Potential Seismic Risk Research Articles

Resolution analysis of the gravity survey network in the middle and south sections of Tan-Lu fault and recent changes in the gravity field

In this paper, we computed the fractal dimension of three survey areas within the central and southern sections of the Tan-Lu fault zone using fractal analysis. Subsequently, simulations were conducted to analyze the gravity response under a forward model of equivalent density changes. Additionally, we thoroughly investigated the seismic monitoring capabilities of the gravity network in the central and southern regions of the Tan-Lu fault. Expanding on these analyses. Recent gravity field variations were examined in the mid-southern segment of the Tan-Lu fault zone and its surrounding areas from 2013 to 2023. The results indicate that the observation capabilities of the northern network in the study area outperform those of the southern gravity network, with the northern network demonstrating a more evenly distributed coverage. The optimal gravity anomaly recovery effect for the entire study area is achieved at a resolution of 0.5° × 0.5°. With an equivalent observable signal in the range of 30 × 10−8 m/s2 to 40 × 10−8 m/s2, the spatial resolution of the gravity network's field source is estimated to be approximately 55 km. From 2013 to 2023, a significant positive change has been observed in the gravity field within the study area. The Tan-Lu fault zone plays a crucial role in governing the crustal movement in this region, with the dextral strike-slip movement trend of the fault persisting. Small earthquakes occur more frequently in the southern section of the fault zone, while strong earthquakes are less common. The alignment of gravity field changes with the fault strike indicates ongoing activity in the fault zone without any signs of locking. In the central segment of the Tan-Lu fault zone in the Shandong region, there appears to be a weaker correlation between gravity field changes and fault trends. This discrepancy may suggest that the area is locked, resulting in the accumulation of stress and strain. It is imperative to monitor the continuous evolution of the gravity field in this region to gain insights into potential seismic risks.

Coseismic Slip and Downdip Afterslip Associated with the 2021 Maduo Earthquake Revealed by Sentinel-1 A/B Data

On 22 May 2021, an earthquake (98.3° E and 34.59° N) struck Maduo town in Qinghai province, occurring along a relatively obscure secondary fault within the block. We utilized 105 archived Sentinel-1A/B acquisitions to investigate the coseismic deformation and the evolution of postseismic displacements in both the temporal and spatial domains, as well as the associated dynamic mechanisms of the 2021 Maduo earthquake. The interference fringes and coseismic deformation revealed that the primary feature of this event was the rupture along a left-lateral strike-slip fault. The released seismic moment was close to 1.88 × 1020 N·m, which is equivalent to an Mw 7.45 event. Simultaneously, the maximum coseismic slip reached approximately 4 m along the fault plane. The evolution of postseismic displacements in both the temporal and spatial domains over 450 days following the mainshock was further analyzed to explore the underlying physical mechanisms. Generally, the patterns of coseismic slip and afterslip were similar, although the postseismic displacements decayed rapidly over time. The modeled afterslip downdip of the coseismic rupture (at depths of 15–40 km) effectively explains the postseismic deformation, with a released moment estimated at 4.57 × 1019 N·m (corresponding to Mw 7.04). Additionally, we found that regions with high coseismic slip tend to exhibit weak seismicity, and that afterslip and aftershocks are likely driven by each other. Finally, we estimated the Coulomb Failure Stress changes (ΔCFS) triggered by both coseismic rupture and aseismic slip resulting from this event. The co- and postseismic ΔCFS show similar patterns, but the magnitude of the postseismic ΔCFS is much lower (≤0.01 MPa). We found that ΔCFS notably increased on the Yushu segment of the Garze-Yushu-Xianshuihe Fault (GYXF), as well as the Maqin–Maqu and Tuosuo Lake sections of the East Kunlun Fault (EKF). Therefore, we infer that these fault segments may have a higher potential seismic risk and should be carefully monitored in the future.

