Potential Seismic Risk Research Articles

SPATIAL AND TEMPORAL DISTRIBUTION CHARACTERISTICS OF CULTURAL RELICS PROTECTION UNITS AND DISASTER RISK ANALYSIS IN BEIJING

Abstract. As the ancient capital of the Six Dynasties and the current capital, Beijing has a rich historical and cultural heritage. As a carrier of culture, cultural preservation units have significant historical, artistic, and scientific value in their own right. In this paper, we use the mean nearest neighbor, kernel density analysis, and standard deviation ellipse tools in ArcGIS 10.2 software to analyze the spatial and temporal distribution characteristics of different types and periods of cultural heritage units in Beijing and their potential seismic and meteorological hazard risks, to provide strong data support for the conservation and use of cultural heritage units in Beijing. The results show that the different types of cultural preservation units in Beijing are unevenly distributed, with the two categories of modern important historical sites and representative buildings and ancient buildings being more numerous and concentrated in Dongcheng District, Xicheng District, and Haidian District in central Beijing, and the three categories of ancient tombs, ancient ruins, cave temples, and stone carvings being less numerous and concentrated in the outer administrative districts of Beijing. In recent years, the relative humidity in Beijing has shown a decreasing trend, while the average temperature has shown an increasing trend, and this dry and hot environment is not conducive to the conservation of cultural preservation units. This dry and hot environment is not conducive to the protection of cultural preservation units and is prone to damage such as cracking, collapse, deformation, and discoloration of bamboo, wood, rocks, and other cultural heritage elements. It is concluded that in terms of specific regions, the number of cultural heritage units in central Beijing is high, the period is late and the risk of seismic hazards is high, while the number of cultural heritage units in the outer administrative regions of Beijing is low, the period is early and the risk of seismic hazards is low. In conclusion, to enhance the conservation and use of cultural heritage units in Beijing, the relevant authorities should strengthen the daily management of the three high-density and high-risk areas of cultural heritage units in Dongcheng District, Xicheng District, and Haidian District, while at the same time not relaxing the emergency disaster prevention and mitigation of the smaller number and earlier period of cultural heritage units in the peripheral administrative districts.

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.

Spatial and Temporal Distribution of Lobate Scarps in the Lunar South Polar Region: Evidence for Latitudinal Variation of Scarp Geometry, Kinematics and Formation Ages, Neo‐Tectonic Activity and Sources of Potential Seismic Risks at the Artemis Candidate Landing Regions

AbstractLobate scarps (thrust faults) in the lunar south polar region (90°–60°S) provide important insights into tectonic history, seismicity, and seismic hazard potential of landing sites. In this study, we discovered 75 new lobate scarps and >500 segments, exhibiting latitudinal variation of geometry and movement directions. Formation ages of 141 prominent scarp segments show fault growth rates and directions, decreasing ages from south pole to mid‐latitude, continuous tectonic activity in the last 100 million years with a peak around 10 Ma, seismic resetting of ages, and timings of global contraction. The scarps are capable of producing small‐medium size moonquakes within 5–10 km depths. The deterministic seismic hazard analysis, considering occurrence of MW 1–4 shallow moonquakes along the scarps in the next few decades, and their seismic ground motion characteristics, suggests variable levels of potential seismic risk at the Artemis candidate landing regions and further probabilistic seismic hazard analysis is necessary.

The 2022 Mw 6.6 Menyuan Earthquake in the Northwest Margin of Tibet: Geodetic and Seismic Evidence of the Fault Structure and Slip Behavior of the Qilian–Haiyuan Strike-Slip Fault

