Postseismic Deformation Research Articles

Stress change in southwest Japan due to the 1944–1946 Nankai megathrust rupture sequence based on a 3-D heterogeneous rheological model

The Nankai trough has repeatedly experienced large megathrust earthquakes at intervals of 100–200 years. The inland region of southwest (SW) Japan has a seismically active period from 50 years before to 10 years after megathrust earthquakes. To assess the activities of inland earthquakes after megathrust earthquakes, we need to quantitatively evaluate the postseismic stress accumulation on the inland source faults considering plausible viscoelastic relaxation. Recent studies have shown the importance of low-viscosity layers along the lithosphere-asthenosphere boundary (LAB layer) in postseismic deformation. In the present study, we focus on the most recent ruptures, the 1944 M7.9 Tonankai and the 1946 M8.0 Nankai earthquakes, estimating the 4-year stress change on the source faults in SW Japan in a forward modeling approach. The 1944–1946 megathrust rupture sequence was followed by severe ~ M7 inland earthquakes, such as the 1945 M6.8 Mikawa and 1948 M7.1 Fukui earthquakes. For stress calculation, we used a highly detailed finite element model incorporating the actual topography and the plausible viscoelastic underground structure from past studies. The calculated inland stress field shows the dominance of the coseismic change during the 1944 and 1946 earthquakes and little contribution from viscoelastic relaxation. In contrast, viscoelastic relaxation has a significant effect on stress in the slab, indicating the importance of quantifying the viscosity of the LAB layer. Based on the calculated stress, we evaluated the change in the Coulomb failure stress (ΔCFS) on each source fault. The ΔCFS is generally positive on the strike-slip faults east of 135°E due to the 1944 rupture. In contrast, the ΔCFS on the faults west of 135°E, including the Median Tectonic Line segments, became positive due to the 1946 rupture. The occurrence of the damaging earthquakes in 1945 and 1948 can be explained by the calculated ΔCFS. The ΔCFS on the recent earthquake faults of the recent damaging earthquakes such as the 2016 M7.2 Kumamoto earthquake is generally negative, suggesting the delay in stress accumulation. The ΔCFS on the source faults of the intra-slab earthquakes differ significantly as large as tens of kilopascals depending on the viscosity of the LAB layer.Graphical

Diatoms as indicators of coseismic, postseismic, and interseismic deformation along subduction zones over centennial and millennial timescales

Diatoms as indicators of coseismic, postseismic, and interseismic deformation along subduction zones over centennial and millennial timescales

Mitigating Atmospheric Delays in InSAR Time Series: The DetrendInSAR Method and Its Validation

AbstractHow to effectively mitigate atmospheric delay signals in InSAR observations has long been a pressing problem in the InSAR community. Here we propose a new method, DetrendInSAR, that addresses this issue by incorporating the spatiotemporal characteristics of displacements and atmospheric delays as a‐priori information. This enables simultaneously modeling and estimating surface displacements, atmospheric delays, and other unmodeled long‐wavelength errors (e.g., orbit errors) in InSAR time series. We use both simulated‐ and real‐data experiments to validate the performance of the proposed method, and results show a 20%–70% reduction of RMSE values for the DetrendInSAR‐obtained displacements compared with four commonly‐used atmospheric delay reduction methods. We also show that the DetrendInSAR method is capable of capturing the spatial and temporal details of sudden deformation jumps as small as 1 cm, due to a magnitude 5.4 earthquake, in InSAR time series. Based on the DetrendInSAR‐corrected ascending and descending Sentinel‐1 InSAR time series, we calculate the 2‐year postseismic east and vertical displacements of the 2021 Mw 7.4 Maduo earthquake, which better illuminate the postseismic deformation.

The earthquake probabilities of the Liupanshan fault zone based on the Coulomb stress and friction constitutive law

As the forefront of the northeastern margin of the Tibetan Plateau, the Liupanshan area is subjected to significant Cenozoic deformation. Considering the background of historical earthquakes and the current seismic activity, the Liupanshan fault poses a risk of strong earthquakes. This paper analyzes the evolution of Coulomb stress induced by the coseismic and postseismic viscoelastic deformation of six historical strong earthquakes that occurred around the Liupanshan area since the twentieth century. Additionally, based on the disturbance in Coulomb stress and the background seismicity rate, the probability of earthquake occurrence is quantitatively evaluated using the frictional constitutive law. The results indicate that northern section of the Liupanshan fault has higher earthquake potential than the southern section, warranting close attention. These findings serve as a reference for medium- and long-term earthquake forecast and risk assessment in the vicinity of the Liupanshan fault.

