Moderate Magnitude Earthquakes Research Articles

Compatible Ground Motion Models for South Korea Using Moderate Earthquakes

Due to a heightened interest in the field of earthquakes after two moderately sized earthquakes occurred in Gyeongju and Pohang, this study explores which ground motion prediction equations are compatible for the South Korea region. Due to data availability, ground motions from five earthquakes of moderate magnitude were used for comparing against selected ground motion models. Median rotated response spectral ordinates at a period of 0.2 s were extracted from these ground motions, which served as a basis for comparison. Twelve ground motion models were considered from the Next Generation Attenuation West, West2, and East programs due to their extensive databases and robust analytical techniques. A comparison of relative residuals, z-score, and each event found that the subset of Next Generation Attenuation—East ground motion prediction equations did not perform as well as the suite of Next Generation Attenuation—West2 ground motion prediction equations, most likely due to the regional simulations involved in developing the database. Interestingly, the ground motion models that performed relatively well were from the set designed for rock conditions.

Radiological risk estimation from the terrestrial gamma dose rate in the seismically active Kopili Fault Zone, India

ABSTRACT Anomalies in terrestrial gamma radiation have been reported in regions of seismic activity. The Kopili Fault in India is well-known for being extremely seismically active. Several mild to moderate-magnitude earthquakes with epicentres along the Kopili Fault Zone have recently been recorded. This necessitates a measurement of variations in gamma radiation and its associated radiological risks to the population in the region in relation to seismic activities. In this work, a portable gamma survey metre was used to measure terrestrial gamma radiations in the earthquake-prone Dhekiajuli area of Sonitpur district, India, which is located in the Kopili Fault Zone. Indoor and outdoor gamma dose rates were found to be 99.4 ± 5.1–195.9 ± 5.1 nGy h−1 (geometric mean: 159.0 ± 8.8 nGy h−1) and 99.4 ± 5.1–198.8 ± 5.1 nGy h−1 (geometric mean: 132 ± 6.5 nGy h−1), respectively. The estimated total annual effective dose equivalents (geometric mean: 0.94 ± 0.05 mSv y−1) were found to be higher than the recommended global average of 0.48 mSv y−1. The excess lifetime cancer risk was also estimated by considering the life span of an individual as 70 years, which ranged from 2.4 × 10−3 to 4.8 × 10−3.

Fluid-assisted intra-plate seismicity at the edge of the Gawler Craton, South Australia

The Australian continent, being void of active plate boundaries, is often perceived as seismically quiescent. However, earthquakes of moderate magnitude (M6+) occur on the continent around once per decade. Such intra-plate activity can pose a significant risk as these earthquakes can occur along fault lines that are either unknown or considered inactive, are often non-periodic, and poorly understood. Within Australia, the spatial distribution of intra-plate seismicity is non-uniform, instead tending to concentrate along certain weak zones of increased activity. One such region is the eastern margin of the Gawler Craton in South Australia, one of the oldest building blocks of the continent. Recently, several new temporary seismic arrays have been deployed in the region, transforming data coverage across southern Australia. In total, 139 new local earthquakes have been recorded, most of which went undetected by the national seismic network. Following relocation, the pattern of earthquakes becomes more localised and appears to coincide with the edge of the Gawler Craton. Further, a spatial association was found between earthquakes and mound springs, which act as the discharge point for groundwater migrating from the Great Artesian Basin. Enhanced fluid pressures (mantle-degassing) within permeable crustal scale fault systems, responding to a regional contractional strain field, appear to be a key driver of seismicity in the area.

The Impact of Moderate Earthquakes on Antidepressant Prescriptions in Ulsan, South Korea: A Controlled Interrupted Time Series Analysis.