AbstractOn 8 January 2022, an Mw 6.6 earthquake occurred along the Lenglongling fault (LLLF) (Menyuan, Qinghai Province, China), in the northeast margin of the Tibetan plateau. Here, we use imaging geodesy observations from pixel-offset tracking (POT) and Interferometric Synthetic Aperture Radar (InSAR) to quantify the coseismic displacement features and then combine InSAR and teleseismic velocity waveforms to constrain a finite-fault model to examine the kinematic slip behavior of the LLLF. We observe maximum displacements of >50 cm in the line-of-sight InSAR observations and >1 m in the east–west POT observations. Our preferred uniform-slip model indicates that the causative fault of this 2022 event ruptured the middle segment of the Qilian–Haiyuan fault (i.e., the LLLF) with a strike of 108.0°, a dip angle of 83.6°, and slip concentrated within a 15×8 km2 area and reaching a maximum value of 4 m. The total scalar seismic moment was 1.24×1019 N·m, and ∼67% of the energy was released in the first 6 s. We speculate that the 2022 event was controlled by complex fault geometries and slip partitioning, thus raising potential seismic risks associated with the outward extrusion of the plateau.

A simplified approach to evaluate cyclic response and seismic fragility of corrosion damaged RC bridge piers

Safety of the existing corrosion damaged reinforced concrete (RC) bridges during a seismic event is a matter of increasing concern. To reduce the enormous economic loss and casualties, it is important to examine the potential seismic risk of corroded RC bridge structures. This paper presents a simplified method to determine the seismic fragility of corroded RC bridge piers by developing a simplified FEM model and seismic fragility analysis. To make the proposed approach realistic, the numerical model is validated with two different experimental studies available in the literature. Obtain results from the simplified numerical model demonstrated excellent agreement with the experimental tests, making it suitable for seismic vulnerability analysis. After validation, the numerical model is further adopted to perform non-linear static pushover analysis of corroded RC bridge piers. Finally, a recently developed software tool SPO2FRAG is utilized to carry out seismic fragility analysis by defining three different damage levels.

Antecedent topography and active tectonic controls on Holocene reef geomorphology in the Great Barrier Reef

The Great Barrier Reef is generally considered a passive tectonic setting, however the effect of antecedent topography and local geological structures on Holocene reef development is poorly understood. Offshore reefs along the central shelf were recently hypothesized to have grown continuously through a possible small Holocene sea level fall, in response to greater local subsidence, in contrast to reefs immediately to the north and south, which experienced synchronous turnoff phases. We tested this hypothesis by isolating four map zones along the GBR shelf and using: (1) a geomorphic reef type classification applying perceived evolutionary “age” as juvenile, mature, and senile domains based on geomorphology; (2) analysis of bathymetry data to understand the role of antecedent topography on the spatial distribution of reef type domains and general sea floor depths; and (3) the distribution of earthquake epicentres as an indication of possible active geological structures (i.e., faults). The results reveal that juvenile reefs (42.25 %) are more abundant in the central shelf, whereas mature-2 (40 %) and senile (31 %) reefs are more abundant in the northern zone. In the south-central zone, mature-2 reefs are prevalent, while the southern zone includes a mixture of juvenile and mature to senile domains with a sharp internal boundary. These results support the hypothesis that the central zone may have experienced greater active subsidence during the Holocene. Bathymetric data support greater regional subsidence in both central and south-central zones, but reefs are less abundant and cover a lesser percentage area of their antecedent platforms in the central zone, consistent with greater subsidence there. The boundaries between the central zone and adjacent zones are the sites of clusters of recent earthquakes, consistent with the occurrence of active geological faults bounding the zone of greater Holocene subsidence. Combined, our data support the occurrence of a tectonically defined region of active greater subsidence in the central GBR shelf that has affected the geomorphology and growth history of reefs through the Holocene. Knowledge of such spatial partitioning of reef behaviour may allow reef managers to better suite their efforts to local conditions, especially in regard to predicted sea level rise, while highlighting potential seismic risks over longer time frames.

Classification of Majene Regency Landslide Prone Areas Using Geographic Information System and Storie Index

On January 14, 2021, several villages in Majene Regency suffered landslides triggered by a M6.2 earthquake. The study’s aim is to use the Index Storie model approach, remote sensing data, and Geographic Information Systems (GIS) to map the distribution of landslide-prone areas as a mitigation basis in Majene Regency to reduce the potential for future landslide disasters. The level of landslide potential was determined based on slope conditions, soil types, rainfall, land use types, and potential earthquake risk. In general, morphological conditions in Majene Regency are dominated by slopes that are still covered in forests and receive relatively low rainfall, resulting in low landslide potential if seismic potential factors are not taken into account. Based on the results of an analysis that considers slope factors and potential seismic risks, the results of a map that illustrates the risk of landslide are quite high in several areas, are Malunda District, Ulumanda District, and Tubo Sendana District.

