The Xiaojiang fault zone (XJFZ) is an important part of the Xianshuihe-Xiaojiang fault system, acting as the eastern boundary of the Chuan-Dian block on the southeastern margin of the Tibetan Plateau and accommodating the lateral extrusion of the block. The faulting activity and paleoseismic history on the southern segment of the XJFZ remain poorly understood. Here, trench excavations and radiocarbon dating revealed that four recent surface-rupturing paleoearthquakes have occurred on the Jianshui fault (JSF) in the southern segment of the XJFZ since similar to 15370 yr BP. The ages of these events, labeled E4-E1 from oldest to youngest, are limited to the following time ranges: 15360-12755, 10845-6900, 1455-670, and 635-145 yr BP, respectively. The most recent event El was most likely the 1606 Jianshui earthquake. These events appear to occur unregularly in time. The time interval between the last two events is 726 +/- 235 yr, and the average recurrence interval for all four events is 4589 +/- 3132 yr. The deformed strata show that the JSF is characterized kinematically by transtension, which likely respond to the apparent change in the direction of clockwise rotation of the Chuan-Dian block around the eastern Himalayan syntaxis. Combined with the analysis of the neighboring NW-striking faults, our study suggests that the south-southeastward motion of the Chuan-Dian block is likely to be firstly accommodated in part by the right-lateral shear and dip-slip motions of the Qujiang and Shiping faults and continues across the Red River fault zone, then is transmitted southward along the Dien Bien Phu fault. Therefore, the southern segment of the XJFZ plays a dominant role in the tectonic deformation of the southeastern Chuan-Dian block, with a high seismic hazard.

The Lenglongling fault (LLLF) is located along the northeastern margin of the Tibetan Plateau and forms a part of the Tianzhu seismic gap along the Qilian-Haiyuan fault zone. Little is known about the recurrence of large earthquakes along the LLLF nor the associated seismic hazards of the gap. Here the six most recent surface rupturing paleoearthquakes of the LLLF are revealed by measurement of offset landforms, trench excavations, and radiocarbon dating. They are labeled E1-E6 from youngest to oldest, and their timings are constrained to the following time ranges: 636-498 to present, 2951-1155, 4016-3609, 5325-4476, 7284-6690, and 8483-7989yearsBP, respectively. The LLLF displays evidence of fresh, recent surface rupture, and the trench sections reveal that the fault ruptured to the ground surface during the most recent event. Based on this fresh surface rupture and historical earthquake records, the latest event E1 was most likely the 1927M8.0 Gulang earthquake. In conjunction with previous studies, Gulang earthquake might be a complicated event characterized by the combined rupture of both strike-slip and thrust faults. The average recurrence interval of the six paleoearthquakes is 1643568years, and the coefficient of variation is 0.34, indicating that the LLLF follows a quasiperiodic recurrence model. Based on this new understanding of the last event, the LLLF may not be a part of the Tianzhu seismic gap. However, an earthquake of up to M(W)7.6 could still rupture the gap sections composed of the Jinqianghe, Maomaoshan, and Laohushan faults.

安徽巢湖—铜陵地区是中国大陆内部1个典型的中强地震活动区,曾发生的1585年巢县南53/4级、1654年庐江东南51/4级等4次地震呈NNE向带状展布,构成了1条醒目的中强地震活动带.野外地表地质调查、浅层物探、钻探资料、年代学样品的采集测试和断裂活动性综合分析等表明该地区矾山断裂、夏家岭断裂和朗村断裂是前第四纪断裂.铜陵断裂是1条中更新世活动的隐伏断裂,可发生中强地震,控制了近地表的3个雁列状构造的演化和发展.4次地震强度呈现了向S递减的特点,而这与晚新生代无为盆地的凹陷幅度明显大于南边的贵池盆地的特点相一致.在深部构造上,铜陵断裂空间分布特征对应着1条NNE向布格重力异常梯级带.巢湖—铜陵地区中更新世活动的铜陵断裂、雁列状分布的构造、新构造的差异运动以及布格重力异常梯级带与该地区中强地震活动带在空间上的对应性,显示了它们应是中强地震孕育和发生的构造标志.

