Xinxiang-Shangqiu Fault starts from Yuhekou in the west and extends eastward into Anhui Province through Xinxiang, Yanjin, Fengqiu, Lankao, Minquan, Shangqiu and Xiayi, with a total length of about 400km and a general strike of NWW. It is a regional concealed fault in Henan Province and a boundary fault between northern North China depression and southern North China depression.

This study focuses on the Fengqiu section of Xinxiang-Shangqiu Fault, which is the boundary structure between the Kaifeng sag, Neihuang uplift and Dongpu sag. Controlled by the NE-NEE trending Changyuan Fault and Yellow River Fault at its east and west end, this fault section has a length of about 30km and controls the Mesozoic to early Cenozoic sedimentation in the Kaifeng sag and the south side of Dongpu sag.

In this paper, the shallow structural characteristics and Quaternary activities of Fengqiu section of the Xinxiang-Shangqiu Fault are revealed by the combination of reflection seismic exploration and drilling detection. Two shallow seismic exploration profiles and one composite drilling geological section are arranged across the fault.

The results of shallow seismic exploration show that the Fengqiu section of Xinxiang-Shangqiu Fault is NWW trending. It is a north-dipping normal fault accompanied by several nearly parallel normal faults, and the fault is still active since the Quaternary.

In the composite drilling geological section at Yaowu, the latest faulted stratum is a clay layer between borehole YW5 and YW7, and the buried depth of the upper breakpoint is between 57.00~61.50m. Combined with the dating results of the collected samples, it is comprehensively judged that the latest activity age of Fengqiu section is the middle of late Pleistocene. Since the middle of late Pleistocene, the whole region is in a relatively stable tectonic period. It is verified that the comprehensive detection method of shallow seismic exploration with drilling can effectively find out the accurate location of hidden faults.

The zone with strong vertical differential movement is often the zone where earthquakes occur. The vertical differential movement between Kaifeng sag and Neihuang uplift is very strong, and the difference reaches nearly 1^{}000 meters since Neogene. Moreover, the structural pattern of the main strong earthquakes in the North China Plain is characterized by zoning in NE direction and segmentation in NW direction, especially at the intersections of NWW-trending faults and NE-trending faults. The Xinxiang-Shangqiu Fault intersects with a series of NE-NEE trending faults, including Tangdong, Changyuan, Yellow River and Liaolan faults from west to east. The Fengqiu section is at the intersection with the Changyuan Fault and the Yellow River Fault, and is located in the Fengqiu M6.5 potential seismic source area of the North China plain seismic belt. The intersection of two groups of Quaternary active faults is a favorable place for the preparation and generation of moderate and strong earthquakes. Therefore, the research results provide seismological basis for the site selection of major engineering projects, urban planning and construction in this area, and have reference value for discussing the geodynamic issues such as deep and shallow structural relationship and structural evolution of Xinxiang-Shangqiu Fault.

The Yangtze fault zone is a typical tectonic regime transition zone of the eastern China. Tectonically, it is characterized by alternated rifts and uplifts and “several crystalline basements with one sediment cover”. Abundant metal metallogenic deposits are developed. Improvement of the velocity model and basement structure will benefit our understanding and knowledge about the regional tectonics. Large volume airgun sources have been broadly applied to seismic surveys due to significant advantages. For instance, they are environmentally friendly, use lower frequencies, and are repeatable. Several seismic and geological research institutions, such as China Earthquake Administration, carried out a three-dimensional comprehensive sounding using the large volume airgun as the seismic source which was fired at the channel of the Yangtze River in 2015. The source-receiver geometry of this seismic experiment covered the whole Anhui Province which locates at the Middle-Lower Yangtze River. The densest observational area is in the Middle-Lower Yangtze River Metallogenic Belt which is a narrow area along the Yangtze River and consists of the Luzong, Tongling, Ningwu, and Anqing-Guichi ore deposits. The Tanlu fault zone, a giant strike-slip fault of more than 2 000km long, passes through the northwestern margin of this area. Geophysical studies have demonstrated copious geological evidences for the Yangtze fault zone, which is approximately 450km long and crosses central China, extending to the eastern coastal area. The present fault and fold systems are the consequences of the repeated tectonic events since the Mesozoic. We collected and analyzed the seismic data of 20 fixed airgun shot points, then utilized tomography, time term method and head wave traveltime inversion based on ray tracing techniques to model the upper crustal velocity and crystalline basement structure of the Anqing-Maanshan segment beneath the Yangtze fault zone. The profile along the Yangtze River consists of 100 PDS-2 seismometers with a spacing of 2km. We applied the linear and phase weighted stack methods to improve the signal-to-noise ratio of the weak seismic phases from the airgun source. According to the comparison between the linear and phase weighted stack results, the phase weighted stack method significantly improves the quality of the stacked data. We applied the band-pass filter to the stacked data to improve the onset of the first arrival, then picked up the seismic phases and assessed the errors of the picked traveltime. The comprehensive results reveal that the upper crust velocity structure and crystalline basement images show a tectonic feature of alternating rifts and uplifts. The upper crust of the Huaining Basin is the thickest area along the Yangtze River. The basement of the Huaining Basin is around 4.5km and there are Mesozoic lacustrine sedimentary layers whose thickness is about 2km. The crystalline basement depth of the Luzong Basin is 4.1km and the consolidated basin shows clear depression basin shape. This feature of the Luzong Basin reveals that it experienced extensional depression. There is a high-velocity zone beneath the crystalline basement of the Luzong Basin, and the velocity is higher than other areas along the Yangtze River. This high velocity zone shows an arc shape, which agrees with the Paleozoic reflection images by the seismic reflection survey. The profile crosses the Yangtze River in Tongling area and there are obvious velocity differences between the two sides of the Yangtze River. The velocity differences show that the Yangtze faults cut the crystalline basement in Tongling. The upper crust velocity structure of the Tongling area shows clear uplift features and its crystalline basement depth is about 2.2km, which agrees with the arc-reflection structures of the upper crust from the seismic reflection data. This uplift image reveals that the upper crust of the Tongling area has experienced extrusion deformations. The consistency of the seismic reflection imaging results with the near surface geology demonstrates that the large volume air-gun source is applicable to land-based seismic survey.