Stress Field Dynamics and Fault Slip Potential in the Paradox Basin

AbstractThe Paradox Basin, straddling Utah, Colorado, Arizona, and New Mexico is characterized by an intricate amalgamation of evaporites and clastic layers and is dominated by prominent salt walls and related subsurface structures. Our research offers a new examination of the stress distribution across the basin, deriving from continuous and discrete stress measurements conducted in boreholes in the region and focal mechanism analysis, emphasizing variations over salt structures. Integrating Coulomb failure criteria with probabilistic methods, we assess potential fault movements resulting from fluid pressure alterations. Our approach provides a comprehensive understanding of the Paradox Basin's state of stress, showing a continuous change of the maximum horizontal stress orientation from N‐S at the Wasatch Fault Zone to WNW‐ESE in the northern part of the Paradox Basin and to WSW‐ENE in the southern part of the basin. Further East, into the Colorado Plateau and the Uncompahgre Uplift, the SHmax orientation becomes E‐W. Decoding stress orientation dynamics has enabled critical insights into fault slip potential, especially in the basin's northern region. The salt wall faults are less likely to slip, and the Paradox Formation's evaporite and clastic rock sequence can serve as a potential low seismic risk target for carbon storage and hydrocarbon extraction.

IMPLEMENTATION OF THE PRISM SURVEY FORM TO CREATE SEISMIC RISK MAPS

This study details a seismic risk assessment of stone and adobe masonry structures in the Agios Dometios Municipality, Nicosia, Cyprus. The study integrates field inspections using the PRISM survey form, designed exclusively for masonry buildings, with advanced analytical procedures. The initial phase involves comprehensive field inspections to evaluate the structural condition and vulnerabilities of these historic masonry buildings. The data gathered from these inspections provide essential insights into potential seismic risks. This data, alongside fragility curves generated from 3D finite element (FE) models using nonlinear time-history analysis, informs the creation of seismic risk maps for Agios Dometios. These maps offer a comprehensive depiction of the area's seismic vulnerability, particularly concerning the masonry structures, serving as invaluable resources for local authorities and conservationists in strategizing preservation and reinforcement measures, and in formulating mitigation plans. This study's approach, blending field inspections with advanced computational analysis, provides a robust framework for assessing the seismic risks of masonry structures. It holds significant implications for preserving architectural heritage in seismically active regions, offering a model that can be replicated in similar urban contexts.

IMPLEMENTATION OF THE PRISM SURVEY FORM TO CREATE SEISMIC RISK MAPS

This study details a seismic risk assessment of stone and adobe masonry structures in the Agios Dometios Municipality, Nicosia, Cyprus. The study integrates field inspections using the PRISM survey form, designed exclusively for masonry buildings, with advanced analytical procedures. The initial phase involves comprehensive field inspections to evaluate the structural condition and vulnerabilities of these historic masonry buildings. The data gathered from these inspections provide essential insights into potential seismic risks. This data, alongside fragility curves generated from 3D finite element (FE) models using nonlinear time-history analysis, informs the creation of seismic risk maps for Agios Dometios. These maps offer a comprehensive depiction of the area's seismic vulnerability, particularly concerning the masonry structures, serving as invaluable resources for local authorities and conservationists in strategizing preservation and reinforcement measures, and in formulating mitigation plans. This study's approach, blending field inspections with advanced computational analysis, provides a robust framework for assessing the seismic risks of masonry structures. It holds significant implications for preserving architectural heritage in seismically active regions, offering a model that can be replicated in similar urban contexts.

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

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

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.

3D fault model and seismotectonics indicate the potential seismic risk in the Daliang Mountains, southeastern Tibetan Plateau

Areas of active tectonics host many active faults and frequently experience moderate to large earthquakes. The possibility of devastating earthquakes makes the development of major infrastructure projects in these areas risky. World-class large-scale step hydroelectric projects have been built along the Jinsha River, such as the Xiangjiaba, Xiluodu, Baihetan and Wudongde reservoirs in the Daliang Mountains of the southeastern Tibetan Plateau. Using the SKUA-GoCAD modelling platform, we created a thorough 3D model of the active faults. Regional geological information, historical strong earthquake catalogues, small earthquakes with fine displacement and 3D seismic tomography are all integrated in this model. The Mabian–Yanjin fault belt consists of a number of discontinuous faults that are either exposed on the surface or concealed, according to the 3D fault model. Some destructive earthquakes, including two enormous M s 7 and many moderate earthquakes, have occurred along this fault belt. Some pre-existing thrust faults, together with numerous immature faults in specific areas, may have been reactivated and changed into strike-slip faults. The Jinsha River basin's seismic and geological concerns must be carefully considered given the existence of such intricate fault networks and seismic activity. Supplementary material: A video of the 3D fault model is available at https://doi.org/10.6084/m9.figshare.c.6949201

