Seismic Zone Research Articles

Numerical investigation of the stress regime effect on injection-induced fault reactivation and associated seismicity

The occurrence of many seismic events in energy production projects is caused by fluid injection-induced reactivation of critically stressed faults. The distribution of local stress regime has a significant influence on natural earthquakes, while its role in controlling injection-induced fault slip behavior and seismicity magnitude remains poorly understood. In this paper, we present a three-dimensional hydro-mechanical coupled fault reactivation study using unified pipe-interface element method (UP-IEM). The accuracy and reliability of the numerical method are evaluated and confirmed by numerical verification and actual observation data in Pohang EGS project, South Korea. The relationship between fault aseismic slip, seismic slip and seismicity magnitude is analyzed. Results show that both aseismic and seismic slip have different spatiotemporal distribution with the variation of stress regime. The seismic slip zone will exceed the pressurized area with the increase of initial slip tendency under the strike-slip-faulting stress regime (σH>σv>σh). Compared with fluid pressure, the seismic slip is mainly determined by a sudden increase of the shear stress at the aseismic slip zone boundary. In addition, the location of the microseismic events moves towards the fluid pressure propagation front. The larger slip area and seismicity magnitude are easier to be induced under strike-slip-faulting stress regime than thrust-faulting stress regime (σH>σh>σv). The tensile failure and higher permeability of the fault induced at injection phase for normal-faulting stress regime (σv>σH>σh) leads to a greater seismogenic hazard at the shut-in stage.

Seismic fragility and vulnerability assessment of a multi-span irregular curved bridge under spatially varying ground motions

Multi-span reinforced concrete (RC) curved box-girder bridges are commonly designed to facilitate traffic flow at highway interchanges. The Aksemsettin Viaduct (henceforth, A Viaduct for brevity) in Istanbul, Turkey, is an eleven-span interchange bridge with a total length of 596.8 m. Located in a high seismicity zone, the A Viaduct is designed with a curved deck, multiple bearings that have different isolation mechanisms at different bents and directions, ten rectangular columns with unequal heights, and a mix of pile foundations and spread footings. The significant length of the viaduct crossed by eleven spans also makes it susceptible to varying ground motion excitations at different foundations. To evaluate the effects of the degree of modeling detail and analysis complexity on the estimated seismic performance, the present study conducts a comprehensive fragility assessment of the specimen viaduct under various ground motion excitation schemes. First, a three-dimensional finite element model is developed with detailed simulations for the deck, columns, bearings, foundations, and abutment components. To enable different ground motion excitations at each foundation, 57 sets of spatially varying ground motions are simulated by considering the realistic surface topography and soil stratigraphy at the bridge site. Cyclic pushover analyses are performed along multiple loading directions to develop the direction-dependent capacity limit state models for hollow rectangular columns. Subsequently, a demand-capacity ratio method is utilized to develop reliable fragility models for bridge columns. Component- and system-level fragilities of the A Viaduct are then assessed under uniform versus multi-support excitations, vertical motions, and ground motions with varying incidence angles. To further capture the seismic damage discrepancies of the same components at different locations, seismic repair cost ratios of the A Viaduct are assessed when subjected to uniform and multi-support excitations. This study highlights the significance of considering multi-support excitations to achieve more realistic seismic fragility and loss estimates for multi-span long curved highway bridges.

A Review paper on seismic response of various slab systems with and without lateral load resisting systems

