Moderate-strong Earthquakes Research Articles

Seismic design of buildings: Where to next?

This paper critically reviews the current building seismic design approach based on the observed performance of modern building stock in recent earthquakes, highlights the inability of the current design approach in controlling seismic damage and losses, and proposes a conceptual framework for next generation seismic design codes that is likely to meet public expectations. In addition to ensuring life-safety in rare earthquakes, the proposed loss-optimization seismic design approach also aims to ensure quick functional recovery and minimum loss (i.e. repair, downtime, and injury/fatality) in moderate-strong earthquakes by limiting damage to building’s structural and non-structural components. Based on comparison of performances of building stock in some recent major earthquakes in different countries, the paper presents some simple strategies to render buildings more resilient and suffer significantly less seismic damage (and consequentially incur less loss). Finally, the paper scrutinizes the efficacy of some commonly used low-damage technologies in minimizing building seismic losses.

Research on thermal infrared anomaly characteristics of moderate strong earthquakes in northeast China

In this article, the daily brightness temperature data from January 2006 to May 2020 of China’s geostationary meteorological satellite FY-2E/G were used to identify the brightness temperature differences before deep and shallow earthquakes in the study area using wavelet transform and the relative wavelet power spectrum (RWPS) methods. The objective was to explore the characteristics of thermal infrared (TIR) radiation anomaly changes before deep and shallow earthquakes in Northeast China by carrying out anomaly extraction and data analysis. The research has shown that five significant earthquakes experienced TIR radiation anomalies in the vicinity of the epicenter approximately 1–2 months before the event. The amplitude of the anomaly ranged from seven to twenty times higher than average, and the anomaly lasted about 3 months. The infrared radiation anomaly characteristics before the earthquake were especially significant in the case of two earthquakes in the Songyuan area. From the research, it was concluded that the TIR radiation anomaly could act as a short-term precursor for earthquake prediction. The method employed in this study would provide great support for predicting deep and shallow earthquakes in Northeast China using satellite thermal infrared technology.

The apparent focal depth, emergence angle, and take-off angle of seismic wave measured by YRY-4-type borehole strainmeter as one kind of strain seismograph

Introduction: In theory, the observation objects and principles of strain seismograph and traditional pendulum seismograph are different, and the characteristics of observed signals should also be dissimilar. The observation results of pendulum seismograph show that seismic waves in inhomogeneous media will undergo refraction, reflection, and attenuation. Then, what signal characteristics can be detected by strain seismograph is great significance for understanding and explaining the observation results.Methods: Using YRY-4 type four-gauge borehole strainmeter as one kind of strain seismograph to detect the strain tensor change of the plane seismic wave emitted from the surface, a five-site strain seismograph observation network was built in Shanxi Province, with continuous observation for 2 years at a sampling rate of 100 Hz. In this paper, two local events occurring in the area covered by the strain seismograph observation network are taken as examples. We systematically studied the characteristics of seismic wave signals recorded by strain seismographs at five sites, inverted for the focal depth of the two local earthquakes and the relationship between the wave velocity and the wave velocity gradient of the focal depth, and calculated the apparent focal depth, the emergence angle and the take-off angle of seismic waves.Results: These results show stable uniqueness and apparent regularity, especially since the inverted focal depths are basically consistent with the seismic solutions based on those traditional pendulum seismographs. The observations from this study show that the strain seismograph can be used as an effective supplement to the pendulum seismograph.Discussion: In the future, we will continue to study the rupture process and focal mechanism of moderate-strong earthquakes and teleseismic earthquakes by combining two kinds of observations.

