Earthquake Hazard Assessment Research Articles

Evaluating interseismic deformation patterns in the North Tabriz Fault (Iran) using enhanced fitting of velocity field and analysis of surface deformation

Understanding the mechanisms and locations of interseismic strain accumulation along faults is essential for assessing earthquake hazards. However, the mechanical response during the transition from deep fault locking to creep behavior remains uncertain. Estimating the slip deficit within these transition zones is challenging. This study challenges the assumption of a constant depth distribution of interseismic slip rate along the fault over time and proposes variable locking depths as an alternative model. By rejecting the constant locking depth assumption, singularity issues during stress theorem resolution are resolved. To address this, we employ a methodology considering creep propagation within a fully elastic medium. This approach incorporates long-term deformation resulting from viscoelastic flow in the upper mantle and lower crust. Including viscoelastic effects improves the fit to interseismic deformation rates, yielding lower locking depths compared to fully elastic models. To conduct the investigation, the GPS velocity field is recovered using the forward problem and the boundary element method. Subsequently, a physics-based inversion approach, deep interseismic creep, is employed to determine interseismic deformation patterns on a strike-slip fault. Furthermore, this study examined the correlation between the dislocation parameters and their relationship, as well as established the probability distributions associated with each faulting parameter. This research highlights the importance of considering variable locking depths in understanding interseismic strain accumulation and the transition to creep behavior along faults. The findings contribute to improved earthquake hazard assessment and mitigation strategies by providing valuable insights into fault behavior mechanics along the North Tabriz Fault.

A Stochastic Model for Induced Seismicity at the Geothermal Systems: A Case of the Geysers

Abstract Induced seismicity has emerged as a source of a significant earthquake hazard associated with recent development of unconventional energy resources. Therefore, it is imperative to develop stochastic models that can accurately describe the observed seismicity rate and forecast its evolution. In this study, a mechanism suggested by linear response theory is incorporated into a stochastic earthquake model to account for changes in the seismicity rate. It is derived that the induced rate can be modeled as a convolution of the forcing, related to fluid injection operations, and a specific response kernel. The model is incorporated into a Bayesian framework to compute the probabilities for the occurrence of the largest expected events during future time intervals. The applicability of the model is illustrated by analyzing the injection and seismicity data at the Geysers geothermal field in California. The suggested approach provides further insight into the probabilistic assessment of earthquake hazard associated with fluid injection operations. It also can be used for probing the rheological properties of the subsurface by analyzing the inherent characteristic timescales associated with the subsurface response to external forcing.

Back‐Propagating Rupture: Nature, Excitation, and Implications

AbstractRecent observations show that certain rupture phase can propagate backward relative to the earlier one during a single earthquake event. Such back‐propagating rupture (BPR) was not well considered by the conventional earthquake source studies and remains a mystery to the seismological community. Here we present a comprehensive analysis of BPR, by combining theoretical considerations, numerical simulations, and observational evidences. First, we argue that BPR in terms of back‐propagating stress wave is an intrinsic feature during dynamic ruptures; however, its signature can be easily masked by the destructive interference behind the primary rupture front. Then, we propose an idea that perturbation to an otherwise smooth rupture process may make some phases of BPR observable. We test and verify this idea by numerically simulating rupture propagation under a variety of perturbations, including a sudden change of stress, bulk or interfacial property and fault geometry along rupture propagation path. We further cross‐validate the numerical results by available observations from laboratory and natural earthquakes, and confirm that rupture “reflection” at free surface, rupture coalescence and breakage of prominent asperity are very efficient for exciting observable BPR. Based on the simulated and observed results, we classify BPR into two general types: interface wave and high‐order re‐rupture, depending on the stress recovery and drop before and after the arrival of BPR, respectively. Our work clarifies the nature and excitation of BPR, and can help improve the understanding of earthquake physics, the inference of fault property distribution and evolution, and the assessment of earthquake hazard.