Interseismic deformation rate of the Haiyuan fault system based on the modified SBAS method

Radar interferograms are usually influenced by factors such as atmospheric artifacts, orbital errors, and terrain errors. It is difficult to reduce the influence by using the conventional small baseline subset (SBAS) method when determining the deformation rate. This study uses the adjustment model with systematic parameters to improve the conventional SBAS method and employs it to determine the interseismic deformation rate of the Haiyuan fault system, providing a data reference for exploring the locking depth, strain accumulation state, and potential seismic risk assessment of different segments of the Haiyuan fault system. The results are as follows: (1) the simulation experiment verifies the feasibility and robustness of the modified SBAS method. This method can effectively reduce the influence of residual signals such as atmospheric artifacts, orbital errors and terrain errors in the interferograms. The deformation rate map can be significantly improved; (2) the deformation rate field in the radar's Line of Sight (LOS) direction shows that there are obvious differences between the north and south sides of Haiyuan fault system, which is consistent with the characteristics of the left-lateral strike-slip movement of the Haiyuan fault system. The deformation rate field and profiles reflect the complex trends among different segments of Haiyuan fault system in detail. (3) the deformation rate of the Jingtai pull-apart basin is higher than that of the surrounding areas, possibly indicating strong regional activity, which provides a reference for studying the seismic risk of the Jingtai pull-apart basin; and (4) the interseismic deformation rate and profiles across the fault show that the middle section of the Lao Hu Shan (LHS) segment and the western and middle sections of the Haiyuan segment are locked.

State-of-the-Art Review on Probabilistic Seismic Demand Models of Bridges: Machine-Learning Application

Optimizing the serviceability of highway bridges is a fundamental prerequisite to provide proper infrastructure safety and emergency responses after natural hazards such as an earthquake. In this regard, fragility and resilience assessment have emerged as important means of describing the potential seismic risk and recovery process under uncertain inputs. Generating such assessments requires estimating the seismic demand of bridge components consisting of piers, deck, abutment, bearing, etc. The conventional probabilistic model to estimate the seismic demands was introduced more than two decades ago. Despite an extensive body of research ever attempting to improve demand models, the univariate demand model is the most common method used in practice. This work presents a comprehensive review of the evolution of demand models capturing machine-learning-based methodologies and their advantage in comparison to the conventional model. This study sheds light on understanding the existing demand models and their associated attributes along with their limitations. This study also provides an appraisal of the application of probabilistic demand models to generate fragility curves and subsequent application in the resilience assessment of bridges. Moreover, as a sound reference, this study highlights opportunities for future development leading to enhancement of the performance and applicability of the demand models.

Effect of fuzzy failure criterion on probabilistic seismic risk analysis under multidimensional performance limit state

Traditional probabilistic seismic risk analysis (PSRA) often adopts accurate limit state boundary to define the structural performance limit state, which ignores the fuzziness of limit state thresholds and boundary. In this paper, considering the fuzzy failure criterion, a novel PSRA method based on fuzzy-random hybrid model is proposed under multidimensional performance limit state. A multiple integral formula based on fuzzy failure criterion is established for PSRA, and the influence of different membership functions and membership intervals are studied. A reinforced concrete (RC) frame-shear wall structure is established as the numerical example. The results show that: Fuzzy failure criterion will lead to the change of failure probability, thus the structural potential seismic risk or capacity could be analyzed. With the increase of structural damage degree, the influence of fuzzy failure criterion is become larger. Different membership functions have different effects on vulnerability curves and capacity hazard surface. With the expansion of membership interval, the influence of fuzzy failure criterion on PSRA is getting larger.