High resolution upper crustal velocity and seismogenic structure of the Huoshan “seismic window” in the Dabie orogenic belt

Huoshan “seismic window” is located in the northern margin of the Dabie Orogen belt, the contact zone between North China and the Yangtze plate, where the seismic activity is mainly concentrated in this area. Small earthquake swarms in this region often appear before significant moderate-strong earthquakes in East China. To reveal the fine structures of several faults and discuss their correlation with the seismic activity, a seismic array composed of 136 sets of short period seismometers was deployed in the Huoshan region and its surrounding areas. Ambient noise data were recorded for 1 month, and a 3-D velocity structure model of the upper crust was constructed. The results show that with the Meishan-Longhekou and Qingshan-Xiaotian faults as the boundary, the Dabie Mountain, Hefei Basin, North Dabie and North Huaiyang show exhibit obvious high and low velocity variation characteristics. The shallow crust along the NW-trending, normal Qingshan-Xiaotian fault, presents a high velocity zonal distribution, which is related to the large number of magmatic and metamorphic rocks exposed under the strong metamorphic power in this region. The NE-trending Tudiling-Luoerling fault comprised three groups of parallel and nearly vertical en echelon secondary faults in the upper crust, which control most of the seismic activities. A relatively low velocity anomaly is observed in the seismic concentrated occurrence layer near the intersection of the fault. It suggests that this area inherits the property of the low velocity detachment zone of the middle crust in the wing of the Dabie Mountain dome structure, and a relatively broken weak structural zone form near the intersection of the fault, which leads to the release of small strain accumulation, thus enriching small earthquake activities. The focal depth of earthquakes above ML3 mainly distribute along the Tudiling-Luoerling fault plane, which is indicated this fault is the main seismogenic fault of greater seismicity in Huoshan “seismic window”. This study provides an important model basis for reliable earthquake location, focal mechanism and the determination of possible earthquake risk sites, and provides a reference for the further study of small earthquake activity mechanism of other “seismic windows” in China.

Temporal distribution characteristics of earthquakes in Taiwan, China

The characteristics of seismic temporal distribution represent an important basis for earthquake prediction and seismic hazard analysis. In this paper, based on the seismic catalogs in Taiwan, and using Poisson (exponential distribution), Gamma, Lognormal, Weibull, and Brownian passage time distributions as target models, we adopt the maximum likelihood method for estimating model parameters. The optimal model for describing the temporal distribution of earthquakes in Taiwan is determined according to the Akaike Information Criterion (AIC), Bayesian Information Criterion (BIC), K-S test, Chi-square test, and coefficient of determination R2 results. The results show that for moderate-strong earthquakes events (MW < 7.0), the Gamma distribution model can well describe the temporal distribution characteristics of earthquakes, while large earthquakes (MW ≥ 7.0) can be described entirely by exponential distribution. In addition, the temporal correlation between earthquakes is also examined through diffusion entropy analysis. The results show that seismic activity features temporal correlation, and earthquakes with relatively small magnitude (MW < 7) are affected by larger events (MW ≥ 7.0), thus suggesting long-term memory in time. In this study, the probability of the occurrence of a major earthquake in Taiwan is also calculated. The results show that the probability of an MW ≥ 7.0 earthquake in Taiwan in the next 10 years reaches 91.3%. The results may be used to inform the selection of seismic time distribution models and the calculation of seismic activity parameters in earthquake prediction and seismic hazard calculation, and hold scientific significance for understanding the mechanism of earthquake genesis.

Numerical simulation of fault deformation and seismic activity in the southern Qinghai–Tibet Plateau

The moderate-strong (M ≥ 5, since 1976; or M ≥ 6.5, overall) earthquakes of the north to south trending (NS-trending) faults and their vicinity in the southern Qinghai–Tibet Plateau exhibit prominent spatial concentration distribution characteristics. However, research on the southern Tibet faults is limited. Hence, this study used a two-dimensional viscoelastic finite element model to simulate crustal movement in southern Tibet based on 1991–2015 GPS velocity data. The current deformation field, tectonic stress field, fault slip, and stress accumulation rates distribution were obtained to analyze the relationship between fault activity and earthquake distribution. The results revealed that the simultaneous effected by of the NE-trending compression and uneven EW-trending tension on the study area. Crustal deformation exhibited simultaneous NS-trending compression and EW-trending stretching. The EW- and NWW-trending faults and the NS-trending faults differed in their mechanical properties and movement modes. The NS faults were primarily subjected to extensional stress with normal motion. The remarkable heterogeneity of the fault segments influenced the distribution of moderate-strong earthquakes and types of earthquake ruptures. The concentrated distribution of moderate-strong earthquakes on the NS-trending normal fault and its vicinity depended largely on the high slip rate, strong tensile stress, and geometric strike of the fault segment. This study aids in understanding the heterogeneity in normal fault activity in southern Tibet and is the basis for seismic hazard assessment.

