Pangusi-Xinxiang Fault is a great-scale, deep-incising buried active fault in the southern margin of the Taihang Mountains. In order to find out the location, characteristics, structure and activities of Pangusi-Xinxiang Fault, shallow reflection profiles with six lines crossing the buried faults were carried out. In this paper, based on the high-resolution seismic data acquisition technology and high-precision processing technology, we obtained clear images of underground structures. The results show that Pangusi-Xinxiang Fault is a near EW-trending Quaternary active fault and its structural features are different in different segment. The middle part of the fault behaves as a south-dipping normal fault and controls the north boundary of Jiyuan sag; The eastern part of the fault is a north-dipping normal fault and a dividing line of Wuzhi uplift and Xiuwu sag. The shallow seismic profiles reveal that the up-breakpoint of the Pangusi-Xinxiang Fault is at depth of 60~70m, which offsets the lower strata of upper Pleistocene. We infer that the activity time of this fault is in the lower strata of late Pleistocene. In this study, not only the location and characteristics of Pangusi-Xinxiang Fault are determined, but also the reliable geological and seismological evidences for the fault activity estimation are provided.

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.

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.

This paper describes the complexity of geological structures and tectonic features in shallow seismic prospecting,as well as the particularity of higher accuracy requirement for its achievements. It is suggested that it should be very important to develop prestack depth migration method for shallow seismic prospecting. The basic principle of prestack depth migration with phase shift method and its algorithm are also expounded in detail,and the relevant PC program is compiled. Based on this method,two theoretic models are tested,and good results are obtained. The results show that the stratigraphic horizons are displayed clearly in the prestack depth migration sections,and the characteristics of geological structure and tectonic features of the theoretic models are expressed fairly well. Furthermore,the method has been applied to process the actual shallow seismic reflection data,and the obtained results are identical with the known geologic structures and tectonic features. All these results demonstrate the reliability and applicability of this algorithm and its software. It is clear that the prestack depth migration method can be effectively used in the processing of actual shallow seismic reflection data.

In addition to a brief account of characteristics of disturbing waves in urban shallow seismic exploration, an exposition of technical facilities and seismic data acquisition techniques for anti-jamming and high-resolution shallow seismic exploration is given in this paper on the basis of shallow seismic experimental data of active fault surveying in Fuzhou City. The technical measures taken for anti-jamming, improving signal to noise ratio and resolution of seismic data are expounded as well. The experiment shows that the effective approach to accomplishing anti-jamming, high-resolution shallow seismic data acquisition is receiving with mini trace intervals, mini offsets, multi-channel and high-frequency Geophones by using mini-vibrator and the matched seismograph.

The Tianshan Mountains are a late Cenozoic rejuvenated mountain range in central Asia. The Urumqi Range front Depression is located along the northern margin of the Tianshan Mountains, consisting of a series of reverse fault-and-fold zones that form a typical thin skinned structural system. The southern Junggar Fault separates the Tianshan Mountains from the Urumqi Depression, in which three rows of reverse fault-and-fold zones are developed. From south to north, the three fault-and-fold zones are named Qigu reverse fault-and-fold zone, Manas reverse fault-and-fold zone and Dushanzi reverse fault-and-fold zone, respectively. Except for the anticlines in Qigu reverse fault-and-fold zone, the other anticlines in the Manas and Dushanzi reverse fault-and-fold zones are fault propagation fold. The shallow seismic exploration profiles show that the anticline consists of an overthrust fault zone, backward reverse fault and two partial anticlines. Four oil seismic exploration profiles show that the lower detachment fault exists in the Jurassic coal bearing strata, and the upper detachment fault exists in Paleogene strata. Some active folds are only formed on the ramps at the front of detachment fault. 2D electrical structure, deep seismic reflection profiling and crustal velocity structure across the northern Tianshan piedmont indicate that the active multilayered thrust tectonic system in the Urumqi Depression joins to a low-velocity(low resistance)layer through a brittle ductile transition zone in the crust of the Tianshan. The low-velocity layer in the upper crust of the Tianshan may be an active ductile shear zone. The brittle ductile transition zone under the Qigu reverse fault fold belt is the key link between the deep-seated active ductile shear zone and the shallow brittle fracture, and it is also the place of strong earthquake generation. The active surface structures in Manas earthquake region recorded only a part of the information of the activities of the deep-seated ductile shear zone.