Earthquake Slip Distribution Research Articles

Ridgecrest Aftershock Stress Drops from P- and S-Wave Spectral Decomposition

ABSTRACT Seismic moment and stress drop are crucial for understanding earthquake rupture processes, but their estimates often have large uncertainties for small earthquakes. Stress drop is typically inferred from an earthquake’s source spectrum based on theoretical models, but poorly constrained path corrections and other modeling assumptions limit the accuracy of stress-drop estimates. Here, we compute stress drops using both P and S waves for the 2019 Ridgecrest earthquake sequence, compare their estimates, and evaluate the associated uncertainties. We use spectral decomposition and apply the analysis to both types of waves for the same set of earthquakes, adjusting some S-wave parameter choices to obtain overall consistency with our P-wave results. Our approach fixes the corner frequency of small calibration earthquakes to reduce scatter in the estimated source parameters of the larger earthquakes. We find that assuming a lower high-frequency fall-off rate for S waves yields more consistent absolute stress-drop estimates between P and S waves. Our stress-drop estimates appear to increase slightly with magnitude for earthquakes with magnitudes >∼3.4. Furthermore, we find that the stress-drop estimates using both types of data exhibit coherent spatial variations. Earthquakes near the Coso geothermal field tend to have lower stress drops, and earthquakes near the M 7.1 hypocenter have higher stress-drop estimates. This spatial pattern is consistently observed in both the P- and S-wave results. We find no strong correlation between our stress-drop estimates and the M 7.1 Ridgecrest earthquake slip distribution, suggesting a heterogeneous stress environment for the Ridgecrest fault system.

Investigation of the Effect of Integrated Offset, GPS, and InSAR Data in the Stochastic Source Modeling of the 2002 Denali Earthquake

This study investigates the effect of geological field measurement (offset), global positioning system (GPS), and interferometric synthetic aperture radar (InSAR) data on the estimation of the co-seismic earthquake displacements of the 2002 Denali earthquake. The analysis is conducted using stochastic source modeling. Uncertainties associated with each dataset limit their effectiveness in source model selection and raise questions about the adequate number of datasets and their type for reliable source estimation. To address these questions, stochastic source models with heterogeneous earthquake slip distributions are synthesized using the von Kármán wavenumber spectrum and statistical scaling relationships. The surface displacements of the generated stochastic sources are obtained using the Okada method. The surface displacements are compared with the available datasets (i.e., offset, GPS, and InSAR) individually and in an integrated form. The results indicate that the performance of stochastic source generation can be significantly improved in the case of using GPS data and in the integrated case. Overall, based on the case study of the 2002 Denali earthquake, the combined use of all available datasets increases the robustness of the stochastic source modeling method in characterizing surface displacement. However, GPS data contribute more than InSAR and offset data in producing reliable source models.

Probabilistic earthquake-tsunami financial risk evaluation for the District of Tofino, British Columbia, Canada

ABSTRACT Southwestern British Columbia in Canada has a high likelihood of facing significant earthquake threats in the future. It is exposed to significant seismic and tsunami hazards, originating from the Cascadia subduction zone and shallow crustal and deep inslab earthquakes. This study presents a new probabilistic earthquake-tsunami loss model for the Cascadia subduction zone by focusing on the District of Tofino, British Columbia. The earthquake occurrence and rupture models for the Cascadia subduction zone are developed by incorporating the time-dependency of earthquake occurrence and by adopting a stochastic source modelling approach, which allows for consideration of heterogeneous earthquake slip distributions. The results produce single-hazard and multi-hazard exceedance probability loss curves for earthquakes and tsunamis from the Cascadia subduction zone. In addition, earthquake risks due to other seismic sources are integrated with the multi-hazard loss curves due to the Cascadia events. In this way, a complete financial exposure from all major seismic and tsunami sources is evaluated. These loss curves can be used for determining the insurance rates for multi-hazard and multi-source risk coverage. The results are beneficial for providing more risk financing options via insurance against the future Cascadia and other seismic events.

