Giant Earthquakes Research Articles

Understanding paleo-earthquakes in the Kuril Trench based on Late-Holocene tsunami deposits in the distal region from wave sources, northern Hidaka, Hokkaido, Japan.

Geological evidence, such as tsunami deposits, is crucial for studying the largest rupture zone of the Kuril Trench in Hokkaido, Japan, due to its poor historical record. Although 17th-century tsunami deposits are widely distributed across Hokkaido, the presence of multiple wave sources during that period, including the collapse of Mt. Komagatake, complicates the correlation with their wave sources. Understanding the regional distribution of these tsunami deposits can provide valuable data to estimate the magnitude of megathrust earthquakes in the Kuril Trench. The northern part of Hidaka, Hokkaido, where tsunamis from multiple wave sources are expected to overlap, is distant from the Kuril Trench. To clarify the depositional history of tsunami deposits in such distal areas, evaluating the influence of the depositional environments on the event layer preservation becomes even more critical. We conducted field surveys in Kabari, located in the northern Hidaka region, identifying three sand layers from the 10th to the 17th century and two layers dating beyond 2.3 thousand years ago. The depositional ages of most sand layers potentially correlate with tsunami deposits resulting from the Kuril Trench earthquakes. Utilizing reconstructed paleo-sea level data, we estimated that most sand layers reached approximately 2 m in height. However, it is noteworthy that the latest sand layer from the 17th century exhibited an unusual distribution, more than 3 m in height. This suggests a different wave source as the Mt. Komagatake collapse. The discovery of multiple sand layers and their distributions is crucial to constraining the maximum magnitude of giant earthquakes in the Kuril Trench and understanding the volcanic tsunami events related to Mt. Komagatake.

Study on earthquake and tsunami hazard: evaluating probabilistic seismic hazard function (PSHF) and potential tsunami height simulation in the coastal cities of Sumatra Island

This study uses integrated geological, geodesy, and seismology data to assess the potential tsunami and Probabilistic Seismic Hazard Function (PSHF) near Sumatra’s coastal cities. It focuses on estimating the possible level of ground shaking due to the seismic activity within the Sumatran Fault Zone (SFZ) and subduction zone. It uses the Peak Ground Acceleration (PGA) as a measure. An amplification factor that is based on the previous study is used. It is calculated through the Horizontal-Vertical Spectral Ratio (HVSR), which measures possible surface ground shaking. The Seismic Hazard Function (SHF) is calculated considering magnitudes 6.5 to 9.0 for subduction sources and 6.5 to 7.8 for SFZ sources. Also, the PGA based on the Maximum Possible Earthquake (MPE) magnitude is estimated, and tsunami heights are simulated to assess the possible hazard risk. The tsunami source model in this study is characterized by considering the possibility of the long-term perspectives on giant earthquakes and tsunamis that might occur in subduction zones around the off-coast of southern Sumatra Island. The potentiality source zone is characterized based on the utilization of the cross-correlation of correlation dimension (DC) based on the shallow earthquake catalog of 2010 to 2022 and the SHmax-rate of surface strain rate. Based on the MPE, the relatively high estimated PGA at the base rock was found around Mentawai and Pagai Utara islands at about 0.224 g and 0.328 g, with the largest estimated PGA based on the MPE at the surface with values of about 0.5 g and 0.6 g. The possible maximum tsunami height (Hmax) estimated based on source scenarios position around the west coast of Sumatera Island, such as for Kota Padang and Kota Bungus, reaches up to 12.0 m and 22.0 m, respectively. The findings provide valuable insight into seismic and tsunami hazards, benefiting future mitigation strategies.

Variation in the thermal and dehydration regime below Central America: Insights for the seismogenic plate interface

Slow earthquakes predominant in Costa Rica indicate unstable faulting of segmented Central American megathrusts, but the recurrence of episodic tremors and slips reported to precede a giant earthquake remains still enigmatic. The underlying mechanism is related to the variation in the coupling along the heterogeneous subduction interface which is poorly understood. In this study, we used up-to-date 3D thermal modeling to provide insights into the along-strike variation in the thermal state and hydraulic distribution beneath the Central American subduction zone. Our results show that the subducted Cocos Plate is much warmer than previously estimated, and the slab geometry exhibits remarkable perturbations along the trench. We found that the regions of large dehydration rate along the slab are consistent with the seismicity occurrence depth beneath the Moho. Below the Nicoya Peninsula and the Guatemala-Nicaragua segment of megathrusts, fluids derived from subducted slab result in increased pore fluid pressures and subsequent recurrence of slow slip events and regular earthquakes.

