A M_W6.4(M_S7.0)earthquake occurred in Gonghe, Qinghai on 26 April 1990. The Gonghe area is located on the northeastern margin of the Qinghai-Tibet Plateau. The geological tectonic movement in this area is mainly affected by the uplift of the Qinghai-Tibet Plateau. There has been no earthquakes larger than moderate strength in the Gonghe Basin since the historical records, and there are no large-scale active faults on the surface of the epicenter area, so the earthquake has aroused great concern. No major earthquakes have occurred in the Gonghe area since 1995, but the data of small earthquakes is very rich, which ensures the completion of the research. The TomoDD method combines the double-difference relocation method with seismic tomography, and solves two problems at the same time, one is the problem of fine positioning of the earthquake, and the other is the calculation of the 3D velocity structure of the earth’s crust. In this paper, we collected 63872 P and S wave arrival time data in Gonghe and surrounding area recorded by Qinghai, Gansu seismic networks and temporary seismic array from January 2009 to January 2019. The 3D crustal velocity structure and source position parameters of the region are inversed. The relationship between the geological structure setting of the main shock and the velocity structure and seismicity of the region was analyzed. The results show that the crustal velocity structure in the Gonghe area shows lateral inhomogeneity. The Gonghe mainshock is located in the low-velocity anomaly directly below the Gonghe Basin, close to the high-low-velocity anomaly boundary. There is an obvious high-speed anomaly in the southwest of the mainshock, which thrusts from underground to near-surface in the northeast direction. It is estimated that the Wayuxiang-Lagan concealed fault is located at 35.95°N, the dip of the fault is about 45° at the deep part. It is inferred that the occurrence of the Gonghe main shock is caused by the sliding of the Wayuxiangka-Lagan Fault whose strike is NWW and dip is SSW under the action of horizontal tectonic stress. The high-velocity anomaly is about 5~40km deep underground in the northeast direction of the Riyueshan Fault, and a large number of small earthquakes occurred around the high- and low-velocity transition zone. It is presumed that under the action of the near-horizontal NE-directed tectonic stress, the high- and low-velocity zones were further interacted to generate faults and ground folds, and a large number of small earthquakes occurred during the fusion process.

China’s seas and adjacent regions are affected by interactions among the Eurasian plate, the western Pacific plate, and the Philippine Sea plate. Both intraplate and plate-edge earthquakes have occurred in these regions and the seismic activities are frequent. The coastal areas of China are economically developed and densely populated. With the development and utilization of marine energy and resources along with the development of national economy, the types and quantity of construction projects in the marine and coastal areas have increased, once an earthquake happens, it will cause huge damage and loss to these areas, therefore, the earthquake-related research for these sea areas cannot be ignored and the need for study on these areas is increasingly urgent. One type of essential basic data for marine seismic research is a complete, unified earthquake catalog, which is an important database for seismotectonics, seismic zoning, earthquake prediction, earthquake prevention, and disaster reduction. Completeness and reliability analysis of an earthquake catalog is one of the fundamental research topics in seismology.
At present, four editions of earthquake catalogs have been officially published in China, as well as the earthquake catalogue compiled in the national fifth-generation earthquake parameter zoning map, these catalogs are based on historical data, seismic survey investigations, and various instrumental observations. However, these catalogs have earlier data deadlines and contain the earthquake records for only the offshore regions of China, which are extensions of coastal land. Distant sea regions, subduction zones, and adjacent sea regions have not been included in these catalogs. Secondly, there were no cross-border areas involved in the compilation of earthquake catalogs in the past. It was not required to use magnitudes measured by other countries’ seismic networks and observation agencies to develop an earthquake catalog with a uniform magnitude scale, moreover, there was no formula suitable for the conversion of magnitude scale in China’s seas areas and adjacent regions. Little research has been conducted to compile and analyze the completeness of a unified earthquake catalog for China’s seas and adjacent regions. Therefore, in this study, we compiled earthquake data from the seismic networks of China and other countries for China’s seas and adjacent regions. The earthquake-monitoring capabilities of different sea areas at different time periods were evaluated, and the temporal and spatial distribution characteristics of epicentral location accuracy for China’s seas and adjacent regions were analyzed. We used the orthogonal regression method to obtain conversion relationships between the surface wave magnitude, body wave magnitude, and moment magnitude for China’s seas and adjacent regions, and established magnitude conversion formulae between the China Seismic Network and the M_L magnitude of the Taiwan Seismic Network and the M_S magnitude of the Philippine Seismic Network. Finally, we developed an earthquake catalog with uniform magnitude scales for China’s seas and adjacent regions.
On the basis of the frequency-magnitude distribution obtained from the magnitude-cumulative frequency relationship (N-T) and the Gutenberg-Richter(GR)law, we conducted a completeness analysis of the unified earthquake catalog for China’s seas and adjacent regions, Then, we identified the beginning years of each magnitude interval at different focal depth ranges and different seismic zones in the earthquake catalog.
This study marks the first time that a unified earthquake catalog has been compiled for China’s seas and adjacent regions, based on the characteristics of seismicity in the surrounding sea regions, which fills the gap in the compilation of the earthquake catalogue of China’s seas and adjacent areas. The resulting earthquake catalog provides a basis for seismotectonics, seismicity study, and seismic hazard analysis for China’s seas and adjacent regions. The catalog also provides technical support for the preparation of seismic zoning maps as well as for earthquake prevention and disaster reduction in project planning and engineering construction in the sea regions. In addition, by evaluating the earthquake-monitoring capability of the seismic networks in China’s seas and adjacent regions and analyzing the completeness of the compiled unified earthquake catalog, this study provides a scientific reference to improve the earthquake-monitoring capability and optimizing the distribution of the seismic networks in these regions.