An evaluation of seismic hazard and potential damage in Gaziantep, Turkey using site specific models for sources, velocity structure and building stock

Assessment of potential seismic risk and losses in urban environments is necessary for several purposes ranging from risk mitigation to city and regional planning. It is well known that loss estimation should be performed within an interdisciplinary setting involving earth sciences and engineering. Field experience from recent events worldwide shows that the spatial variability of seismic damage is due to the combined effects of earthquake source properties, local site conditions and structural characteristics. In this study, a scenario-based multi-input damage estimation framework in an urban region was utilized for the Gaziantep city center (southeastern Turkey) that is located in a region of high seismic hazard with no large events in the instrumental era. Initially, a thorough geological and seismo-tectonic assessment of the area was performed followed by estimation of two critical scenario events with moment magnitude (Mw) of 6.5 and 6.6 on nearby active faults. Then, a regional velocity model was compiled from regressions of existing regional geotechnical and seismic data in terms of the VS30 parameter. As the next step, field surveys for the assessment and classification of buildings in the study area were performed followed by vulnerability analyses. As the last step, the mean damage ratios were computed at 198 neighborhoods within the city center. The results indicate not only a high hazard but also high risk in the Gaziantep area due to the combination of close proximity to the faults along with local site effects and building fragilities.

Laboratory characterization of cyclic hydraulic fracturing for deep shale application in Southwest China

As one of the most promising shale gas reservoirs in China, the Lower Silurian Longmaxi formation in the Sichuan Basin has produced a large amount of shale gas during the last few years. However, two significant concerns have been raised during the contemporary shale gas development in this area: dramatic increases in well depths and potential induced seismicity . The extreme depths have resulted in higher in-situ stress and reservoir breakdown pressures . The other concern is whether recent earthquakes are related to hydraulic fracturing operations since they are close in space and time. An advanced fluid injection protocol-cyclic fluid injection has been proposed and used to lower the breakdown pressure of reservoirs and mitigate the potential seismic risks caused by hydraulic stimulations. In this study, we combine a series of laboratory experiments and a numerical simulation model to investigate the breakdown mechanism, seismic risks, permeability enhancement performance of cyclic fluid injection. The results indicate that the cyclic injection method decreases the shale breakdown pressure by ∼25% compared with the conventional monotonic rate injection , which is the result of fatigue failure near the fluid injection borehole induced by pore pressure fluctuations lagging behind the periodical injection pressure changes. Even though more acoustic emission events are observed during and post-the cyclic injection, the maximum acoustic emission amplitude decreases by 26%, which is equivalent to transforming AE events with large amplitudes to more AE events with small amplitudes. Moreover, fracture morphology and permeability measurement results indicate that cyclic injection creates hydraulic fractures with higher fracture tortuosity but smaller aperture and lower permeability, which contributes to the fatigue mechanism of rock breakdown. Our experimental results and theoretical analysis initially validate the potential of using cyclic injection methods to perform hydraulic fracturing stimulation in shale reservoirs to lower breakdown pressure and mitigate seismic risks.

Late Quaternary activity of the Qingchuan Fault, eastern Tibetan Plateau margin: Insights from stream channel offsets and catchment erosion

The Qingchuan Fault (QCF) is the main fault of the northeastern segment of the Longmenshan Fault zone (LMSFZ) on the eastern Tibetan Plateau boundary. The QCF accommodates ongoing deformation in the eastern Tibetan Plateau; however, its fault motion and potential seismic risk are still debated. This study combines a systematic analysis of deflected stream channels along the fault using 10-m digital elevation models with field investigations and measurements of the cosmogenic 10Be-derived erosion rates. The degree of channel deflection due to the interaction between strike-slip motion and channel growth processes is analyzed, followed by a quantitative extraction of the actual tectonic offsets and a calculation of the erosion rates. The long-term average strike-slip rates calculated from channel offsets range from 0.4 ± 0.1 to 1.7 ± 0.1 mm/a along the fault, with those in the southwestern section lower than those in the central section. Such differences may be attributed to slip partitioning of the northeastern extension of the Yingxiu–Beichuan Fault. In addition, analysis of stream longitudinal profiles and along-fault topographic variations illustrate that the small thrust component of the QCF decreases to the northeast, and a minor normal component exists at its northeastern end. The distributions of strike-slip and vertical-slip motions of the QCF indicate that fault slip of the central LMSFZ propagates to the northeast across the Minshan uplift and continues to slip along the QCF. Moreover, thrusting of the southern-central segment of the LMSFZ and dextral strike-slip faulting of the QCF may both accommodate complex deformation related to eastward expansion of the Tibetan Plateau. These findings have implications for constraining potential seismic hazards and understanding characteristics of the regional tectonic deformation.

