Running across the Zhenjiang and Nanjing area, the Mufushan-Jiaoshan Fault is an important near EW-trending fault in Nanjing and Zhenjiang area. It extends from Mufu Mountain through Yanziji, Qixia Mountain, and Longtan to Jiao Mountain of Zhenjiang, with a total length of about 75km. The overall trend of the Mufushan-Jiaoshan Fault is nearly east-west, dipping to the north, the southern side of the fault is Ningzhen Mountain, the north side is the hollow land along the river and the Yangzhou low hilly plain. The fault is divided into the western and eastern sections by the NW-trending fault near Xiashu Town in Jurong, namely the Mufushan-Qixiashan section and the Zhenjiang section.
Due to the long-term activity of the Mufushan-Jiaoshan Fault, the northern part of the Mufu Mountain, Qixia Mountain and other complex anticlines suffered large-scale fault depression, forming the Yizheng Sag in the north and the Ningzhen Uplift in the south of the Yangtze River. There is a significant differential up-and-down movement of the fault block along the fault. In the Yizheng Sag, there are huge deposits of the Upper Cretaceous, as well as the thicker Paleogene and Neogene, indicating that the Mufushan-Jiaoshan Fault is a long-term active normal fault. On the Bouguer gravity anomaly map and aeromagnetic anomaly map, the expressions of the Mufushan-Jiaoshan Fault are very obvious, indicating that the fault has a large cutting depth and is a large-scale fault.
There have been many destructive earthquakes in the Nanjing-Zhenjiang area, most of which occurred at the intersection of NW-trending faults and near-EW-trending Mufushan-Jiaoshan Fault. In particular, the Yangzhou M6 earthquake in 1624 had a great impact, and the Mufushan-Jiaoshan Fault is possibly the seismogenic structure of this earthquake. With the planning and construction of a series of Yangtze River crossing passages across the fault in Nanjing and Zhenjiang, whether the Mufushan-Jiaoshan Fault is an active fault and whether it has a greater earthquake risk also becomes the focus of attention in this area.
It is of great significance to study the nature, characteristics and the latest active times of the Mufushan-Jiaoshan Fault for the prevention and reduction of earthquake disaster in Zhenjiang city and Nanjing city. Previous work mainly focused on the Nanjing section, and judged that its latest activity age is late Middle Pleistocene; there has not been a systematic study on the fault in the Zhenjiang section, and its latest activity age is still unclear. Based on the project of “Urban active fault exploration and seismic risk assessment in Zhenjiang City”, we carried out a series of shallow seismic explorations along the Mufushan-Jiaoshan Fault in the Zhenjiang section, and on this basis, representative points were selected to carry out drilling joint profiling to study the Quaternary activity characteristics of the Mufushan-Jiaoshan Fault. The results are of great significance for urban earthquake disaster reduction, urban planning and land use.
The results of shallow seismic exploration show that the Zhengjiang section of the Mufushan-Jiaoshan Fault is dominated by normal faulting, and the trend is NEE, dipping to the north, with a dip angle of about 50°~60° and a displacement of 3~7m on the bedrock surface. All breakpoints of Mufushan-Jiaoshan Fault show that only the bedrock surface was dislocated rather than the interior stratum of Quaternary.
On the Qiaotou village site, there is no sign of dislocation in the stratum above the Middle Pleistocene, the lower part of Middle Pleistocene Xiashu formation has been dislocated, the displacement of the bottom boundary of the Middle Pleistocene on both sides of the fault is 3.2m. According to the characteristics of dislocated stratum, the latest active age of Mufushan-Jiaoshan Fault is late Middle Pleistocene. There is no evidence of activity since late Pleistocene. The fault activity is dominated by normal faulting on the Jinshan site, and there is no evidence of faulting in the Holocene. Based on the comprehensive analysis, the latest active age of the Zhenjiang section of the Mufushan-Jiaoshan Fault is the late Middle Pleistocene, and there is no evidence of activity since the late Pleistocene. According to the dating results, the latest activity time is after(222±22)ka and before the late Pleistocene.
Affected by the erosion of the Yangtze River, the Quaternary in the study area is dominated by the Holocene, the Lower Pleistocene is absent, and the Middle Pleistocene is absent or thin. Therefore, the stratum displacement identified by drilling is mainly developed in the bedrock and the bottom of the Quaternary, resulting in the uncertainty of identifying the latest displacement of the fault, and it is difficult to identify the precise magnitude of the displacement. This is the shortcoming of this work.