Investigating paleoseismicity using high-resolution airborne LiDAR data - A case study of the Huangxianggou fault in the northeastern Tibetan plateau

Fault-offset landforms have long been recognized as holding important information about paleoseismic slip. Constructing an along-strike fault slip distribution could help reveal a fault's long-term rupture patterns and facilitate a more precise assessment of its future behavior. In this study, we documented the paleoseismic history of the Huangxianggou Fault, an oblique sinistral-thrust segment of the West Qingling Fault in the northeastern region of the Tibetan Plateau, using LiDAR-derived high-resolution DEM (0.1 m/pixel) and measurement of offset landforms. A total of 46 well-preserved and well-shaped landforms were chosen for horizontal and vertical displacement measurements, and the dense measurement data allow us to generate the cumulative offset probability distribution curves of horizontal and vertical displacements. Statistical analysis revealed at least seven surface-rupturing events, each with similar coseismic horizontal displacements of ∼7.0 m and vertical displacements of ∼0.7 m, in agreement with previous paleoseismic trench results. Using empirical relationships between moment magnitude and horizontal displacement, a plausible moment magnitude range of Mw7.3–7.7 was determined for these paleoearthquakes. Furthermore, by evaluating rupture parameters and fault slip rate, we determined a recurrence interval of 2.7–3.4 kyr for significant surface-rupturing events on this fault. The elapsed time since the last earthquake closely approaches this interval, suggesting a potential seismic risk for the Huangxianggou Fault. Our results emphasizes the importance of high-resolution topographic data in paleoseismic investigations, enabling the identification of numerous offset landforms and precise displacement measurements across faults. Paleoearthquake counts derived from horizontal and vertical displacement analyses were found to be consistent, highlighting the significance of vertical displacements in quantifying paleoearthquakes for strike-slip faults with a thrust component.

Crustal response to water loads and expansion of triggered seismicity around the Xiluodu Reservoir, Southwest China

<p>The transition to low-carbon energy generation requires a diverse portfolio of energy sources. Large hydropower stations play a crucial role in providing eco-friendly energy but can lead to crustal deformation and seismic activity due to reservoir impoundment and discharge. The mechanism behind how impoundment-induced deformation influences reservoir-triggered seismicity remains unclear. We investigate this at the world��s 4<sup>th</sup> largest hydropower station in Xiluodu, China, using interdisciplinary analyses of relocated earthquakes, geodetic data, and numerical simulations. Geodetic observations confirm both a linear elastic response to hydrologic loading and the transition towards a relaxed and flexural response. Notably, approximately 81% of the earthquakes since impoundment occurred within ~15 km of the subsidence center. These events temporally relate to rapid hydrologic loading/unloading periods, with their spatiotemporal outward migration potentially caused by viscous relaxation of load stresses in the lower crust and upper mantle. The reservoir-induced flexural deformation and subsequent viscous relaxation may control the distribution and expansion of triggered seismicity. This research highlights the urgent need to enhance geohazard monitoring efforts around the subsidence center and emphasizes the vital importance of carefully considering this factor during the construction of large reservoirs to mitigate potential seismic risks.</p>

Insight into the 1 December 2016 Mw 6.2 Juliaca Earthquake, Southern Peru, by InSAR Observations and Field Investigation