A large fault partially reactivated during two contiguous seismic sequences in Central Italy: The role of geometrical and frictional heterogeneities

Earthquakes can rupture multiple fault segments as well as faults with complex geometry, or heterogeneous pre-stress and frictional properties. These observations have been documented mainly for moderate-to-large earthquakes by inverting geodetic and seismic data and by studying the influence of fault orientation and rheology within the regional stress field.In this work we have studied the Gorzano fault, GF, a large normal fault within the active fault system of Central Italy that during the last two largest Italian seismic sequences, L'Aquila (2009) and Amatrice-Visso-Norcia (2016–2017), was reactivated via a series of 5.0 < Mw < 6.0 events. We calculated moment tensor solutions for 134 M > 3 events and evaluated their normalized slip-tendency. Merging these results with high resolution earthquake catalogs, available M > 5 earthquake slip distributions, and frictional properties characterizing the activated fault, we develop a mechanical model and discuss potential earthquake rupture scenarios.The GF is an optimally oriented fault within the regional stress field and from, the reactivation via aftershock or mainshock slip of complementary fault portions from 2009 to 2017 indicates that the fault behaves as a single fault structure. The geometrical and mechanical heterogeneities suggest that the most likely slip behavior of GF is the reactivation of different fault portions with M > 5.0. However, due to favorable initial stress conditions, we suggest that a seismic rupture can produce the complete reactivation of the fault, resulting in a M 6.5–6.6 earthquake as documented in paleoseismological data.

Characterization of the co-seismic pattern and slip distribution of the February 06, 2023, Kahramanmaraş (Turkey) earthquakes (Mw 7.7 and Mw 7.6) with a dense GNSS network

Two consecutive earthquakes with the magnitudes of Mw 7.7 and 7.6 (February 06, 2023) occurred on the East Anatolian Fault Zone (EAFZ) segments and unfortunately resulted in significant devastation to human life and cities in Turkey and Syria. In this study, we aimed to analyse the co-seismic displacements and fault slip distributions of these seismic events. Our unique high-spatial-resolution Global Navigation Satellite System (GNSS) network (comprising 73 permanent GNSS stations and 40 campaign observation sites), providing the recent geodetic dataset for the region, allows better constraint of the co-seismic surface displacements and slip distributions of both earthquakes. The three largest total displacements were identified as 466 cm, 362 cm, and 360 cm. The Fault interactions along the EAFZ were obvious during the consecutive earthquakes. The ruptures mainly occurred in the left-lateral components of the fault segments, with the maximum slips of 7.25 m and 9.43 m for the first event along the EAFZ and the second event on the Çardak Fault, respectively.

Probabilistic Tsunami Hazard Analysis for Vancouver Island Coast Using Stochastic Rupture Models for the Cascadia Subduction Earthquakes

Tsunami hazard analysis is an essential step for designing buildings and infrastructure and for safeguarding people and assets in coastal areas. Coastal communities on Vancouver Island are under threat from the Cascadia megathrust earthquakes and tsunamis. Due to the deterministic nature of current megathrust earthquake scenarios, probabilistic tsunami hazard analysis has not been conducted for the coast of Vancouver Island. To address this research gap, this study presents a new probabilistic tsunami hazard model for Vancouver Island from the Cascadia megathrust subduction events. To account for uncertainties of the possible rupture scenarios more comprehensively, time-dependent earthquake occurrence modeling and stochastic rupture modeling are integrated. The time-dependent earthquake model can capture a multi-modal distribution of inter-arrival time data on the Cascadia megathrust events. On the other hand, the stochastic rupture model can consider variable fault geometry, position, and earthquake slip distribution within the subduction zone. The results indicate that the consideration of different inter-arrival time distributions can result in noticeable differences in terms of site-specific tsunami hazard curves and uniform tsunami hazard curves at different return period levels. At present, the use of the one-component renewal model tends to overestimate the tsunami hazard values compared to the three-component Gaussian mixture model. With the increase in the elapsed time since the last event and the duration of tsunami hazard assessment, the differences tend to be smaller. Inspecting the regional variability of the tsunami hazards, specific segments of the Vancouver Island coast are likely to experience higher tsunami hazards due to the directed tsunami waves from the main subduction zone and due to the local underwater topography.