The Effect of the Wenchuan and Lushan Earthquakes on the Size Distribution of Earthquakes along the Longmenshan Fault

Changes in the stress state of faults and their surroundings is a highly plausible mechanism explaining earthquake interaction. These stress changes can impact the seismicity rate and the size distribution of earthquakes. However, the effect of large earthquakes on the earthquake size distribution along the Longmenshan fault has not been quantified. We evaluated the levels of the b value for the stable state before and after the large earthquakes on 12 May 2008 (Wenchuan, MS 8.0) and 20 April 2013 (Lushan, MS 7.0) along the Longmenshan fault. We found that after the mainshocks, the size distribution of the subsequent earthquakes shifted toward relatively larger events in the Wenchuan aftershock zone (b value decreased from 1.21 to 0.84), and generally remained invariable in the Lushan aftershock zone (b value remained at 0.76). The time required for the b value to return to stable states after both mainshocks was entirely consistent with the time needed by the aftershock depth images to stop visibly changing. The result of the temporal variation of b values shows decreasing trends for the b value before both large earthquakes. Our results are available for assessing the potential seismic risk of the Longmenshan fault as a reference.

Slip Rate and Paleoseismology of the Bolokenu‐Aqikekuduk (Dzhungarian) Right‐Lateral Strike‐Slip Fault in the Northern Tian Shan, NW China

AbstractThe ∼1,000 km‐long Bolokenu‐Aqikekuduk fault (Dzhungarian fault, BAF) is one of the major right‐lateral strike‐slip faults that cut across the Tian Shan Range. Although the BAF plays an important role in accommodating crustal shorting of the Tian Shan and cuts through densely populated cities, little is known about its late Quaternary tectonic activity or earthquake history. Here we quantify the late Quaternary dextral strike‐slip rate of the BAF along the Jinghe segment based on interpretation of high‐resolution remote sensing images and structure‐from‐motion (SfM)‐derived DEMs, field observations and the abandonment ages of displaced alluvial fans, which were constrained by optically stimulated luminescence (OSL) and cosmogenic 10Be depth profile dating methods. Using the offset of fan risers and gullies incised into the fan surfaces, we yielded a right‐lateral strike‐slip rate of 3.2 + 1.4/−1.1 mm/a. Compared with the entire crustal shortening rates across the Tian Shan, the BAF accommodates ∼23% of the N‐S crustal shortening rate. Additionally, a paleoseismic trench reveals four events since the late Pleistocene with an average recurrence time of ∼4–6 ka. The last event occurred after ∼6.6 ka, which is slightly larger than the average recurrence time, suggesting that the BAF represents a potential high seismic risk for the densely populated area nearby.

Seismogenic Faults of the Changning Earthquake Sequence Constrained by High-Resolution Seismic Profiles in the Southwestern Sichuan Basin, China

Abstract The seismicity rate in the southwestern Sichuan basin, China, dramatically increased after 2014. The associated moderate earthquakes may have been induced by salt mining or shale gas exploration. The location of the seismogenic faults causing these moderate earthquakes has not been confirmed, resulting in a lack of understanding of the earthquake mechanisms in the study area. The detailed structural characteristics of pre-existing faults, which are typically responsible for induced seismicity, are unclear. In this study, we used high-resolution seismic reflection profiles in conjunction with geological, seismologic, and geodetic data to reveal the 3D distributions of the seismogenic faults. Basement thrust faults in the Changning anticline were identified using seismic interpretations and are associated with the 2019 Changning earthquake sequence. The geometry and location of these pre-existing faults are consistent with previous studies of the seismology and structural geology in the area. The well-developed pre-existing fault system in the sedimentary cover and basement makes the Changning area vulnerable to induced earthquakes. Present-day reactivation of the basement fault system reveals the unstable state of the local tectonic stress field. It is possible that the potential seismic risk in this region could be increased by industrial activity in the southwestern Sichuan basin.