On 1 December 2016, an Mw 6.2 earthquake characterized by normal faulting occurred in the highlands of the central Andes in southern Peru, marking the region’s largest shallow event. The occurrence of the earthquake provides a significant chance to gain insight into the regional tectonic deformation and the seismogenic mechanism of the shallow normal-faulting earthquake, as well as the regional potential seismic risk. Here, we first utilize Sentinel-1A interferometric synthetic aperture radar (InSAR) data to extract the coseismic and postseismic deformation associated with this earthquake and then determine the detailed coseismic slip and postseismic afterslip distribution of this event. Coseismic modeling results indicate that the coseismic rupture is mainly characterized by normal faulting with some dextral strike-slip components. Most coseismic slip is confined to a depth range of 2–12 km, indicating an obvious slip deficit area in the shallow fault part. Further postseismic modeling reveals that the majority of afterslip is concentrated at depths of 0 to 5.4 km. The relatively shallow postseismic afterslip makes up for the coseismic slip deficit area to some extent. Through a joint analysis of the inversions, seismic data, and regional geology and geomorphology, we infer that the occurrence of this 2016 normal-faulting event is a result of regional gravitational collapse. In addition, we investigate the relationship between the 2016 earthquake and great historical earthquakes near the subduction zone of the central Andes and find that the 2016 event is likely promoted in advance by these events through our calculations of the coseismic and postseismic Coulomb stress changes. Finally, we should pay more attention to the nearby Falla Huaytacucho-Condoroma fault and the western segment of the Vilcanota Fault because of their relatively high stress loading.

Cyclic behavior of channel-encased braces incorporating round HSS

Bracings made with cold-formed round hollow structural shapes (HSS) are commonly utilized in ductile concentrically braced frames (CBFs) in seismic regions for their efficiency in terms of high load-bearing capacity and ease of construction. Bracings are expected to sustain a ductility demand that ranges between 10 and 20 without fracture when ductile CBFs subject to severe earthquake ground motions. However, the experimental findings accentuate that ductile braces, even those with round HSS that possess impractically small diameter-to-wall thickness ratios (D/t), are prone to premature fracture. Thus, developing a simple and cost-effective performance-enhancing system for existing conventional CBFs incorporating round HSS could be imperative to mitigate the potential seismic risk. For this purpose, an existing round HSS is encased in two channels to form a buckling-controlling mechanism that is expected to improve the seismic hysteretic behavior, consequently, the energy dissipation capacity of ductile braces. Experimental and parametric numerical studies have been conducted to comprehend the level of improvement in the cyclic behavior and the impact of geometric parameters (i.e., slenderness and D/t ratios). The overarching results indicate that channel-encased bracing improves the seismic hysteretic behavior, yielding a stable and symmetric cyclic response. In addition, the results suggest that the optimal design parameters, including gap amplitude and encasing thickness, play a critical role in achieving desired ductility level.

A multiscale analysis of adjacent fault dislocation mechanism induced by tunnel excavation based on continuous-discrete coupling method

Tunnelling usually causes adjacent fault dislocation that further induces serious disasters and threats, such as earthquakes, while its physical mechanism is still not clear. In this paper, we establish a multiscale numerical model of tunnel excavation adjacent to a fault by a coupled continuous-discrete method. The discrete element method (DEM) is employed to simulate the meso-mechanical behaviours of the fault fracture zone, and the finite difference method (FDM) is used to describe the macrodynamic characteristics of the hanging wall and footwall. A synthetic rock mass (SRM) model is developed to build the fractured rock to present the discontinuity and heterogeneity of the fault zone. The macro and meso mechanism of fault dislocation induced by tunnel excavation are analyzed, respectively. Results show that the fault experiences a different local dislocation form changing from upward movement to downward movement along the fault surface at the macro-scale. The weak transfer ability of the fault for deformation between the hanging wall and footwall, the reduced macro shear strength of the fault during the unloading process, and the meso joint slip and intact rock failure in the fault fracture zone are three main reasons for fault dislocation. The random distribution characteristics of the joints have remarkable influence on fault deformation. The fault slips more easily when the joint dip is close to the fault orientation. A higher joint density and a larger joint length provide a favourable environment to accumulate more connected joint surface, resulting in a larger slip displacement. Sensitivity analyses are conducted on several critical parameters including tunnel location, fault thickness, and stress condition, with the purpose of evaluating the safety of a potential tunnel site and predicting the potential seismic risks when tunnelling adjacent to a fault.