2019 M7.1 Ridgecrest earthquake slip distribution controlled by fault geometry inherited from Independence dike swarm

Faults often form through reactivation of pre-existing structures, developing geometries and mechanical properties specific to the system’s geologic inheritance. Competition between fault geometry and other factors (e.g., lithology) to control slip at Earth’s surface is an open question that is central to our knowledge of fault processes and seismic hazards. Here we use remote sensing data and field observations to investigate the origin of the 2019 M7.1 Ridgecrest, California, earthquake rupture geometry and test its impact on the slip distribution observed at Earth’s surface. Common geometries suggest the fault system evolved through reactivation of structures within the surrounding Independence dike swarm (IDS). Mechanical models testing a range of fault geometries and stress fields indicate that the inherited rupture geometry strongly controlled the M7.1 earthquake slip distribution. These results motivate revisiting the development of other large-magnitude earthquake ruptures (1992 M7.3 Landers, 1999 M7.1 Hector Mine) and tectonic provinces within the IDS.

Real‐Time Prediction of Alongshore Near‐Field Tsunami Runup Distribution From Heterogeneous Earthquake Slip Distribution

AbstractReal‐time tsunami prediction is necessary for tsunami forecasting. Although tsunami forecasting based on a precomputed tsunami simulation database is fast, it is difficult to respond to earthquakes that are not in the database. As the computation speed increases, various alternatives based on physics‐based models have been proposed. However, physics‐based models still require several minutes to simulate tsunamis and can have numerical stability issues that potentially make them unreliable for use in forecasting—particularly in the case of near‐field tsunamis. This paper presents a data‐driven model called the tsunami runup response function for finite faults (TRRF‐FF) model that can predict alongshore near‐field tsunami runup distribution from heterogeneous earthquake slip distribution in less than a second. Once the TRRF‐FF model is trained and calibrated based on a discrete set of tsunami simulations, the TRRF‐FF model can predict alongshore tsunami runup distribution from any combination of finite fault parameters. The TRRF‐FF model treats the leading‐order contribution and the residual part of the alongshore tsunami runup distribution separately. The interaction between finite faults is modeled based on the leading‐order alongshore tsunami runup distribution. We validated the TRRF‐FF modeling approach with more than 200 synthetic tsunami scenarios in eastern Japan. We further explored the performance of the TRRF‐FF model by applying it to the 2011 Tohoku (Japan) tsunami event. The results show that the TRRF‐FF model is more flexible, occupies much less storage space than a precomputed tsunami simulation database, and is more rapid and reliable than real‐time physics‐based numerical simulation.

Neotectonic faults in the Southern Chile intra-arc (38°S–40.5°S): Insights about their seismic potential and the link with the megathrust earthquake cycle

Megathrust earthquakes are a primary geological hazard in subduction zones. In oblique subduction margins, however, seismic threat must be also considered concerning crustal strike-slip faults driving the parallel-to-the-trench component of the convergent vector. These faults have proven their capacity to produce moderate-to-large shallow earthquakes, causing severe damage for surrounding areas. The Southern Chile Subduction Zone (SCSZ) is characterized by the oblique convergence between the Nazca and the South America plates. Between 37°S and 46°S, slip partitioning is significantly led by intra-arc faults like the Liquiñe-Ofqui Fault System (LOFS) and subsidiary NW to NE striking structures. Despite it has been demonstrated that the behavior of these faults is seismogenic, the inland evidence of Holocene deformation along them is scarce. This has concealed to accurately define individual active faults, discussing their seismic potential, and addressing their link with the megathrust earthquake cycle. In this contribution, we first present field evidence for Holocene deformation on intra-arc faults in the area. Based on this, we define 5 active faults and discuss their seismic capacity. To assess the link with the megathrust earthquake cycle, we calculate the Coulomb stress changes induced on these faults by the Mw 9.5 Valdivia Earthquake slip distribution and an interseismic period of 300 years. We conclude that 1) the identified neotectonic faults have the potential for producing moderate-to-large earthquakes (Mw 5.5 to 6.8) and 2) their occurrence would be enhanced by the coseismic and the interseismic stages of the subduction cycle. With this, we propose that the intra-arc faults addressed in this paper, and certainly others in the SCSZ, must be considered as significant sources of seismic hazard.