Re-Evaluating the Surface Rupture and Slip Distribution of the AD 1609 M7 1/4 Hongyapu Earthquake Along the Northern Margin of the Qilian Shan, NW China: Implications for Thrust Fault Rupture Segmentation

The Hexi Corridor is located beyond the northeastern edge of the Tibetan Plateau, and it is bounded by a series of active thrusts along the northern margin of the Qilian Shan and the southern piedmont of the Longshou Shan. Historically, five destructive earthquakes have occurred along the Hexi Corridor, which indicates that this region poses high potential seismic risks. The 1609 Hongyapu earthquake occurred along the Fodongmiao-Hongyazi fault in the northern Qilian Shan, China, and it killed more than 840 people and destroyed a large number of buildings. Presently, there are different opinions as to the distribution and length of the surface rupture of this event along the Fudongmiao–Hongyazi fault. Thus, we searched all of the fault scarps on the Holocene surfaces and suspected surface rupture locations related to the 1609 earthquake based on previous studies and developed detailed remote-sensing interpretations along the fault. An abundance of north-facing scarps on the younger fans and terrace faces, slightly higher than the active modern stream bed, were found along the Fodongmiao-Hongyazi fault in the area ranging from the Hongshuiba River (39.52°N, 98.41°E) in the west to the Shuiguan River (39.07°N, 99.37°E) in the east. Based on our research, we estimate a surface rupture length as ∼98 km based on the distribution of the fault scarps on Late Holocene surfaces and constraints provided by age dating. Most of the surface ruptures are preserved as fault scarps and indicate an average vertical surface offset of ∼1.0 m, a value found consistently in three segments of the fault. The surface rupture features indicate that segments of the fault ruptured together coseismically during the 1609 earthquake, i.e., a multisegment rupture. Using the surface fault traces, length of 98 or 90 km (without the Shuiguan River section), dip of 30° inferred from previous reflection profiles, a rigidity of 3.3 × 1010 N/m2, and dip slip average as 1.9 m converted from our observations of the offsets, we computed the magnitude of this event as ca. Mw 7.2–Mw 7.4.

Induced Seismicity Completeness Analysis for Improved Data Mining

The study of induced seismicity at sites of fluid injection is paramount to assess the seismic response of the earth’s crust and to mitigate the potential seismic risk. However statistical analysis is limited to events above the completeness magnitudemc, which estimation may significantly vary depending on the employed method. To avoid potential biases and optimize the data exploitable for analysis, a better understanding of completeness, detection capacity and censored data characteristics is needed. We apply various methods previously developed for natural seismicity on 16 underground stimulation experiments. We verify that different techniques yield differentmcvalues and we suggest using the 90% quantile of themcdistribution obtained from high-resolution mapping, withmcdefined from the mode of local magnitude frequency distributions (MFD). We show that this distribution can be described by an asymmetrical Laplace distribution and the bulk MFD by an asymmetric Laplace mixture model. We obtain an averaged Gutenberg-Richter parameterb=1.03±0.48and a detection parameterk=3.18±1.97 from mapping, with values subject to high uncertainties across stimulations. We transfer Bayesianmcmapping developed for natural seismicity to the context of induced seismicity, here adapted to local three-dimensional seismicity clouds. We obtain the new prior parameterizationmc,pred=1.64log10(d3)−1.83, withd3the distance to the 3rd nearest seismic station. The potential use of censored data and ofmcprediction is finally discussed in terms of data mining to improve the monitoring, modeling and managing of induced seismicity.