Geologic and Geophysical Evidence of Repeated Normal Faulting on the Itozawa Fault—the Source of the Mw 6.6 Iwaki Earthquake Triggered by the Mw 9.0 Tohoku-Oki Megathrust Earthquake, Northeast Japan

ABSTRACT The 2011 Mw 9.0 Tohoku-Oki earthquake ruptured the 500 km long and 200 km wide convergent plate margin between the North American and Pacific plates, and changed the crustal stress field and triggered widespread seismic activity in northeast Japan. In particular, many crustal earthquakes struck the southern Fukushima area. The largest inland normal-faulting earthquake with Mw 6.6 occurred on the northwest-trending Yunodake fault and the north-northwest-trending Itozawa fault on 11 April 2011. The coseismic surface ruptures appeared along the previously identified active and presumed active faults. To investigate the near-surface structure of the Itozawa fault, we conducted ground-penetrating radar (GPR) profiling across the fault, and two drilling surveys on its hanging-wall and footwall blocks. The GPR survey line about 50 m long was located near the previous trenching site. The GPR two-way travel-time sections were collected by common-offset modes by 50 and 100 MHz GPR systems. We acquired common midpoint ensembles on both sides of the surface rupture for depth conversion of the time sections. The resulting GPR sections show detailed subsurface structures to a depth of about 7 m. We identified event horizons for the 2011, penultimate, antepenultimate, and preantepenultimate earthquakes, indicating that the Itozawa fault has ruptured repeatedly as a normal fault. The vertical displacements during these earthquake events, obtained from the GPR sections, were about 0.8, 0.3, 0.4, and 0.7 m, respectively. These observations suggest that the coseismic surface offset amount on the Itozawa fault varies greatly. The recurrence intervals of surface-rupturing earthquakes on the Itozawa fault, calculated from the previous research and this study, are much longer than those of giant interplate earthquakes along the Japan trench, such as the 2011 Tohoku-Oki earthquake. We conclude that not every giant earthquake along the Japan trench triggers a rupture of the Itozawa fault.

Fujioka, K.: Earth Science of Cataclysm: From Giant Earthquake, Abnormal Climate to Great Extinction

Fujioka, K.: Earth Science of Cataclysm: From Giant Earthquake, Abnormal Climate to Great Extinction

Low-intensity anomaly involving ML≥4 events preceding strong earthquakes in Tibet

Seismic quiescence or enhanced phenomena are anomalous changes against the background of normal seismic activity. Preliminary studies have found that earthquakes with a magnitude of ML≥4 often occur at a low occurrence frequency before giant earthquakes in Tibet. This study analyzed the catalog of ML≥4 earthquakes from 2008 to 2022 and examined the anomalous occurrence of ML≥4 earthquakes preceding most ML≥6 earthquakes. When the monthly occurrence frequency of ML≥4 earthquakes was lower than 4 times over six consecutive months, the subsequent occurrence of ML≥6 earthquakes was highly likely as evidenced by observations. The anomalous characteristics of low-intensity activities were analyzed as a medium- and short-term forecasting index for large earthquakes in the Tibetan area.

Analysis of the Extreme Tsunami Risk to Sanya New Airport in the South China Sea

The Manila trench in the South China Sea (SCS) is identified as being most susceptible to the future major earthquakes. Once a submarine earthquake occurs, the coastal areas and ocean engineering projects around SCS will be affected. Based on the Sanya new airport project, this paper presents an analysis of tsunami impacts to the project region. A series of numerical simulations of tsunami are carried out and compared under different magnitudes of earthquakes. An extreme tsunami induced by a giant earthquake of M9.3 is simulated and analyzed in detail. The tsunami propagation scenarios and surface elevation in the region are presented. The inundation map and flow velocity distribution are analyzed. The impacts of this human project to the coasts are discussed by comparing tsunami wave height with and without the artificial island. According to the numerical results and relevant analysis, the giant tsunami will have great impacts to the artificial island.