Satellite based detection of pre-earthquake thermal anomaly, co-seismic deformation and source parameter modelling of past earthquakes

The presented work brings satellite-based detection of pre-earthquake transient thermal anomaly and coseismic deformation mechanism using InSAR (SAR Interferometry) observations of the two major earthquakes that occurred recently (the Iran-Iraq border earthquake of Nov. 12, 2017 (Mw 7.3) and the New Mirpur, Pakistan earthquake of 24th Sept. 2019 (Mw 5.4)). Near Iran-Iraq border earthquake, a rise of 4–6 ​°C from the normal temperature in both day and night Land Surface Temperature (LST) maps along the SW part of the fault is observed. In case of the New Mirpur, Pakistan earthquake, a rise of 3–5 ​°C from normal temperature in both day and night LST maps around the SSW and NW side of the epicenter is observed. Further, Sentinel-1A microwave satellite data employing InSAR technique have been used to estimate co-seismic ground deformations and fault geometry and slip distribution of both earthquakes. The results show that both events occurred due to blind reverse fault mechanism dipping NE with shallow dip. The weightage of strike slip component and dip slip component is more or less equal to each other in total slip distribution for Iran-Iraq border earthquake. Similarly, New Mirpur, Pakistan earthquake have more strike slip components than dip slip components in the weightage in total slip distribution. Considerable number of aftershocks have also occurred in the regions as estimated by coulomb static stress along the SW side of the fault geometry of Iran-Iraq border earthquake and for New Mirpur, Pakistan earthquake, along the SSW, NW, and east side of the fault geometry. The correlation between high stress regions before and after the occurrence of earthquakes using thermal anomaly map and Coulomb static stress map has been also observed.

Airborne LiDAR-Based Mapping of Surface Ruptures and Coseismic Slip of the 1955 Zheduotang Earthquake on the Xianshuihe Fault, East Tibet

ABSTRACTSurface ruptures and coseismic slip distributions of large earthquakes are the keys to understanding earthquake rupture processes, analyzing rupture history of associated faults, and assessing earthquake hazards. Detailed mapping of surface ruptures of large historical earthquakes is needed but is difficult in remote regions. The 1955 Ms 7.5 Zheduotang earthquake occurred in a prominent restraining bend of the central sinistral Xianshuihe fault and within a high-relief and densely vegetated mountain range. This study characterizes the 1955 earthquake surface rupture via 50 cm resolution airborne light detection and ranging (LiDAR) data, combined with field investigations. Our mapping of geomorphic features showed that relatively fresh mole tracks and fault scarps are still preserved beneath the dense vegetation cover. The 1955 earthquake ruptured at least 30 km in length, which consisted of four sections separated by stepovers or changes in the strike. Overall, the multistranded rupture was more complex than that of other historical earthquakes to the northwest along the Xianshuihe fault but consistent with its local structural setting. We collected 47 LiDAR-derived and 48 field-based left-lateral (with minor vertical) measurements. The clustering of the smallest offsets suggests that the average sinistral coseismic displacement of the 1955 earthquake was ∼2.1 m based on LiDAR-derived data and ∼1.5 m based on field measurements. This difference highlights the ambiguity and difficulties associated with surface rupture investigations of historical earthquakes decades after the event. The rupture length (∼30 km) and average sinistral displacement (1.5–2.1 m) suggest a moment magnitude of 6.6–7.4 based on empirical relationships of strike-slip earthquakes worldwide. The magnitude is smaller than the widely accepted Ms 7.5 in the catalog, suggesting that the previously reported magnitude was possibly overestimated. Our data have implications for the seismic hazard evaluation of the Sichuan–Tibet railway, which passes through the northern part of the ruptured fault.

Stochastic source modeling and tsunami simulations of cascadia subduction earthquakes for Canadian Pacific coast

ABSTRACT This study presents new stochastic source models for the Cascadia subduction earthquakes in the Pacific Northwest, which can trigger massive tsunamis along the shoreline of Vancouver Island. An extensive set of 5,000 stochastic source models is generated for the moment magnitude ranges between 8.1 and 9.1, and regional tsunami hazard simulations are performed at the grid resolution of 270 m. The results from the stochastic tsunami simulations are characterized by evaluating the regional tsunami hazard metric that is based on the geometric mean of the maximum wave heights along the Vancouver Island coast. Subsequently, using the probability distribution of the regional tsunami hazard parameter, representative source models are identified by capturing the average as well as rare rupture cases and then detailed tsunami hazard results, such as maximum wave height maps and wave profiles at specific locations, are examined. Numerical results highlight the directivity effects of tsunami generation and wave propagation on tsunami hazards along the Canadian Pacific coast and the earthquake source characterizations in terms of fault geometry and earthquake slip distribution. The developed source models and tsunami simulation results serve as the first step for performing probabilistic tsunami hazard analysis for the Cascadia subduction zone.