Development of an Exposure Vulnerability Index Map Using GIS Modeling for Preliminary Seismic Risk Assessment in Sabah, Malaysia

This research was conducted with a view to updating the management of earthquakes through an exposure vulnerability and potential seismic risk assessment, along with its application in Sabah (a state in East Malaysia). A set of indicators and methodologies has been proposed in this study with the goal of evaluating the level of exposure vulnerability and potential risk of certain locations to earthquake events at the local district scale. This study specifically involves the development of exposure vulnerability indicators; the statistical analysis method to standardize multivariate data together with a weight calculation of indicator variables; and a mathematical combination of different indicators for the development of the index map using the spatial analysis function of Geographical Information System (GIS) tools. Then, the derived exposure vulnerability index (EVI) map is overlaid with the seismic hazard in determining the geographical location of the most vulnerable areas and their exposure to seismic hazard events. As a result, and based on the available data, the exposure vulnerability index map shows that most districts in Sabah are at relatively low and moderate levels of risk except for a few districts, with several major cities in Sabah, such as Kota Kinabalu, Penampang, Sandakan and Tawau municipality, being situated at a high or very high exposure index. The combination of EVI maps and hazard maps indicate the dominance of the two factors influencing the potential level of earthquake risk. Studies reveal most of the southwest and central parts of the region are not at risk, as both exposure and hazard factors are at a low level. The proposed approach depicts an instrument for identifying cost-effective risk reduction initiatives by providing a scientific method for regional risk planning and management strategies. This research represents the first attempt to evaluate Sabah’s vulnerability to this type of natural disaster by understanding the spatial relationship between exposure vulnerability and earthquake hazard, which undoubtedly could be improved in several aspects.

Upper crustal velocity and seismogenic environment of the <em>M</em>7.0 Jiuzhaigou earthquake region in Sichuan, China

On August 8, 2017, a magnitude 7.0 earthquake occurred in Jiuzhaigou County, Sichuan Province, China. The deep seismogenic environment and potential seismic risk in the eastern margin of Tibetan Plateau have once again attracted the close attention of seismologists and scholars at home and abroad. The post-earthquake scientific investigation could not identify noticeable surface rupture zones in the affected area; the complex tectonic background and the reason(s) for the frequent seismicity in the Jiuzhaigou earthquake region are unclear. In order to reveal the characteristics of the deep medium and the seismogenic environment of the <i>M</i>7.0 Jiuzhaigou earthquake region, and to interpret the tectonic background and genesis of the seismicity comprehensively, in this paper, we have reviewed all available observation data recorded by the regional digital seismic networks and large-scale, dense mobile seismic array (China Array) for the northern section of the North–South Seismic Belt around Jiuzhaigou earthquake region. Using double-difference seismic tomography method to invert the three-dimensional P-wave velocity structure characteristics of the upper crust around the Jiuzhaigou earthquake region, we have analyzed and discussed such scientific questions as the relationship between the velocity structure characteristics and seismicity in the Jiuzhaigou earthquake region, its deep tectonic environment, and the ongoing seismic risk in this region. We report that: the P-wave velocity structure of the upper crust around the Jiuzhaigoug earthquake region exhibits obvious lateral inhomogeneity; the distribution characteristics of the shallow P-wave velocity structure are closely related to surface geological structure and formation lithology; the <i>M</i>7.0 Jiuzhaigou earthquake sequence is closely related to the velocity structure of the upper crust; the mainshock of the <i>M</i>7.0 earthquake occurred in the upper crust; the inhomogeneous variation of the velocity structure of the Jiuzhaigou earthquake area and its surrounding medium appears to be the deep structural factor controlling the spatial distribution of the mainshock and its sequence. The 3D P-wave velocity structure also suggests that the crustal low-velocity layer of northeastern SGB (Songpan–Garzê Block) stretches into MSM (Minshan Mountain), and migrates to the northeast, but the tendency to emerge as a shallow layer is impeded by the high-velocity zone of Nanping Nappe tectonics and the Bikou Block. Our results reveal an uneven distribution of high- and low-velocity structures around the Tazang segment of the East Kunlun fault zone. Given that the rupture caused by the Jiuzhaigou earthquake has enhanced the stress fields at both ends of the seismogenic fault, it is very important to stay vigilant to possible seismic hazards in the large seismic gap at the Maqu–Maqên segment of the East Kunlun fault zone.