Integrated mechanical environment of pre- and post-rupture fault and asperity origin of the 2011 giant Tohoku-Oki earthquake.

It is a key to know mechanical environment (ME) of pre- and post-rupture fault of giant earthquakes at subduction zones for predicting earthquake and tsunami disaster. However, we know little about its details till now. In this paper, using the inverted stress change three hours before and three hours after the mainshock in the rupture zone of the 2011 Tohoku-Oki Mw 9.0 earthquake, we show a quantitative integrated ME in the rupture zone, including principal stress, pore-fluid pressure and friction strength. We discover from this environment a large asperity composed of two asperities induced by relatively high friction coefficients and relatively lower pore-fluid pressures. The integrate ME quantitatively explained the reasons of the overshoot and relatively lower shear strength of the trench, which caused huge displacement and tsunami at the trench. We suggest that the asperities favor the horst and graben structure system which provides a geology environment for interseismic stress accumulation and thus for breeding the megathrust tsunami earthquake.

Coseismic Stress Change and Viscoelastic Relaxation after the 2008 Great Sichuan Earthquake

Long-term stress accumulation influenced by coseismic stress changes and postseismic viscoelastic relaxation is considered critical to triggering giant earthquakes. Nevertheless, how the stress increase is interrupted by aftershocks and how it influences the megaseismic cycle remain enigmatic. In this study, based on the Mohr–Coulomb failure criterion at the nucleated segments of the 2008 great Sichuan earthquake, the stress variation associated with four M > 6 aftershocks was calculated for the period from 2010 to 2017. The results show that (1) the spatial distribution of coseismic stress change is correlated with the rupture pattern of large events and has a fundamental impact on triggering subsequent earthquakes and (2) postseismic viscoelastic relaxation leads to increased Coulomb stress accumulation at the northern and southern edges of the seismogenic Longmenshan fault, which results in enhanced fault instability and the potential for future large events.

Precursory Tidal Triggering of the 2011 Mw 9.0 Tohoku Aftershocks

Precursory earth tidal triggering is believed to influence earthquake timing preferentially when a region is critically stressed. However, whether and how the recurrence of aftershocks after a giant earthquake is affected by tidal triggering remains perplexing. To provide insight into this study, we utilized the Schuster test to explore the tidally induced stress variation correlated with the 2011 Mw 9.0 Tohoku earthquake aftershock sequence by determining the tidal phase angle at the occurrence time of events and the periodic characteristics of the aftershocks. Our results show that the aftershocks were triggered by short-period tides, including semidiurnal and diurnal tides. The rupture associated with the mainshock likely resulted in a critical stress state in the focal region, which is conducive to tidal triggering. We subdivided the aftershock catalog into several subsets, using a depth of 30 km and a magnitude of 5 as discriminators. The analysis of these subsets reveals that weaker and deeper earthquakes are best correlated with Earth tides, which will be helpful to investigate the mechanisms of tidal correlation.

Did a 3800-year-old Mw ~9.5 earthquake trigger major social disruption in the Atacama Desert?

Early inhabitants along the hyperarid coastal Atacama Desert in northern Chile developed resilience strategies over 12,000 years, allowing these communities to effectively adapt to this extreme environment, including the impact of giant earthquakes and tsunamis. Here, we provide geoarchaeological evidence revealing a major tsunamigenic earthquake that severely affected prehistoric hunter-gatherer-fisher communities ~3800 years ago, causing an exceptional social disruption reflected in contemporary changes in archaeological sites and triggering resilient strategies along these coasts. Together with tsunami modeling results, we suggest that this event resulted from a ~1000-km-long megathrust rupture along the subduction contact of the Nazca and South American plates, highlighting the possibility of Mw ~9.5 tsunamigenic earthquakes in northern Chile, one of the major seismic gaps of the planet. This emphasizes the necessity to account for long temporal scales to better understand the variability, social effects, and human responses favoring resilience to socionatural disasters.