With the ongoing modern trends of the construction industry, slab systems like flat slab and post tensioned slabs are widely used in the construction. Flat and post tensioned slab are widely favored by architects and clients for aesthetic reasons. They also do possess a huge advantage structurally over conventional slab arrangement such as Less depth of the slab is required , increasing the floor-to-floor height , longer spans are possible , no beam projections , reduced self-weight of the building and many more. But it comes with its own disadvantages as well such as Brittle punching (shear) failure. Which requires additional reinforcement along the connections of column and slab. Which increases the longitudinal steel required. Slab – column connections are the first point of yielding in higher seismic zones with buildings without lateral load resisting system (LLRS). In higher seismic zones the slabs can resist only the gravity loads and can’t resist the lateral dynamic loading and hence may require additional lateral load resisting system (LLRS) to resist lateral loads such as seismic and wind loads. Thus it becomes essential to study the seismic behavior of conventional slab , flat slab and post tensioned slab systems in high rise RCC structure with and without various LLRS ( lateral load resisting system).This study is aimed to study various literatures related to effects of lateral loads on flat and post tensioned slab system and different LLRS (lateral load resisting system) to make the structure more resistant and economical against such lateral loads considering parameters like story displacement , base shear , stiffness of the connections and time period.

Earthquake Experiences of Nursing Students Residing in Earthquake Zone, the Disaster of the Century: A Qualitative Study.

This study was carried out to examine the experiences of nursing department students regarding earthquakes with a phenomenological approach. The type of research is phenomenological research, one of the qualitative research methods. The research was carried out with 22 nursing students who experienced the earthquake in the Turkey earthquake on February 6, 2023. The data were collected using the "Semi-Structured Interview Form". In this study, "earthquake experience" was discussed as a phenomenon, and the data obtained from the phenomenon after content analysis were evaluated in five themes as follows: Experiences during the earthquake, experiences after the earthquake, search-rescue operations, social support and daily life after the earthquake. It was seen that they acted with the instinct of protection during the earthquake and then tried to shelter and communicate. The study reveal that the disaster preparedness and competencies of nursing students should be increased.

Multi-model seismic susceptibility assessment of the 1950 great Assam earthquake in the Eastern Himalayan front

The seismic susceptibility and mitigation management is paramount concern in tectonically active area like Northeastern India. This area has been devastated innumerably during the 1950 Assam great earthquake. The present study area falls in the foreland basin (Brahmaputra Valley) of Eastern Himalaya. This region is seismically vulnerable due to the tectonic complexity caused by the convergence of the Eurasian, Indian, and Burmese plates. In such, an area optimal disaster management and preparedness is necessary to define the non-linear character of seismic susceptibility, where population and unscientific urbanization have increased manifold. Therefore, for the present study, various multi-criteria decision making (MCDM) methods such as analytical hierarchy process (AHP), fuzzy-AHP (FAHP), and maximum entropy technique (MaxEnt) have been used for determining the seismic susceptibility, by assigning weightage to nine controlling factors such as: predominant frequency (f0), geology (G), vulnerability index (K), peak amplification (A0), liquefaction potential (LP), groundwater condition (WT), shear wave velocity (Vs30), peak ground acceleration (PGA), and land use/land cover (LU). The MaxEnt model exhibits the highest accuracy (87.5%) when the performance of the models was compared using the receiver operating characteristic curve (ROC) and area under the curve (AUC) value. Further, overlay analysis of best seismic susceptibility model using MaxEnt and PGV-based Japan Meteorological Agency (JMA) intensity shows that 40% the study area is in the very high and high seismic risk zone. In tectonically active areas, this kind of integration work is essential to improves the mitigation strategy and aids urban planners in designing earthquake-resistant buildings.

SEISMIC CONDITIOT{S IN BAGHDAD REGION ANI) EVALUATION OF SETSMIC DESIGN FORCES

In this paper, a study of the earthquakes that have affected Baghdad region in Iraq is made" The documents collected from different references are analyzed to determine the seismic zone of Baghdad. Evaluation of seismic design forces for equivalent static analysis of earthquakes in Baghdad region is mc"de according to the Iraqi seismic code and the lnternational Building Code (I8C,2000). The studies reached that intensity greater than V on Mercalli Scale has never been recorded on the site at Baghdad. While Seismicity Map of Iraq, proposed by Iraqi Seismic Code, reveals that, Baghdad places in a zone of intensity between (VI-VII) on the Modified Mercalli Scale. Also, the studies reached that magnitude greater than 5.7 on Richter Scale has never been recorded on Baghdad. When calculating the total horizontal seismic design force acting on buildings and structures according to the formula of the Iraqi Seismic Code Requirements for Buildings (1997), the coefficient Z (seismic hazard zoning coefficient) shall be talien as (0.05) for Baghdad region.

