Currently, the study on the active fault in the land areas is relatively mature, while there is still lack of detection and research on active faults in the sea areas. Marine exploration, which is different from land areas, has a prominent problem due to the existence of strong reflecting interfaces such as water surface and seafloor in the sea, thus the recording is often accompanied by interference of multiples on seafloor reflections. In addition, because of the characteristics of marine seismic exploration, the source exciting in the water and the geophone receiving in the water, ghost wave usually can be recorded simultaneously during the reflected wave propagation. This phenomenon makes it difficult to distinguish the effective waves and the noise, and has always plagued the data and seriously affects the quality of records. In the offshore and other regions of complex structures, such as inclined interfaces, it is difficult to eliminate the interference of multiples accurately by traditional multiples suppression methods, which are based on the horizontal interface assumption. This paper combines the sea area seismic data and its acquisition method, uses simplified model to simulate the multiples based on the time-distance analysis of multiples and their ghost wave in inclined interface. The time-distance characteristics of the multiples and their ghost waves from different interfaces(including the inclined interface)are obtained, and they are consistent with the actual records. The multiples time-distance simulation can help to distinguish the causes of reflected waves, summarize the multiple-wave time-distance characteristics from different interfaces(including inclined interfaces), and analyze the relationship between the characteristics of multiple waves and primary waves. In particular, this simulation has a significant effect on characterizing the internal multiples that are difficult to identify due to inconspicuous periodicity and the multiples of the inclined interface which present the phenomenon that the vertex of the time-distance curve is shifted. On this basis, relying on the time-distance analysis of ghost wave, we analyze the travel time difference characteristics between reflected waves and their accompanying ghost waves. The differences of the travel time characteristics of different orders ghost wave and reflected wave are summarized and the symmetry of the travel time difference between inclined interface and horizontal interface of ghost waves and reflected waves is analyzed. We simulate the distraction of the ghost wave event with the event of the reflected wave and analyze the influence of the ghost wave on the sea area seismic records. These results can improve the practical interpretation of seismic data. At last, the time-distance information is used to synthesize sea area seismic records, which can help us carry out the effective data processing and understand the characteristics of the time-distance and velocity of multiples in different interfaces and the layer artifact caused by multiples. This study combines the time-distance simulation of multiples and their ghost wave with conventional seismic data processing to analyze the pre-stack and post-stack features of multiple waves and their ghost waves in the seismic records of the sea area. The results of this study are conducive to the effective identification of multiples in seismic records in the sea, provide a theoretical basis for multi-wave suppression and prediction, and may facilitate the future study of sea-area seismic activity detection.

The Pengxian blind fault is a typical active fault in the central Longmen Shan front belt. It has important reference value for understanding the growth mode and process of the eastern Tibetan plateau. Because the fault is covered by the thick Upper Cenozoic strata in the western Sichuan Basin, its three-dimensional spatial distribution, structural style and formation mechanism remain unclear. In this paper, based on several high-resolution 3-D seismic reflection profiles, together with near-surface geological data and borehole data, we investigate the structural geometry of the Pengxian blind fault and build a 3-D model based on the results. We analyze the shape and scale of underground spatial distribution of the fault through a three-dimensional fault model. According to the theory of fault-related fold and fold-accommodation fault, this paper discusses the forming mechanism of the Pengxian buried structures. The shallow tectonic deformation in front of Longmen Shan is closely related to the detachment layer of the Middle and Lower Triassic, and this detachment layer f1 horizontally propagates into the Longquanshan anticline in the western Sichuan Basin. The Pengxian buried fault is a typical fault-bend fold and the f1 horizontally propagates into the western Sichuan Basin with a fault slip of 3.5km. The Pengxian blind fault is a high angle(50°~60°)thrust fault developed in the front wing of the kink-band zone, striking NE-SW, with a total length of~50km; But the fault is not connected with the Dayi buried fault in the south section of Longmen Shan. They are two different faults, and this defines the scale of the Pengxian blind fault. This limitation makes sense for analyzing and evaluating the magnitudes of potential earthquake. All above study provides research basis for further analysis of the potential seismic risk in this area. The Pengxian blind fault is parallel to the anticlinal axis with small amount of offset as a fold-accommodation fault. We believe that the fault formation is related to the fold deformation of the fold front limb. The study reveals the geometry, kinematics and formation mechanism of the Pengxian active fault, and provides a basis for further analysis of fault activity and hazard. Therefore, there is little possibility of strong earthquakes at the Pengxian blind fault due to its formation mechanism of the fault which is generally characterized by fold deformation and shortening deformation. In this paper, we discuss the location of Pengxian blind fault in the middle of Longmen Shan and Sichuan Basin. Because the Pengxian buried structures are in the transition area, the shortening amount in Pengxian indicates that the absorption in the basin is quite limited. It reflects the blocking effect of Sichuan Basin. In the study, we find that the relationship between folds, faults and sediments is an important part of tectonic interpretation; the theory of fault-related fold and fold-accommodation fault is well used for analysis. This would have great significance for the study of structural deformation, which can help to build a three-dimensional model of fault.