Using RSQSim to Determine Seismic Sequence in Eastern Taiwan Fault System

Abstract Understanding the spatial and temporal patterns of seismic activity, along with fault interactions in Taiwan, is essential for earthquake hazard assessment and advancing knowledge of regional tectonics. This study employs the Rate and State Earthquake Simulator (RSQSim) to simulate the eastern Taiwan fault system, integrating fault geometry from the multidisciplinary Taiwan Earthquake Model. We applied long-term simulations spanning 400,000 yr to conduct earthquake sequences and recurrence intervals on five distinct faults in eastern Taiwan: Milun fault, Longitudinal Valley fault, Central Range structure, Luyeh fault, and Taimali Coastline structure. The simulated earthquake catalogs are compared against the historical record in terms of seismicity, frequency–magnitude statistics, and recurrence patterns. The model reasonably reproduces key observational constraints, including spatial patterns, magnitude probabilities fitting a gamma distribution, and periods of quiescence resulting from fault interactions. Overall, the results demonstrate RSQSim’s potential for physics-based seismic hazard modeling and provide insights into regional seismotectonic processes in eastern Taiwan for constructing sustainable cities and communities.

Geoelectric studies in earthquake hazard assessment: the case of the Kozlodui nuclear power plant, Bulgaria

AbstractThe study presents the results of geoelectric research for seismic risk assessment on the example of the Kozlodui nuclear power plant in Bulgaria. The image of the geoelectric structure in the study area was obtained using one-dimensional inverse electrical resistivity modeling of the full five-component magnetotelluric data and quasi-three-dimensional inverse conductivity modeling of the geomagnetic responses recorded during the summer 2021 field campaign. According to the presented results, the geoelectrically anomalous structure is divided into two levels. The near-surface anomalous structure in the immediate reach of human geotechnical activity corresponds to the electrically conductive sedimentary fill. The mid-crustal layer is coincident with the low seismic velocity zone at the brittle and ductile crust interface, revealed in previous studies. The presented results imply that the geological environment is not affected by large faults capable of transmitting seismic energy from tectonically active areas, however, in further studies, attention should be paid to the strike-slip fault systems adjacent to the study area.

Integrated Amphibious Distributed Acoustic Sensing for Seismic Monitoring in the Xinfengjiang Reservoir

Abstract The rapidly advancing technology of distributed acoustic sensing (DAS) has profoundly impacted the field of underwater geophysics. Our study investigates the effectiveness of DAS in underwater geological stability monitoring, with a particular focus on microseismic monitoring in the Xinfengjiang reservoir. The 6.2 km long acquisition setup, covering both land and reservoir bottom, was verified using temporary shore-based short-period seismometers to ensure reliable data acquisition in various environments. Higher background noise was observed on the land section compared with the lakebed section during the day, whereas both sections exhibited similar noise levels at night. We confirmed that the DAS system was capable of detecting distant microseismic events, some of which were previously unreported. These detections exhibited temporal and phase consistency with neighboring seismometers. Comparison of signal-to-noise ratios indicates that the lakebed section demonstrates higher sensitivity. This system delivers cost-effective performance through natural settling, negating the requirement for costly embedding methods. Moreover, the DAS system identified “comet-like” small-scale signals on the lakebed that had eluded shore-based seismometers. This exemplifies the exceptional high-density and high-resolution capabilities of DAS technology in both aquatic and terrestrial environments. This study underscores the pivotal role of the DAS technology in conducting underwater microseismic monitoring, real-time seismic monitoring, seismic mechanism research, and earthquake hazard assessment.

The latest activity of the slope fault zone (Pearl River Mouth) in northern South China Sea and implications for earthquake hazard assessments