Detailed seismic structure beneath the earthquake zone of Yogyakarta 2006 (Mw ∼6.4), Indonesia, from local earthquake tomography

The earthquake, which occurred in Yogyakarta, Indonesia, on May 26, 2006, at 22:53:58 UTC with Mw ∼6.4, was one of the most destructive earthquakes in Indonesia. The earthquake caused thousands of fatalities, tens of thousands of injuries, and hundreds of thousands of house damages in the Yogyakarta area and its surroundings at a loss of billions of dollars. Previous studies from seismic tomography and satellite radar imaging hypothesized that the earthquake was caused by activating a so far unknown fault east of the Opak Fault. Although, in the beginning, the Opak fault was suspected to be the source of the Yogyakarta earthquake in 2006. This assumption was made because the damage was maximum in the Bantul area west of the Opak Fault. This study demonstrates that our seismic tomography achieved a higher resolution than the previous study and could resolve a failed complex fault system. We utilized more aftershocks (2170 events) and smaller grid sizes for seismic tomography inversion. Four focal mechanisms from aftershocks for Mw ≥ 4.5 were also conducted to support structure interpretation in the study area. Our results successfully delineate the Opak Fault and the second fault, namely the Ngalang Fault, parallel to the eastern part of the fault at a depth of 9 km. Two faults could be indicated by the velocity contrast of Vp, Vp/Vs ratio, and Vs from a horizontal section tomogram. Our focal mechanisms also support seismic tomography, revealing two fault planes in our study area. The results show that the two faults are connected by the Oyo Fault, which is ruptured in the opposite direction compared to the two faults.

The relationship between earthquake risk perceptions, religious orientation, spiritual well-being in individuals with and without earthquake experience: a cross-sectional study

The physical and psychological effects of earthquakes on individuals with their experience dimension are important. This study aimed to examine the relationship between earthquake risk perception, religious orientation, and spiritual well-being among individuals with and without earthquake experience. The data collection instruments included a socio-demographic information questionnaire, earthquake risk perception scale, religious orientation scale, and three-factor spiritual well-being scale. Statistical evaluations were performed using independent samples t test, one-way ANOVA test, Mann–Whitney U test, Kruskal–Wallis test (Levene), Pearson correlation, and multiple linear regression analyses. About 59.9% of the participants had experienced an earthquake. Individuals with earthquake experience scored 33.04 ± 7.80 on the earthquake risk perception scale, 100.65 ± 20.80 on the religious orientation scale, and 119.66 ± 18.87 on the three-factor spiritual well-being scale. Those without earthquake experience scored 31.57 ± 7.74, 96.70 ± 18.46, and 114.09 ± 18.04 on the respective scales. The average scores on the earthquake risk perception scale were found to be statistically significant with respect to gender, while the average scores on the religious orientation scale and the three-factor spiritual well-being scale were found to be statistically significant with respect to both gender and substance use. The regression analysis revealed that religious orientation and three-factor spiritual well-being significantly predicted 13.5% of the variance in earthquake risk perception. Studies to increase individuals’ risk perception are important in minimizing the destructive effects of earthquakes in countries in the earthquake zone.

Crustal shear wave velocity and radial anisotropy beneath the Mississippi embayment from ambient noise tomography