Numerical estimation of maximum possible sizes of paleo-earthquakes and tsunamis from storm-derived boulders

Estimating the magnitudes of potential large earthquakes and associated tsunami hazards along a subduction zone is important for risk evaluation. Coastal boulder deposits can serve as valuable geological indicators in intertidal zones with high wave velocity, even though finer sediments are generally washed away. This report presents a new method to constrain the maximum possible sizes of paleo-earthquakes and tsunamis using boulders of storm wave origin as a constraint in numerical simulations. The fundamental assumption is that presently observed storm-derived boulders have not moved a great distance by past tsunami waves. This illustrative case study uses the sizes and spatial distributions of storm wave boulders on the reef at Kudaka Island, Okinawa Prefecture, which faces the Ryukyu Trench. In all, 47 tsunami scenarios with different locations and fault parameters were assumed. Results show that tsunami waves with a maximum water level of 2.2 m and maximum flow speed of 1.5 m/s at a beach of Kudaka Island did not strike the island. Under this condition, earthquakes of Mw≥8.3 are unlikely to have occurred in the central Ryukyu Trench if one obeys an empirical scaling law for subduction earthquakes or ≥2 m of maximum possible slip near the trench if the fault size is fixed as 100 km × 50 km. Those tsunami and earthquake sizes could not have been generated during this period if one assumes that the reef of Kudaka Island and emplacement of storm boulders began more than 3500 years ago. This finding implies that the seismogenic mechanism of the Ryukyu Trench and the risk of a giant earthquake differ from those of other trenches such as the Japan Trench and the Chilean Trench, where giant earthquakes of Mw≥9.0 have occurred repeatedly during the past. The proposed method would enable researchers to estimate the maximum possible sizes of the paleo-earthquakes and tsunami waves in any region, even in regions with a vague or unknown history of past events because of a lack of sandy tsunami deposits or seismic records.

20th-century strain accumulation on the Lesser Antilles megathrust based on coral microatolls

The seismic potential of the Lesser Antilles megathrust remains poorly known, despite the potential hazard it poses to numerous island populations and its proximity to the Americas. As it has not produced any large earthquakes in the instrumental era, the megathrust is often assumed to be aseismic. However, historical records of great earthquakes in the 19th century and earlier, which were most likely megathrust ruptures, demonstrate that the subduction is not entirely aseismic. Recent occurrences of giant earthquakes in areas where such events were previously thought to be improbable have illustrated the importance of critically evaluating the seismic potential of other “low-hazard” subduction zones, such as the Lesser Antilles.Using the method of coral microatoll paleogeodesy developed in Sumatra, we examine 20th-century vertical deformation on the forearc islands of the Lesser Antilles and model the underlying strain accumulation on the megathrust. Our data indicate that the eastern coasts of the forearc islands have been subsiding by up to ∼8 mm/yr relative to sites closer to the arc, suggesting that on the time scale of the 20th century, a portion of the megathrust just east of the forearc islands has been locked. Our findings are in contrast to recent models based on satellite geodesy that suggest little or no strain accumulation anywhere along the Lesser Antilles megathrust. This discrepancy is potentially explained by the different time scales of measurement, as recent studies elsewhere have indicated that interseismic coupling patterns may vary on decadal time scales and that century-scale or longer records are required to fully assess seismic potential. The accumulated strain we have detected will likely be released in future megathrust earthquakes, uplifting previously subsiding areas and potentially causing widespread damage from strong ground motion and tsunami waves.

Stratigraphy of deep-sea marine sediment using paleomagnetic secular variation: Refined dating of turbidite relating to giant earthquake in Japan Trench

Recent studies of the sedimentary record of the Japan Trench indicate unique earthquake-induced depositional characteristics. To correlate such deposits to historical earthquakes, we studied the stratigraphy of two sedimentary cores obtained from basins of the Japan Trench at 7400 m and 7600 m water depth using paleomagnetic secular variation (PSV). Because of their high sedimentation rates, results show that excellent geomagnetic records are preserved in the sediments in spite of the great water depth. Paleomagnetic secular variation, especially declination during the past 3000 years revealing a distinctive feature of large oscillation, offers an opportunity to make precise stratigraphic correlations. Identification of boundaries between thick fine turbidite intervals and hemipelagite intervals was made based on rock magnetic properties. Successful applications of extraction of paleomagnetic data solely from the hemipelagic interval demonstrate that stratigraphic positions of turbidite in paleomagnetic secular variation record are mutually well correlated in PSV variations. Even over long distances between sites, the turbidites induced by earthquakes can be correlated exactly. The turbidite ages were determined by referring to the PSV master curve. Especially, the ages of turbidite units regarded as induced by the Jogan earthquake can be inferred from two cores that closely approximate its documented age.

