The Yingkou-Weifang fault zone (YWFZ) is the part of the Tanlu fault zone across the Bohai Sea, and is also an important part of the tectonics of the eastern Bohai Bay Basin. Many studies have been carried out on the neo-tectonics and activities of the YWFZ in recent years. In this paper, the neo-tectonics and activities of the YWFZ, and other related issues were studied again, based on our previous work and results of other researchers. The neo-tectonic movement in the Bohai Sea area began in the late Miocene (12~10Ma BP), which originated from the local crust horizontal movement, the tectonic stress field is characterized by NEE-SWW and near E-W horizontal compression. The neo-tectonics of the YWFZ is represented mainly by Neogene-Quaternary deformation, due to rejuvenation of Paleogene faults. Many faults have developed. The neo-tectonics and activities of YWFZ have characteristics of segmentation and weakening, because of the development of the NE-trending Northwest Miao Island-the Yellow River Estuary fault zone, which crosses the YWFZ. Earthquakes in the east of Bohai Sea are distributed along the Northwest Miao Island-the Yellow River Estuary fault zone, only few and small earthquakes along the Liaodong Bay and the Laizhou Bay section of the YWFZ. We made a preliminary analysis of the mechanics for this phenomenon.

The study area of this article covers the continental shelf of the East China Sea and the Okinawa Trough. Tectonically, the area is the seaward extension of the eastern China mainland, consisting of the East China Sea shelf basin, the Diaoyudao islands uplift-fold zone, and the Okinawa Trough Basin developed in Cenozoic. Lying at the conjunction between the Eurasian and Philippine plates, the neotectonic movement since Miocene and resultant geologic structure of this area are complicated and peculiar. Based on pervious data and studies, this paper makes a systematic and in-deep analysis to the features of the neotectonic movement in this region, involving geomorphology, geological structure, magma activity and earthquakes. Then, the dynamic conditions for the neotectonic movement of the study area are discussed.
Neotectonic movement of East China Sea started from middle Miocene and the mechanism of the tectonic stress field changed from sinistral transtension to sinistral transpression. The neotectonic movement in this area is inhomogeneous, with the continental shelf basin inclining and subsiding slightly to the southeast, the Okinawa trough dominated mainly by crustal active rifting, and the Diaoyu Islands fold belt characterized by lateral compressive bending uplift. The active faults, mainly trending NNE and NE, are dominantly distributed in the continental shelf basin, especially in the Okinawa trough. Magmatism and earthquake activity are also mainly distributed in the east of the continental shelf basin, especially in the Okinawa trough. The neotectonic movement in East China Sea is co-influenced by the back arc mantle uplift which is caused by the subduction of the Philippine plate beneath the continental shelf of East China Sea and results in the NW-SE rifting of Okinawa trough, and the southeastward movement of South China block which is pushed by the lateral extrusion of eastern Tibet.

Seismogenic structure is the core of seismo-geology. The Bohai Bay Basin area in North China is highly active in terms of seismicity,where six earthquakes of M≥7.0 have occurred. After the 1966 M7.2 Xingtai event,some researchers suggested that the seismogenic structure of this earthquake was associated with the Cenozoic normal faults and the fault-depression basins the faults controls. In 1986,however,some authors proposed that this quake should be attributed to a high-angle fault beneath the basin.
The purpose of this paper is to give a systematic elucidation on seismogenetic structures in the Bohai Bay Basin area,North China,which are built on the geological studies in combination with exploration to deep structures in the seismic areas. The paper analyzes and compares the geometric features and structural attributes as well as their dynamic conditions of the Bohai Bay Basin in two evolution stages,i.e.the Eogene when the fault-depression formed and mid Miocene(12～10Ma)when the neotectonics developed. It emphasizes the distinct dynamic conditions in these two stages that formed different structural systems. In the stage of fault-depression,this area was subject to extension in NW-SE direction,which produced many gentle normal faults in the shallow subsurface that characterized the fault-bounded depression basins. While in the neotectonic stage,a set of conjugate fault system consisting of NE-trending right-lateral slip-strike faults and NW-directed left-lateral strike-slip faults were generated by the NEE to approximately EW-orientated horizontal compressional stresses. The structure of the first stage was pre-existing,while that of the second stage has both inheritance and variance to the first stage,i.e.superposition and reform,which accounts for the gestation and occurrence of the present-day major earthquakes in this area.