In 2016, two consecutive moderate magnitude earthquakes occurred in Ulsan, South Korea. Therefore, we aimed to investigate the impact of earthquakes on the mental health of residents in Ulsan. We used data from the 2015-2017 Korean Health Insurance Review & Assessment Service National Patient Sample. We conducted an interrupted time series analysis using location-based controls. Changes in the number of antidepressants, benzodiazepines, and zolpidem prescriptions in Ulsan were compared to controls. Overall changes in weekly prescriptions 1 year after the first earthquake, compared to a non-earthquake scenario, were estimated. In antidepressant prescriptions, the increase in trend after an earthquake was significantly higher than controls. However, the changes in benzodiazepines and zolpidem prescribing were not significant. Overall, the impact of the earthquake on weekly antidepressant prescriptions at 1 year was estimated as a 1.32 (95% CI, 1.18-1.56) rate ratio compared to the non-earthquake scenario. This corresponded to an increase of 1,989.7 (95% CI, 1,202.1-3,063.0) in the number of prescriptions. Among subgroups, the increase was highest among males aged 20-39 years. The moderate earthquake in Ulsan was associated with an increase in antidepressant prescriptions. The increase in the male group aged 20-39 was the highest. The impact may vary according to the context of the population.

Caprock integrity at Çanakkale-Tuzla hydrothermal system inferred from magnetotelluric modeling using particle swarm optimization

The impermeable caprock within a geothermal system serves the purpose of effectively sealing the reservoir, resulting in the elevation of both pressure and temperature. This sealing mechanism plays a crucial role in the long-term preservation of the system, while also contributing to its overall sustainability. Caprock failure subsequent to seismic activity near a geothermal site can lead to the permeation of the caprock structure, resulting in diminished sealing capabilities and a decline in the reservoir temperature. Additionally, this process alters the geochemical composition of the water by creating a hydrothermal mixture zone that disrupts the resistivity structure of the caprock, which is typically characterized by low resistivity values due to its substantial clay content and mineral alteration. This study focuses on investigating the integrity of the caprock at ơnakkale-Tuzla geothermal field in Turkey, where the water temperature and conductivity were reported to have decreased after a moderate magnitude earthquake and subsequent aftershocks. For this purpose, we performed magnetotelluric (MT) measurements, a method known for its sensitivity to geochemical reactions. These measurements were conducted along two parallel profiles that encompassed a total of 32 stations. Particle swarm optimization (PSO) technique was employed to overcome subtle difficulties associated with conventional inversion methods when modeling the MT data of complex formations. This is the first study that overcomes the difficulties emanating from the caprock failure by modeling MT data using PSO. Our modeling approach produced resistivity images that we interpreted as the signature of the failed caprock following the earthquake at the study site. Our results appear to confirm the documented geochemical changes or hydrothermal mixture zone about caprock structure.

Dynamic performance of the Mosque-Cathedral of Córdoba under different earthquake scenarios: The Abd al-Rahman I sector

The Mosque-Cathedral of Córdoba is one of the most important monuments in Spain. Owing to its authenticity, its integrity and its influence on later architecture, it was declared as a World Heritage Site by the UNESCO in 1984. The monument is located in Andalusia, in southern Spain. This region presents a moderate seismic hazard, and it is affected by two kinds of seismic sources: a) far away earthquakes of large/very large magnitude; b) close earthquakes of moderate magnitude. Particularly, the Mosque-Cathedral had to endure the well-known 1755 Lisbon's earthquake (Mw = 8.5, at 488 km) and the 1504 Carmona earthquake (Mw = 6.8, at 82 km). This research has analysed its dynamic behaviour under several earthquake scenarios: code-base response spectrum, previous historic earthquakes and fault maximum magnitude earthquakes. However, after the seismic hazard analysis and due to the lack of faults registered surrounding the building, no worst-case scenario considering the maximum expected magnitude has been found. Owing to the complexity of the building, this work has focused on the Abd al-Rahman I sector, which is the most aged part, dating from the VIII century. A refined 3D numerical model has been developed and calibrated through free ambient vibration tests. The distribution of the maximum amplitudes (internal displacements and absolute accelerations) under the different scenarios has been comparatively presented. Also, the seismic performance has been assessed considering the drifts and the damage expected. The results showed that the damage would be concentrated in the contact between the arcades and the courtyard wall. Also, the lower part of the North-South closing wall would be damaged. According to the seismic performance, the building is expected to present moderate damage. In contrast, the analysis of the drifts, according to the codes, suggest that the building would resist each damage limit. Also, it was shown that the far fault earthquake scenario is more demanding than the close fault earthquake scenario. Next, it should be noted that the behaviour of the building for a seismic action of 475-year return period is expected to be similar to the far-fault earthquake scenario. The most demanding earthquake scenario has been the 975-year return period one.

