The research area involved in this paper is the middle-southern segment of Liaocheng-Lankao fault zone(Lanliao fault zone)and its adjacent area. In order to study the fine crustal structure image and the tectonic features of the faults in this tectonic zone, we conducted a 70km-long deep seismic reflection profile along EW direction in Puyang City, Henan Province and got clearer lithospheric structure image along the profile.

As regards data acquisition, we applied the geometry with 30m group interval, 1 160 recording channels and more than 90 folds. Seismic wave exploding applies the 30kg shots of dynamite source with the hole depth of 40~50m. In addition, in order to ensure the signal-to-noise ratio of the deep reflector, explosive quantity of dynamite source is increased to 96kg every 1 000m interval. In data processing, the most important thing is to improve the signal-to-noise ratio. Data processing methods mainly include one-dimensional time-varying filtering combined with two-dimensional filtering, tomographic static correction, residual static correction, deconvolution, normal moveout correction(NMO), dip moveout correction, common mid-point(CMP)stack and post-stack denoising, post-stack migration, etc.

The section with high signal-to-noise ratio has been obtained. There are obvious characteristics of reflection wave groups in the crust, which reflects abundant information about geological structure. On this section, according to this study, the characteristics of deep and shallow structure and crustal reflection structures on both sides of the Lanliao fault zone are obviously different. The crust in this area is composed of brittle upper crust and ductile lower crust. There are rich reflective layers and clear tectonic framework in the upper crust. In the western area of Lanliao fault zone, there is a set of dense reflectors with strong energy, which reflects the sedimentary interface of different times since Mesozoic in the basin. The basement slope with gentle dip to the east is the bottom boundary of the “dustpan-shaped” sedimentary depression. The reflected wave of the crystalline basement presents a group of strong reflection wave groups with good continuity in the eastern area of Lanliao fault zone, which are parallel unconformities on the Ordovician strata of Paleozoic or older strata. There are some secondary faults in the hanging wall of Lanliao Fault, which together with the Lanliao fault zone control the tectonic framework of “dustpan-shaped” sedimentary depression, the Dongpu sag. The reflection structure of the lower crust is relatively simple. On the whole, it is mainly arc reflection with strong energy and short duration.

The depth of Moho surface beneath the central-southern Lanliao fault zone in this area is 31.7~34.8km, where the fault is characterized by a strong reflection band with piecewise continuous distribution in horizontal direction and a duration of about 0.3~0.8s in vertical direction. And it is a transition zone with a certain thickness after geological deformation, rather than a sharp first-order discontinuity, which is consistent with the research results of Li Songlin et al.(2011). This profile reveals 2 deep faults(F_D1 and F_D2)that offset the Moho surface, extend down to the top of the upper mantle and create conditions for the upwelling of hot materials from asthenosphere and the energy exchange in this area. It may also be the cause of arc reflection in the lower crust.

The deep seismic reflection profile shows that faults in the upper crust are well developed. Lanliao Fault is the largest boundary fault in this area, which controls the formation and evolution of the “dustpan-shaped” sedimentary depression and plays an important role in the filling of Paleogene strata in the sag. Pucheng Fault F_P1 and Weixi Fault F_P3 are developed in the hanging wall of Lanliao Fault, which are basement normal faults in the same direction as Lanliao Fault and control the structural framework of the depression. Pucheng Fault, Weixi Fault and Lanliao Fault constitute a domino fault system, which makes the basement of the depression incline to the SEE direction. In addition, a reverse secondary normal fault(Changyuan Fault F_P2)is developed in the hanging wall of Lanliao Fault, which intersects with Weixi Fault F_P3 at TWT 3.0s. These faults and Lanliao faults jointly control the basic structural pattern of the sedimentary sag.

The deep and shallow tectonic framework in this area is controlled by the shallow faults in the upper crust and the deep faults in the lower crust. Deep faults(F_D1 and F_D2)create conditions for the upwelling of hot materials from asthenosphere, while shallow faults play an important role in the formation and evolution of basin structures.