Hydrochemical Characteristics of Earthquake-Related Thermal Springs along the Weixi–Qiaohou Fault, Southeast Tibet Plateau

The Weixi–Qiaohou Fault (WQF) is considered an important zone of the western boundary of the Sichuan–Yunnan block, and its seismicity has attracted much attention after a series of moderate–strong earthquakes, especially the Yangbi Ms6.4 earthquake that occurred on 21 May 2021. In the present research, we investigate major and trace elements, as well as hydrogen and oxygen isotopes, of 10 hot springs sites located along the WQF, which are recharged by infiltrated precipitation from 1.9 to 3.1 km. The hydrochemical types of most analyzed geothermal waters are HCO3SO4-Na, SO4Cl-NaCa, and SO4-Ca, proving that they are composed of immature water and thus are characterized by weak water–rock reactions. The heat storage temperature range was from 44.1 °C to 101.1 °C; the circulation depth was estimated to range between 1.4 and 4.3 km. The results of annual data analysis showed that Na+, Cl−, and SO42− in hot springs decreased by 11.20% to 23.80% north of the Yangbi Ms5.1 earthquake, which occurred on 27 March 2017, but increased by 5.0% to 28.45% to the south; this might be correlated with the difference in seismicity within the fault zone. The results of continuous measurements of NJ (H1) and EYXX (H2) showed irregular variation anomalies 20 days before the Yangbi Ms6.4 earthquake. In addition, Cl− concentration is more sensitive to near-field seismicity with respect to Na+ and SO42−. We finally obtained a conceptual model on the origin of groundwater and the hydrogeochemical cycling process in the WQF. The results suggest that anomalies in the water chemistry of hot spring water can be used as a valid indicator of earthquake precursors.

Analysis on the Characteristics of Crustal Structure and Seismotectonic Environment in Zigui Basin, Three Gorges

The Zigui Basin in the Three Gorges area is a syncline running in the north-south axial direction; the sediments in the basin are mainly late Triassic-late Jurassic sandy and argillaceous rocks. Since the Three Gorges Project began undergoing impoundment in May 2003, nearly 20,000 mini-earthquakes have occurred in the Zigui–Badong region, including five earthquakes with magnitudes greater than Ms 5.0. Herein, a 3D gravity inversion method was introduced to investigate the density structure of the Zigui Basin and its adjacent areas. A comprehensive analysis of the geological structure of the area was carried out, based on focal mechanism solutions of six moderate–strong earthquakes in the area. The Zigui Basin is a low–density area from the periphery, and the sediment in the east is thicker but less dense than in the west. The shallow part of the Zigui Basin is a weak bottom layer prone to slippage, and the deep part (5–10 km) could comprise lithological strata such as limestone, sandstone, and shale, which easily undergo dissolution by leaking reservoir water. Under the action of external forces such as long-term infiltration and unloading of reservoir water, fissures will expand and squeeze then earthquakes are likely induced in the deep strata. Furthermore, new buried faults in the western and southeastern edges of the core area of the Zigui Basin could also trigger an earthquake under long–term pressurization and reservoir water penetration.

Research on application of focal mechanism and site conditions in judgment of Hebei earthquake influence field