Estimating seismic vulnerability in West Bengal by AHP-WSM and AHP-VIKOR

West Bengal is situated primarily in the Surma Valley at the foothills of the Himalayas and near the western foreland of the Assam-Arakan Orogenic Belt. Several low to moderate-magnitude earthquakes are felt in the region frequently. In this study, we use integrated multi-criteria decision-making (MCDM) models to assess the seismic vulnerability in West Bengal. Twenty-four parameters that were susceptible to seismicity in the region have been used to evaluate geotechnical, structural, social, and physical vulnerability. The analytical hierarchy process (AHP) model was used to estimate the priorities of the parameters, which was then used to estimate seismic vulnerability using the VIseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR) and the weighted sum method (WSM). The results reveal that approximately ∼17.81% of the total area and ∼65.36% population may fall under a high to very high-vulnerable zone, causing concerns for planning and disaster mitigation. The receiver operating characteristic curve estimated to validate the results, indicate that the AHP-VIKOR performs better for seismic vulnerability estimation. The results of this study may help various mitigation and planning agencies in identifying earthquake-vulnerable zones and preparing in advance for any potential large magnitude earthquakes that may occur in the region.

The March 2020, Mw 5.7 Magna, Utah, earthquake—documentation of geologic effects and summary of new research

The March 18, 2020, Mw 5.7 Magna earthquake was the largest earthquake in Utah since the 1992 ML 5.8 St. George earthquake. The Magna earthquake occurred in the northwest corner of the Salt Lake Valley, home to 1.2 million people. Immediately following the earthquake, the Utah Geological Survey organized teams to collect perishable field data on the geologic effects of ground shaking near the epicenter, as well as establish a web-based digital clearinghouse to collect, distribute, and archive data related to the earthquake. This earthquake also coincided with the beginning of the COVID-19 global pandemic, which added extra challenges to our earthquake response. Teams used a small, unmanned aircraft system to obtain aerial photos and videos of geologic effects to supplement ground-based reconnaissance. The observed geologic effects of ground motions from the Magna earthquake include liquefaction in the form of sand boils, tension cracks, lateral spreading, and localized subsidence. No primary surface fault rupture was observed. The areas with the highest observed concentration of liquefaction features were close to the shore of Great Salt Lake and near the epicenter, northeast of the town of Magna. Photos and other documentation of the geologic effects associated with this earthquake are critical in helping to understand the hazards associated with moderate magnitude earthquakes in the Wasatch Front region. The earthquake sequence and associated geologic effects were well documented, due to the proximity to a major metropolitan area and the mainshock and aftershocks occurring within the densest part of the Utah Regional Seismic Network. In the two years since the earthquake, numerous studies have been published documenting and interpreting data to characterize the Magna event and discuss how new data add to what is known about seismic hazards along the Wasatch Front.