Plate‐Locking, Uncertainty Estimation and Spatial Correlations Revealed With a Bayesian Model Selection Method: Application to the Central Chile Subduction Zone

AbstractInversions of geodetic data are regularly used to estimate interseismic locking in subduction zones. However, the ill‐posed nature of these problems motivates us to include prior information, physically consistent with processes of the subduction seismic cycle. To deal with model instabilities, we present an inversion method to estimate both plate‐locking and model uncertainties by inverting Global Navigation Satellite System derived velocities based on a Bayesian model selection scheme. Our method allows us to impose positivity constraints via a multivariate folded‐normal distribution, with a specified covariance matrix. Model spatial correlations are explored and ranked to find models that best explain the observed data and for a better understanding of locking models. This approach searches for hyperparameters of the prior joint multivariate probability density function (PDF) of model parameters that minimize the Akaike Bayesian Information Criterion (ABIC). To validate our approach, we invert synthetic displacements from analytic models, yielding satisfactory results. We then apply the method to estimate the plate‐locking in Central Chile (28°–39°S) and its relation to the coseismic slip distribution of earthquakes with magnitudes Mw &gt; 8.0, on the subduction zone since 2010. We also search among different prior PDFs for a single ductile‐fragile limit depth. Our results confirms a spatial correlation between locked asperities and the 2010 Mw 8.8 Maule and 2015 Mw 8.3 Illapel earthquake rupture zones. The robustness of our locking model shows potential to improve future seismic and tsunami hazard estimations.

The giant 1960 tsunami in the context of a 6000‐year record of paleotsunamis and coastal evolution in south‐central Chile

AbstractThe tsunami associated with the giant 9.5 Mw 1960 Chile earthquake deposited an extensive sand layer above organic‐rich soils near Queule (39.3°S, 73.2°W), south‐central Chile. Using the 1960 tsunami deposits, together with eye‐witness observations and numerical simulations of tsunami inundation, we tested the tsunami inundation sensitivity of the site to different earthquake slip distributions. Stratigraphically below the 1960 deposit are two additional widespread sand layers interpreted as tsunami deposits with maximum ages of 4960–4520 and 5930–5740 cal BP. This &gt;4500‐year gap of tsunami deposits preserved in the stratigraphic record is inconsistent with written and geological records of large tsunamis in south‐central Chile in 1575, 1837, and possibly 1737. We explain this discrepancy by: (1) poor preservation of tsunami deposits due to reduced accommodation space from relative sea‐level fall during the late Holocene; (2) recently evolved coastal geomorphology that increased sediment availability for tsunami deposit formation in 1960; and/or (3) the possibility that the 1960 tsunami was significantly larger at this particular location than other tsunamis in the past &gt;4500 years. Our research illustrates the complexities of reconstructing a complete stratigraphic record of past tsunamis from a single site for tsunami hazard assessment.

Subduction earthquakes controlled by incoming plate geometry: The 2020 M > 7.5 Shumagin, Alaska, earthquake doublet

In 2020, an earthquake doublet, a M7.8 on July 22nd and a M7.6 on October 19th, struck the Alaska-Aleutian subduction zone beneath the Shumagin Islands. This is the first documented earthquake doublet involving a megathrust event and a strike-slip event. The first event partially ruptured a seismic gap, which has not hosted large earthquakes since 1917, and the second event was unusual as it broke a trench-perpendicular fault within the incoming oceanic slab. We used an improved Bayesian geodetic inversion method to estimate the fault slip distributions of the major earthquakes using Interferometric Synthetic Aperture Radar (InSAR) wrapped phase and Global Navigation Satellite Systems (GNSS) offsets data. The geodetic inversions reveal that the Shumagin seismic gap is multi-segmented, and the M7.8 earthquake ruptured the eastern segment from 14 km down to 44 km depth. The coseismic slip occurred along a more steeply, 26∘ dipping segment, and was bounded up-dip by a bend of the megathrust interface to a shallower 8∘ dip angle connecting to the trench. The model for the M7.6 event tightly constrained the rupture depth extent to 19-39 km, within the depth range of the M7.8 coseismic rupture area. We find that the M7.6 event ruptured the incoming slab across its full seismogenic thickness, potentially reactivating subducted Kula-Resurrection seafloor-spreading ridge structures. Coulomb stress transfer models suggest that coseismic and/or postseismic slip of the M7.8 event could have triggered the M7.6 event. We conclude that the segmented megathrust structure and the location of intraslab fault structures limited the rupture dimensions of the M7.8 event and are responsible for the segmentation of the Shumagin seismic gap. Our study suggests that the western and shallower up-dip segments of the seismic gap did not fail and remain potential seismic and tsunami hazard sources. The unusual earthquake doublet provides a unique opportunity to improve our understanding of the role of the subducting lithosphere structure in the segmentation of subduction zones.