With the development of photogrammetry technology and the popularity of unmanned aerial vehicles (UAVs)technology in recent years, using UAV photogrammetry technology to rapidly acquire high precision and high resolution topographic and geomorphic data on the fault zone has gradually become an important technical means. This paper first summarizes the basic principle and workflow of a new digital photogrammetry technology, SfM (Structure from Motion), which is simple, efficient and low cost. Using this technology, we conducted aerial image acquisition and data processing for a typical fault landform on the northern of Caka Basin in Qinghai. The digital elevation model (DEM)with 6.1cm/pix resolution is generated and the density of point cloud is as high as 273 points/m². The coverage area is 0.463km². Further, the terrain and slope data parallel to the fault direction are extracted by topographic analysis method, and combined with the contour map and the slope diagram generated by the DEM, a fine interpretation and quantitative study of complex multilevel geomorphic surfaces is carried out. Finally, based on the results of sophisticated interpretation of geomorphology, we got the vertical displacements of the T₁ terrace to the T₃ terrace as (1.01±0.06)m, (1.37±0.13)m and (3.10±0.11)m, and the minimum vertical displacements of the T₄ terrace and the T₅ terrace as (3.77±0.14)m and (5.46±0.26)m, respectively, through the topographic profile data extracted by DEM. Such vertical displacement parameters are difficult to obtain directly by traditional remote sensing images, which shows the great application prospect of UAV photogrammetry technology in the quantitative study of active tectonics.

Traditional method to generate Digital Elevation Model (DEM)through topographic map and topographic measurement has weak points such as low efficiency, long operating time and small range. The emergence of DEM-generation technology from high resolution satellite image provides a new method for rapid acquisition of large terrain and geomorphic data, which greatly improves the efficiency of data acquisition. This method costs lower compared with LiDAR (Light Detection and Ranging), has large coverage compared with SfM (Structure from Motion). However, there is still lack of report on whether the accuracy of DEM generated from stereo-imagery satisfies the quantitative research of active tectonics. This research is based on LPS (Leica Photogrammetry Suit)software platform, using Worldview-2 panchromatic stereo-imagery as data source, selecting Kumishi Basin in eastern Tianshan Mountains with little vegetation as study area. We generated 0.5m resolution DEM of 5-km swath along the newly discovered rupture zone at the south of Kumishi Basin, measured the height of fault scarps on different levels of alluvial fans based on the DEM, then compared with the scarp height measured by differential GPS survey in the field to analyze the accuracy of the extracted DEM. The results show that the elevation difference between the topographic profiles derived from the extracted DEM and surveyed by differential GPS ranges from -2.82 to 4.87m. The shape of the fault scarp can be finely depicted and the deviation is 0.30m after elevation correction. The accuracy of measuring the height of fault scarps can reach 0.22m, which meets the need of high-precision quantitative research of active tectonics. It provides great convenience for rapidly obtaining fine geometry, profiles morphology, vertical dislocations of fault and important reference for sites selection for trench excavation, slip rate, and samples. This method has broad prospects in the study of active tectonics.

The theories, techniques and methods for the exploration of active faults in the terrestrial domain are relatively mature, while such efforts in the water domain remain very few. In this study, the AAE shallow profiler was used to detect the underwater three-dimensional topography and active faults in the Qionghai area, Xichang for the first time. Based on the SKUA-GOCAD software platform and its DSI interpolation method, three-dimensional modeling of the exploration data was carried out. The survey profiles clearly reveal three different reflection interfaces, including the underwater interface, the interface between the silt layer and shallow sedimentary layer, and the bottom of the shallow sedimentary layer. The three-dimensional topography of the Qionghai area was mapped initially. Moreover, evidence of active faults was first found in several survey profiles from the reflection interface cutoff. This study also analyzed and discussed the working principle and characteristics of the AAE shallow profiler, including their parameters and various factors of exploration. The mapped three-dimensional topography and active faults in the Qionghai area of Xichang can provide a reference for research on the active tectonics underwater in the future.