Coseismic and post-seismic characteristics of the 2021 Ganaveh earthquake along the Zagros foredeep fault based on InSAR data

SUMMARY The Ganaveh earthquake on 2021 April 18 (Mw 5.8) occurred in the southwest of the Dezful embayment of the Zagros Mountain belt, Iran, as a mainly compressive event. The InSAR coseismic displacement maps reveal a maximum of 17 cm of surface displacement in the satellite line of sight direction. InSAR inversion indicates a low-angle NE-dipping causative fault plane with a maximum slip of 95 cm at ∼6 km depth. It highlights the occurrence of the Ganaveh earthquake within the competent layers of the Zagros sedimentary cover, beneath the Gachsaran formation. A slight sinistral slip component (2.9 cm) is retrieved which is compatible with the USGS focal mechanism. Time-series analysis of SAR images after the main shock until the end of 2021 indicates a maximum of 7 cm of post-seismic surface displacement with a similar strike and pattern as the coseismic phase. This similarity and the distribution of aftershocks suggest an afterslip mechanism for the post-seismic phase. The inversion of post-seismic cumulative displacement evaluates a maximum of 30 cm slip at a depth of ∼5 km along the coseismic causative fault. A regional compressional stress regime (N041°E for the direction of the σ1 stress axis) is constrained by using the focal mechanisms of 39 earthquakes occurring between 1968 and 2021, including the Ganaveh main shock and its five larger aftershocks. Applying this direction of compression on the Ganaveh fault plane also results in a minor sinistral movement, consistent with the geodetic results. The relocated main shock and aftershocks as well as our InSAR coseismic displacement situations on the hanging wall of the Zagros Foredeep fault highlight it as the causative fault of the Ganaveh earthquake. To fit the geometry of the Ganaveh rupture plane with the Zagros Foredeep fault, we modelled a listric fault plane and its slip distribution using the available geological data. The retrieved slip variation on the listric plane is in close agreement with the slip pattern on the modelled planar geometry. The low dip angle of the rupture plane combined with a listric geometry highlights the thin-skin characteristics of the Zagros Foredeep fault as the causative fault of the Ganaveh earthquake. The occurrence of this moderate magnitude earthquake on the Zagros Foredeep fault underlines its role as the western structural boundary for the recurrence of Mb > 5 events in the Dezful embayment.

Editorial: Source and effects of light to moderate magnitude earthquakes – Volume II

EDITORIAL article Front. Earth Sci., 14 March 2023Sec. Solid Earth Geophysics Volume 11 - 2023 | https://doi.org/10.3389/feart.2023.1164767

Study of land subsidence by radar interferometry and hot spot analysis techniques in the Peshawar Basin, Pakistan

Land subsidence caused by anthropogenic activities is frequently reported in many megacities worldwide, affecting over 500 million residents. For the first time, this work is reporting substantial ground subsidence in the fifth largest city of Pakistan. Observation of surface deformation using the Small Baseline Subset (SBAS), Interferometric Synthetic Aperture Radar (InSAR) technique on Sentinel-1A datasets from 2015 to 2019 show subsidence up to 3.23 cm. Geologically, this region is going through active deformation associated with Himalayan orogeny. From August 1973 till December 2018, around ten thousand low- to moderate-magnitude earthquakes are reported.We used the emerging hot spot analysis on InSAR and earthquake data to assess the role of seismicity on subsidence. Four variables were analyzed; ground displacement measured by InSAR, earthquake count, earthquake depth, and earthquake magnitude. Analysis of InSAR data indicates that the vast majority of the area is subsiding. This investigation also reveals that earthquake activity near Peshawar is decreasing. In contrast, the earthquake activity is unstable but high in the direction of Tarbela Dam, which is the world's largest earth-filled dam.No systematic groundwater monitoring program has been implemented, and limited published data suggest that the water demand quadrupled in the last decade. A decline in the water table is also reported. Optimized hot spot analysis of water pumping data for 2017 shows a few isolated mild hot spots in the urban center. Excessive groundwater demand and Land-use change from agriculture to urban may have played a significant role in land subsidence in this region.