In the northern region of the South China Sea, located at the intersection of the continental shelf and slope, there have been recorded four earthquakes with magnitudes M ≥ 6.0. This pattern of seismic activity suggests the presence of a previously unidentified active submarine fault. Notably, no active faults have been documented in this area prior to our investigation, with earlier studies predominantly focusing on the structural morphology and sedimentary basin evolution associated with the South China Sea's spreading phenomenon. Through the examination of seismic profiles and historical earthquake records, we have identified a newly discovered fault, termed the Slope Fault Zone (SFZ). The SFZ exhibits diverse structural components, including a listric normal fault in the western sector and a strike-slip fault zone in the eastern sector. Analysis of shallow seismic profiles and borehole data has revealed that the SFZ intersects with strata from the late Pleistocene epoch, confirming its classification as an active fault. The derived fault parameters indicate that the western segment of the SFZ has the potential to generate earthquakes of considerable magnitude, ranging from M 6.7 to 7.2. Furthermore, given the significant occurrence of submarine landslides along the southern boundary of the SFZ, there exists a risk that such seismic events could trigger slope failures and subsequent tsunamis. In summary, our research has unveiled the presence of an active fault capable of precipitating submarine earthquakes, landslides, and tsunamis.

Intra-plate Jal Az-Zor strike-slip faulting deciphering the enigma of local earthquakes in Kuwait

Abstract Kuwait National Seismic Network (KNSN) data show the clustering of earthquakes in northern and southern clusters. Spatial correlation between these clusters and oil fields led previous studies to declare that oil production/injection triggered earthquakes, but some suggested the possibility of tectonic causes. This study addresses the genuine objective of uncovering the origin of Kuwait earthquakes by analysing relationships between earthquake spatial and temporal patterns, oil production/injection, structural and tectonic setting, and subsurface fluid pressures. A kinematic model of the Jal Az-Zor dextral-slip fault was presented as a decipherer to the earthquake's origin. The northern and southern clusters represent leading quadrants, where increased mean stress causes earthquakes. Dibdibah Trough and Kuwait Bay represent trailing quadrants with decreased mean stress and a lack of earthquakes. The small percentage of earthquakes falling outside clusters are caused by the concentration of regional compressive stresses related to Arabian Plate motion on pre-existing faults. Triggering earthquakes by oil field operations requires 10% pressure increase above the original pressures, which never occurs in Kuwait oil fields. The results of this study emphasize the significance of understanding fault kinematics to assess earthquake hazards and the need to focus on engineering requirements for developments in the leading quadrants areas.

Landslide hazard assessment of the fault zone considering the fault effect: a case study of the Lixian–Luojiabu fault zone in Gansu Province (China)

The earthquake landslide hazard assessment method is mainly based on the traditional Newmark model. However, when the landslide hazard assessment is carried out along the fault zone, the calculated results are often different from the actual situation because the influence of fault effect is not fully considered. Therefore, how to construct a landslide hazard assessment model suitable for the fault zone is a technical problem to be solved by researchers. Taking the Lixian–Luojiabu fault zone in Gansu Province in China as the study area, this paper put forward the concept of fault effect correction coefficient exploringly, systematically studied the relative distance relationship between the landslide and fault zone, and the relative position relationship between landslide and upper and lower sides of the fault zone. The value table of the fault effect correction coefficient along the Lixian–Luojiabu fault zone was established, and the corresponding distribution map of the fault effect correction coefficient was drawn. Based on this, an improved Newmark model for the landslide hazard assessment along the fault zone was constructed. On the basis of systematic analysis of the slope and engineering geological rock group in the study area, the traditional Newmark model and improved Newmark model considering fault effects were used, respectively, to carry out the earthquake landslide hazard assessment under the condition of 10% exceeding probability in 50 years, and the ROC curve and Kappa coefficient methods were used to compare and analyze the evaluation results. The results showed that the AUC value and Kappa coefficient of the danger area obtained by the improved model with the Newmark model were 0.841 and 0.822, respectively, which were significantly higher than the calculated values of the traditional Newmark model, indicating that the model had a good improvement effect. The Newmark improved model, considering the fault effect, fully considered the influence of distance from the fault zone and fault upper and lower side effects, and the research results can provide a new reference for the landslide hazard assessment along the fault zone.