Mufushan-Jiaoshan Fault is a major fault with strong seismic risk in the Nanjing-Zhenjiang area, especially at the intersection between the fault and the NW-trending fault, which has the seismogenic environment of destructive earthquake. It is necessary to attach great importance to the prevention of earthquake damage in the relevant area.

Running across the east of Zhenjiang city, the Wufengshan-Xilaiqiao Fault and Dantu-Jianshan Fault are two important NW-trending faults in Zhenjiang area. They controlled the Cretaceous stratigraphic deposition and Mesozoic volcanic activities, and also have obvious control effects on modern geomorphology and Quaternary stratigraphic distribution.
There have been many destructive earthquakes in Zhenjiang area, most of which occurred at the intersection of NW-trending faults and near EW faults. It is of great significance to study the nature, characteristics and the latest active age of the NW-trending faults in Zhenjiang area for the prevention and reduction of earthquake disaster in Zhenjiang City, but the past targeted research work and the knowledge of activity of the faults are very limited. Based on the project of “Urban active fault exploration and seismic risk assessment in Zhenjiang City”, a series of shallow seismic exploration work has been carried out on the two major NW-trending faults in Zhenjiang area, and representative points were selected to carry out drilling joint profiling to study the Quaternary activity characteristics of these two faults. The results are of great significance for urban earthquake disaster reduction, urban planning and land use.
The results of shallow seismic exploration show that the Wufengshan-Xilaiqiao Fault is dominated by normal faulting, dipping to the northeast, with a dip angle of about 60° and a displacement of 5~9m on the bedrock surface. The Dantu-Jianshan Fault is dominated by normal faulting, dipping to the southwest, with a dip angle of about 50°~55° and a displacement of 2~7m on the bedrock surface. All breakpoints of Wufengshan-Xilaiqiao Fault and Dantu-Jianshan Fault reveal that only the bedrock surface was dislocated, not the interior stratum of Quaternary.
On the Dalu site, there is no sign of dislocation in the stratum above the Middle Pleistocene, and the bottom boundary of the Middle Pleistocene has been dislocated, with a displacement of 2m. The dislocation of the bottom boundary of the lower Pleistocene is 3.2m on both sides of the fault, and the maximum displacement of the bedrock surface is 9.1m. The characteristics of the fault surface developed in the drill cores indicate that the latest activity of the fault is of sinistral normal faulting. According to the characteristics of dislocated stratum, the latest active age of Wufengshan-Xilaiqiao Fault is early Middle Pleistocene. On the Fangxian site, there is no sign of fault in the stratum above the Middle Pleistocene, and the bottom of the Middle Pleistocene may be affected by the fault. The displacement of the bottom boundary of Baishan Formation on both sides of the fault is 2m, and the maximum displacement of the bedrock surface is 6.7m. Due to the insufficient evidence of dislocation of Baishan Formation, the latest active age of Dantu-Jianshan Fault is estimated to be between early Pleistocene and early Middle Pleistocene.
The NW-trending Su-Xi-Chang Fault is an important regional fault in the Yangtze River Delta region. Its latest active age is the early Middle Pleistocene, and the displacement in the Quaternary is about 3m. The Wufengshan-Xilaiqiao Fault and the Dantu-Jianshan Fault can be regarded as spatial extension of the Su-Xi-Chang Fault to the northwest, and their activities are also consistent. This study shows that the two NW-trending faults in the Zhenjiang area have significant activity since the Quaternary, and are the main faults with relatively high earthquake risk in this area. Therefore, the intersection of these two faults with EW-trending faults and NE-trending faults should be the focus of attention for earthquake damage prevention in the Zhenjiang area.
The bedrock depth in the Zhenjiang area is relatively shallow, and the stratification difference within the cover layer is small, resulting in an unsatisfactory effect by the geophysical exploration methods. The Lower Pleistocene of the Quaternary system is basically missing, and the boundaries of the Middle and Upper Pleistocene are difficult to distinguish. Developed mainly in the bedrock and the bottom of the Quaternary, the stratum displacement is difficult to judge whether it was caused by sedimentary difference or fault activity. Therefore, the quantitative study of fault activity in this paper is still insufficient.