Seismotectonic Analysis of the 7 October 2021 Mw 5.9 Harnai Earthquake, Pakistan

ABSTRACTAn earthquake of moderate magnitude 5.9 occurred northeast of Harnai (Baluchistan), Pakistan, on 07 October 2021. This event caused several deaths and injuries due to the collapse of many mud houses in the epicentral area according to the Provincial Disaster Management Authority (PDMA). The event occurred along the Quetta syntaxis, which is one of the most seismically active zones of the country. The source mechanism of the mainshock based on the moment tensor inversion technique was determined using seismic data from the local network. Stress patterns and active tectonics within the Harnai area were investigated on the basis of recent event and previously available focal mechanism solutions. The 2021 earthquake source mechanism was oblique slip with 12 km focal depth and appears to be associated with the Harnai–Karahi fault zone. Interestingly, the nodal plane oriented in the east–west direction having a high dip corresponds to reverse faulting, whereas the low dip nodal plane trending northwest–southeast-depicts a strike-slip mechanism. The upper crustal stress field and current tectonic deformation in this region are governed by the oblique convergence between the Indian and Eurasian plates along the Chaman fault zone marking the transform plate boundary. The local tectonic stress pattern anomalously supports the low dip nodal plane of the determined fault plane solution representing transpressional environment in which originally produced reverse fault is being reactivated with a dominantly strike-slip sense of movement. In this area, two stress regimes, strike-slip and thrust mechanism, were identified based on homogenous stress patterns. The recent Harnai earthquake occurred in a region where thrust-faulting environment due to horizontal principal compression (SHmax) directed in north-northwest–south-southeast act as first order stress owing to the collision of the Indian and Eurasian plates. The SHmax direction of other subset areas has a similar orientation but different stress ratio (R′), which depicts strike-slip faulting. The presence of a rigid (Katawaz) block along the plate boundary, which impedes the Indian plate motion, causes the second-order stresses that result in strike-slip sense of movement in the pre-existing reverse faults. The same stress seems to be responsible for bending of the existing faults to produce en echelon structures within the Sulaiman range and generates connecting faults in the form of a bookshelf model.

Source characteristics of the aftershocks of the Wenchuan and Lushan earthquake sequences in the Longmen-Shan fault zone

After the occurrence of the 2008 Wenchuan Mw 7.9 earthquake, the Longmen-Shan fault zone exhibits highly active seismicity. In the years between 2008 and 2022, successive moderate magnitude aftershocks followed in the region. In this study, we used high-quality seismic data from the National Earthquake Data Center of China to estimate the source parameters of 184 moderate magnitude events (Mw 3.9–6.2) in the Longmen-Shan Fault zone. The dataset comprised the aftershocks of two sequences that occurred in the area, including the 2008 Wenchuan earthquake sequence and the 2013 Lushan earthquake sequence. They have been classified according to their focal mechanism. First, our results suggested that the values of apparent stress varied from approximately 0.1–11 MPa, which are higher than the global average. The strike-slip earthquakes have the highest average apparent stress among the types of earthquakes. The above results indicate that the moderately high levels of energy release from earthquakes in this region could result in high ground shaking potential. This behavior may be associated with the high stress accumulation and the strong deformation characteristics in the intraplate environment of the Longmen-Shan Fault zone. The values of the stress drop vary from approximately 0.24–39 MPa and appear to show a slightly increasing trend with the seismic moment. The stress drop level of the Lushan earthquake sequence is higher than the mean value of intraplate earthquakes, while the Wenchuan earthquake sequence is typical of intraplate earthquakes. Second, we investigate the radiated energy enhancement factor (REEF) to quantify the source complexities. The results show that the earthquakes have REEF values between 1.2 and 7.1, and most events are consistent with expectations based on the Brune ω-square model. There exist differences in the source complexity of earthquakes within the source area, and the average ω-square source model could result in an unreliable estimate of the radiated seismic energy of some events. The observation of moderate magnitude earthquakes suggests that the availability of different source parameters will help us to assess the seismic hazard and predict the shaking potential in the earthquake area.

