore pressure change determined by mean stress changes in those surroundings.
The 11 March 2011 off the Pacific coast of Tohoku Earthquake
(Mw 9.0) produced megathrust displacements of at least 40 m.
The resulting tsunami devastated the Honshu coast southwest of regions
struck by earthquake-generated tsunami in 1611, 1896 and 1933. The 1896
Meiji-Sanriku earthquake was also an underthrusting earthquake, but the
1933 Sanriku-oki earthquake was a trench-slope normal faulting event;
both generated inundation heights of 10 to 25 m along the coast of
Iwate prefecture. Possible occurrence of a great outer trench-slope
earthquake seaward of the 2011 Tohoku Earthquake along a southwestward
extension of the 1933 fault zone is a concern. The second largest 2011
aftershock, an outer rise Mw 7.7 normal faulting earthquake
occurred near the southern end of the 1933 rupture. Additional
aftershock activity has been distributed along a trend below the trench
and diffusely spread in the outer rise, seaward of the megathrust
region where the largest slip occurred. Coulomb stress perturbations of
at least 5-10 bars are calculated for outer rise normal fault geometries
for mainshock slip models. Whether a future great trench slope event
will occur is uncertain, but the potential tsunamigenic hazard can be
gauged by the huge inundations accompanying the 1933 rupture.
Observations of flexure indicate the effective elastic thickness of the oceanic lithosphere is 2 to 3 times smaller than the seismic or thermal thickness of oceanic lithosphere. The effective elastic thickness is a function of temperature and hence age of the lithosphere at the time of loading. Recent results of experimental rock mechanics indicate that the strength of rocks is a strong function of temperature and that the oceanic lithosphere responds to loading by thinning rapidly from its seismic thickness to it rheologic thickness. We have used a yield stress envelope based on experimental rock mechanics to estimate the maximum bending stresses associated with the load of the Hawaiian Islands near Oahu. These results indicate that the oceanic lithosphere is capable of supporting stresses of at least 1 kbar for long periods of geological time (>50 m.y.).
The similar to 1300-km-long rupture zone of the 2004 Andaman-Sumatra megathrust earthquake continues to generate a mix of thrust, normal, and strike-slip faulting events. The 12 June 2010 M(w) 7.5 event on the subducting plate is the most recent large earthquake on the Nicobar segment. The left-lateral faulting mechanism of this event is unusual for the outer-rise region, considering the stress transfer processes that follow great underthrusting earthquakes. Another earthquake (M(w) 7.2) with a similar mechanism occurred very close to this event on 24 July 2005. These earthquakes and most of their aftershocks on the subducting plate were generated by left-lateral strike-slip faulting on north-northeast-south-southwest oriented near-vertical faults, in response to north-northwest-south-southeast directed compression. Pre-2004 earthquake faulting mechanisms on the subducting oceanic plate are consistent with this pattern. Post-2004, left-lateral faulting on the subducting oceanic plate clusters between 5 degrees N and 9 degrees N, where the 90 degrees E ridge impinges the trench axis. Our study observes that the subducting plate off the Sumatra and Nicobar segments behaves similarly to a chip of the India-Australia plate, deforming in response to a generally northwest-southeast oriented compression, an aspect that must be factored into the plate deformation models.
A complete set of closed analytical expressions is presented in a unified manner for the internal displacements and strains due to shear and tensile faults in a half-space for both point and finite rectangular sources. These expressions are particularly compact and systematically composed of terms representing deformations in an infinite medium, a term related to surface deformation and that is multiplied by the depth of observation point. Several practical suggestions to avoid mathematical singularities and computational instabilities are also presented. The expressions derived here represent powerful tools both for the observational and theoretical analyses of static field changes associated with earthquake and volcanic phenomena.
A complete set of closed analytical expressions is presented in a unified manner for the internal displacements and strains due to shear and tensile faults in a half-space for both point and finite rectangular sources. Several practical suggestions to avoid mathematical singularities and computational instabilities are presented. -from Author
Two large (Mw 7.9) earthquakes occurred on 4 and 18 June
2000, south of Sumatra, beneath the Indian Ocean. Both earthquakes were
predominantly left-lateral strike-slip on vertical N-S trending faults
that we interpret to be reactivated fracture zones. The 4 June Enggano
earthquake occurred at the edge of the rupture area of the 1833
subduction earthquake. The first strike-slip subevent within the
subducting plate triggered a thrust subevent on the plate interface,
which comprised at least 35% of the total moment and ruptured SE away
from the 1833 earthquake. The 18 June earthquake in the Wharton Basin is
one of the largest shallow strike-slip faulting earthquakes ever
recorded. A small second subevent with reverse slip is required to fit
the body waves. The orientation of both subevents in our preferred model
is consistent with the current stress field in the region. Both the June
2000 earthquakes are consistent with recent models of distributed
deformation in the India-Australia composite plate. The occurrence of
the Enggano earthquake implies that the stress field within the Indian
plate continues to a depth of 50 km in the subducting slab. The purely
strike-slip source model of the Wharton Basin earthquake obtained by
[2001] matches the P waves very poorly and fits the S waves no better
than our preferred model. The strike-slip subevents of both earthquakes
had few aftershocks and higher stress drops than the subduction thrust
subevent of the Enggano earthquake. This difference is consistent with
previous observations of oceanic and subduction earthquakes.