The determination of seismic influence field in post-earthquake work, a quickly gived reasonable map of seismic intensity distribution, was an important basis for emergency rescue after the earthquake and was important for the government to understand the disaster situation, deploy work and estimate the disaster loss. In this paper, the isoseismal maps of moderate strong earthquakes in Hebei Province were collected and sorted out, it was compared with the theoretical isotherm map generated by the regional earthquake intensity attenuation relationship based on the focal mechanism solution. The results show that, with the increase of magnitude, the similarity was higher between the theoretical isoseismal map and the actual isoseismal map in the high intensity area （≥Ⅶ）, the theoretical isoseismal map was calculated by the attenuation relationship of seismic intensity with focal mechanism solution. In addition, according to the spatial variation of aftershock frequency within 24 hours after the earthquake, the theoretical isoseismal line in the polar region is modified, which is more consistent with the actual isoseismal line. That is to say, the theoretical calculated intensity is closer to the actual investigation intensity value. Finally, the grid of Hebei area was divided, and the bedrock PGA of the earthquake case on each grid center point was calculated according to the attenuation relationship of ground motion. Then, the site category attributes were extracted, considered site amplification factor, and the conversion of bedrock PGA to surface PGA was completed. The surface PGA was converted into intensity and compared with the actual earthquake isoseismal map. The results show that the similarity between the seismic influence field calculated by considering the site amplification effect and the actual isoseismal line was very high in the high intensity area, and the similarity is higher than the intensity attenuation relation method based on the focal mechanism solution.

Crustal P-wave velocity structure and earthquake distribution in the Jiaodong Peninsula, China

The Jiaodong Peninsula of eastern China is densely populated and prone to frequent moderate-strong earthquakes that are mostly distributed along a group of northeastern oriented Mesozoic-Cenozoic faults. An improved understanding of the seismic velocity structure in the area is of great significance for the roles that the faults played in the formation and evolution of the various tectonic features and for the assessment of future earthquake risks. By utilizing earthquake records of the Shandong Provincial Seismic Network for the period from January 2013 to January 2020, this study simultaneously re-locates earthquakes and determines the three-dimensional P-wave velocity structure beneath the Jiaodong Peninsula using regional P-wave travel times by applying the double-difference tomography method. After the relocation, the travel time residuals are reduced by an order of magnitude, and the epicenters are more concentrated and demonstrate a closer spatial relationship with known active faults. The resulting P-wave velocity structure at different horizon depths indicates lateral heterogeneities in the study area. Clear differences in the characteristics of velocity anomalies are observed between the Jiaobei Uplift, Jiaolai Basin and Sulu ultra-high pressure metamorphic belt. The anomalies are mostly NE oriented, which is consistent with the strike of the regional faults and may suggest structural control of the faults to the geological configurations. Earthquakes generally occurred along the edges of high or low velocity regions, and areas accommodating the intersections of the Penglai-Weihai, Penglai-Qixia and Mouping-Jimo fault zones have the greatest potential for future damaging earthquakes in the area.

Lower Portion Rupture of a Thrust Fault during the 2017 Mw 6.3 Jinghe Earthquake: Implications to Seismic Hazards in the Tian Shan Region

AbstractThe 2017 Mw 6.3 Jinghe earthquake represents one of the few large earthquakes that are well recorded by seismic instruments and Interferometric Synthetic Aperture Radar (InSAR) observations in the seismically active Tian Shan region. In this study, we use the rupture fault solution (dip, dip direction, and slip sense) from seismologic and InSAR results, along with analysis of our collected surface mapping data, to determine the subsurface fault-plane geometry of the seismogenic Jinghenan fault. This geometric model, integrated with the coseismic slip distribution from seismologic and InSAR data, reveals that: (1) the Jinghenan fault extends downward from the land surface at a dip of ∼46° S (upper ramp), then bends to ∼42° S (lower ramp) at the depth of 9–13 km; (2) the coseismic rupture is confined within the Jinghenan lower ramp, and its upper limitation is approximately coincident with the fault-bend location. This coseismic rupture pattern and seismic behavior can be broadened to other active thrust faults within the Tian Shan, suggesting that, during moderate-strong earthquakes, such faults may only rupture partially in the down-dip extension, and the unruptured fault portion remains to pose high-seismic risk in the future.