Exceedance of design seismic actions during the 2016-2017 central Italy seismic sequence: sensitivity to two seismic hazard models

In Italy, seismic ground motion intensity for structural design relies on probabilistic seismic hazard analysis (PSHA). Research has shown that, even in the case of a moderate magnitude earthquake, it is expected that ground motion intensities larger than the design counterparts are observed at some sites in the epicentral region. The area where such an exceedance has possibly occurred can be assessed via ShakeMap. In the case of seismic sequences, ShakeMap envelopes allow to identify the fraction of the region of interest subjected to at least one exceedance of design seismic actions. For the 2016-2017 central Italy sequence, ShakeMap envelopes reveal that exceedance of the design intensity enforced by the current building code occurred in an area covering thousands of square kilometers, depending on the spectral and exceedance return period of the design intensity. This study quantifies the exceedance area of ground motion intensity according to the PSHA results based on two alternative PSHA models for Italy. One is that at the basis of the official PSHA for Italy adopted by the current building code, known as MPS04; the other relies on a grid-seismicity source model deriving from a set of source models recently developed for a new PSHA study for the country (MPS19). Looking at ShakeMap envelopes, it is found that the estimated exceedance area is of the same order of magnitude for the two hazard models, at least for the spectral and exceedance return periods considered herein.

SEISMICITY of the RUSSIAN PART of EAST EUROPEAN PLATFORM and ADJACENT TERRITORIES in 2016–2017

Seismic observations by 46 stationary seismic stations, including seven temporary seismic stations located in the area of Novovoronezh and Kursk nuclear power plants, and by two arrays were carried out on the Russian territory of the East European Platform. A feature of seismicity in 2016–2017 is a manifestation of swarms of weak earthquakes in the northwest in the Leningrad region and the adjacent territory of Finland, as well as earthquakes on the Ukrainian Shield with Мs(est.)=3.8 in Krivoy Rog, where mass explosions are carried out in mines, but earthquakes of moderate magnitude МL=2.6–3.9 also occur (2007, 2013). Weak earthquakes in the peripheral parts (in the southwest, west and northwest) and in zones associated with paleorift structures: in the northeast – with the Kirov-Kazhim and Central Russian aulacogenes continue to be recorded. Weaker natural seismicity with ML≤2.5 was recorded in Karelia and the regions bordering Finland, near the Kandalaksha Bay, near the Khibiny and Lovozero massifs on the Kola Peninsula and in the territory of the Voronezh crystalline massif.

A Deeper Look Into the 2021 Tyrnavos Earthquake Sequence (TES) Reveals Coseismic Breaching of an Unrecognized Large‐Scale Fault Relay Zone in Continental Greece

AbstractLarge magnitude (Mw ∼ ≥6) earthquakes in extensional settings are often associated with simultaneous rupture of multiple normal faults as a result of static and/or dynamic stress transfer. Here, we report details of the coseismic breaching of a previously unrecognized large‐scale fault relay zone in central Greece, through three successive normal fault earthquakes of moderate magnitude (Mw 5.7–6.3) that occurred over a period of ∼10 days in March 2021. Specifically, joint analysis of InSAR, GNSS and seismological data, coupled with detailed field and digital fault mapping, reveals that the Tyrnavos Earthquake Sequence (TES) was accommodated at the northern end of a ∼100 km wide transfer structure, by faults largely unbroken during the Holocene. By contrast, the southern section of this relay zone appears to have accrued significant slip during Holocene. InSAR‐derived displacements agree with the loci of eight subtle, previously undetected, faults that accommodated coseismic and/or syn‐seismic normal fault slip during the TES. Kinematic modeling coupled with fault mapping suggests that all involved faults are interconnected at depth, with their conjugate fault‐intersections acting largely as barriers to coseismic rupture propagation. We also find that the TES mainshocks were characterized by unusually high (>6 MPa) stress‐drop values that scale inversely with rupture length and earthquake magnitude. These findings, collectively suggest that the TES propagated north‐westward to rupture increasingly stronger asperities at fault intersections, transferring slip between the tips of a well‐established, but previously unrecognized, relay structure. Fault relay zones may be prone to high stress‐drop earthquakes and associated elevated seismic hazard.