Qilian Shan and Hexi Corridor, located in the north of Tibetan plateau, are the margin of Tibetan plateau's tectonic deformation and pushing. Its internal deformations and activities can greatly conserve the extension process and characteristics of the Plateau. The research of Qilian Shan and Hexi Corridor consequentially plays a significant role in understanding tectonic deformation mechanism of Tibetan plateau. The northern Yumushan Fault, located in the middle of the northern Qilian Shan thrust belt, is a significant component of Qilian Shan thrust belt which divides Yumushan and intramontane basins in Hexi Corridor. Carrying out the research of Yumushan Fault will help explain the kinematics characteristics of the northern Yumushan active fault and its response to the northeastward growth of the Tibetan plateau.Because of limited technology conditions of the time, different research emphases and some other reasons, previous research results differ dramatically. This paper summarizes the last 20 years researches from the perspectives of fault slip rates, paleao-earthquake characteristics and tectonic deformation. Using aerial-photo morphological analysis, field investigation, optical simulated luminescence(OSL)dating of alluvial surfaces and topographic profiles, we calculate the vertical slip rate and strike-slip rate at the typical site in the northern Yumushan Fault, which is(0.55±0.15)mm/a and(0.95±0.11), respectively. On the controversial problems, namely "the Luotuo(Camel)city scarp" and the 180 A.D. Biaoshi earthquake, we use aerial-photo analysis, particular field investigation and typical profile dating. We concluded that "Luotuo city scarp" is the ruin of ancient diversion works rather than the fault scarp of the 180 A.D. Biaoshi earthquake. Combining the topographic profiles of the mountain range with fault characteristics, we believe Yumu Shan is a part of Qilian Shan. The uplift of Yumu Shan is the result of Qilian Shan and Yumu Shan itself pushing northwards. Topographic profile along the crest of the Yumu Shan illustrates the decrease from its center to the tips, which is similar to the vertical slip rates and the height of fault scarp. These show that Yumu Shan is controlled by fault extension and grows laterally and vertically. At present, fault activities are still concentrated near the north foot of Yumu Shan, and the mountain ranges continue to rise since late Cenozoic.

It's very difficult and time-consuming to calculate the precise location of the reflection points in the reflection time-distance simulation of 3D complex tectonic model. In order to analyze the P-wave reflection time-distance characteristic systematically and accurately,the paper regards 3D curved interface as the envelope of 3D dipping interface with different tendencies and inclinations,and presents a new method for calculating P-wave reflection time-distance from 3D curved interface,using the principle of reflection from 3D dipping interface. Based on the dip layer CDP theory,the location of shot points and reflection travel times are obtained from the positions of receivers and surface CDPs,finally the 3D P-wave reflection records of shot gather are received,assuming that the distribution of interface reflection points is known. Numerical simulation results of shot gather show that this method has high computing efficiency and can be applied to analysis of the P-wave reflection time-distance characteristic with different positions of shots; especially it can reveal the relation between reflection points and time-distance curve. The reflection time-distance feature comparison of 3D curved interface and 3D dipping interface shows that it's very hard to distinguish time-distance characters between two types of interfaces only from the same survey line orientation,and this problem can be solved by comparing time-distance differences from different survey orientations.

Seismic method is a necessary exploration method for detecting active faults buried directly beneath major cities in deep coverage area.Different array length must be adopted for different detecting depth.The Xiadian Fault is a seismogenic fault and related to the 1679 Sanhe-Pinggu earthquake(M=8.0).The deep and moderate-deep structural characteristics of the fault are revealed from the deep and moderate-deep seismic profiles across the fault.To research the activity of the fault away from the earthquake region,moderate-shallow seismic reflection detection experiment was developed with the working parameters as 5m group interval,15m offset,10 folds,60 active receiving channels,single-ended spread shooting by Wacker source,and one point receiving by 40Hz geophones.Based on the results of moderate-shallow seismic detection,a shallow seismic profile was laid across the fault detected by moderate-shallow seismic profiling.The shallow seismic reflection detection experiment was developed by using 2m group interval and hammer source as well as other ways similar to the moderate-shallow seismic reflection.It shows by the results of moderate-shallow and shallow seismic detection that the Xiadian Fault is well imaged at the depth below 200m on the seismic profile of 5m group interval,but it is invisible at the depth above 200m on the profile.The fault on the seismic profile of 2m group interval is obvious,but the shallowest reflection(depth about 30m)on the profile is uninterrupted.It can be educed that the activity of Xiadian Fault weakens about 30km southwest of the epicenter of the 1679 M8.0 Sanhe-Pinggu earthquake.