Imaging of shallow multiple basins and middle to lower crustal structure beneath the Mississippi embayment is still limited. No tomography studies have delineated multiple basins as effectively as those from reflection and drilling experiments. Several studies have constructed different velocity models for the middle to lower crust. We take advantage of the Northern Embayment Lithosphere Experiment dataset and long-term deployment of 277 3-component broadband stations installed from 1990 to 2018 to image crustal shear wave velocity and radial anisotropy in the Mississippi embayment. We first construct 5–40s group velocity maps for Rayleigh wave and 5–30s ones for Love wave. In the 5 s group velocity map, we observe that low velocity features correlate spatially with the sediment thickness from the Crust 1.0 model. High velocity anomalies are associated with the Ozark uplift and the Nashville Dome. In the 32 s group velocity map, high-low velocity boundaries align with 40 km crustal thickness contours from the Crust 1.0 model. We then invert Rayleigh and Love group velocity dispersion for shear wave velocity and radial anisotropy at each grid point and construct a 3D model accordingly. At the depth of 0–5 km of the model, we find that low velocity features characterize the Mississippi Valley Graben, Rough Creek Graben, Black Warrior Basin, and coastal flood plain. High velocity features mark thinly sedimented regions, like the Ozark uplift and the Nashville Dome. Regions with high gravity anomalies are characterized with negative anisotropies. At the depth of 5–12 km, we observe low velocity features in the Missouri Batholith, centering around 10 km. This region is characterized with negative radial anisotropy (Vsh < Vsv), inferring possible intrusions. High-low velocity boundaries correlate with the Appalachian-Ouachita thrust front. At the depth of 12–24 km, the Mississippi Valley Graben is filled with high velocity material, which may be related to the formation of the graben due to isostatic equilibrium. At the depth of 24–43 km, high velocity anomalies characterize the lower crust of the Mississippi embayment, consistent with high density features from the inversion of free air anomaly. The high velocity anomaly might be responsible for the formation of the embayment due to isostatic adjustment. The average velocity in the lower crust is approximately 4.3 km/s. Mafic Pikwitonei granulite is a possible material, indicating relative strong lower crust. This work provides useful information to explain earthquake occurrence in the New Madrid Seismic Zone and regional tectonic settings.

Experiences and psychosocial challenges of volunteer nurses in Turkey devastating earthquake zones: Lessons to be learnt for prevention of health system problems in disasters: A qualitative study.

This research aimed to investigate the experiences and psychosocial challenges encountered by volunteer nurses who provided care in the zones affected by the devastating earthquake that struck Turkey in 2023. This qualitative study involved semistructured, in-depth interviews with 15 volunteer nurses who were actively working in earthquake-affected regions. The study was conducted between June 2023 and July 2023. Participants were selected from diverse provinces (Hatay, Gaziantep, Adıyaman, Kahramanmaraş, and Malatya) affected by the earthquake, ensuring maximum variability. Individual online interviews were conducted using Google Meet, with data collection continuing until saturation was achieved. The study adhered to the COREQ checklist for reporting qualitative research. Three main themes and eight subthemes were developed: (1) Management and Coordination (failure to meet basic needs, bureaucracy, duty, and authority issues, problems with supplies and equipment); (2) Professional Experiences (working conditions, education, perspective on the profession); and Psychosocial Problems and (3) Coping Methods (psychological problems, methods of coping with problems). The study showed that volunteer nurses encountered management and organizational obstacles, were profoundly impacted by the disaster's psychosocial aspects, and often struggled with inadequacies in handling psychological challenges. Despite these challenges, the nurses reported a sense of competence in delivering care services. The insights derived from this study hold valuable lessons for future disaster response strategies. For this reason, it is recommended to plan the necessary training and initiatives to professionally strengthen the field of disaster nursing.

Structural behavior of historical Obruk Inn under different earthquakes

Masonry structures is one of the most preferred structure types throughout history. The advantageous of these structures can be categorized as longevity, affordability and easy access to materials. Due to a lack of information and constructive errors, masonry structures suffer major damage under effect of earthquakes. While the vertical load carrying capacity of a masonry structure is excellent, its performance under horizontal loads is very poor. The brittle behavior of masonry structures, in particular, causes the structure to suffer significant damage or collapse completely during an earthquake. Türkiye is situated over a major earthquake zone. Throughout history, there has been numerous major earthquakes. These earthquakes have demolished the masonry structures resulted in significant life and economic losses. Therefore, in recent days, the examination of the seismic resilience performance of masonry structures as well as the required strengthening have become a pivotal issue. Thus, the aim of this study is to analyze the seismic performance of historical Obruk Inn subjected to different earthquake effects via finite elements method (FEM). To do this, the plans obtained from on-site inspections for historical Obruk Inn to create structural FEM model and its performance was evaluated under the influence of various earthquake excitations. As a result of the analyses, it was determined that the historical Obruk Inn structure should have immediate be strengthened against a possible earthquake.