On 14 November 2001,an extraordinarily large earthquake(M_S 8.1)occurred on the Hoh Sai Hu segment of the eastern Kunlun Fault,northern Tibetan Plateau. The seismogenic fault,Hoh Sai Hu segment,is a left-lateral fault with a high slip rate in the geological history,and the average slip rate reaches(14.8±2.8)mm/a since the late Pleistocene. Different slip rates of Hoh Sai Hu segment can affect the fault motion in the future. So,the paper analyzes the effect of different slip rates and different initial friction coefficients on the fault surface of the Hoh Sai Hu segment of eastern Kunlun Fault on the rupture behaviors of the fault. In the research,we apply the single degree of spring block model controlled by the rate- and state-dependent frictional constitutive laws. Using the fault dislocation model and based on ancient earthquake researches,historical earthquakes data and the achievements of previous researchers,we obtained the parameters of the model. Through the numerical simulation of rupturing motion of the Hoh Sai Hu segment in the future 6500 years under different slip rates,we find that a faster annual slip rate will shorten the recurrence interval of earthquake. For example,the earthquake recurrence interval is 2100a at a slip rate of 0.014m/a,which agrees with previous research results,but,the recurrence interval will be 1000～1500a and 2100～2500a,corresponding to the slip rates of 0.018m/a and 0.008m/a,respectively. Slip rate of fault has no regular effect on the coseismic slip rate and displacement of fault in an earthquake. The initial friction coefficient on the fault surface has effect on earthquake recurrence interval. A smaller initial friction coefficient will lengthen earthquake recurrence interval. At the same time,the smaller initial friction coefficient will lead to larger slip rate and displacement of fault when earthquake occurs.

Basing on the fault dislocation model of Yoshimitsu Okada and Steketee and filed scientific investigation,we calculate theoretically space variation of the displacement fields,including vertical and horizontal displacements of the Wenchuan earthquake along the near zone(within 30km to the fault)of Yingxiu-Beichuan reverse fault.In the simulation,we interpret the space variation of the displacement field in the near zone of Yingxiu-Beichuan reverse fault in details.However,we can't describe the space variations in much detail by the field scientific investigation and limited data of GPS stations.Comparing with the results of field science investigation on surface rupture zone,our computational results show that the displacement fields have the same variation trend.At the same time,the displacement field declines drastically with distance to the outcrop of the fault,which agrees with the present research,and the velocity of this decline is much faster on the foot wall of fault than that on the hanging wall.By the simulation,we get the main conclusions:the vertical displacement of ground surface resulting from faulting in the earthquake shows the strong spatial inhomogeneity,and most large values of vertical displacement concentrate on the terminals of the fault,i.e.nearby Yingxiu and Beichuan.The displacement of the ground surface,including horizontal and vertical component,varies more drastically on both terminals of the fault than that of the middle section of the fault.The vertical displacement changes drastically along the direction of strike in the hanging wall of the fault than that of the foot wall.Except on the terminals of the fault,the horizontal displacement distributes homogenously in space.On the whole,except on the terminals of the fault,the amplitude of the displacement field on the hanging wall of the fault is larger than that of the foot wall.

Based on structural data of the Minghuazhen Formation(N₁²—N₂)and base of Quaternary system from Research Center of China Offshore Petroleum Company,there are about 600 faults developed in the region from Yellow River Estuary to the Changxing Island.Among them,nearly 500 faults trend NE-NEE,amounting to 83 percent of the whole fault group.The faults are about 5～20km long,and the longest one is 40～50km.Some of this set of faults result from reactivation of NE—NEE trending Tertiary faults,and the rest are the newly-generated.They form a NE-striking fault zone about 50km wide with right-lateral strike slip component.This fault zone is not controlled by Tertiary faults;it is a newly generated fault zone during Neogene.It proves the former speculation of the existence of the newly-formed Yellow River Estuary-Northwest Miao fault zone.