Testing Megathrust Rupture Models Using Tsunami Deposits

AbstractThe 26 January 1700 CE Cascadia subduction zone earthquake ruptured much of the plate boundary and generated a tsunami that deposited sand in coastal marshes from northern California to Vancouver Island. Although the depositional record of tsunami inundation is extensive in some of these marshes, few sites have been investigated in enough detail to map the inland extent of sand deposition and depict variability in tsunami deposit thickness and grain size. We collected 129 cores in marshes of the Salmon River estuary in Oregon and reanalyzed 114 core logs from a 1987–88 study that mapped the inland extent of circa 1700 CE sandy tsunami deposits. The ca. 1700 CE tsunami deposit in the Salmon River estuary is easily recognized in cores ≤1 m deep in which a buried marsh peat is overlain by a well sorted sand bed with a sharp lower contact that thins and fines inland. We use tsunami deposit data and models of sandy tsunami sediment transport (using Delft3D‐FLOW) to test 15 rupture models that could represent a ca. 1700 CE earthquake. At least 12–16 m of slip offshore of the Salmon River, which results in 0.8–1.0 m of coastal coseismic subsidence, is required to match the ca. 1700 CE sand deposit's inland extent, which is consistent with models of heterogeneous megathrust slip in ca. 1700 CE. Our methods of detailed tsunami deposit mapping, combined with sediment transport modeling, can be used to test models of megathrust ruptures and their tsunamis to potentially improve earthquake and tsunami hazard assessments.

Tsunami hazard evaluation of river embankment structures incorporating their vulnerability to seismic strong motion

Development of coastal areas in Japan for various land uses since the 1960s has contributed to industrial upgrades and improved the efficiency of transportation networks. However, there are concerns about the vulnerability of developments on alluvial plains and reclaimed lands to geological events, like ground subsidence due to liquefaction during large earthquakes. Realistic assessment of earthquake and tsunami hazards and evaluation of possible countermeasures require accurate estimation of the amount of subsidence that can be expected from liquefaction at coastal and riverside sites supporting various structures. In this study, to evaluate the amount a river embankment structure might be expected to settle as a result of strong motion from an assumed Nankai Trough great earthquake, we conducted a numerical simulation using the soil–water coupled finite deformation analysis code GEOASIA. We then investigated the effect of the estimated embankment subsidence on tsunami inundation, which was simulated by using nonlinear shallow-water equations and a grid spacing as fine as 3.3 m. The influence of urban structures on the inundated area was taken into account by using a structure-embedded elevation model (SEM). The results showed that subsidence of river embankments and the collapse of parapet walls on top of them would increase both the depth and area of inundation caused by a tsunami triggered by a Nankai Trough scenario earthquake. Our findings underscore the importance of evaluating not only earthquake resistance but also vulnerability of coastal and riverside structures to strong motion in tsunami hazard analyses. Furthermore, the importance of tsunami inundation analysis using a SEM for predicting the behavior of tsunami flotsam in urban areas was demonstrated.

Block motion, slip rates, and earthquake hazard assessment of boundary faults in the Sichuan–Yunnan region, China

Block motion, slip rates, and earthquake hazard assessment of boundary faults in the Sichuan–Yunnan region, China

Linked and fully coupled 3D earthquake dynamic rupture and tsunami modeling for the Húsavík–Flatey Fault Zone in North Iceland