Estimation of Co-Seismic Surface Deformation Induced by 24 September 2019 Mirpur, Pakistan Earthquake along an Active Blind Fault Using Sentinel-1 TOPS Interferometry

Surface deformation caused by an earthquake is very important to study for a better understanding of the development of geological structures and seismic hazards in an active tectonic area. In this study, we estimated the surface deformation due to an earthquake along an active blind fault using Sentinel-1 SAR data. On 24 September 2019, an earthquake with 5.6 Mw and 10 km depth stroke near Mirpur, Pakistan. The Mirpur area was highly affected by this earthquake with a huge collapse and the death of 34 people. This study aims to estimate the surface deformation associated with this earthquake in Mirpur and adjacent areas. The interferometric synthetic aperture radar (InSAR) technique was applied to study earthquake-induced surface motion. InSAR data consisting of nine Sentinel-1A SAR images from 11 August 2019 to 22 October 2019 was used to investigate the pre-, co- and post-seismic deformation trends. Time series investigation revealed that there was no significant deformation in the pre-seismic time. In the co-seismic time, strong displacement was observed and in post-seismic results, small displacements were seen due to 4.4 and 3.2 Mw aftershocks. Burst overlap interferometry and offset-tracking analysis were used for more sensitive measurements in the along-track direction. Comprehensive 3D displacement was mapped with the combination of LOS and along-track offset deformation. The major outcome of our results was the confirmation of the existence of a previously unpublished blind fault in Mirpur. Previously, this fault line was triggered during the 2005 earthquake and then it was activated on 24 September 2019. Additionally, we presented the co-seismically induced rockslides and some secondary faulting evidence, most of which occurred along or close to the pre-existing blind faults. The study area already faces many problems due to natural hazards where additional surface deformations, particularly because of the earthquake with activated blind fault, have increased its vulnerability.

Dominance of transient rheology in far-field postseismic deformation following the 2012 Mw 7.8 Haida Gwaii and 2013 Mw 7.5 Craig earthquakes

The Mw 7.8 2012 Haida Gwaii earthquake and the Mw 7.5 2013 Craig earthquake occurred along the Queen Charlotte transpressive margin, two months and 340 km apart. On and near Vancouver Island, hundreds of kilometres southeast of the two events, many continuous Global Navigation Satellite Systems sites underwent no discernable coseismic motion but up to 1 cm southeast postseismic motion (away from epicenters) which lasted for only 2 – 3 years. To resolve the postseismic signal of the two earthquakes, we used a minimum of four years of measurements before the Haida Gwaii earthquake to remove the longer-term motion of these sites that reflect mainly the locking of the Cascadia megathrust. To study the geodynamic process that governed the observed far-field postseismic motion, in particular its short duration, we employ a model of an elastic lithosphere with thickness 20 km and rigidity (μE) 32 GPa overlying Burgers-viscoelastic mantle layers in a self-gravitating spherical Earth which captures the regionally integrated effect of Earth rheology despite the complex and controversial tectonics of the study area. We find that the short-lived far-field postseismic motion was controlled entirely by the transient rheology. The observations can be explained by a steady-state (Maxwell) viscosity ηM of the upper mantle no lower than 1×1019 Pa s with a transient (Kelvin) viscosity ηK of about 6×1017 Pa s (Kelvin relaxation time τK ∼1.2 years) extending to large depths such as > 400 km. The far-field postseismic deformation is the result of the elastic plate serving as a stress guide but resisted by the asthenospheric mantle undergoing transient creep. The lithosphere-asthenosphere coupling is quantified by a “plate Kelvin response time” τKE=ηK/μE. Rheological parameters can be scaled to other values, but as long as τK and τKE stay unchanged, the far-field deformation results remain the same. Our observations presented a unique opportunity to quantify the effect of the transient rheology separately from that of the steady-state rheology.