The Anqiu-Juxian Fault is the latest active fault in Tanlu fault zone, which is also the seismogenic fault of Tancheng M8.5 earthquake in 1668. In order to probe the shallow structure and the characteristics of faults in the eastern graben of Tanlu fault zone, we applied the high-resolution shallow seismic reflection method with multifold overlaying and stacking. In addition, we laid out two shallow seismic reflection lines across the Anqiu-Juxian Fault and the eastern graben of Tanlu fault zone. The shallow seismic profiles clearly reveal the stratigraphic interface morphology and shallow fault characteristics. The results show that the eastern graben of Tanlu fault zone is a graben basin consisting of multiple faults, and the thickness of Quaternary strata and graben structure characteristics are obviously affected and controlled by Changyi-Dadian Fault F₁ and Baifenzi-Fulaishan Fault F₂. Also, the eastern and western sides of the graben are the basement uplift areas, and the sediment thickness of the Quaternary strata in uplift areas is less than 30m. There are thick Cenozoic strata deposited in the barben, the stratigraphic morphology changes greatly laterally, showing an inclined form which is shallow in the west and deep in the east, and the Cenozoic strata are in angular unconformity contact with the overlying strata. The deepest part of Quaternary strata in the graben is located near the horizontal distance of 7400m, and its depth is about 190m. The Anqiu-Juxian Fault revealed by the shallow seismic reflection profile is composed of two branch faults dipping in opposite direction, which merge into one fault in the deep section. According to the discernible buried depth of the upper breakpoints of these faults and the characteristics of the Quaternary activity, the activity of Baifenzi-Fulaishan Fault on the western boundary of the eastern graben of Tanlu fault zone is relatively weak and the discernible depth of the upper breakpoint is 53m, we infer that the Baifenzi-Fulaishan Fault is a pre-Quaternary fault. The Changyi-Dadian Fault on the eastern boundary of the eastern graben of Tanlu fault zone not only cut the bedrock’s top interface, but also revealed signs of dislocation since Quaternary. The discernible depth of the upper breakpoint of Changyi-Dadian Fault is about 26~33m. The Anqiu-Juxian Fault is the latest active fault in the study area, which possess the characteristics of large scale and large penetration depth. The fault controls the deposition of the Cenozoic strata in the graben and plays an important role in the formation of the the eastern graben of Tanlu fault zone. The discernible depth of the upper breakpoint of Anqiu-Juxian Fault is about 17~22m. Therefore, we infer that the active ages of Changyi-Dadian Fault and Anqiu-Juxian Fault are the late Pleistocene and Holocene, respectively. The research results can provide seismological evidence for further understanding of activity mode and activity age of the seismogenic fault of the 1668 Tancheng M$8\frac{1}{2}$ earthquake, as well as the near-surface characteristics and activity of the Banquan segment of the Tanlu fault zone.