Abstract. Tsunamigenic earthquakes pose considerable risks, both economically and socially, yet earthquake and tsunami hazard assessments are typically conducted separately. Earthquakes associated with unexpected tsunamis, such as the 2018 Mw 7.5 strike-slip Sulawesi earthquake, emphasize the need to study the tsunami potential of active submarine faults in different tectonic settings. Here, we investigate physics-based scenarios combining simulations of 3D earthquake dynamic rupture and seismic wave propagation with tsunami generation and propagation. We present time-dependent modeling of one-way linked and 3D fully coupled earthquakes and tsunamis for the ∼ 100 km long Húsavík–Flatey Fault Zone (HFFZ) in North Iceland. Our analysis shows that the HFFZ has the potential to generate sizable tsunamis. The six dynamic rupture models sourcing our tsunami scenarios vary regarding hypocenter location, spatiotemporal evolution, fault slip, and fault structure complexity but coincide with historical earthquake magnitudes. Earthquake dynamic rupture scenarios on a less segmented fault system, particularly with a hypocenter location in the eastern part of the fault system, have a larger potential for local tsunami generation. Here, dynamically evolving large shallow fault slip (∼ 8 m), near-surface rake rotation (± 20∘), and significant coseismic vertical displacements of the local bathymetry (± 1 m) facilitate strike-slip faulting tsunami generation. We model tsunami crest to trough differences (total wave heights) of up to ∼ 0.9 m near the town Ólafsfjörður. In contrast, none of our scenarios endanger the town of Akureyri, which is shielded by multiple reflections within the narrow Eyjafjörður bay and by Hrísey island. We compare the modeled one-way linked tsunami waveforms with simulation results using a 3D fully coupled approach. We find good agreement in the tsunami arrival times and location of maximum tsunami heights. While seismic waves result in transient motions of the sea surface and affect the ocean response, they do not appear to contribute to tsunami generation. However, complex source effects arise in the fully coupled simulations, such as tsunami dispersion effects and the complex superposition of seismic and acoustic waves within the shallow continental shelf of North Iceland. We find that the vertical velocity amplitudes of near-source acoustic waves are unexpectedly high – larger than those corresponding to the actual tsunami – which may serve as a rapid indicator of surface dynamic rupture. Our results have important implications for understanding the tsunamigenic potential of strike-slip fault systems worldwide and the coseismic acoustic wave excitation during tsunami generation and may help to inform future tsunami early warning systems.

The relationship between peak ground acceleration and landform for earthquake hazard assessment in Bulukumba Regency

The location of Bulukumba Regency, which is traversed by the Walanae Fault, indicates that this area has the potential for earthquakes. The potential for this earthquake is also reinforced by the condition of the Bulukumba Regency landform, which is composed of landforms of volcanic and tectonic origin. The purpose of this study was to analyze the hazard potential of the earthquake through the peak ground acceleration approach and to analyze the relationship between the landform and the peak ground acceleration value in Bulukumba Regency. The methods used in this study are statistical methods, descriptive qualitative, and spatial analysis. The results of this study indicate that the value of peak ground acceleration (PGA) in Bulukumba Regency based on the earthquake historical report for the period 1921-2023 is 67-121 gal. The PGA value, at 67-88 gal with low hazard criteria, is a site on the land from the volcanic process. The PGA value, at 89-121 gal with low hazard criteria, is a site on the land from structural and fluvial processes. Output of this research be expected can become input for the revision of spatial plan in Bulukumba Regency.

The sharp turn: Backward rupture branching during the 2023 Mw 7.8 Kahramanmaraş (Türkiye) earthquake

Multiple lines of evidence indicate that the 2023 Mw 7.8 Kahramanmaraş (Türkiye) earthquake started on a splay fault, then branched bilaterally onto the nearby East Anatolian Fault (EAF). This rupture pattern includes one feature previously deemed implausible, called backward rupture branching: rupture propagating from the splay fault onto the SW EAF segment through a sharp corner (with an acute angle between the two faults). To understand this feature, we perform 2.5-D dynamic rupture simulations considering a large set of possible scenarios. We find that both subshear and supershear ruptures on the splay fault can trigger bilateral ruptures on the EAF, which themselves can be either subshear, supershear, or a mixture of the two. In most cases, rupture on the SW segment of the EAF starts after rupture onset on its NE segment: the SW rupture is triggered by the NE rupture. Only when the EAF has initial stresses very close to failure can its SW segment be directly triggered by the initial splay-fault rupture, earlier than the activation of the NE segment. These results advance our understanding of the mechanisms of multi-segment rupture and the complexity of rupture processes, paving the way for a more accurate assessment of earthquake hazards.