Relocation, Focal Mechanisms and Stress Field Characteristics of Earthquake Swarms in the Songyuan Area of Jilin Province, China

Two earthquake swarms, the Qianguo swarm and Ningjiang swarm, have been observed since 2013 in the Songyuan area, Jilin Province, China. Using the seismic data of broadband permanent and temporal stations that recorded a larger number of earthquakes in the two swarms, we analyze the distribution of aftershocks and the focal mechanisms of these earthquakes and investigate the stress field and faulting properties of the Songyuan area. The relocated hypocenters of the Qianguo earthquakes are distributed along a NNW direction at focal depths of 4–13 km, while the dominant distribution of relocated Ningjiang earthquakes is along a NE direction at depths of 8–16 km. The focal mechanism solutions of 36 earthquakes with ML ≥ 3.6 demonstrate a combined strike-slip and thrust faulting mechanism with centroid depth concentrated at 3–7 km for the Qianguo swarm and a strike-slip mechanism with centroid depth at 5–7 km for the Ningjiang swarm. The full moment tensors of seven moderate–strong earthquakes show that these earthquakes contain a high percentage of non-double-couple components. The regional stress field is inverted using the focal mechanism parameters of the 36 earthquakes. In the Qianguo area, the horizontal maximum principal compressive stress ( $$\sigma_{1}$$ ) is in the E–W direction with a dip angle of 14.1°. In the Ningjiang area, the $$\sigma_{1}$$ is in the ENE–WSW direction with a dip angle of 9.2°. The $$\sigma_{1}$$ directions of the two areas are slightly different, but both approximately along an E–W direction. The comprehensive results of this study show that the Qianguo swarm is likely caused by the movement of a buried fault in the NNW direction oblique to the Changling–Dashanzi fault, whereas the Fuyu–Zhaodong fault in the NE direction is responsible for the Ningjiang swarm. Both the Qianguo and Ningjiang swarms are probably closely related to the thrusting effect of the subduction of the Pacific Plate into the Northeast Asian continental margin and the complex geological conditions in the Songyuan area.

Ground Motion Model for Spectral Displacement of Intermediate-Depth Earthquakes Generated by Vrancea Seismic Source

In support of displacement-based design (DBD), an attenuation model for the prediction of the spectral displacement of intermediate-depth earthquakes generated by Vrancea source is proposed. DBD is an alternative to force-based design, the main benefits being a better and confident description of the structural response and the removal of some of the inconsistencies of force-based code design. The basic input for DBD is the displacement response spectrum (DRS). Vrancea intermediate-depth source is responsible for the seismic hazard for most of the Romanian territory. The source produces, on average, two or three earthquakes with MW >7.0 per century, the prominent characteristics being the large displacement demand and large predominant periods (≈ 1.5 s) for sites located in the Romanian Plain. The model is applicable for sites positioned in front of the South-Eastern Carpathian Arc on type B and C soils. Equations predicting spectral displacement were developed by two-stage regression analysis, using a database containing national analog records of moderate-strong earthquakes and the available digital records, of smaller earthquakes. The model was extended for periods up to 8.0 s using national digital strong motion records and Japanese high-quality digital records of earthquakes triggered by a similar seismo-tectonic environment. The model successfully reproduced observed data, for both type B and C soils and the goodness of fit was tested using methods available in literature.

Identification of Precursory Anomalies before Moderate-strong Earthquakes in Junction of Shanxi-Hebei-Inner Mongolia Area

In this paper, we take the Junction of Shanxi-Hebei-Inner Mongolia area as study region using earthquake corresponding relevancy spectrum method (ECRS method) to identify comprehensive precursory anomalies before moderate-strong earthquake. On base of single-parameter relevancy spectrum database with target earthquake magnitude as Ms4.7 and initial earthquake magnitude as Ms1, we carry on multi-parameter analysis and find that result with time interval of 9 months and anomaly threshold with 0.40 times standard deviation has better prediction efficiency. Its anomaly corresponding rate and earthquake corresponding rate are 6/10 and 9/9 respectively.