Assessment of coastal and mangrove vulnerability in the Andaman Island, Indian Ocean

Coastal regions are highly susceptible to the effects of global warming, including rising atmospheric and sea surface temperatures, increased cyclone frequency, and sea level rise. Thus, it is imperative to examine coastal vulnerability to minimize the impact of multiple hazards and protect coastal resources, such as mangroves. Particularly in India studying the vulnerability of coastal zones of Andaman and Nicobar Islands which fall in seismic zone V is critical for conservation efforts. We conducted a vulnerability analysis of coastal zones impacted by the 2004 earthquake, causing varying degrees of ground upliftment and subsidence. We compared coastal vulnerability among sites that experienced uplift, no change, and subsidence (the southern portion). Our analysis utilized the Coastal and Mangrove Vulnerability Index (CVI and MVI) to measure and compare vulnerability in six zones distributed along uplift and subsidence gradient. High-resolution satellite imagery including WorldView-2, 3, and GeoEye-1 from year 2022 are utilized on this study. The CVI and MVI offers a good way to measure and compare vulnerabilities across sites and offer insights for better management. The CVI and MVI results indicate that approximately 34% of coastal grids and over 23% of mangrove grids across all zones are highly to extremely highly vulnerable. Subsided zones were found to be more vulnerable than uplifted zones. These findings suggest that large-scale natural disturbances such as tectonic displacement have the potential to impact coastal vegetation and mangrove cover can become even more vulnerable. In conclusion, our study emphasizes the importance of vulnerability analyses in coastal regions, especially in areas prone to seismic activity. Our findings have direct implications for conservation and restoration efforts and underscore the need for continued monitoring and mitigation efforts to safeguard coastal resources for long-term sustainability.

The assessment of probabilistic seismic risk using ground-motion simulations via a Monte Carlo approach

Accurately characterizing ground motions is crucial for estimating probabilistic seismic hazard and risk. The growing number of ground-motion models, and increased use of simulations in hazard and risk assessments, warrants a comparison between the different techniques available to predict ground motions. This research aims at investigating how the use of different ground-motion models can affect seismic hazard and risk estimates. For this purpose, a case study is considered with a circular seismic source zone and two line sources. A stochastic ground-motion model is used within a Monte Carlo analysis to create a benchmark hazard output. This approach allows the generation of many records, helping to capture details of the ground-motion median and variability, which a ground motion prediction equation may fail to properly model. A variety of ground-motion models are fitted to the simulated ground motion data, with fixed and magnitude-dependant standard deviations (sigmas) considered. These include classic ground motion prediction equations (with basic and more complex functional forms), and a model using an artificial neural network. Hazard is estimated from these models and then we extend the approach to a risk assessment for an inelastic single-degree-of-freedom-system. Only the artificial neural network produces accurate hazard results below an annual frequency of exceedance of 1 × 10–3 years−1. This has a direct impact on risk estimates—with ground motions from large, close-to-site events having more influence on results than expected. Finally, an alternative to ground-motion modelling is explored through an observational-based hazard assessment which uses recorded strong-motions to directly quantify hazard.