Predicting the Remaining Time before Earthquake Occurrence Based on Mel Spectrogram Features Extraction and Ensemble Learning

Predicting the remaining time before the next earthquake based on seismic signals generated in a laboratory setting is a challenging research task that is of significant importance for earthquake hazard assessment. In this study, we employed a mel spectrogram and the mel frequency cepstral coefficient (MFCC) to extract relevant features from seismic signals. Furthermore, we proposed a deep learning model with a hierarchical structure. This model combines the characteristics of long short-term memory (LSTM), one-dimensional convolutional neural networks (1D-CNN), and two-dimensional convolutional neural networks (2D-CNN). Additionally, we applied a stacking model fusion strategy, combining gradient boosting trees with deep learning models to achieve optimal performance. We compared the performance of the aforementioned feature extraction methods and related models for earthquake prediction. The results revealed a significant improvement in predictive performance when the mel spectrogram and stacking were introduced. Additionally, we found that the combination of 1D-CNN and 2D-CNN has unique advantages in handling time-series problems.

From the Editorial Board of the <i>Izvestiya, Physics of the Solid Earth</i> Journal

On February 6, 2023, catastrophic earthquakes struck Turkey, causing extensive destruction and numerous casualties. These seismic events immediately captured the attention of the global geophysical community, leading to the emergence of preprints and articles analyzing various aspects of the earthquakes on the Internet and in print. The Izvestiya, Physics of the Solid Earth journal also received submissions from Russian scientists containing the results of their geophysical investigations related to the Turkish earthquakes. Consequently, the editorial board of the journal decided to dedicate a special issue to this topic. This issue features articles by Russian scientists from academic institutions and universities: Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences (IFZ RAN); Institute of Earthquake Prediction Theory of the Russian Academy of Sciences (ITPZ RAN); Institute of Geosphere Dynamics of the Russian Academy of Sciences (IDG RAN); Geological Institute of the Russian Academy of Sciences (GIN RAN); Kola branch of the Geophysical Service of the Russian Academy of Sciences; Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences (IZMIRAN); the Faculties of Physics and Geology at Moscow State University; Gubkin Russian State University of Oil and Gas; as well as colleagues from Firat University in Turkey. The articles included in this issue cover a wide range of subjects. The geological situation and tectonic position of the earthquakes are described in the article by H. Çelik et al., along with the seismic rupture parameters obtained through fieldwork conducted in the earthquake’s epicentral zone by researchers from the Geological Institute of the Russian Academy of Sciences in collaboration with Turkish colleagues. D.A. Simonov and V.S. Zakharov present the results of a preliminary seismotectonic analysis based on GNSS observations in their article. Yu.L. Rebetskii’s article presents the tectonophysical zoning of seismogenic faults in Eastern Anatolia based on estimations and analysis of Coulomb stresses. R.E. Tatevosyan et al. provide insights into the historical earthquake of 1888 along the northeastern extension of the East Anatolian faults, including an estimate of its magnitude. A.I. Filippova and A.S. Fomochkina developed models of displacements in earthquake sources based on surface seismic waves, while V.O. Mikhailova et al. utilized satellite interference data on displacements on the Earth’s surface. O.V. Pavlenko and V.A. Pavlenko investigated the effects of radiation directivity of earthquake sources. V.B. Smirnova et al. present the results of a posteriori analysis of seismic regime anomalies preceding the earthquake in Turkey. S.V. Baranova et al. offer an earthquake aftershock hazard assessment using an automated system previously developed by the authors. The articles by V.V. Adushkin et al. and S.A. Ryabova et al. consider the geomagnetic and geoelectric effects induced by the Turkish earthquakes. Special Issue Editors V.B. Smirnov P.N. Shebalin

Seismogenic structures and earthquake mechanisms in the Changning area, China: Insights from seismicity and tomography