Strike-slip faults and normal faults are dominant active tectonics in the interior of Tibetan plateau and control a series of basins and lakes showing extension since the Late Cenozoic, by contrast with the thrust faulting along the orogenic belts bordering the plateau.The late Neotectonic movement of those faults is key information to understand the deformation mechanism for Tibetan plateau.The Gyaring Co Fault is a major active right-lateral strike-slip fault striking~300° for a distance of~240km in central Tibet, in south of Bangong-Nujiang suture zone.The Gyaring Co Fault merges with the north-trending Xainza-Dinggye rift near the southern shore of Gyaring Co.From NW to SE, Dongguo Co, Gemang Co-Zhangnai Co, Zigui Co-Gyaring Co form the Gyaring Co fault zonal drainage basin.Some scholars have noticed that the formation of lakes and basins may be related to strike-slip faults and rift, but there is no analysis on the Gyaring Co fault zonal drainage basin and its response to regional tectonics.In recent years, a variety of quantitative geomorphic parameters have been widely used in the neotectonic systems to analyze the characteristics of the basin and its response mechanism to the tectonic movement.In this paper, we applied ASTER GDEM data on the ArcGIS platform, extracted the Gyaring Co fault zonal drainage basin based on Google Earth images(Landsat and GeoEye)and field work.We acquired basic geomorphic parameters of 153 sub-basin(such as grade, relief, average slope, area) and Hypsometric Index (HI) value and curve.Statistical results have indicated significant differences in scale(area and river network grade)in north and south sides of the fault.Southern drainage basins` relief, slope, HI value are higher than the northern basins, and the overall shape of hypsometric curve of northern basins are convex compared with southern concavity.Along the strike of the Gyaring Co Fault, average slope, and HI value are showing generally increasing trending and hypsometric curve become convex from west to east.By comparing and analyzing the lithology and rainfall conditions, we found that they have little influence on the basic parameters and HI value of drainage basins.Therefore, the changes of basin topographic differences between northern and southern side of fault and profile reveal the Gyaring Co Fault has experienced differential uplift since the late Cenozoic, southern side has greater uplift compared to the north side, and the uplift increased from NW to SE, thus indicate that normal faulting of the Gyaring Co Fault may enhanced by the Xainza-Dinggye rift.The early uplift of the Gangdise-Nyainqentanglha Mountain in late Cenozoic might provide northward inclined pre-existing geomorphic surfaces and the later further rapid uplift on the Gangdise-Nyaingentanglha Mountain and Xainza-Dinggye rift might contribute to the asymmetrical development of the Gyaring Co fault zonal drainage basin.

The Lenglongling Fault(LLLF)is a major active left-lateral strike-slip fault along the northeastern margin of the Tibetan plateau.Fault slip rate is of great significance for researching the dynamics of tectonic deformation in NE Tibetan plateau and understanding the activity and seismic risk of the fault.However, slip rate of the LLLF, which remains controversial, is limited within~3~24mm/a, a relatively broad range.Taking Niutougou site(37.440 2°N, 102.094 0°E)and Chailong site(37.447 3°N, 102.063 0°E)in the upstream of Talihua gully in Menyuan County, Qinghai Province as the research objects, where faulted landform is typical, we analyzed the displacement evolution model and measured the slip amounts by back-slip of the faulted landform using high-resolution DEM from Terrestrial LiDAR and high-precision satellite images of Google Earth, and by collecting and testing samples from stratigraphic pit excavated in the faulted landform surface and stripping fresh stratigraphic section, we determined the abandonment age of the surface.Holocene slip rate obtained from Niutougou site and Chailong site is(6.4±0.7)mm/a and(6.6±0.3)mm/a, respectively, which have a good consistency.Taking into account the error range of the slip rate, the left-lateral slip rate of the LLLF is(6.6±0.8)mm/a since Holocene, which is between the previons results from geological method, also within the slip rate range of 4.2~8mm/a from InSAR, but slightly larger than that from GPS((4.0±1.0)mm/a).Late Quaternary slip rate of Qilian-Haiyuan fault zone, which displays an arc-shape distribution, turns to be the largest in LLLF region.The most intensive uplift in the LLLF region of the NE Tibetan plateau confirms the important role of the LLLF in accommodating the eastward component of movement of Tibetan plateau relative to the Gobi-Ala Shan block from one side.