Variations in Forearc Stress and Changes in Principle Stress Orientations Caused by the 2004–2005 Megathrust Earthquakes in Sumatra, Indonesia

Coseismic changes in principal stress orientation in the northern Sumatra subduction zone due to two giant megathrust earthquakes there in 2004 and 2005 are estimated to investigate the in-situ stress. The two megathrust earthquakes, the 2004 Sumatra-Andaman and the 2005 Nias-Simeulue events, are both among the 11 largest earthquakes ever recorded. Previous studies have shown that these giant earthquakes perturbed the stress field in the Sumatra subduction zone enough to alter the principal stress directions there, and here we investigate whether these changes can be used to better understand spatial variations in stress along the subduction zone. We used 330 previously published focal mechanisms to estimate pre- and post-mainshock principal stress orientations in 3 outer forearc segments and assessed whether orientation differences were resolved and what they imply about the pre- and post-mainshock stress fields. Our results agree with previous studies in establishing that coseismic changes in stress orientation in the forearc are resolvable, and consistent with a low level of stress in the outer Sumatran forearc before the earthquake, with almost all the shear stress on the megathrust relieved in the 2004 and 2005 earthquakes. In this study, we reveal that both the stress orientations and coseismic changes in them exhibit along-strike variations, with a decrease in both the pre-mainshock stress and stress drop found in the rupture area of 2005 relative to that of the 2004 earthquake. The forearc segment between the 2004 and 2005 rupture areas, which coincides with a well-known megathrust rupture barrier beneath the island of Simeulue is observed to have a characteristic signature, with lower shear stress relative to the pre-mainshock stress field and higher shear stress relative to the post-mainshock stress field in the adjacent segments.

Impact of economic development levels on the mortality rates of Asian earthquakes

Buildings in areas with high economic development levels have strong earthquake resistance, and the mortality rate caused by earthquakes is low. From 1990 to 2015, a total of 387 earthquakes (excluding the earthquakes that caused the tsunami) occurred in Asia. The paper took Asian countries as an example to quantitatively estimate the impact of economic development on the mortality of earthquakes. Based on spatial statistics and regression analysis, the paper obtained the mortality rate of every historical earthquake and drew the magnitude-mortality rate curves for three groups at different economic levels, namely, Group I (per capita GDP range of $12,500-$45,000), Group II (per capita GDP range of $1,700-$12,500), and Group III (per capita GDP range of $550-$1,700). With a M 6 earthquake, the mortality rate of Group I, II and III was 0.0002‰, 0.0071‰ and 0.0871‰ respectively. However, due to the powerful destructiveness of giant earthquakes, as the magnitude of the earthquakes increases, the differences among the three groups decrease. Furthermore, if the economic development of Asian countries maintains its pace of the past 20 years, the vulnerability of Groups II and III will reach the current level of Group I in the year of 2046. Then if earthquakes that have occurred in the past occur again, the death toll will be reduced from 399,509 to 107,112. In general, as the GDP per capita doubles, the earthquake mortality rate will drop by 19%–25%, and the disaster-reduction goals proposed by the Sendai Framework can be achieved.

The hazard of coseismic gaps: the 2021 Fukushima earthquake

SUMMARY Subduction zones are associated with significant seismic hazards around the world and determining the future locations of large earthquakes within these systems is a perpetual challenge of the Earth sciences. This study presents back-projection results from the 2021 Mw 7.1 Fukushima earthquake which show that the rupture area of this event filled a previously identified coseismic gap within the rupture area of the 2011 Mw 9.1 Tohoku-oki earthquake. These results, combined with observations of a similar coseismic gap from the 2010 Mw 8.8 Maule, Chile earthquake that was subsequently filled by a Mw 7.1 aftershock, demonstrate that future assessments of seismic hazards following giant earthquakes should include the identification of coseismic gaps left within main shock rupture areas.