Retrofitting RC beam-column joint subassemblies using UHPC jackets reinforced with high-strength steel mesh

Outdated building codes in seismic zones often did not require seismic detailing on beam-column joints, leaving many existing structures vulnerable to earthquakes. To address this issue, three different ultra-high-performance concrete (UHPC) jackets were proposed for retrofitting seismically-deficient exterior beam-column joints, with variables including construction method (cast-in-place or precast) and inclusion of high-strength steel bar meshes. The effectiveness of these jackets was investigated using cyclic loading tests on beam-column joint subassemblages. The results demonstrated that all three UHPC jackets considerably improved the strength, stiffness, and energy dissipation of the beam-column joint subassemblage, as well as both repairable and collapse drifts. However, the cast-in-place UHPC jacket, when not reinforced with steel meshes, failed to effectively improve the ultimate drift capacity of the original beam-column joint subassemblage. Moreover, retrofitting with precast UHPC jackets using chemical anchors failed to generate sufficient composite action. Only the cast-in-place UHPC jacket, when reinforced with high-strength steel meshes, successfully delayed localized joint shear damage and allowed for effective utilization of beam flexural capacity. It improved the joint shear strength by 66%, initial stiffness by approximately 35%, and total energy dissipation by 140%. Finally, strength models were suggested for evaluating the joint shear strength and beam flexural capacity of UHPC-retrofitted beam-column joints.

‘In order not to cry, we averted our eyes from each other:’ experiences of special education professionals working in the field during the Turkey earthquake

Objectives This study aims to explore the experiences of 12 special education professionals who volunteered in earthquake zones, utilizing a phenomenological approach. Methods A qualitative methodology, specifically content analysis, was employed to analyze the data gathered from these professionals. Results Four major themes emerged: ‘Professionals,’ ‘Children/Individuals with Special Needs,’ ‘Parents,’ and ‘Circumstances, Needs, and Services.’ The findings revealed that individuals with Intellectual and Developmental Disabilities (IDDs) and their families were significantly and negatively affected by the earthquake, experiencing challenges in psychological, social, and educational areas. Furthermore, it was found that the basic needs of individuals with special needs and their families were not adequately met, and services were neither systematically provided nor easily accessible. Conclusions The results underscore the critical impact of natural disasters on individuals with IDDs and their families. It highlights the necessity for immediate implementation of services adhering to accessibility standards and the initiation and consistent continuation of community-based rehabilitation services.

Spatio-temporal characteristics of seismic strain anomalies reveal seismic risk zones along the Longmenshan fault zone and adjacent areas

Introduction: Identifying and quantifying earthquake precursors, and analyzing their physical mechanisms, continues to be a challenge for earthquake forecasting. In this study, orthogonal functions were developed to effectively identify precursor anomalies, thereby improving the forecasting of strong earthquakes.Methods: To study the spatio-temporal contour anomalies in seismic strain fields, we assessed them for seismic activity variables and natural orthogonal function expansion, in six strong earthquakes near the Longmenshan Fault Zone, China, that have occurred since 2008.Results: We observed that, prior to these earthquakes, the temporal factor (the time variation characteristics of the strain field) displayed anomalies with high/low values exceeding the mean square error within a stable context. The anomalies exhibited multi-component characteristics and were primarily concentrated in the first four-strain fields. Short-term and impending-earthquake anomalies were observed in the temporal factor before the 2008 Wenchuan (M8.0) and 2013 Lushan (M7.0) earthquakes, while medium-term and long-term anomalies appeared before the other four strong earthquakes, without notable short-term anomalies. The temporal evolution of strain field contour anomalies, and the strain contours positive and negative intersection, showed that central areas surrounded by multiple strain field contour anomalies were potential locations for strong earthquakes. This suggests a potential approach for earthquake location forecasting. Since 2009, there have been five strong earthquakes, each affected to varying degrees by anomalous strain fields from the 2008 Wenchuan (M8.0) earthquake.Conclusion: The results of this study corroborate the findings of the focal mechanism’s node shear stress, indicating significant physical implications of the anomalies and the reliability of these conclusion.

Uneven regional distribution earthquake danger zones and of cell towers and cells in Türkiye

Zoning potential danger derived from earthquakes is crucial for the development of policies dealing with the future of the cities. Determination of the potential danger zones regarding earthquakes with the telecommunication infrastructure is crucial for the development of policies dealing with the future of the cities. By utilizing the cartogram mapping technique, this paper aims to display potential earthquake danger zones with the uneven distribution of the cell towers and cells on a population cartogram for Türkiye. This is crucial for the cities regarding the future potential communication crises after disasters. Policymakers should provide and develop well-functioning communication networks (GSM networks) for the organization of aid and search and rescue operations since the collapse of the communication infrastructure renders all post-disaster processes insoluble and dysfunctional.