The Longtan reservoir is located in Tian'e County, Guangxi Zhuang Autonomous Region, southwestern China on the upper reaches of Hongshui River, the main stream of the Pearl River. The dam of the reservoir is 200m high, and the maximum water depth can be up to 194m as the water level reaches 400m. The reservoir storage capacity is 27.3 billion cubic meters, so it is a typical high-dam reservoir with large storage capacity. Terrain of the reservoir is high in the west and low in the east. The reservoir is located at the confluence of the Hongshui River, Buliu River, Nanpan River, Beipan River, Mengjiang River and Caodu River. The construction of Longtan hydropower station officially started in July 2001, and the reservoir impoundment was on September 30, 2006. The power station is equipped with 9 sets of 700 000kW water turbine generator units, with a total installed capacity of 6.3 million kW and an average annual generating capacity of 18.7 billion kW·h. So its storage and hydropower capacity rank third only to the world-famous Three Gorges hydropower project and the ultra-large hydropower project in Xiluodu of Jinsha River in China. Seismicity enhanced rapidly in the reservoir area after the impoundment. More the 5 000 earthquakes have been recorded so far, with the maximum magnitude of M_L4.8, which occurred on September 18, 2010. The earthquakes are mainly concentrated in the deep water area where fault zones run through. Assuming the seismogenic fault can be simulated by a plane and most small earthquakes occur nearby the fault plane, the information of seismogenic fault can be obtained by the hypocenter location parameters of small earthquakes.

The receiver function which carries the information of crustal materials is often used to study the shear-wave velocity of the crust as well as the crustal anisotropy. However, because of the low signal-to-noise ratio in Pms(P-to-S converted phase from the Moho), the crustal anisotropy obtained by shear-wave splitting technique for a single receiver function usually has large errors in general. Recent advance in the analysis method based on Pms arrival time varying with the back-azimuth change can effectively overcome the above defects. Thus in this paper, we utilize the azimuth variations of the Pms to study the crustal anisotropy in Chongqing region for the first time. According to the earthquake catalogue provided by USGS, seismic waveform of earthquakes with magnitude larger than 5.5 and epicenter distance range of 30°~90° between January 2015 and December 2016 are collected from 14 broadband seismic stations of Chongqing seismic network. We carry out the bootstrap resampling to test the reliability of the radial maximum energy method for the observation data. In addition, we also applied the receiver function H-Kappa analysis in this paper to study the crustal thickness and Poisson's ratio.
Our results show the crustal thickness ranges from 40~50km, and there is a thin and thick crust in the southern and northern Chongqing, respectively. The crustal average Poisson's ratio ranges from 0.23~0.31, the Poisson's ratio reaches the maximum value in the central part of Chongqing, while the Poisson's ratio in the northern and southern parts of Chongqing is obviously low. We obtain the crustal anisotropy from 9 stations in total. The delay time of crustal anisotropy distributes between 0.08s and 0.48s, with the average value of 0.22s. Among them, the CHS, QIJ and WAZ stations in central Chongqing have relatively large crustal delay time(>0.3s), followed by ROC station in the western Chongqing(0.25s), while the delay time in CHK station in northern Chongqing and WAS station in southern Chongqing are 0.08s, showing relatively weak crustal anisotropy. The fast polarization directions(FPDs)also change obviously from south to north. In southern Chongqing, FPDs are dominant in NNE-SSW and NEE-SWW, while the FPDs in WAZ station change to NWW-SEE, and the FPDs appear to be NW-SE in CHK in the northern Chongqing. In general, the FPDs are sub-parallel to the strikes of faults in most areas of Chongqing areas.
Combined with other results from GPS observations, tectonic stress field and XKS splitting measurements, the main conclusions can be suggested as following: The cracks preferred orientation in the upper crust is not the main source of crustal anisotropy in Chongqing area. The crust and lithospheric upper mantle in the eastern Sichuan fold belt(ESFB)and Sichuan-Guizhou fault fold belt(SGFFB)are decoupled, and the deformation characteristics in the north and south parts of ESFB and SGFFB is different. The complex tectonic deformation may exist beneath the mountain-basin boundary, causing the fast directions of crustal anisotropy different from that in other areas of ESFB and SGFFB. The faults with different strikes may weaken the strength of average crustal anisotropy in some areas. The crustal deformation in southern Dabashan nappe belt(DNB)may be mainly controlled by the fault structure.