Shallow seismic reflection method is a commonly used technique in urban active fault detection,however,special geotectonic environment may sometimes make reflection survey inapplicable.In such cases,high-resolution seismic refraction could be a feasible option.In this study,we use the finite difference method as the main technique and the conventional methods of refraction data interpretation as auxiliary means in the interpretation of high-resolution shallow refraction data for active fault detection in Lanzhou area.After a comprehensive analysis of first-break refraction travel-time characteristics,the velocity structure and interface structure along each profile have been obtained.A detailed description of the detection results from SS04-1 and SS11-2 seismic profiles is presented in this paper.The main stratigraphic interfaces and tectonic features identified by the two profiles are quite consistent with the results from drilling surveys along the profiles.Our results indicate that high-resolution seismic refraction is an effective replacement in areas where reflection seismic survey is hard to carry out.

Seismic refraction method is tentatively used in the exploration of urban active faults where strong interference of surface waves exists and it is difficult to use seismic reflection survey. Original seismic refraction data are calculated and inversed by using time-terms, curve of differential time-distance and finite-difference tomography, to investigate the effect of the new technique in the exploration of urban active faults.In this paper, velocity structures and interface structures are obtained after the shallow seismic refraction data in the western segment of Xushui fault of western Zhengzhou are calculated and inversed by using the above-mentioned three calculation methods, and structural characteristics and depths of main geologic strata are got by integrating inversion results and features of seismic phases. The results of these three methods are similar, and they are confirmed by drilling data in the profile. The seismic refraction method can be used in the exploration of urban active faults.

Jiashi region, Xinjiang is a strong earthquake area in western China. In recent years, several great earthquake swarms have occurred in this region, causing tremendous hazards. In order to get an insight into the relation between the deep structures and the generation of great earthquake swarm in this region, a generalized inversion technique for determining probability distributions of spatial locations of earthquake events through the travel times of P and S waves in random and vertically inhomogeneous medium, is used in this paper. Seismic data recorded by temporal digital seismic network deposed in this region were located using this method. The located earthquakes show linear distribution in north-northwest and north-northeast directions, among which the former is more distinct than the later. Based on the obtained results, the deep structural background of seismic activities in Jiashi region is discussed. The results indicate also the close relation between the earthquake and fault structures in Jiashi region. It is clear that the generation of earthquake swarm might be related to the buried fault in the vicinity of seismic source area, and might be the result of violent crustal deformation on the northern margin of Tarim basin and the present tectonic movement. These complicated structural framework and peculiar environmental conditions might be responsible for the development and generation of the strong earthquake swarm in Jiashi region.

The crystalline basement velocity structure of Changbaishan Tianchi volcanic area is established by using Three-Dimensional Finite-Difference method and Pg data from four wide-angle reflection/refraction profiles and one three-dimensional array which was deployed in Changbaishan Mountain area. This paper presents the characteristics of the velocity structure of crystalline basement and the interface with 5.9～6.0km/s P-wave velocity in the crystalline basement. Inversion results reveal that the velocity of surface layer in the southern part is higher than that in the northern part of the studied area. In general, the depth of crystalline basement of the studied area is within the range of 2.0～3.0km, with the deepest of about 4.0km and the shallowest of about 1 5km near Songjiang. There are two low velocity areas in this region, one is beneath the Protection Station of Tianchi volcano, and the other is located beneath Erdaobaihe and Chixi Protection Station. In these two areas the depths of crystalline basement are about 4.0km. We found that the intense lateral variation of velocity and depth of crystalline basement in the seismic profile coincides well with the location of fault. Therefore, it is suggested that the intense lateral variation of velocity and the abrupt change of the depths of crystalline basement can be taken as an indication of the occurrence of fault.