Subduction erosion and basal accretion in the Central Chile subduction wedge inferred from local earthquake tomography

We analyze records of ambient seismicity from Central Chile to investigate mechanisms of tectonic erosion and accretion in an Andean margin. The seismograms were recorded by a temporary network of 39 stations deployed between 32.5°S and 34.0°S from April to November 2017. We employ an automatic earthquake catalogue generator to estimate 8463 P-wave and 5482 S-wave arrival times from 924 hypocenters, which were then used to jointly determine hypocenters and 3D models of Vp and Vp/Vs. Previous investigations of the nearby Illapel region suggest that the Coastal Cordillera acts as a subduction wedge, at the bottom of which are accreted crustal slices detached from the overriding plate by tectonic erosion. These slices may be subducted beyond the downdip frictional limit in a way that differs from a traditional orogenic wedge (type A-subduction). Our results reveal a wedge geometry with: (1) body wavespeed anomalies near the interplate contact below 30 km depth, which we interpret as accretionary complexes formed by basal accretion of crustal slices, and (2) latitudinal differences of those anomalies, which we attribute to eroded material from both plates that changes the basalt-eclogite transition depth in the subducted Nazca plate. Based on these, we infer that the development of this basal accretionary complex by subduction erosion could be responsible for the uplift of Coastal Cordillera in Central Chile, and that the retroshear zone of the subduction wedge is controlled by local conditions inside the mantle wedge. Moreover, we suggest that the accretionary complex beneath the Central Chile subduction wedge behaves as seismic barrier that can explain the 1985 Mw 8.0 Valparaíso earthquake slip distribution and the southeastward migration of aftershocks of 2017 Mw 6.9 Valparaíso earthquake. Finally, we suggest that the subduction wedge influences continental structures on a scale of millions of years.

FinDerS(+): Real-Time Earthquake Slip Profiles and Magnitudes Estimated from Backprojected Displacement with Consideration of Fault Source Maturity Gradient

The Finite-Fault Rupture Detector (FinDer) algorithm computes rapid line-source rupture models from high-frequency seismic acceleration amplitudes (PGA). In this paper, we propose two extensions to FinDer, called FinDerS and FinDerS+, which have the advantage of taking into account a geological property of the source fault, its structural maturity, as well as its relation to the earthquake slip distribution. These two new algorithms calculate real-time earthquake slip profiles by backprojecting seismic and/or geodetic displacement amplitudes onto the FinDer line-source. This backprojection is based on a general empirical equation established in previous work that relates dynamic peak ground displacement (PGD) at the stations to on-fault coseismic slip. While FinDerS projects PGD onto the current FinDer line-source, FinDerS+ allows the rupture to grow beyond the current model extent to predict future rupture evolution. For an informed interpolation and smoothing of the estimated slip values, FinDerS and FinDerS+ both employ a generic empirical function that has been shown to relate the along-strike gradient of structural maturity of the ruptured fault, the earthquake slip distribution, and the rupture length. Therefore, while FinDer derives magnitudes from a relatively uncertain and general empirical rupture length-magnitude relations, FinDerS and FinDerS+ provide alternate and better informed magnitude estimates using the mean slip of the profiles derived from the integration of fault source maturity. The two new algorithms can incorporate both seismic strong-motion and geodetic displacement data. In order to recover PGD from strong-motion instruments, we double-integrate and high-pass filter (&gt;0.075 Hz) the seismic acceleration records. Together, the three algorithms exploit the full spectrum of ground-motions, including high frequencies to derive a source fault model (FinDer) and low frequencies to determine the static offsets along this model (FinDerS and FinDerS+). We test the three algorithms for the 2019 MW7.1 Ridgecrest (California), 2016 MW7.0 Kumamoto (Japan), and 2008 MW7.9 Wenchuan (China) earthquakes. Conclusively, low-frequency PGD data and integration of the fault maturity gradient do not speed-up calculations for these events, but provide additional information on slip distribution and final rupture length, as well as alternative estimates of magnitudes that can be useful to check for consistency across the algorithm suite. The FinDer algorithms systematically outperform previously established real-time PGD-based magnitude estimates in terms of speed and accuracy. The resulting slip distributions can be useful for improved ground-motion prediction given the observed relationship between seismic radiation and fault maturity.