Coseismic and Early Postseismic Deformation Mechanism Following the 2021 Mw 7.4 Maduo Earthquake: Insights from Satellite Radar Interferometry and GPS

Exploring the deformation mechanism of the 2021 Mw 7.4 Maduo Earthquake is crucial for better understanding the seismic hazard of the faults with low strain rates inside the Bayan Har block. This study leverages deformation information derived from Sentient-1 A/B images and GPS data to investigate in detail the co- and postseismic deformation mechanisms using multiple methods. The main results are as follows. First, the postseismic InSAR time series robustly identified the reactivation of the Changmahe fault, indicating the impact of the Maduo event on surrounding active faults. Second, the joint inversion of Interferometric Synthetic Aperture Radar and GPS revealed that (1) there was a complementary and partially overlapping relationship between the coseismic slip and postseismic afterslip of the main rupture; and (2) the Changmahe fault exhibited thrust compression dislocation in the early stage and experienced a sustained compressive effect from afterslip in the one year after the mainshock. Third, modeling the processes of viscoelastic relaxation and poroelastic rebound revealed that the postseismic deformation was probably caused by a combination of afterslip (near-field) and viscoelastic relaxation (near and far field). Fourth, the stress changes driven by the Maduo event revealed that the seismic gaps inside the Maqin-Maqu segment and the Kunlun Pass-Jiangcuo fault will be potential seismic risks in the future.

Integrated Investigation on Heterogeneous Lower Crust Rheology in Kyushu and Afterslip Behavior Following the 2016 Mw7.1 Kumamoto Earthquake

AbstractThe viscoelastic lower crust beneath Kyushu Island, influenced by the volcanic arc, interplays with active crustal faults in this region and helps to shape local tectonics. In this study, we employed a three‐dimensional viscoelastic finite element model to gain insights into the lithospheric rheology and crustal faulting kinematics, through modeling the postseismic deformation processes of the 2016 Mw 7.1 Kumamoto earthquake. Our model reveals a viscosity of 2 × 1020 Pa s for the lower crust and 2 × 1019 Pa s for the upper mantle. A reduced lower crust viscosity of 2 × 1019 Pa s in the volcanic arc area is required for better reproducing the Global Positioning System data. The stress‐driven afterslip decays rapidly over time and is up to 0.3 m within 5 years after the earthquake. We propose additional normal‐component afterslip to better explain the complex postseismic deformation in the near field, which may be due to the interaction between the fault and volcano Aso.

GNSS imaging coseismic and postseismic slip associated with the 2021 M 8.2 Chignik, Alaska earthquake

The coseismic and postseismic slip associated with the 2021 M 8.2 Chignik, Alaska earthquake is imaged using the geodetic modeling method. Further, the spatio-temporal evolution of afterslip and aftershocks (0–60 days) is also investigated based on the postseismic deformations captured by Global Navigation Satellite System (GNSS) sites in this study. The coseismic slip is mainly concentrated at depths of 20–50 km with a maximum of 3.92 m. After this earthquake, a significant afterslip can be observed in the shallow region, which is distributed around the coseismic rupture region. Afterslip is primarily accumulated at depths of 10–30 km, and the maximum reaches 1.29 m, which is located at a longitude of 157.19°W, latitude of 55.09°N, and depth of 21.80 km. The spatio-temporal properties of afterslip indicate that the spatial extent and magnitude of afterslip continuously increase during the 60 days after the earthquake, and the fault activity in the first seven days is significantly strong. Meanwhile, the fault slip rate during the time span of 0–7 days is the largest with a maximum of 0.054 m/day. The fault slip rate gradually decreases with time, implying that the fault activity is slowly weakening. The Coulomb Failure Stress (CFS) distribution suggests that afterslip and most aftershocks are located at the southeastern region of the hypocenter, which is covered by positive CFS. Moreover, in addition to coseismic rupture effects, afterslip may be a possible triggering mechanism of early aftershocks as evidenced by the fact that the spatial distributions of afterslip and aftershocks are highly consistent.

Subduction intraslab-interface fault interactions in the 2022 Mw 6.4 Ferndale, California, earthquake sequence.

The Mendocino triple junction-the intersection of the Pacific, North American, and Gorda plates-activates a collection of disparate faults that reconcile Cascadia subduction with San Andreas transform motion. The 20 December 2022 Mw 6.4 Ferndale, California, earthquake occurred within this complex zone as strike-slip faulting within the subducting Gorda slab. Here, we analyze the seismic and geodetic signatures of the mainshock and aftershock sequence to illuminate its role within complex tectonic surroundings. We find aftershocks on varied fault structures within the uppermost Gorda slab, yet seismicity on the subduction interface itself was notably absent. Nevertheless, we identify small but coherent postseismic deformation that is well modeled by aseismic slip on this interface, likely triggered by stresses generated at the updip limit of coseismic rupture. This sequence demonstrates the potential for interactions between intra-slab earthquakes and slip on the subduction megathrust, highlighting the need to consider this and other subduction zones as coupled systems of interacting faults.