The Longmenshan Fault zone,trending in NE,lies between the Songpan-Ganzi orogenic belt and the Yangzi block.It consists of four major faults,such as the Houshan Fault,and related thrusting sheets.It is a nappe structure characterized by forward spreading.It formed during the Indo-China movement and was active many times since then.Since the Quaternary,this fault zone has been very active,and exhibits differential activity on its various sections.In this work,we make an integrated analysis of this fault zone based on data of geomorphology,geology,Bouguer gravity anomalies,and earthquakes.The results show that the near NS-striking Leidong Fault,located along Beichuan-Anxian,is the boundary between the middle and northeastern sections of the Longmenshan Fault zone.The two sections have high distinctive activity.The middle section is very active since late Pleistocene time with frequent medium-and small-sized earthquakes,while the northeastern section has weak activity since Quaternary with occasional small earthquakes.Due to the compression and uplift of the Tibetan Plateau and lateral sliding of blocks,the Sichuan-Qinghai block moves towards SEE,resulting in an active boundary of the block.This boundary includes the Mingshan uplift and the middle and southwestern sections of the Longmenshan Fault zone,both of which are truncated by the Mingshan uplift.And the northeastern section of the Longmenshan Fault zone has been abandoned.

The Indonesia region is one of the most seismically active zones of the earth. On December 26, 2004 an M_S 8.7 (given by China Seismograph Network, M_W=9.3 given by USGS) earthquake occurred off the west coast of northern Sumatra, Indonesia. Its magnitude classifies it as the fourth largest earthquake in the world since 1900 and the largest since the 1964 Alaska earthquake. The spatial distribution of the relocation of larger aftershocks (M＞4.5) following the main shock suggests a length and width of the rupture of about 1200km and 200km, respectively. The shock triggered massive tsunamis that affected several countries throughout South and Southeast Asia. It is a shallow interplate event of thrust type in the trench. Its epicenter is located at the northwestern end of the Indonesia-Melanesia plate boundary tectonic zone. In 2004, eight events of M≥7 happened in this zone, showing a migration from east to west. It implies that these shocks represent a correlated and consistent dynamic process along this subduction zone. These interplate events are associated with convergence of several plates and their fast motion in this region, which result in strong and complex structures and deformation. The India-Australia plate is underthrusting toward the Sunda continental block or Burma plate at a low angle, producing a great locked area on the shallow portion of the subduction zone where enormous strain is accumulated. Interseismic uplift recorded by coral growth and horizontal velocities measured by GPS show the geometry of the locked portion of the Sumatra subduction zone. The vertical and horizontal data are reasonably well reconciled with a model in which the plate interface is fully locked over a significant width. This locked fault zone extends to a horizontal distance of 132km from the trench, which corresponds to a depth of 50km. The sudden ruptures and large-scale slip of this locked area as the release of stress are the direct cause of the M 8.7 earthquake near Indonesia in 2004.

The Zhangjiakou-Bohai fault zone in the northern part of North China area is a seismotectonic zone controlling the present-day strong earthquake activity. Under the effect of NEE-directing regional principal compressive stress,a series of NE trending active tectonic zones were engendered in this area. Together with the Zhangjiakou-Bohai fault zone,they make up a group of conjugate shear fracturing systems,controlling the occurrence of the present-day strong earthquakes. This paper focuses mainly on the feature of crustal deformation around this fault zone. The secular GPS crustal deformation image has reflected the relatively complete left-lateral strike-slip movement of this active fault zone. However,the crustal deformation images of different stages indicate that a series of NE-trending large-scale anomalous gradient zones appeared along the Zhangjiakou-Bohai zone before the occurrence of moderate strong earthquakes. These anomalous zones have indicated separately the activities of the Tangshan-Hejian,Sanhe-Laishui and Yan-huai-Shanxi seismotectonic zones,and represented the medium term precursors of the moderate strong earthquake along the Zhangjiakou-Bohai fault zone. Furthermore,the results of this study suggest that the crustal deformation that appears before the occurrence of strong earthquake reflects the strain activity in the deep seismogenic zone,while the disorderly and unsystematic crustal deformation images that occur after the occurrence of strong earthquake reflect the adjusting movement of the covering strata.