The study area is located at the junction of the northern margin of the Qinling orogenic belt and the southern margin of the North China Block. In order to study the fine crustal structure and the deep-shallow structural features of faults in this area, we conducted deep seismic reflection profiling with the seismic profile of 100km long, directing NE-SW in Zhumadian City, Henan Province, and got clear lithospheric structure images along the profile. As regards the data acquisition, we applied the geometry of 25m group interval, 1000 recording channels and more than 60 folds. Seismic wave exploding applies the 30kg shots of dynamite source with the borehole depth of 25m. The shot interval is 200m. In data processing, we focused on improving the signal-to-noise ratio. Data processing methods mainly include first break removal, tomographic static correction, abnormal amplitude elimination, amplitude compensation, pre-stack denoising, surface consistent deconvolution, velocity analysis, several iterations of the residual static correction, dip moveout, post-stack time migration and post-stack denoising, etc. The profile with high signal-to-noise ratio was obtained. The reflection wave group characteristics is obvious in the crust, which reflects abundant information about geological structure. Along the profile, the crust is characterized by double-layer reflection structure, and the Moho surface is composed of a series of laminated arc-shaped strong reflections. The thickness of the upper crust is about 14.8~20.7km, and the total thickness of the crust is about 32.0~35.1km. The upper crust is dominated by the inclined, densely stratified or arc-shaped reflections. The lower crust is dominated by arc-shaped and inclined reflection, and there is a reflective transparent zone under the Moho surface. The reflection sequences with different directions and shapes in the upper crust constitute the nappe structure in southwest segment and the structural model of two concaves with one uplift in NE segment, which correspond to the north Qinling nappe, Zhumadian-Huaibin depression, Pingyu-Xiping uplift and a secondary depression, respectively. There are abundant arc-shaped reflection sequences in the lower crust, which may represent multi-stage magmatic activities. The deep seismic reflection profile shows that faults in the upper crust are well developed. According to the characteristics of reflected wave field in the profile, four groups of fault structure which contain ten faults with different scales are interpreted. Among them, faults F_P1, F_P2 and F_P3 constitute the thrust fault system in the northern margin of Qinling Mountains, and F_P5 and F_P7 are boundary faults of Zhumadian-Huaibin depression. These faults are all developed within the upper crust. In addition, the Fault F_PM is a large fault that cuts through the lower crust and Moho surface. The deep seismic reflection profile reveals the crustal structure and deep-shallow structural features of faults at the junction of the northern margin of the Qinling orogenic belt and the southern margin of the North China block, which provides seismological evidence for the analysis of structural differences, the deep earth's interior processes and deep-shallow structural relationships between the Qinling-Dabie orogenic belt and the southern margin of the North China block. The lower crust of the study area is divided into two parts by deep faults that dislocate the Moho surface. These two parts have distinct reflective structures, suggesting that the area has experienced intense complex tectonic movements. The faults in the upper crust control the formation of basin-mountain structure and stratigraphic deposition of this area. And deep faults in the crust that disrupt Moho surface create conditions for the upwelling and energy exchange of deep materials. All of these have regulated the composition of material and the distribution of energy in the crust. The deep faults cutting through the lower crust and Moho surface and the south-dipping arc-shaped and inclined strong reflection sequences developed in the lower crust should indicate the large-scale subduction of the southern margin of the North China block towards the south-trending Qinling orogenic belt.

The Zhuyangguan-Xiaguan fault is a major fault in the Nanyang Basin. Together with the the Shangxian-Danfeng fault in the south and the Tieluzi fault in the north, it serves as the north boundary of the East Qingling Mountains, as well as the dividing line between North China and South China blocks. This work studied the spatial extension, activity and shallow structure of Zhuyangguan-Xiaguan Fault by combination of shallow seismic exploration of three profiles across the fault and a composite drilling cross-section data.
The anti-interference and high resolution shallow seismic reflection exploration method based on Vibseis techniques was used in the seismic survey. The results show the existence of the main fault and its southern branch. It can be determined that the the Zhuyangguan-Xiaguan fault is a NWW-trending normal fracture. The composite drilling cross-section reveals that the buried depth of the fault's up-breakpoint is about 17.6 to 20.5 meters and the latest active time is the late Middle Pleistocene.
As one of the major buried faults in the Nanyang Basin, the Zhuyangguan-Xiaguan fault has restricted the development of Nanyang City for a long time due to its unclear location and activity characteristics. The results of this study can provide geological and geophysical evidence for seismic risk assessment and site selection for the major lifeline projects in Nanyang City.

To test the effect of three-dimensional seismic reflection methods used in active fault survey, we have done a three-dimensional shallow seismic reflection exploration experiment around the Luhuatai Fault in the west of Yinchuan Basin. The experiment uses swath geometry of 8 lines and 10 shots. Every two adjacent swaths overlap 3 survey lines, thus 5 swaths and 28 survey lines are laid in total. The ground sampling grid is 5m×20m and the CMP grid is 2.5m×5m. The data volume that reflects the three-dimensional spatial structure of the Luhuatai Fault is obtained.In data processing, we select the suitable three-dimensional seismic data process modules. The main processes are composed of raw data input, three-dimensional geometry defining and checking, anomalous trace edit and first arrival mute, spherical divergence compensation, surgical filtering to eliminate surface waves, surface-consistent amplitude compensation, surface-consistent deconvolution, velocity analysis and residual static correction(twice iteration), DMO and the third time velocity analysis, final stacking, three-dimensional post-stack de-noising and horizontally interpolating, one-pass 3-D migration.
3-D seismic data interpretation uses the way of human-computer interaction. Through a variety of methods such as multi-line profiles contrasting, time slicing, three-dimensional visualization, and 3-D coherence cube technology, the reflection horizons are discerned and tracked, and the three-dimensional data volume reflecting the spatial variation of strata and faults is obtained. The results after fine processing and synthetical interpretation show that the Luhuatai Fault consists of two normal faults that incline to each other. The major fault inclines to SE, and the minor fault inclines to NW. The distance between them gradually increases from north to south. In addition, the minor fault merges into the major fault at the depth of approximately 780~800m. The up-breakpoint of the major fault has a tendency of deepening from north to south. The up-breakpoint depth is about 25~30m in the northern part of experimental area, and about 35~40m in the southern part of experimental area.
The experimental results show that the three-dimensional seismic data has the advantages of large volume of data, information-rich, high accuracy of migration, and high precision of tomography. It can reflect the three-dimensional spatial distribution of strata and faults in different aspects, and it is beneficial for the imaging of complex structures and faults.