Postseismic deformation mechanism of the 2021 Mw7.3 Maduo earthquake, northeastern Tibetan plateau, China, revealed by Sentinel-1 SAR images

The postseismic deformation mechanism is crucial for understanding the evolution of postseismic crustal stress, strain, and aftershocks. Here, we used ∼ 1 year Sentinel-1 data to obtain the time-dependent postseismic deformation of the 2021 Mw 7.3 Maduo earthquake and inverted afterslip distribution. We calculated the frictional parameter of the causative fault based on the time series afterslip. A wide range of viscoelastic relaxation models with varying lower crust viscosities were also tested to constrain the rheological structure. Our findings indicated that (1) Time-dependent postseismic deformation conforms to a logarithmic function. In the north of the fault, the attenuation time decreases first and then increases from east to west, while the south of the fault is the opposite. (2) The afterslip mainly occurred in the downdip direction of the coseismic slip, and there is an excellent complementary relationship between them in space. The partial shallow afterslip overlapped with the coseismic ruptures, mainly caused by the low frictional parameter (a-b = 10-3 ∼ 10-2). (3) Considering the postseismic viscoelastic relaxation, when the viscosity coefficient is small, the maximum deformation in 1 year after the earthquake is only about 6 mm, which only accounts for about 6 % of the InSAR observed deformation. It indicates that afterslip plays a significant role, and viscous relaxation plays a secondary role.

Resolving a ramp-flat structure from combined analysis of co- and post-seismic geodetic data: an example of the 2015 Pishan Mw 6.5 earthquake

SUMMARY Previous studies have shown that it is difficult to determine whether the 2015 Pishan earthquake occurred on a uniform fault or a ramp-flat fault with variable dip angles due to the similar goodness of data fit to coseismic and afterslip models on these two fault models. Here, we first present the InSAR deformation obtained from both ascending and descending orbits, covering the coseismic period and cumulative 5-yr period after the 2015 Pishan earthquake. We then determine the preferred fault geometry by the spatial distributions between the positive Coulomb failure stress change triggered by main shock and the afterslip. Based on the preferred fault model, we finally use a combined model to determine the contributions of elastic and viscoelastic deformation in the post-seismic deformation. We find that the Pishan earthquake prefers to occur on a ramp-flat fault, and the coseismic slip is mainly distributed at a depth of 9–13 km, with a maximum slip of about 1.3 m. The post-seismic deformation is primarily governed by afterslip, as the poroelastic rebound-induced deformation fails to account for the observed post-seismic deformation and the contributions from the viscoelastic relaxation mechanism can be considered negligible in the combined model. Moreover, the modelled stress-driven afterslip and observed kinematic afterslip have good consistency, and the difference between the root mean square error of the two afterslip models is only 4.3 mm. The results from the afterslip model indicate that both of the updip and downdip directions distribute the afterslip, and slip in the updip direction is greater than that of the downdip direction. Meanwhile, the maximum cumulative afterslip after 5 yr is approximately 0.26 m which is equivalent to a released seismic moment of a Mw 6.47.

Geodetic signature of a weak Lithosphere-Asthenosphere Boundary in postseismic deformation of large subduction earthquakes

The rheology of the seismically imaged Lithosphere-Asthenosphere Boundary (LAB) is an important new question in plate tectonics. If the LAB is associated with ponding of partial melts as inferred from many seismic studies, it should have a low viscosity that minimizes resistance to plate motion and subduction. Here, we propose that recently observed postseismic enhanced landward motion (ELM) in coastal areas outside the rupture zone of large subduction earthquakes provides the first geodetic evidence for a low-viscosity LAB beneath subducting oceanic lithosphere. Using three-dimensional viscoelastic finite element models, we demonstrate that a low-viscosity LAB readily leads to postseismic ELM over broad coastal areas far beyond the rupture zone. If the LAB thickness is assumed to be 10 km, key spatiotemporal characteristics of the observed ELM can be well explained by an LAB viscosity of 5 × 1016 Pa s, orders of magnitude lower than typical asthenospheric viscosities. A thicker LAB such as 20 km with a higher viscosity may also explain the postseismic ELM but is incompatible with existing, albeit limited, near-field vertical deformation observations. The small thickness and the low viscosity of the model LAB are consistent with inferences from seismological observations and support the notion of ponding melts. Our preliminary weak-LAB models also predict diagnostic deformation features that can be tested by future onshore and offshore geodetic observations. Whether a weak LAB is ubiquitously present before and after plate subduction and how its presence and spatial heterogeneity impact postseismic and plate-scale deformation are important research targets for future investigations.