The basic principle and method of crustal stress measurement by borehole breakouts are introduced in this paper,and some problems in determining the direction of the horizontal principal stresses from the shear rupture of the borehole walls are discussed.Several thousand groups of data obtained from the logs of four-arm dipmeter of 15 oil wells in Damintun depression of Liaohe oil field were collected.Basing on the statistics and analyses of these data,we calculate the predominant direction of the long axes of borehole breakout ellipses in each oil well at different depths in order to reveal the variation of the principal stress directions with depth.On the basis of the predominant directions of the long axes of borehole breakout ellipses,we calculate and acquire the predominant directions of the maximum horizontal principal stress at different depths for all15oil wells.The results show that the predominant direction of the long axes of the borehole breakout ellipses is about N10°W—N10°E,while the predominant direction of the maximum horizontal principal stress is about N80°～100°E,with a mean of N90°E and a general trend of NEE.This conclusion coincides well with the values obtained from focal mechanism solutions.The variation of the predominant direction of the maximum horizontal principal stress with depth is relatively small,about10°～15°.This may indicate that the direction of modern tectonic stress field in Damintun depression of Liaohe oil field is stable and is possibly controlled by the same tectonic stress field.

The Bohai Sea is located in the east of the Bohai Bay Cenozoic rift basin, and has been characterized by intense tectonic activities since Quaternary time. Many major earthquakes of M≥7 had occurred in this area in history. Although a great number of detailed studies on the land part of the basin have been made, little has been done on the research of the Quaternary sediments in the Bohai Sea area. The isopach map of Quaternary system for this area has not been compiled so far. Basing on the previous studies, we used the data of the thickness of Neogene - Quaternary system, and the thickness of the Guantao and Minghuazhen Groups of Neogene to compile the isopach map of the Quaternary system with the help of GIS and image processing. This map shows that the Quaternary system is generally 300～600m thick, and locally 800～1000m thick in the studied area. The isopach in the western and eastern parts of the Bohai Sea exhibits NW- and NE-trending belt-like shape, respectively.

Previous studies suggested that the Kuqa, Xinjiang M7.4 earthquake of 1949 is associated with the NEE trending Qiulitage Fault of the active tectonic zone at the southern foot of the Tianshan Mountain. Recently we have made a more detailed analysis of the seismotectonic setting of this event based on new data and results of crustal seismic sounding, petroleum geology, and research of active faults. Our work indicates that the underthrusting of the Tarim block beneath the Tianshan, as well as faulted block uplift and lateral overthrusting and spreading of the upper crust of Tianshan have given rise to the development of the Kuqa basin and thrust-fold system along the southern margin of the Tianshan Mountain. All these are thin-skinned structures developed in the sedimentary cover. The NE-trending Kuqa-Yixi No.1 Well Fault is an important transfer fault in the Kuqa basin, which is located in the NE-trending Urumqi-Kuqa-Keping tectonic zone. The results of seismological research on the M7.4 earthquake indicate that the earthquake bears no relation to the Qiulitage Fault, but is related to the Kuqa-Yixi No.1 Well Fault.

The latest geological and geophysical data show that the Cangdong fault is a listric fault in the upper crust. The plane of the fault becomes a detachment plane at the 10km depth in the crust. The Cangdong fault has undergone two rifting processes in Mesozoic and Cenozoic time. It formed in late Jurassic as a normal fault, and became a thrust fault by the end of early Cretaceous. It was a normal fault in Eocene, evidenced by the Mesozoic structure, and controlled the distribution of stratum of early Tertiary. Palaeogene is the major active period for the Cangdong fault, the major character of the fault formed in this period. The fault's occurrence, development history and activity are different in different segments. The activity of the fault has been weak since Neogene. Based on the shallow seismic exploration, it is suggested that the Cangdong fault is not active since later Pleistocene on the whole and has little seismicity.