Three-dimensional broadband simulation of near-fault seismic ground motion considering complete source-path-site effect: Modeled by fast multipole indirect boundary element method

Efficient and accurate numerical methods are essential for analyzing seismic wave propagation and amplification in near-fault complex sites. Understanding the complete process of ground motion simulation, including fault rupture, path propagation, and near-surface complex site response, is crucial for studying earthquake damage mechanisms, seismic zoning, and designing large-scale engineering structures. In this study, we propose a fast multipole indirect boundary element method (FMIBEM) to achieve broadband and high-efficiency simulation, enabling a comprehensive analysis of the complete process involving seismic ground motion. The FMIBEM significantly reduces the computational and storage costs associated with 3D near-fault complex site seismic wave scattering problems to O(N). We validate the accuracy of the method by comparing it with the analytical solution. Compared to the conventional indirect boundary element method (IBEM), our proposed method reduces computational time by over 95 % and storage costs by nearly 90 %. FMIBEM greatly enhances the efficiency of the boundary element method for simulating seismic wave scattering in near-fault complex sites. To demonstrate the effectiveness of our approach, we apply the FMIBEM method to two typical 3D near-fault complex site examples of seismic wave scattering. The simulation results successfully capture both the local site amplification effect and the characteristic near-fault seismic features, such as the hanging wall effect, permanent displacement effect, and large velocity pulse.

Verification of regulatory formulas for assessing the level of accelerations in SP 286.1325800.2016 "Construction facilities of increased responsibility. Rules of detailed seismic zonation" based on real data

The normative formulas of SP 286.1325800.2016 for estimation of peak ground accelerations in earthquakes were checked on records obtained in the near-fault zones of strong earthquakes (MS ~6.9÷7.15) of Japan made by K-NET and KiK-net stations. It was found that the recorded values of peak accelerations have a fairly large scattering even in the selected narrow range of magnitudes, which is obviously due to local site effects (soil response, topographic effects, etc.), as well as to differences in the characteristics of the earthquake sources and the paths of seismic wave propagation. Calculations by the normative formulas produced estimates that are near the lower limit of the recorded peak accelerations, and in the near-source zones, they noticeably underestimate the recorded peak accelerations. In general, the formulas of SP 286.1325800.2016 give us only approximate estimates, and therefore, it is necessary to develop more reliable methods for estimating peak accelerations and other parameters of seismic motion, taking into account soil conditions and regional characteristics, with components of probabilistic analysis.

InSAR, Gravity, and Geomagnetic Observations Suggest the 2020 Mw 6.5 Stanley Earthquake Occurred on a Blind Strike-Slip and a Normal Fault

ABSTRACT The 2020 Mw 6.5 Stanley earthquake occurred in western North America and is the largest earthquake in Idaho state in the past ∼40 yr. The hypocenter is located at the western margin of the Centennial Tectonic Belt (CTB), which is a subprovince of the Basin and Range and characterized by a series of normal faults. In this study, the coseismic Interferometric Synthetic Aperture Radar observations, geophysical data, and aftershocks are jointly collected to estimate the seismogenic fault of the 2020 Stanley earthquake. The best-fitting fault models suggest the earthquake occurred on two blind faults. Slip on the main, west-dipping, seismogenic fault was sinistral and on the second fault predominantly normal slip with a minor component of right-lateral strike slip. Geophysical observations including gravity and geomagnetic data are consistent with the fault interpretations. The Coulomb failure stress (CFS) change indicates that the rupture of the main seismogenic fault had a positive triggering effect on the slip of the second fault and may have increased the rupture risk of the Sawtooth fault. Moreover, a potential seismic hazard risk zone with a notably low occurrence of aftershocks is found in the west of the central segment of the main seismogenic fault.