On July 28,1976,the great Tangshan earthquake(M7.8)occurred in the Tangshan area of Hebei Province,which shocked the whole world.Before this earthquake,there was no earthquake with magnitude over M7.0 in this area.After this earthquake,the crustal structures and tectonics around Tangshan earthquake area remain unclear.In order to investigate the fine crustal structures,the main fault geometries and the relations between the deep-shallow tectonics in this area,a deep seismic reflection profiling with 40m receiver spacing and 200m shot spacing as well as 60-fold across the Tangshan Fault zone was carried out in the Fengnan region of Tangshan in 2009.Because our results have much higher spatial resolution than that of previous results of deep geophysical prospecting,some new features of the crustal structures and fault tectonics were revealed by this study.The results show that the thickness of the crust is about 32～34km along the profile,the Moho gradually deepens from east to west.Between Fengnan county and Xuanzhuang town,the reflections in the middle-lower crust and crust-mantle transitional zone are staggered by the deep Tangshan Fault,and dislocation occurs on the Moho on both sides of the deep fault,indicating the strike-slip effect of the deep Tangshan Fault.Tangshan Fault belt revealed by deep seismic reflection profile is a huge intra-continental strike-slip fault,and its shallow part appears as a typical flower-shaped structure,incising and disturbing the lower crust and crust-mantle transitional zone in the deep part.The complex faults and structures coexisting in both deep and shallow parts of the crust are the tectonic background for the Tangshan Earthquake,and also an important factor controlling the earthquake activity in the area.

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.

The M_S 8.0 great Wenchuan earthquake of May 12th,2008 was generated by abrupt faulting of the Yingxiu-Beichuan Fault along the Longmenshan Fault zone.The earthquake produced not only the surface ruptures along the Yingxiu-Beichuan Fault and Guanxian-Jiangyou Fault,but also surface rupture,highway's pavement arching,sand-boils and waterspouts in various degrees in the areas such as Shifang and Mianzhu of the Chengdu plain.To know the shallow geological structures under the surface rupture zone,a high-resolution shallow seismic reflection profile of 6350m long in near-EW direction was completed.This profile is located at the Shigu town,Shifang city,where a suspected earthquake surface rupture zone was discovered.In this study,a trace interval of 3m,shot interval of 18m,and a 300-channel 25-fold observation system was used.In order to give consideration of both near-surface reflections and dipping interface imaging,we adopted the split-spread geometry and asymmetrical zero-offset receiving technique.For suppressing random-noise and raising signal to noise ratio of seismic data,30 times vertical stacking of vibrator signals was made for each common-shot gather after correlation of individual records.By using the above work method and spread geometry,we obtained high-resolution images of structures in the depth range of 15～800m after data processing.The result shows that there are the buried thrust fault thrusting to the plain and the back-thrust fault under surface rupture zone,and that the activity of the buried thrust fault may be the main causes for folding and deformation in near-surface strata and for the coseismic surface rupturing.