The southern segment of the Xiaojiang Fault (SSXF) is located at the intersection of the Xianshuihe-Xiaojiang Fault and Red River-Ailao Shan fault systems in the southeast margin of the Tibetan plateau.Based on the interpretation of remote sensing image,the SSXF clearly shows the linear feature and continuous distribution as a single,penetrating fault.It has a total length of about 70km,trends generally about 20° to the northeast and protrudes slightly in the middle to the east.A typically geomorphologic phenomenon about the synchronous left-lateral dislocation of ridges and gullies can be found at Liangchahe,Longtan Village along the SSXF.The distribution of faults,the sedimentary features,attitude variance and the primary dating results of the offset strata in the trench section across fault sag ponds reveal three paleoseismic events rupturing obviously the surface,which demonstrates that the SSXF has the ability of recurrence of strong earthquakes.High-precision topographic map about two gullies and the platform between them with synchronous dislocation is acquired by using the Trimble 5800 GPS real-time difference measurement system.The dislocation is (18.3±0.5)m.As the top geomorphologic surface between the above two gullies and their adjacent area,the terrace surface T2 stopped accepting deposits at ～ 2606a,based on the linear regression analysis of three dating data.According to the geological method,a sinistral strike-slip rate of (7.02± 0.20) mm/a on the SSXF in the Holocene is obtained,which has a good consistency with the results provided by using GPS data.The preliminary results about the Holocene activity and slip rate of the SSXF demonstrate that the southward or south-southeast motion of the Sichuan-Yunnan block in the SE Yunnan region has not been absorbed by the possible shortening deformation and the sinistral strike-slip rate of the SSXF has not been drastically reduced.The SSXF is a Holocene fault with obvious activity.This preliminary understanding provides some basic geological data for the seismic risk evaluation of the SSXF in the future,and for the establishment and inspection of the seismotectonic model about the Sichuan-Yunnan block.

The M S6.4 Menyuan earthquake occurred on the northern side of the Lenglongling fault (LLLF) in the mid-western of the Qilian-Haiyuan fault zone on January 21, 2016. The earthquake epicenter was distant from the Minle-Damaying and Huangcheng-Shuangta faults, eastern of the Northern Qilian Shan fault zone. A near northwest-striking rupture plane intersects the two faults at a certain angle. The focal mechanism solution shows that this was a thrust-type earthquake, slightly different from the strike-slip movement with a thrust component of the LLLF. Field geological mapping, tectonic geomorphology analysis, trench excavation and 14C dating reveal that (1) the LLLF has been obviously active since the Holocene, and may behave with characteristic slip behavior and produce M W7.3–7.5 earthquakes; (2) the LLLF appears as a flower structure in terms of structure style, and dips NNE at a steep angle; and (3) the most recent earthquake event occurred after 1815–1065 a BP. An associated fault, the Northern Lenglongling fault (NLLLF), is located at the northwestern end of the LLLF. Consequently, the NLLLF was continually subject to tectonic pushing effects from the left-lateral shear at the end of the LLLF, and, accordingly, it bent and rotated outward tectonically. Subsequently, the fault deviated from the dominant rupture azimuth and activity weakened. In the late Quaternary, it behaved as a thrust fault with no obvious deformation at the surface. This is indicated by the arc shape, with a micro-protrusion northeastward, and no geologic or geomorphic signs of surface rupturing since the late Quaternary. However, such faults could still rupture at depth, producing moderate-strong earthquakes. The geometric and kinematic properties of the NLLLF are in good agreement with the occurrence and kinematic properties of nodal plane 2, and with the distribution characteristics of the aftershocks and seismic intensity. Therefore, the NLLLF is a more suitable seismogenic structure for the M S 6.4 Menyuan earthquake. In addition, the thrust movement of the NLLLF accommodates subsequent movement of the LLLF. During the historical evolution of the NLLLF, the LLLF and the NLLLF have affected the local topography through tectonic uplift.