On July 31^th, 2016, a moderately strong earthquake of M_S5.4 hit the Cangwu County in Guangxi Zhuang Autonomous Region. The focal depth of this earthquake is about 10 kilometers. This earthquake occurred in the junction area of Guangxi Zhuang Autonomous Region, Hunan Province and Guangdong Province. Nanning, Guangzhou, Shenzhen and other cities felt this earthquake.
The Cangwu County disaster area is unique in terms of geographical position, tectonic geology, landform, economic development situation, population distribution and climate condition, etc. Based on the investigation to the earthquake hit area, and the analysis of its special natural environment, social economical conditions and humanities, seven general disaster characteristics of the Cangwu M_S5.4 earthquake are summarized from the point of view of earthquake disaster emergency rescue and reconstruction. namely, the low population density in the disaster area, the single building structure type and the low-level economic development, the short duration of ground motion, the small number and low magnitude of aftershocks, no large landslide, debris flow and other secondary geological disasters caused by this earthquake, the area is prone to typhoon and other climate disasters which are likely to aggravate earthquake disaster, and the earthquake occurred in an area of weak seismicity in South China.
This paper introduces the basic situation of the M_S5.4 Cangwu earthquake and analyzes the seven disaster characteristics of this earthquake. In order to better respond to moderate-strong earthquake in weak seismicity regions of South China, this paper summarizes some experience and revelations about the earthquake in the M_S5.4 Cangwu earthquake emergency response process, and puts forward some corresponding countermeasures of earthquake disaster reduction in weak seismicity regions in southern China.
In the future work, we should pay more attention to pre-disaster prevention, and strengthen earthquake-monitoring capability. In order to reduce the casualties caused by collapse of houses, we should improve the seismic fortification standards of houses, carry out relevant researches on earthquake damage prevention measures of karst areas. And in order to carry out comprehensive disaster reduction, we should strengthen cooperation with the meteorological department, and carry out more comprehensive earthquake emergency drills.

In this paper,we calculate receiver functions of body wave under the 14 stations in Shaanxi Province from 3-component digital waveform data of teleseismic earthquake events and obtain the thickness and Poisson ratio in crust of this area through H-kappa stacking.Through analysing the characteristics of crustal structure in Shaanxi Province,we discuss the relationship between seismic activity,crustal structure and geological structure in Shaanxi Province.The results show that(1)Crustal thickness in western Shaanxi is thicker than that in the east.Crustal thickness in the south and north of Shaanxi(≥40km)is larger than that in Weihe Basin,middle Shaanxi(about 34～40km).Among 14 stations,the crust beneath Huayin station is the thinnest(34km),which locates on the boundary between eastern Weihe Basin and Shanxi Province,and the biggest thickness(48km)appears beneath Longxian station at the northwestern end of Weihe Basin.(2)Poisson ratio in Shaanxi Province is about 0.24～0.29,which may be related to rock compositions.Poisson ratio in the north of Weihe Basin has higher values than those in the south.(3)There exist some relations between seismic activity and geological structure.The Weihe Basin with frequent earthquakes locates in a compound position of several tectonic systems.The Hanzhong Basin and Ankang Basin in the south of Shaanxi are controlled by several major faults,where the seismicity is relatively low.Seismic activity in northern Shaanxi is the lowest because of stable geological structure.Poisson ratio reflects material composition of earth interior.Our analysis suggests that seismic activity in the region with high Poisson ratio is higher than that with low Poisson ratio.

We present the theory and method for inversing the kinematics parameters of a fault zone and then use this method to study the present kinematic characteristics of the Altun fault zone The results show that the Altun fault zone is generally compressive in the direction of S14癊,its compressive rate is 1.13 mm/a,and the rate of its left lateral shear movement is 0.17mm/a