Subslab heterogeneity and giant megathrust earthquakes

The nucleation and rupture processes of giant megathrust earthquakes (M ≥ 9.0) in subduction zones are still controversial. Most previous studies have focused on the subducting plate interface, and the structure beneath the subducting slab and its influence on earthquake generation remain unclear. Here, we present high-resolution seismic velocity tomography beneath six regions where giant earthquakes have occurred. Subslab low-velocity (slow) anomalies are revealed, which may reflect hot mantle upwelling. The giant earthquake hypocentres are generally located above the edges of the slow anomalies or above the gaps between them. Large coseismic slips of the giant earthquakes mainly occurred above gaps between the slow anomalies. We suggest that differential buoyancy force between the slow anomalies and their gaps may be an important factor for earthquake nucleation, and the rupture extent of a giant earthquake may be constrained by the slow anomalies. Hence, it is necessary to conduct seismic tomography to investigate the detailed subslab structure, which may help to pinpoint the potential location and damage zone of a future giant earthquake. Mantle heterogeneity beneath subducting plates may influence giant megathrust earthquakes, according to seismic tomography of the subslab structure beneath six megathrusts that have ruptured in M ≥ 9.0 earthquakes.

Decadal Seismicity Prior to Great Earthquakes at Subduction Zones: Roles of Major Asperities and Low-Coupling Zones

Decadal forerunning seismic activity of magnitude Mw ≥ 5.0 is mapped for all 45 mainshocks of Mw 7.7 to 9.1 at subduction zones of the world from 1993 to mid 2020. The zones of high slip in nearly all great earthquakes were nearly quiescent beforehand and are identified as the sites of great asperities and zones of strong seismic coupling. Much forerunning activity occurred at smaller asperities along the peripheries of the rupture zones of many great and giant mainshocks. Those sizes of great asperities as ascertained from forerunning activity generally agree with the areas of high seismic slip as determined by others from geodetic and tide-gauge data and finite-source seismic modeling. Asperities are strong, well-coupled portions of plate interfaces. Different patterns of forerunning activity on time scales of about 5 to 45 years are attributed to either the sizes and spacing of asperities (or lack of). This permits many great asperities to be mapped decades before they rupture in great and giant shocks. Several poorly coupled subduction zones such as Java, Lesser Sunda, Marianas, Tonga and Kermadec are characterized by few great thrust earthquakes and little, in any forerunning activity. Rupture zones of many great and giant earthquakes are bordered either along strike, updip, or downdip by zones of lower plate coupling. Several bordering regions were sites of forerunning activity, aftershocks, and slow-slip events. The detection of forerunning and precursory activities of various kinds should be sought on the peripheries of great asperities as well as within zones of high co-seismic slip.

The Alaska Convergent Margin Backstop Splay Fault Zone, a Potential Large Tsunami Generator Between the Frontal Prism and Continental Framework

AbstractThe giant tsunami that swept the Pacific from Alaska to Antarctica in 1946 was generated along one of three Alaska Trench instrumentally recorded aftershock areas following great and giant earthquakes. Aftershock areas were investigated during the past decade with multibeam bathymetry, ocean bottom seismograph wide‐angle seismic, reprocessed legacy, and new seismic reflection images. Summarized and updated here are previous papers and additional data. Tectonic structures collocated with aftershock area boundaries indicate possible lengths of rupture in future great earthquakes. NE aftershock area boundaries relate to subducted lower plate structures whereas the SW zone upper plate retains Beringian structural relicts. The lower to middle slope transition separating a stronger continental framework rock from a weaker accreted prism occurs along splay fault zones previously interpreted as backstops in seismic images. Damage zones along splay faults are generally 1‐km‐wide dipping typically 21°. Splays form slip paths from the plate interface to the seafloor much shorter than the 3–4° dipping plate interface beneath the frontal prism. Associated seafloor vent structures indicate overpressured fluids at depth. Splay fault dip and its rigid hanging wall impart greater seafloor uplift than the accreted prism per unit of slip making them effective tsunami generators. Backstop splay fault zones (BSFZs) run along the entire Alaska Trench. Beneath the frontal prism, active bend faults add rugosity to the plate interface and km high relief is commonly imaged in reprocessed legacy and new seismic data. The 1946 Unimak great (M8.6) earthquake epicenter is located near the BSFZ.