Mechanism and implications of the post-seismic deformation following the 2021 Mw 7.4 Maduo (Tibet) earthquake

SUMMARY A major earthquake shook the Chinese county of Maduo, located in the Songpan-Ganzi terrane on the Tibetan Plateau, on 21 May 2021. Here, we investigate the post-seismic deformation process of this event, with the aim to understand the fault geometry, friction behaviour and regional rheology. To keep the self-consistency between co- and post-seismic deformation models, we first constrain the fault geometry and coseismic slip model of this event, which are directly used in modelling the post-seismic deformation. The coseimsic slip model reveals that the majority of coseismic slip is confined at the middle (3–15 km) of the brittle layer, leading to significant shallow slip deficit. Secondly, we obtain the post-seismic deformation in the first 450 d following the 2021 Maduo earthquake using the GPS and InSAR displacement time-series data. Thirdly, a combined model incorporating afterslip and viscoelastic relaxation is built to explain the observed post-seismic deformation. Our results suggest that the viscoelastic relaxation effect should be considered in the observation period, in order to avoid the unphysical deep afterslip in the ductile lower crustal layer. Combined analysis on viscosities inferred from this study and previous studies suggests a weak lower crust with steady-state viscosity of 1018–1019 Pa s beneath the Songpan-Ganzi terrane, which may give rise to the distributed shear deformation and the development of subparallel secondary faults within the terrane. Besides, the inferred afterslip on uppermost patches of the middle fault segment suggests a rate-strengthening frictional behaviour that may be related to the coseismic slip deficit and rupture arrest of the Maduo earthquake.

Spatiotemporal postseismic due to the 2018 Lombok earthquake based on insar revealed multi mechanisms with long duration afterslip

Abstract The Lombok earthquake in August 2018 triggered a sequential rupture with doublet earthquake up to Mw 6.9. This tectonic activity occurred near the main earthquake due to the decay of residual energy from one event to another. This activity is suspected to be a post-seismic deformation process such as afterslip and viscoelastic. In this paper, we conducted a study to determine the deformation pattern. Each of these processes can be investigated by extracting InSAR observational data. Time series from Sentinel-1 SAR is processed using LiCSBAS as data observation and then compare with the model based on exponential and logarithmic functions. The results of combined logarithmic and exponential fitting suggest the Lombok multi-event earthquakes were influenced by seismic activity from dual-releasing residual energy comprises of afterslip and viscoelastic as a dual mechanism with long duration rather than single mechanism.

Rheological Structure and Lithospheric Stress Interaction in the Alaska Subduction Zone Gleaned From the 2018 Mw 7.9 Oceanic Crustal Earthquake

AbstractPostseismic 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.

Satellite A-DInSAR pattern recognition for seismic vulnerability mapping at city scale: insights from the L’Aquila (Italy) case study

ABSTRACT L’Aquila downtown (Central Italy) is situated in a highly seismic region, making it susceptible to numerous historical and recent earthquakes. Among these, the earthquake of Mw 6.3 on 6 April 2009, and the one of Mw 6.7 on 2 February 1703, caused severe damage or complete destruction of the majority of buildings in the historical center. An integrated statistical analysis of A-DInSAR and seismic related building damage data is illustrated. By comparing the seismic damage maps from the 2009 and 1703 earthquakes with the A-DInSAR map produced with Cosmo-SkyMed descending orbit images (acquired between 2010 and 2021), a correlation between post-seismic deformations (in terms of average velocity) and building damage intensity has been identified. Furthermore, ground and building velocities have been separately examined, in order to evaluate the impact of building features and reconstruction efforts on ground deformations. The geostatistical analysis revealed a widespread subsidence motion (until −2 mm/year) across the whole study area. Notably, neighboring points did not exhibit consistent deformation velocities, indicating a lack of spatial correlation. Additionally, Cluster Analysis has allowed recognition of recurring subsidence/uplift trends, which, in terms of shape of curve displacement vs. time, appears independent on building damage intensity or reconstruction interventions. Our results pave the way for a novel utilization of long-term series of satellite SAR data in high-risk seismic zones, serving as a valuable tool to map the most susceptible areas and mitigate seismic risk.