A New Approach to Calculate Earthquake Slip Distributions

A transdimensional, probabilistic approach is more flexible than traditional least squares fits and provides better handling of sharply varying slip distributions.

Multi-Hazard Portfolio Loss Estimation for Time-Dependent Shaking and Tsunami Hazards

Megathrust subduction earthquakes generate intense ground shaking and massive tsunami waves, posing major threat to coastal communities. The occurrence of such devastating seismic events is uncertain and depends on their recurrence characteristics (e.g. inter-arrival time distribution and parameters) as well as elapsed time since the last major event. Current standard probabilistic loss models for earthquakes and tsunamis are based on a time-independent Poisson process and uniform earthquake slip distribution. Thereby, considerations of more realistic time-dependent earthquake occurrence and heterogeneous earthquake slip distribution are necessary. This study presents an innovative computational framework for conducting a time-dependent multi-hazard loss estimation of a building portfolio subjected to megathrust subduction earthquakes and tsunamis. The earthquake occurrence is represented by a set of multiple renewal models, which are implemented using a logic-tree approach, whereas earthquake rupture characterization is based on stochastic source models with variable fault geometry and heterogeneous slip distribution. By integrating these hazard components with seismic and tsunami fragility functions, multi-hazard loss potential for a coastal community can be evaluated quantitatively by considering different possibilities of earthquake recurrence and rupture characteristics. To demonstrate the implementation of the developed time-dependent multi-hazard loss model, the Tohoku region of Japan is considered.

Self-similar stochastic slip distributions on a non-planar fault for tsunami scenarios for megathrust earthquakes

Megathrust earthquakes that occur repeatedly along the plate interface of subduction zones can cause severe damage due to strong ground motion and the destructive tsunamis they can generate. We developed a set of scenario earthquakes to evaluate tsunami hazards and tsunami early warning systems for such devastating earthquakes. Although it is known that the slip distribution on a fault strongly affects the tsunami height distribution in near-field coastal areas, the slip distribution of future earthquakes cannot be exactly predicted. One way to resolve this difficulty is to create a set of scenario earthquakes in which a set of heterogeneous slip distributions on the source fault is stochastically generated based on a given slip probability density function (SPDF). The slip distributions generated in this manner differ from event to event, but their average over a large ensemble of models converges to a predefined SPDF resembling the long-term average of ruptures on the target fault zone. We created a set of SPDF-based scenario earthquakes for an expected future Mw 8.2 Tonankai earthquake in the eastern half of the Nankai trough, off southwest Japan, and computed the ensuing tsunamis. We found that the estimated peak coastal amplitudes among the ensemble of tsunamis along the near-field coast differed by factors of 3 to 9, and the earliest and latest arrivals at each observation site differed by 400 to 700 s. The variations in both peak tsunami amplitude and arrival time at each site were well approximated by a Gaussian distribution. For cases in which the slip distribution is unknown, the average and standard deviation of these scenario datasets can provide first approximations of forecast tsunami height and arrival time and their uncertainties, respectively. At most coastal observation sites, tsunamis modeled similarly but using a uniform slip distribution underpredicted tsunami amplitudes but gave earlier arrival times than those modeled with a heterogeneous slip distribution. Use of these earlier arrival times may be useful for providing conservative early warnings of tsunami arrivals. Therefore, tsunami computations for both heterogeneous and uniform slip distributions are important for tsunami disaster mitigation.Graphical abstract