INNOVATIVE USE OF SHAPE MEMORY ALLOYS AS REINFORCEMENTS FOR CONCRETE BEAM-COLUMN JOINTS: AN OVERVIEW

Shape memory alloys have two unique properties of shape memory effect (SME) and superelasticity (SE) that are the ability for large inelastic deformations recovery after heating (SME) and stress removal (SE). In recent years, structural engineers used these materials in the field of civil engineering’s, such as the applications of SMAs in the repair, retrofitting, and rehabilitation of concrete structures, dampers, vibration isolation systems, vibration control, and prestressing members, etc. To overcome and reduce the potential seismic risk of structures, understanding the characteristics of SMAs materials under different loading conditions is one of the critical steps. Despite the various types of researches carried out on the SMAs' structural applications, there was a need for a review of the progress of the current method in structures. To address it, a brief review of the applications of SMAs in Reinforced Concrete (RC) beam-column joints was conducted.

The new seismic hazard model ESHM20 of Europe: Investigating the implications to the seismic design and risk assessment of major industrial facilities across Europe

AbstractThe seismic performance and safety of major European industrial facilities have a global interest for the whole of Europe and its citizens. However, the seismic design of these facilities is based on national, sometimes outdated seismic hazard analyses. The results of the commonly developed, fully harmonized newly released European Seismic Hazard Model ESHM20 provide a pertinent reference for seismic hazard at European scale and have been officially adopted as an “acceptable representation of the seismic hazard in Europe” in the ongoing revision of Eurocode 8. This study presents a large-scale investigation of the impact of the potential adoption of ESHM20 on the design of new industrial facilities as well as on the potential seismic risk of existing facilities at European level with respect to the current seismic codes. The horizontal elastic response spectra using ESHM20 in combination with the revised Eurocode 8 for selected industrial sites are compared with the respective response spectra of the national regulations for return periods of 475, 2500 and 5000 years. In addition, a single containment LNG tank is analysed for an industrial site in Germany using the design approach for liquid filled tanks according to the revised Eurocode 8. Furthermore, a deterministic and probabilistic seismic risk assessment of a vessel installed in a five-storey frame is performed for industrial sites in Greece and Germany. The examples show that a consistent procedure all over Europe would be desirable and a benefit for engineers in terms of comparability and achievement of the same safety targets. Based on the conducted illustrative studies, the consequences of a potential adoption of the revised Eurocode 8 and ESHM20 hazard maps are discussed and summarized with respect to the standard harmonisation process in Europe.

Machine learning for the prediction of evaluation of existing reinforced concrete structures performance against earthquakes

Earthquakes are challenging disasters that pose a huge threat to the urbanized world. In particular, the majority of the existing reinforced concrete (RC) building stock in developing countries such as Turkey is under huge seismic risk. These structures are at risk of partial or complete collapse under the effects of strong ground motions, due to some deficiencies in the structures. Therefore, seismic evaluation of existing buildings with a predominantly RC structural system is vital to reduce the potential seismic risk. In this study, machine learning (ML) techniques have been used for the prediction of the existing RC buildings’ performance against earthquake. The k-fold cross-validation has been employed to check the accuracy of the ML techniques. Random Forest (RF) provided the highest performance among the other ML techniques used. Sensitivity analysis have also been performed to determine the most significant factors in the prediction of the performance of the buildings. The results show that the building age, concrete compression strength, maximum column stirrup distance, steel yield strength, and the existence of corrosion have a high impact on the assessment of building performance.

Structural height, amplification and damages during the superficial earthquakes at Casamicciola, Ischia Island (2017), and Santa Venerina, Catania (2018), Italy