We have made a study to the piedmont fault zone of Taihang Mountain based on geological and geophysical data of recent years. Our new insights suggest that this fault zone began to emerge in Mesozoic and formed mainly in Early Tertiary. It consists of a series of NE-NNE strike faults, which were arranged obligue in a left-lateral manner. Its structures and activities have evident segmentation. Along the middle and north segment, the faults, such as the Baoding-Shijiazhuang fualt, are of large detachment faults. They stretch about 70km horizontally in the tilt direction with horizontal offsets of 17km and vertical offset of 5000-6000m during Early Tertiary. This fault zone belongs to the detachment structure in the upper crust rather than a deep fault. It has weak activities since Quaternary and has no direct cause relation with major earthquakes. It is, however, still somewhat of importance to studies of regional seismotectonics and earthquake prediction, because both the south and north section of this fault zone intersect with other seismic zones which have different strikes.

The Yingkou-Weifang fault zone, which is practically one part of Tanlu fault zone in Liaohe-Bohai, lies in the east edge of Bohai Gulf Cenozoic rift basin. It can be divided into two parts, the northern and southern part, by the Beijing-Penglai fault zone. The northern part consists of two faults which interweave like a braid each other. The southern part consists of two parallel faults, and is cut into four parts by Huangbei, Laibei, and Weibei NEE trending fault. The horizontal stretch and vertical movement of the northern part of the fault zone are strong in the Paleogene period, controlls the rifting basin development; nevertheless the right-lateral slip has been prominent since the late Oligocene. The activity of the southern part is weak in the Cenozoic Era, but the cross faults have evident horizontal stretch and vertical action. In the Cenozoic Era, the activity of the fault zone migrated to the middle part from the northern and southern part, and the activity of northern part probably also had the trend from west to east. A NE trending seismic zone, which obliquely cross the Yingkou-Weifang fault zone in the middle of Bohai, is probably the extending part of the Huangheko Liaocheng newly generated seismotectonic zone towards the sea.

The Zhangjiakou penglai Northwest trending fault zone is an important seismotectonic zone in North China.We have done a preliminary study about its seismotectonic characters on the basis of the geological,geophsical and seismic activity data.The fault zone,which consists of nearly 20 NW-NWW trending faults,is a crust structure one which has an important controlling effect on the regional teconics of the Cenozoic Era.The fault zone is left lateral slip on the whole.In the Palaeogene period the zone's middle part was very active,after that its northwest and southeast sections became active in the Neogene period.The fault zone merges with several NE trending active teconic zone,so it owns a kind of tectonic combination that NW and NE trending faults intersect each other and includes 5 complex tectonic merging parts.The major earthquakes of M≥6 and most of middle small earthquakes assemble these parts.Both NW and NE trending fualts can cause earthquakes.So it demonstrates the character of conjugate ruptures.But the NE trending fault can produce bigger earthquakes than those of NW trending fault.The Zhangbei Shangyi 6.2 earthquake can be the result of northwestward extending along this fault zone.

By the analysis of deformation in outcrop area and fissure measurement of core rocks in Zhangqiang depression and its adjacent area, we divide the geological history of this region into eight tectonic stress phases and determine the tectonic stress states and deformation forms of each phase. We conclude that the tectonic stress fields of the late Jurassic and the Cretaceous resulted in the formation and development of faulted basins, and the stress state of the late Jurassic was nearly E-W extension. Between the end of Fuxin Group and the beginning of Quantou Group sedimentation stages, the stress fields resulted in the close of basin faulting stage and deformation of the late Jurassic caused by the change of stress states from E-W extension to E-W compression. In the Cretaceous phase, the principal stress direction was E-W compression which caused the regional depression as a whole in the early period and uplifting and erosion widely in the later time. The principal stress direction was NW-SE compression in the Eogene, and was NEE-SWW compression since the Neogene. Two phases of stress fields in Cenozoic only caused some reactive faults, the deformational strength was less than that in Jurassic and the Cretaceous.