The investigation and study of fault activities are a basic work for urban earthquake prevention and disasters reduction.In order to find out the location,characteristics and activities of the Laoyachen Fault in Zhengzhou,the high-resolution shallow seismic P and S wave survey profiling across the Laoyachen Fault was carried out at the end of 2006,and different seismic sources along with combinations of diverse observation geometries with different parameters were used.The fine structures in different depths beneath the profile were obtained and the patterns as well as characteristics of the Laoyachen Fault were determined.The results show that the Laoyachen Fault,running in NW and dipping in NE,is a normal fault and its dip angle is about 60°～70°,which incises strata of Eocene,Permian,Carboniferous or Ordovician epoch and goes up to the top boundary of Eocene stratum at the 800～850m depth.There is no any reflector of offset stratum found in Q+N strata.The borehole geological sections across steep slopes of earth surface present that the layers inferred from reflected seismic wave groups of shallow seismic profile are well correspondent with boring geological layers.The borehole results reveal that the three reference laminas,i.e.the boundary between Malan loess and silt with clay soil at about 21m in depth,the calcareous gravel clay layer of 53.9m deep,and the calcareous silt layer of 61.9m deep,all have not depth variations at the two sides of surface steep slopes and are situated almost at the same ground surface elevations,which suggests that the steep slopes at the earth's surface should not result from the activities of Laoyachen Fault.In this study,through shallow seismic P wave and S wave exploration as well as combination of joint borehole geological sections,not only the location and characteristics of Laoyachen Fault was determined,but the geological and seismological evidences for the fault activity estimations were provided.

Yinchuan Basin is a graben-like downfaulted Cenozoic era basin located on the west edge of Ordos Massif.Its activity is violent and deposition is very thick.Yinchuan City is located in the middle of Yinchuan Basin.The seismic petroleum exploration shows that a buried active fault lies in the east of Yinchuan City,named as the Yinchuan buried fault,which strikes NNE and dips west,with a total length of more than 80km.Because the seismic petroleum exploration did not gain any explained signals at the depth ranging from 0 to 400m,so whether the Yinchuan buried fault is active or not in the late Quaternary and its exact surface projective location hasn't been known yet.It has been a “worry” in the urban planning and development of Yinchuan for a long time.Under the financial support of the national and local governments,we launched the project entitled “The prospecting of active fault and earthquake risk assessment in Yinchuan City”.In order to facilitate the exploration,we selected Xinqushao village in the southeast suburb of Yinchuan City to be the site for the integrated test exploration of the Yinchuan buried fault before the exploration,based on the information obtained from the seismic petroleum exploration.Considering that the thick Quaternary sediment in Yinchuan reaches to 1609m,and that the depositional environment is the Yellow River flood plain and the lateral change of lithology is complex,we adopted in the test exploration the train of thoughts of “inferring an unknown fact from a known fact,and from deep to shallow and directly to the top”.The experimentation has been developed step by step according the working order of multilevel seismic exploration→composite geological profile drilling→trenching.Along the same measuring line at Xinqushao,first,we adopted the seismic reflection exploration of primary wave in three levels with the group interval of 10m→5m→1m to catch the master fault of the Yinchuan buried fault,and by tracing upward layer by layer in the order of the three exploration ranges,i.e.1400～400m→600～80m→150～20m,the position of the master fault at ±20m depth under the ground and its offset trace were primarily identified.And then,along the master fault and within the range of 100m at its both sides,9 boreholes of 20.5～100m were arranged for the composite geological profile drilling.The resulting information about the throws of the master fault was obtained,they are 20.34m,9.66m and 2.25m respectively at the depth of 43.75m,20.33m and 13.04m from the ground,and the buried depth of the upper offset point ≤8.34m.At the same time,using the intact core specimen from the fault plane of the borehole No.7,we calculated the dip angle of the fault as 71°at the depth of 55.27m and figured out the exact position of its extension to the earth's surface.Finally,a large-scale trial trench,which is 40 meters long,8～12 meters wide and 6 meters deep,was arranged across the master fault.The trenching revealed that the actual buried depth of the upper offset point of the master fault is 1.5m and there are seismic remains,such as offsets of 5 stages,sand liquefaction and surface rupture,etc.Among the 5 stages offsets,4 events occurred prior to 3170±80 a BP,belonging to the mid to late Holocene paleo-earthquakes.The age of the last event cannot be determined and it is inferred to be the result of the M8.0 Yinchuan-Pingluo earthquake in 1737.In a word,through the comprehensive test exploration,we find that the Yinchuan buried fault is a Holocene active fault,which lays solid base for the next exploration.