It is important to detect the fine velocity structures of the crust and uppermost mantle to understand the regional tectonic evolution, earthquake generation processes, and to conduct earthquake risk assessment. The inversion of uppermost mantle velocity and Moho depth are strongly influenced by crustal velocity heterogeneity. In this study, we collected first arrivals of Pg and Pn and secondary arrivals of Pg wave from the seismograms recorded at Fujian provincial seismic network stations. New 3-D P-wave velocities were inverted by multi-phase joint inversion method in Fujian Province. Our results show that the fault zones in Fujian Province have various velocity patterns. The shallow crust is characterized by high velocity that represents mountains, while the mid-lower crust shows low velocities. The anomalous velocities are correlated closely with tectonic faults in Fujian Province. Velocity anomalies mainly show NE-trending distribution, especially in the mid-lower crust and uppermost mantle, which is consistent with the NE-trending of the regional main fault zones. Meanwhile, a part of velocity patterns show NW trending, which is related to the secondary NW-oriented faults. Such velocity distribution also shows a geological structural pattern of "zoning in east-west direction and blocking in north-south direction" in Fujian area.
In the crust, a low velocity zone is found along Zhenghe-Dapu fault zone as mentioned by previous study, however our result shows the low velocity exists at depth of 20~30km in mid-lower crust. Compared with previous study, this low velocity zone is larger and deeper both in range and depth.
The crustal thickness of 28~35km from our joint inversion is similar to the results from the receiver functions of previous studies. The thinnest crust(28km)is observed at offshore in the north of Quanzhou; while the thickest crust(35km)is located west of Zhangzhou near the Zhenghe-Dapu fault zone. Generally, thinner crustal thickness is found in offshore of Fujian Province, and thicker crustal thickness is in the mainland. However, we also found that crustal thickness becomes thinner along the east side of Yongan-Jinjiang Fault.
The values of Pn velocities in the region vary from 7.71 to 8.26km/s. The velocity distribution of the uppermost mantle presents a large inhomogeneity, which is correlated with the distribution of the fault zone. High Pn velocity anomalies are found mainly along the west side of the Zhenghe-Dapu fault zone(F₂), and the east side of the Shaowu-Heyuan fault zone(F₁), which is strip-shaped throughout the central part of Fujian. Low Pn velocity anomalies are observed along the coast and Taiwan Straits, including the Changle-Zhaoan fault zone, the coastal fault zone, and the Fuzhou Basin. We also found a low Pn velocity anomaly zone, which extends to the coast, in the Shaowu-Heyuan fault zone at the junction of the Fujian, Guangdong and Jiangxi Provinces. In the west of Taiwan Straits, both high and low Pn velocity anomalies are observed.
Our results show that the historical strong earthquakes(larger than magnitude 6.0) are mainly distributed between positive and negative anomaly zones at different depth profiles of the crust, and similar anomalies distribution also exists at the uppermost mantle, suggesting that the occurrence of strong earthquakes in the region is not only related to the anomalous crustal velocity structure, but also affected by the velocity anomaly structure from the uppermost mantle.

In order to understand the mechanism of the 1668 M_S8.5 earthquake occurred in Tancheng, it is important to probe the fine deep geological structure beneath the epicenter. A MT profile 20km south of the epicenter has been deployed. There are 17 sites along the profile, with a 3km average separation. Signals in Ex, Ey, Hx and Hy were measured in a cross manner, with x-axis orientated to the north. Record length for each site was at least 20h. The impedance and phase at sites in high cultural noisy environment were estimated by remote reference technique. As the Tanlu Fault Zone(TLFZ)is in NNE, nearly northerly, thus YX mode was considered as TM mode. Gauss-Newton inversion was done in 2-D mode with only the TM impedance and phase as input data. The electrical sections of 10km and 40km depth were respectively obtained after 8 iterations. The both initial models were created by Bostic approximation. The sections reveal the following features.
The TLFZ consists of five faults, from east to west numbered as F₀ to F₄. F₁ is the primary fault, steeply dipping west down to mantle, which has turned into a buried one overthrust by the east dipping Fault F₀. F₂ and F₃ dip east at 45 degrees, parallel to F₄, truncated by F₁ at depth. F₄ dips east in the shallow subsurface and gradually dips to west toward depth through the entire crust merging with F₁ to form a bigger one. These four faults constitute a flower-shaped structure, showing the nature of strike-slip of the TLFZ, associated with normal faulting in the late Yanshanian to early Himalayan. F₁ dips west, overthrust by east-dipping F₀, implying the compression from the westward subduction of the Pacific plate, thus present-day compression is superposed on the early tensile and strike-slip feature.