A rapid method to assess the potential seismic risk of a building due to its height or, equivalently, to the number of stories above ground is described. It was applied, despite already existing studies in this regard, to two earthquakes, those of Casamicciola, Ischia Island, on 21 August 2017 and Santa Venerina, Catania, on 26 December 2018; although characterized by a moderate magnitude (Mw 4.0 and Mw 4.8) and short duration, they produced victims and considerable damage. Accelerometric recordings of seismic stations in the areas of the two earthquakes were acquired and the pseudoacceleration spectra and dynamic amplification factors of the ground were obtained from them. By inversion of the algebraic relation between a building’s elastic period of vibration T0 and its height H, the so-called ‘critical’ heights (and corresponding number of stories above ground) to which corresponded the ‘greatest’ dynamic amplifications were identified: buildings with a number of stories above ground equal to the ‘critical’ values were considered potentially more exposed to seismic risk. For verification of the method, ca. 200 buildings in the areas of the earthquakes were surveyed and the resulting damages were related to the number of stories above ground. The results showed that, even though the two earthquakes were of moderate magnitude and short duration, the amplifications of the ground (at Casamicciola equal to 3 for reinforced concrete buildings and 2.4 for masonry buildings; at Santa Venerina 2 and 1.7 respectively) produced appreciable accelerations in buildings with two stories above ground, which turned out to be the ones with the greatest damage. The principle underlying the method consists of rapid numerical calculations performed on the pseudoacceleration spectra of the ground. Therefore, in areas with historical seismicity where accelerometric recordings are available, it is possible to identify buildings with potential exposure to seismic risk based on the number of ‘critical’ stories above ground and to subject them to more careful controls.

Detailed Imaging of a Seismogenic Fault That Potentially Induced the Two 2019 Weiyuan Moderate Earthquakes in the Sichuan Basin, China

Abstract Induced earthquakes are becoming a significant issue. Several destructive induced earthquakes (Ms ≥5.0) have occurred in shale gas fields located at the southwestern Sichuan basin, China, in the recent years. Specifically, two moderate earthquakes with magnitudes of Ms 5.4 (occurred on 8 September 2019) and 5.2 (occurred on 18 December 2019) exceeded the largest earthquake ever recorded in the Weiyuan. It remains unclear which seismogenic faults were responsible for the two moderate events due to insufficient knowledge of the subsurface structure and contradictory hypocenter depths obtained from different seismological methods. In this study, mainshock locations, focal mechanisms, and precise relocations of microseismicity were used to map the 3D geometry of the seismogenic fault. The result shows that the two moderate earthquakes occurred on the same fault. High-resolution seismic reflection profiles indicate several preexisting faults at various depths and a potential seismogenic fault. No large-scale faults are identified in the sedimentary cover above the Cambrian at the shallow centroid depth of these earthquakes. However, the seismic reflectors show phase discontinuous feature, indicating the existence of preexisting faults in the basement. A preexisting fault in the basement is consistent with a seismogenic fault that may have induced the two moderate earthquakes. Our study suggests that poroelastic stress propagation is likely responsible for the basement fault reactivation. The rupture on a stressed basement fault was triggered and produced two moderate earthquakes in a short period during hydraulic fracturing. The previous strategy of avoiding direct injection of fluids into preexisting faults to reduce seismic risk in operation region is not enough to avoid the possibility of the coupled poroelastic stress triggering deep fault rupture. We need to reevaluate the potential seismic risk of shale gas development in Weiyuan, the southern Sichuan basin shale gas field considering the preexisting faults in sedimentary and in basement and the effect of the fully coupled poroelastic stress field.

Sharp Changes of Crustal Seismic Anisotropy Across the Central Tanlu Fault Zone in East China

AbstractBoth seismic and geodetic data suggested that the ∼120‐km long Weifang segment of the Tanlu fault zone, a large‐scale active strike‐slip system at east China, is a seismic gap with no obvious along‐strike shear motion at surface. Measuring crustal deformation around the segment is crucial to constrain stress/strain buildup and potential seismic risk at the fault. We measured crustal and upper mantle seismic anisotropy using P‐to‐S converted waves at the Moho (Pms) and core‐mantle boundary (SKS) recorded by broadband arrays across the Weifang fault segment. The measured crustal anisotropy inside the fault zone shows a fast direction of ∼NNE, parallel to the fault orientation. Right east to the fault zone, the fast axis rotates by almost 90° to ESE. The crustal anisotropy within the fault zone could be caused by aligned microcracks and foliated minerals due to long‐lasting shear motion inside the fault zone.

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.