The Changning area, located in southwestern Sichuan Basin, China, was previously known to be a seismically inactive region. However, in recent years, the region has experienced an increase in the rate of seismic activity. To gain a better understanding of the seismogenic structures and earthquake mechanisms in the region, we deployed 298 short-period seismic stations and collected 47 days of continuous waveform data following the 2019 Ms 6.0 Changning earthquake. Using a machine-learning-based earthquake location workflow (LOC-FLOW; Zhang et al., 2022), we detected and located over 60,000 seismic events. These events were then used for three-dimensional Vp and Vs inversion using a double-difference tomography method (tomoDD). The results show that the earthquake distribution has distinct zoning characteristics with different mechanisms. In the Changning-Shuanghe anticline, most earthquakes are distributed in areas with large velocity and Vp/Vs gradients, typically occurring in regions with high velocity and low Vp/Vs, where tectonic stresses are prone to accumulate. Long-term water injections may promote fault activation in the southeast of Changning anticline. Earthquakes around the salt mining well were found to occur in sedimentary cover, indicating that the basement fault has not been activated but rather acts as a fluid-flowing path. In the Changning shale gas block, earthquakes showed different triggering mechanisms, accompanied by different velocity characteristics. The spatial variations in earthquake locations and velocity characteristics can be explained by the terrain at shallow depths, syncline structures, and the distribution of fluids and gas reservoirs. Our study provides new insights into the detailed seismogenic structures and earthquake mechanisms in the Changning area. These findings can be used to improve earthquake hazard assessment in the region.

Surface deformation induced by the 2016 Meinong earthquake and its implications to active folds

We present 230 field observations on the location, trending, and displacement vectors of the coseismic surface cracks induced by the 2016 Meinong earthquake in the Guanmiao area, SW Taiwan. Coseismic surface cracks trends from the north to northeast. The coseismic deformed region moved toward the W-WNW. In Guanmiao town, surface cracks were mainly distributed on both limbs of the Guanmiao syncline. The preseismic deformation was also observed along the axial trace of the Guanmiao syncline. These results give clues to high structural activities in SW Taiwan. We argue that Guanmiao syncline is an active fold with both coseismic activity and interseismic creeping, which induced nonnegligible micro-geohazards because of the continual loss. We report a new case of the normal bending-moment fault, the Luosianliao fault, which locates between the Guanmiao syncline and Chungchou anticline. However, the linkage between the shallow Luosianliao fault and the deep-seated causative fault of Guanmiao aftershocks are not known yet. We demonstrate the kinematic process of coseismic surface deformation and argue that the bending-moment fault could provide an opportunity to understand the recurrence interval of folding. The mechanism of earthquake-induced folding amplification through high fluid-pressure rocks may play a critical role in assessing earthquake hazard risks in regions with similar geology to SW Taiwan.

Unified earthquake catalogue and mapping of Gutenberg–Richter parameters for the East African Rift System

BackgroundThe initial phase of earthquake hazard assessment involves the consolidation of diverse magnitude scales, thereby requiring the homogenization of various magnitudes. Moment magnitude (Mw) emerges as the preferred descriptor for a range of magnitudes, encompassing local magnitude (ML), teleseismic magnitude (e.g., mb and MS), duration magnitudes (MD), and other magnitude proxies. Unlike alternative scales, Mw does not exhibit saturation at high magnitudes, enhancing its reliability. To achieve uniformity in magnitude representation, diverse regression techniques are employed, with the General Orthogonal Regression (GOR) method being widely regarded as the most dependable, accounting for uncertainty in both independent and dependent variables.MethodsThis study utilized the International Seismological Centre (ISC) Catalogue (http://www.isc.ac.uk/) to compile an array of events related to the East Africa Rift System (EARS). Subsequently, the General Orthogonal Regression method was applied to merge and harmonize the collected data. Furthermore, the research computed Gutenberg-Richter b-values using the newly unified magnitude.ResultsNotably, the conversion relationships between magnitude proxies, including MS-mb, mb-Mw, MS-Mw, and ML-Mw, exhibited robust correlations, with coefficients of 0.86, 0.80, 0.88, and 0.94, respectively. In contrast, the relationship between ML and mb proxies revealed a notably weaker correlation, registering a coefficient of 0.54. Ultimately, the study identified a magnitude of completeness and a b-value of 3.8 and 0.71, respectively, for the EARS region, providing valuable insights for earthquake hazard assessment in this area.ConclusionGenerally, the homogeneous catalogue is a step forward in seismicity assessment and geodynamic activities in the EARS. Hence, developing the empirical equations for the area is essential for future studies on seismic hazards and engineering applications due to the peculiarity of EARS’s geological and tectonic characteristics.