Based on MT data, it is inferred that the 1668 Tancheng M8.5 earthquake occurred at the junction of F₁ and F₃ about 15km deep. Thus it was likely resulted from westward compression of the Pacific plate, leading to thrust of the Sulu uplift along F₀, inducing activity of F₁ at depth, reactivated F₃, and adjusting the stress distribution in the region.

In this paper we present results of spectral structure of crustal velocity inhomogeneity beneath the southeastern margin of Tibetan plateau and its adjacent region based on the S wave envelope broadening algorithm. The spectral structure of 8~16Hz band is selected to analyze the special character of crustal inhomogeneity and discuss the correlation between strong earthquakes and inhomogeneities. The result shows that strong and complex inhomogeneities of crustal medium are found in the southeastern margin of Tibetan plateau and its adjacent region. In the upper part of upper crust, the strong and small scale inhomogeneities are imaged in the Longmengshan fault zone and the north of the Anninghe fault zone, the weak and large scale inhomogeneites are imaged in the section from Huolu to Daofu of Xianshuihe fault zone and the south of the Anninghe fault zone. In the lower part of upper crust, strong inhomogeneites are found in the Longmengshan fault zone, Lianfeng fault zone, the north of the Anninghe fault zone and the sections from Huolu to Daofu of the Xianshuihe fault zone, weak inhomogeneites are found in the section from Daofu to Kangding of Xianshuihe fault zone. In the middle crust, strong inhomogeneities are observed in the section of the Baoxing to Dujiangyan, the Baoxing to Kangding, and Kangding to Shimian, and weak inhomogeneities are observed in the northwestern section from Huolu to Kangding, and the Lianfeng fault zone. Comparing the medium inhomogeneities with the location of the strong earthquakes, our results suggest existence of high correlation between them. Strong earthquakes are often located in the transitionary zone between the strong and the weak inhomogeneities. The spatial distribution of the strong and the weak medium inhomogeneities may be related to the broken medium from the strong movement of geological tectonic and the heat flow upwelling along active faults induced by frequent tectonic and volcanic activity.

The fault F₅ is considered as the most active fault in the Tanlu fault zone(Yi-Shu fault zone), which is located from Weifang of Shandong Province to Jiashan of Anhui Province, with a length of 360km. It has always been a focus of concern to many geoscientists because of its complexity and importance. But, for a long period of time, there exists biggish indetermination in the accurate position and active ages of the fault F₅ in Suqian section of Tanlu fault zone. Seismic reflection exploration is the main technique in present urban active faults detecting. In order to investigate the spatial distribution, characteristics and activities of the fault F₅ in covered terrains, we carried out a systematic survey to the fault with shallow seismic prospecting method and obtained the accurate position and development characteristics of the fault. The results show that the fault F₅ continues to develop toward south rather than ending at the Huancheng South Road of Suqian City. F₅ is mainly composed of two main faults, which dip in opposite directions and almost vertically. Near the Sankeshu town, F₅ is composed of three faults with right-stepping, forming a small pull-apart basin with length of 6km, width of 2.5km, controlling the deposition of Neogene and Quaternary strata. By combining the results of composite drilling section and trenching, we make a conclusion that the western branch of fault F₅ is a Holocene active fault, and the eastern branch is a Pleistocene active fault. Our general view is that fault F₅ is a Holocene active fault.

High-frequency S-wave seismogram envelopes of microearthquakes are broadened with increasing travel distance,which is called S-wave envelope broadening.Multiple forward scattering and diffraction for the random inhomogeneities along seismic ray path are the main reasons to cause the S-wave envelope broadening,so the phenomenon of S-wave envelope broadening is used to study the inhomogeneity of medium.The peak delay time of S-wave,which is defined as the time lag from the direct S-wave onset to the maximum amplitude arrival of its envelope,is accepted to quantify the phenomenon of S-wave envelope broadening.The 204 small earthquake records in Changbaishan Tianchi volcano were analyzed by S-wave envelope broadening algorithm.The results show that the phenomenon of S-wave envelope broadening in Changbaishan Tianchi volcano is obvious,and the peak delay time of S-wave has a positive correlation with hypocenter distance and frequency of S-wave.The relationships between the peak delay time of S-wave and the hypocenter distance for different frequency bands were got by statistics method.The results are beneficial to the understanding of the S-wave envelope broadening phenomena and the quantitative research on the inhomogeneities of the crust medium in the Changbaishan Tianchi volcano region.