GEODETIC EVIDENCE FOR POST-SEISMIC DEFORMATIONS FOLLOWING THE 2014 NORTH AEGEAN MW 6.9 EARTHQUAKE

The 2014 North Aegean Sea earthquake was a strong (Mw 6.9) event that caused significant crustal deformations. In the present study we investigate the long-term impact of the earthquake on the kinematics of the North Aegean Trough (NAT). For this purpose, we analyzed GPS observations collected from May 2010 to April 2022 at five permanent GPS reference stations. Two of these stations are located close to the epicenter(s) on the Islands of Lemnos and Samothrace. We processed the data using the Precise Point Positioning (PPP) technique. The analysis of the obtained coordinate time-series revealed a post-seismic deformation (PSD) period lasting for more than two years leading to cumulative 2D post-seismic displacement of 22 mm and 27 mm for Samothrace and Lemnos, respectively. The magnitudes of these post-seismic slip vectors correspond to 23% and 49% of the co-seismic vectors at Samothrace and Lemnos, respectively. The long-term analysis showed that after the end of the PSD period the stations are characterized by stable velocities that are noticeably different compared to the velocities prior to the event. We observed a change in the velocity in the order of 2 mm/yr for both Samothrace and Lemnos. It is the first time that PSD and velocity changes have been reported for the 2014 North Aegean Sea earthquake shedding light on the characteristics and the impact of this important earthquake on the kinematics of NAT.

Evaluation of earthquake potential using a kinematic crustal block motion model in Java, Indonesia, based on GNSS observation

Assessing the earthquake potential in Java Island is of paramount importance due to its status as one of the world's most seismically active regions, a concern that is heightened by the island’s high population density. This study presents a comprehensive analysis of crustal deformation in Java Island, utilizing observations from Global Navigation Satellite System (GNSS) gathered over a decade, from 2008 to 2018. The GNSS data revealed a distinct non-linear trend, primarily due to the persistent post-seismic deformation following the 2006 Mw7.7 Java earthquake. To enhance the accuracy of our analysis, we employed viscoelastic relaxation modeling for data correction. Among the eleven unique crustal block motion models created, MODEL04 emerged as the optimal model for assessing earthquake potential. The seismic moment deficit rates obtained from this model provide valuable insight into the region's potential to generate future seismic events. Notably, our findings suggest that the convergence of the Australian plate with Western and Eastern Java carries the potential to produce earthquakes of Mw8.7 and Mw > 7.8, respectively. An exploration of the inland fault interfaces revealed seismic moment deficit rates suggestive of the potential for Mw7.0 earthquakes.

Characterization and prediction of InSAR-derived ground motion with ICA-assisted LSTM model

Interferometric Synthetic Aperture Radar (InSAR) is a highly effective and widely used approach for monitoring large-scale ground deformation. The precise and timely prediction of deformation holds significant importance in mitigating and preventing geological hazards, particularly considering the long revisit cycle of satellites and the considerable time required for data processing. In this study, we propose a strategy that predicts spatiotemporal InSAR time series based on Independent Component Analysis (ICA) and the Long Short-Term Memory (LSTM) machine learning model. Unlike traditional methods that rely on physical or statistical models, the proposed strategy leverages the power of ICA and LSTM to achieve accurate predictions without such dependencies. ICA is employed to decompose and capture the InSAR displacement signals of interest caused by various natural or anthropogenic processes and to characterize each individual signal. The spatiotemporal unsupervised K-mean cluster method is then applied to partition large-scale deformation fields into homogeneous subregions, considering the spatial variations and temporal nonlinearities of time series. This process facilitates the refinement of the model, thereby enhancing the accuracy of large-scale predictions. The neural network models are then individually constructed for each cluster, and the optimal parameters are determined through a grid search strategy. Subsequently, the proposed framework is implemented and assessed using two datasets featuring distinct deformation patterns: Case I involves land subsidence in Willcox Basin, USA, while Case II focuses on post-seismic deformation following the 12 November 2017 Mw 7.3 Sarpol-e Zahab earthquake. The results demonstrate that our proposed ICA-assisted LSTM outperforms the original LSTM model on large-scale deformation prediction, with the average prediction accuracy for one-step prediction (12 days in our case) being improved by 34% and 17% for cases I and II, respectively. Furthermore, we perform iterative predictions on the spatiotemporal InSAR measurements with varying temporal characteristics for the subsequent five steps using Sentinel-1 data and evaluate its performance and limitations. The successful prediction of land subsidence and post-seismic deformation provides further evidence that the proposed prediction strategy can be effectively employed in monitoring other large-scale geohazards characterized by prolonged and gradual deformation. This capability enables expedited decision-making and timely implementation of risk mitigation measures.