A Framework to Assess the Seismic Resilience of Urban Hospitals

The phenomenon of hospital functional interruption has been widely observed in the historical moderate‐strong earthquakes, indicating that hospital functionality cannot be well considered in the current seismic design methods. The concept of seismic resilience pays enough attention to postearthquake functionality of buildings, and it is particularly significant for the urban hospitals which play critical role in the urban postearthquake rescue and recovery. This study proposes a framework to assess the seismic resilience of urban hospitals, by incorporating the fault tree analysis (FTA) to consider the interdependency between the damage of nonstructural components and the functionality of medical equipment, as well as the effect of external supplies on the functionality of hospital. The proposed framework is then applied to a case‐study hospital, and the results indicate that this hospital needs 1.1 days to resume emergency functionality under REDi repair strategy after design basis earthquake (DBE), while it needs 28.8 days to resume emergency functionality under REDi repair strategy after maximum considered earthquake (MCE). It is found that the seismic resilience of this hospital after MCE cannot meet the community requirements on the recovery time, and necessary measures are needed to improve the seismic resilience. The proposed framework provides the quantitative results of seismic resilience assessment in the preearthquake environment and can further support emergency response planning and seismic retrofits strategies.

Locking Status and Earthquake Potential Hazard along the Middle-South Xianshuihe Fault

By combining the seismogenic environment, seismic recurrence periods of strong historical earthquakes, precise locations of small–moderate earthquakes, and Coulomb stress changes of moderate–strong earthquakes, we analyze the potential locking status of a seismically quiet segment of Xianshuihe fault between Daofu County and Kangding City (SDK). The interseismic surface velocities between 1999 and 2017 are obtained from updated global positioning system (GPS) observations in this region. After removing the post-seismic relaxation effect caused by the 2008 Mw 7.9 Wenchuan earthquake that occurred around the fault segment, the observed velocities reveal a pronounced symmetric slip pattern along the SDK trace. The far field slip rate is 7.8 ± 0.4 mm/a, and the fault SDK is confirmed to be in an interseismic silent phase. The optimal locking depth is estimated at 7 km, which is perfectly distributed on the upper edge of the relocated hypocenters. A moment deficit analysis shows cumulative seismic moment between 1955 and 2018, corresponding to an Mw 6.6 event. Finally, based on a viscoelastic deformation model, we find that moderate–strong earthquakes in the surrounding area increase the Coulomb stress level by up to 2 bars on the SDK, significantly enhancing the future seismic potential.

Activity of the Lenglongling fault system and seismotectonics of the 2016 M S6.4 Menyuan earthquake

The M S6.4 Menyuan earthquake occurred on the northern side of the Lenglongling fault (LLLF) in the mid-western of the Qilian-Haiyuan fault zone on January 21, 2016. The earthquake epicenter was distant from the Minle-Damaying and Huangcheng-Shuangta faults, eastern of the Northern Qilian Shan fault zone. A near northwest-striking rupture plane intersects the two faults at a certain angle. The focal mechanism solution shows that this was a thrust-type earthquake, slightly different from the strike-slip movement with a thrust component of the LLLF. Field geological mapping, tectonic geomorphology analysis, trench excavation and 14C dating reveal that (1) the LLLF has been obviously active since the Holocene, and may behave with characteristic slip behavior and produce M W7.3–7.5 earthquakes; (2) the LLLF appears as a flower structure in terms of structure style, and dips NNE at a steep angle; and (3) the most recent earthquake event occurred after 1815–1065 a BP. An associated fault, the Northern Lenglongling fault (NLLLF), is located at the northwestern end of the LLLF. Consequently, the NLLLF was continually subject to tectonic pushing effects from the left-lateral shear at the end of the LLLF, and, accordingly, it bent and rotated outward tectonically. Subsequently, the fault deviated from the dominant rupture azimuth and activity weakened. In the late Quaternary, it behaved as a thrust fault with no obvious deformation at the surface. This is indicated by the arc shape, with a micro-protrusion northeastward, and no geologic or geomorphic signs of surface rupturing since the late Quaternary. However, such faults could still rupture at depth, producing moderate-strong earthquakes. The geometric and kinematic properties of the NLLLF are in good agreement with the occurrence and kinematic properties of nodal plane 2, and with the distribution characteristics of the aftershocks and seismic intensity. Therefore, the NLLLF is a more suitable seismogenic structure for the M S 6.4 Menyuan earthquake. In addition, the thrust movement of the NLLLF accommodates subsequent movement of the LLLF. During the historical evolution of the NLLLF, the LLLF and the NLLLF have affected the local topography through tectonic uplift.