On the basis of the data of seismicity,geological structures and geophsics,we have done an analysis on the seismogeological chracteristics of the Jiexiu-Xinxiang-Liyang northwest trending seismic zone located in the southeast area of North China. This seismic zone is a recent crust shear rupture zone under the uniform modern tectonic stress field in a large scale; and along it there are a series of newly-generating northwest trending faults which continued or began to develop since the Neogene period. They make up an active fault zone which extends through different tectonic units. Therefore,it is a newly formed seismic zone.

In the study of seismotectonics,much attention is usually paid to active fault zones which have long evolution history and large scales.However there are also newly-generated seismotectonic zones in the recent tectonic stage.Seismicity has a close relation with both kinds of tectonic zones.It can be seen that Tangshan-Hejlan-Cixian seismic zone is a new crustal shear fracture zone which has been developed since the Neogene as well as a newly-generated seismotectonic zone in North China based on analysis of the data of earthquakes and geological structures.

Jianghan-Dongting Lake basin is a large-scale Meso-Cenozoic basin in South China. Its geological structure, deep-seated structure, tectonic evolution, neotectonic activity and seismicity are analysed basing on the data of geology, geophysis and earthquakes in the basin region.The basin consists of Jianghan and Dongting Lake depressions and Huarong uplift. WNW-EW-trending secondary segs and positive land forms controlled by the faults developed in Jianghan depression, but NEN-NE striking secondary positive forms and segs controlled by the faults developed in Dongting Lake depression. The basin has undergone a complex process o'f tectonic evolution. There is intensive neotectonic activity in the basin region. Mid-intensity earthquakes are closely related to the structures with differential activities in Quaternary.

Based on comprehensives analysis of deep structure, formation of Cenozoic basin and its dynamical characteristics, the formation mechanism of the basin and its relation to movement of the upper mantle in the eastern part of North China are discussed in this paper. The experimental study have been carried out using the centrifugal technique, in which the differential density of material is adopted instead of differential temperature.The experimental result shows that the upper mantle convection, the upheaval and diapirism and the gravity isostasy produce a monodirectional tensile force for the movement of the continental crust in North China. The tensile force represents a main mechanism for formation of dustpan-shaped basin.The authors suggest that the driving force for formation and development of the eastern North China basin is closely related to gravitational effect and movement of the upper mantle.

From new data of tectonic evolution,fault activity,neotectonic movement,recent tectonic activity and seismicity in Beijing area,the authors suggest that the characteristics of neotectonic movement in the northern and southern parts of this area are different. Neotectonic activity in the southern part is weaker than that in the northern part. Seismic risk in the future has also the same tendency.

Based on the recent data from petroleum geological prospecting and the reexplana-tion of the relevant segment of deep seismic sounding profile from Yuanshi county, He-bei Province to Jinan, Shandong Province, the tectonic background and causative fault of Xingdai MS7.2 earthquake have been analysed in this paper. The results have shown that the epicentre of MS7.2 earthquake was located at the eastern margin of southern sub-depression within Shulu fault basin. The sub-depression developed in a fault block which was formed from the cover of platform cut and bound by four listric faults. There are two high angle faults beneath the fault block. By contrast with previous opinion, the authors propose that there is no simple corelation between seismicity, major fault and fault-controlled depression. The causative fault of MS7.2 earthquake was neither the gentle-dipping Xinghe listric fault, nor the high angle F3 fault, and the deep-seated eastern fault, but was the combination of the three faults. The high angle fault was the main part of the causative fault.

Basined on comprehensive prospecting and investigation, the authors have ascertained that the 1679 San-he-Pinggu M = 8 earthquake occurred in the intersection region of active faults having deep-seated structural background. The NE-trending New Xiadian Fault, which was characterized by dextrall tensile-shear dislocation, was the seismogenic fault of the 1679 M = 8 earthquake. It is suggested that the macroscopic epicenter of the earthquake should be located in Pangezhuang area, where the vertical displacement of seismic faul’ was up to 3.16m. According to the average seismic slip rate in this area, and the displacement value of earthequake with a certain magnitude, the recurrence interval of M = 7.5, M=7.0 and M = 8.5 earthquakes in the magistoseismic area of 1679 M = 8 earthquake on Xiadian Fault Zone have been estimated to be 3800,1750, and 800 years (the lower limit), respectively.