Earthquake Threats in Ranau – From The Sources of Mensaban and Mesilou Fault

Unlike the majority of Malaysia’s other states, Sabah is characterised by frequent seismological activity; on average, an earthquake of moderate magnitude occurs roughly every 20 years, originating primarily from one of two major sources: either a local source or a regional source. Sabah has seen an upsurge in low to moderate seismic activity in recent years as a result of the fault activities. Between 1900 and lately, magnitudes ranging from MW 2.9 to 6.0 were recorded. While big magnitude earthquakes are relatively uncommon, the area has previously been struck by disastrous earthquakes. Fortunately, the region is demarcated by active Quaternary fault networks. As a result, the area’s seismicity is calculated using line sources corresponding to these faults. Two major fault systems are suspected of being the cause of such activity: the Mensaban fault zone and the Mesilou fault zone, as well as several additional nearby faults. This article explains the process for doing a probabilistic seismic hazard analysis (PSHA) while taking into consideration the peak ground acceleration (PGA) on bedrock in the Ranau region for a 10% and 2% chance of exceedance. The PGA estimate values for Ranau are between 0.08g to 0.16g for PGA 10%, while for PGA 2% was between 0.15g to 0.28g. The PGA value is divided into the following five earthquake hazard classes based on a quarterly geostatistical analysis method. These are “very low,” “low,” “medium,” “high,” and “very high” classes. In general, this quarterly classification is a good way to see how much local seismic activity there is, based on the PGA value. Which can be seen in 10% probability, 19.88 percent of the study area was in “very low,” 20.19 percent was low, 19.98 percent medium, and 19.92 percent high class. 2% probability, it was found that 19.74 percent of the total area was very low class, 20.06 percent low class, 19.79 percent middle class, and 19.82 percent high class. Only 20.6 percent of the area was “very high”.

Ensuring Earthquake-Proof Development in a Swiftly Developing Region through Neural Network Modeling of Earthquakes Using Nonlinear Spatial Variables

Northern Pakistan, the center of major construction projects due to the commencement of the China Pakistan Economic Corridor, is among the most earthquake-prone regions globally owing to its tectonic settings. The area has experienced several devastating earthquakes in the past, and these earthquakes pose a severe threat to infrastructure and life. Several researchers have previously utilized advanced tools such as Machine Learning (ML) and Deep Learning (DL) algorithms for earthquake predictions. This technological advancement helps with construction innovation, for instance, by designing earthquake-proof buildings. However, previous studies have focused mainly on temporal rather than spatial variables. The present study examines the impact of spatial variables to assess the performance of the different ML and DL algorithms for predicting the magnitude of short-term future earthquakes in North Pakistan. Two ML methods, namely Modular Neural Network (MNN) and Shallow Neural Network (SNN), and two DL methods, namely Recurrent Neural Network (RNN) and Deep Neural Network (DNN) algorithms, were used to meet the research objectives. The performance of the techniques was assessed using statistical measures, including accuracy, information gain analysis, sensitivity, specificity, and positive and negative predictive values. These metrics were used to evaluate the impact of including a new variable, Fault Density (FD), and the standard seismic variables in the predictions. The performance of the proposed models was examined for different patterns of variables and different classes of earthquakes. The accuracy of the models for the training data ranged from 73% to 89%, and the accuracy for the testing data ranged from 64% to 85%. The analysis outcomes demonstrated an improved performance when using an additional variable of FD for the earthquakes of low and high magnitudes, whereas the performance was less for moderate-magnitude earthquakes. DNN, and SNN models, performed relatively better than other models. The results provide valuable insights about the influence of the spatial variable. The outcome of the present study adds to the existing pool of knowledge about earthquake prediction, fostering a safer and more secure regional development plan involving innovative construction.