Fault activity characteristics in the northern margin of the Tibetan Plateau before the Menyuan Ms6.4 earthquake

Fault deformation characteristics in the northern margin of the Tibetan Plateau before the Menyuan Ms6.4 earthquake are investigated through time-series and structural geological analysis based on cross-fault observation data from the Qilian Mountain–Haiyuan Fault belt and the West Qinling Fault belt. The results indicate: 1) Group short-term abnormal variations appeared in the Qilian Mountain–Haiyuan Fault belt and the West Qinling Fault belt before the Menyuan Ms6.4 earthquake. 2) More medium and short-term anomalies appear in the middle-eastern segment of the Qilian Mountain Fault belt and the West Qinling Fault belt, suggesting that the faults' activities are strong in these areas. The faults' activities in the middle-eastern segment of the Qilian Fault belt result from extensional stress, as before the earthquake, whereas those in the West Qinling Fault belt are mainly compressional. 3) In recent years, moderate-strong earthquakes occurred in both the Kunlun Mountain and the Qilian Mountain Fault belts, and some energy was released. It is possible that the seismicity moved eastward under this regime. Therefore, we should pay attention to the West Qinling Mountain area where an Ms6–7 earthquake could occur in future.

Thermal infrared anomalies associated with multi-year earthquakes in the Tibet region based on China’s FY-2E satellite data

Using the brightness temperature (TBB) and outgoing long-wave radiation (OLR) data from the FY-2E meteorological satellite, the thermal infrared anomalous change of 20 moderate–strong earthquakes in Tibet from January 12, 2010, to April 30, 2015, are studied. The study calculates the wavelet spectrum change of TBB and OLR based on the Morlet wave and discusses the regulation and characteristics of the anomalous change before and after the earthquakes. The results show that TBB anomalies appeared in 17 of the 20 MS⩾5.0 earthquakes. Anomalies of long-wave radiation occurred in 16 earthquakes. Moreover, their durations, locations and amplitudes are similar. The duration from appearance to disappearance of each anomaly is 30–40days, the abnormal area is mainly distributed along the faults near the epicentre, and the anomalous maximum amplitude of TBB and OLR’s relative energy spectrum are both times the average. The depths of the moderate–strong earthquakes in the study area are mainly distributed within the upper 20km, which suggests that thermal infrared can represent the radiation characteristics of shallow earthquakes better. Finally, thermal infrared anomalies of two major earthquakes – the Yushu MS7.1 Earthquake and the Nepal MS8.1 Earthquake are calculated, and both show thermal infrared anomalies. There are few studies on the thermal infrared anomalies of multi-year earthquakes in the Tibet region that use the FY-2E satellite. This study discovers some characteristics of thermal infrared radiation associated with earthquakes in Tibet and looks at the relationship between thermal anomalies and faults. Studying and summarizing thermal infrared anomaly patterns associated with moderate–strong earthquakes in Tibet provide important reference values and can significantly aid earthquake research in this region.

Research on Static Stress Triggering and Seismicity in Minxian and Adjacent Area, Gansu

On July 22, 2013, an Ms6.6 earthquake occurred in Minxian-Zhangxian, Gansu Province, China, which caused serious damages. Based on Okada's elastic half-space model, we used thrust, strike-slip and thrust-strike as receiver faults respectively to calculate Coulomb stress changes (ΔCFS) of three moderate-strong earthquakes. The results show that the thrust and thrust-strike models are better. More than 90% of aftershocks located in NWW and SEE ,the stress increased areas, which is consistent with strike of Lintan-Tanchang fault (LTF). Therefore, Dieterich’s rate-friction law is used to simulate ΔCFS caused by the activity of the temporal evolution. It shows the seismicity of Minxian and adjacent area is the most frequent and that the distribution of earthquakes is perpendicular to the strike of LTF. The activity degrees vary for the LTF. Tanchang is the strongest, followed by the middle and western, and Minxian is the weakest. Except Minxian, the activities of all areas are above the background seismicity during 300 years and it will be up to the background for 400 years.