Earth model-space exploration in Southern California: Influence of topography, geotechnical layer, and attenuation on wavefield accuracy

Accurately predicting the seismic wavefield is important for physics-based earthquake hazard studies and is dependent on an accurate source model, a good model of the subsurface geology, and the full physics of wave propagation. Here, we conduct numerical experiments to investigate the effect of different representations of the Southern California Earthquake Center and Harvard community velocity models on seismic waveform predictions in the vicinity of the San Andreas fault in Salton Trough. We test general preconceptions about the importance of topography, near-surface geotechnical layering, and anelastic attenuation up to a maximum frequency of 0.5 Hz. For the Southern California Earthquake Center model developed without topography, we implement 1D and linear model extensions that preserve the geologic structure and a pull-up approach that adapts the original model to topographic variations and distorts the subsurface. The Harvard model includes an elevation model, so we test the squashed topography representation, which flattens it. For both community models, we modify the top 350 m by partially applying the Ely geotechnical layer using a minimum shear wave velocity of 600 m/s and incorporate an Olsen attenuation model using a ratio of 0.05. We evaluate the resulting 24 model representations using the classical waveform misfit and five moderate-magnitude earthquakes. Only the inclusion of attenuation consistently improves the wavefield predictions. It becomes more impactful at higher frequencies, where it significantly improves the performance levels of the crude 1D and linear extension models close to that of the original version. The pull-up topography representation also enhances the waveform prediction ability of the original model. Squashing the topography of the elevation-referenced Harvard model produces better seismogram fits, suggesting that seismic imagers construct community tomographic models without topography to avoid issues related to missing model parameters near the free surface or discrepancies with a different elevation model. Although full implementation of the Ely geotechnical layer that would permit shear wave velocities as low as 90 m/s proves computationally expensive, our partial implementation provides slightly better results in some cases. Our results can serve as recommendations for implementing these community models for future validation or optimization studies.

An Improved Source Model of the 2021 Mw 6.1 Yangbi Earthquake (Southwest China) Based on InSAR and BOI Datasets

The azimuth displacement derived by pixel offset tracking (POT) or multiple aperture InSAR (MAI) measurements is usually used to characterize the north-south coseismic deformation caused by large earthquakes (M > 6.5), but its application in the source parameter inversion of moderate-magnitude earthquakes (~M 6.0) is rare due to the insensitive observation accuracy. Conventional line-of-sight (LOS) displacements derived by the Interferometric Synthetic Aperture Radar (InSAR) have limited ability to constrain the source parameters of the earthquake with near north-south striking. On 21 May 2021, an Mw 6.1 near north-south striking earthquake occurred in Yangbi County, Yunnan Province, China. In this study, we derive both the coseismic LOS displacement and the burst overlap interferometry (BOI) displacement from the Sentinel-1 data to constrain the source model of this event. We construct a single-segment fault geometry and estimate the coseismic slip distribution by inverting the derived LOS and BOI-derived azimuth displacements. Inversion results show that adding the BOI-derived azimuth displacements to source modeling can improve the resolution of the slip model by ~15% compared with using the LOS displacements only. The coseismic slip is mainly distributed 2 to 11 km deep, with a maximum slip of approximately 1.1 m. Coulomb stress calculation shows a maximum Coulomb stress increment of ~0.05 Mpa at the north-central sub-region of the Red River Fault. In addition, there is a small Coulomb stress increase at the Southern end of the Weixi-Weishan fault. The potential seismic risks on the Weixi-Weishan and Northwest section of the Red River faults should be continuously monitored.