Xianshuihe Fault is an active fault which originated from the eastern margin of the Tibetan plateau and formed by the orogenic events in Songpang-Ganzi area. The origin of Xianshuihe Fault is discovered in the NW of Ganzi, then it extends to the SE, passing through Luhuo, Daofu, Qianning, Kangding, Luding, Moxi and disappears after passing through Shimian. Based on previous studies, Xianshihe Fault is a sinistral strike-slip fault. According to GPS and InSAR data, the horizontal component of average slip rate for Xianshuihe Fault is approximately 7.5~16.7mm/a. As a crucial member of the regional earthquake zone, Xianshuihe Fault separates Sichuan-Yunnan block and Bayankala block. More importantly, Xianshuihe Fault is responsible for a great number of large magnitude earthquakes especially in the Qianning-Kangding segment, a segment of Xianshuihe Fault which consists of three branches. From east to west, they are Yalahe Fault, Selaha Fault and Zheduotang Fault which are all active since Holocene. Yalahe Fault is responsible for a M7 earthquake that occurred around 1700AD. Selaha Fault is responsible for another M7 earthquake which occurred around 1725AD. Around 1955AD, a M7.5 earthquake occurred which was related to Zheduotang Fault.
According to the 1:50k Xianshihe Active Faults Map(1995) and relevant researches, it is discovered that, from north to south, the Holocene active Zheduotang segment starts from Kangding airport to Zheduotang village. The total length of Zheduotang segment is around 30km which includes the surface rupture zone of the 1955 M7.5 earthquake. Due to the absence of researches, the northern part of the Zheduotang Fault, which is to the north of the Kangding airport, remains unstudied. Based on satellite image, we discovered that there are signs of faults to the north of Kangding airport. Therefore, we selected four sites to carry out field investigations and trench analysis. The first site is to the NW of the Duoriagamo village. Based on satellite image and DEM data, many typical faulted geomorphologic features are discovered. To the NW of this site, both the fan and the terrace are offset. By analyzing the DEM data, the offset of T1 terrace is around 7.8m and the offset of Fan1 is around 15.6m. To the SE of this site, the fan is also offset by sinistral movement which has an offset value of 21.7m. The second site is to the NW of the Muyazuqing school where 2.6m of sinistral offset between the fan and the T1 terrace are measured. To the SE of this site, obvious offset of fan and floodplain are observed which both have sinistral offset of 2.5m. The third site is to the south of first Duoriagamo village. The fault here shows two parallel branches. The fourth site is near the Tonglilongba and there are 37.5m of horizontal offset of the fan.
Based on trench analysis, 17 stratigraphic units are defined from which carbon samples are acquired for geochronological analysis. By constraining the age of each stratigraphic unit, the age of four deformation events are defined. Event 1 is the youngest which occurred between 5 821~3 148a BP. Event 2 occurred between 13 060~10 745a BP, Event 3 occurred between 13 687~11 420a BP and Event 4 occurred between 41 443~13 715a BP. According to the integration results of our analysis, the location of northwestern segment of Zheduotang Fault is defined. It is discovered that, the NW segment of Zheduotang Fault is located between the Kangding airport and Duoriagamo village with a total length of 15km. The trace of Zheduotang Fault is also defined. From north to south, Zheduotang Fault passes through Duoriagamo village, Tonglilongba, Kangding airport, Zheduoshan nek, Ertaizidaoban and disappears near Zheduotang village. Moreover, after Holocene, the Zheduotang Fault is dominated sinistral slip movement along with minor vertical component. Different from previous researches, we believe that the Holocene active Zheduotang segment extends 15km further to the NW. This discovery provides some basis for perfecting the plane geometric images of the three active faults in Qianning-Kangding segment of Xianshuihe fault zone, such as Zheduotang Fault, Selaha Fault and Yalahe Fault, and is of great significance for understanding the strain distribution and strong earthquake rupture mode of each branch fault in Qianning-Kangding segment of Xianshuihe fault zone.

Landslides and rock falls along the highway are common geological hazards in Southwest China. As an influencing factor on potential landslides behavior, roads or distance to roads have been successfully used in landslide susceptibility assessments in mountainous area. However, the relationship between the road-cut and the slope stability is not clear. Therefore, we performed two-dimensional slope stability calculation using the general limit equilibrium (GLE)method incorporated in the software SLOPE/W of GeoStudio for stability analysis of slopes. Our studies show that the man-made roads influence on the slope stability mainly exists in two ways:One is to create a new steep slope, which will result in rock falls and shallow landslides along the roads; the other is to influence the stability of the original slope, which will result in comparatively huge landslides. For the latter, our simulation study reveals that the road location, namely at which part of a natural slope to construct a road is important for the slope stability. For a natural slope with a potential slip surface, if a road is constructed at or near the slope toe where the potential slip surface surpasses, it will greatly degrade the slope's factor of safety (Fs) and make the slope unstable; however, if a rode-cut is near the top of the slope, it will increase the slope's Fs and make the slope more stable. The safety location is different for different slope angle, steeper slope needs a higher location for a safety road-cut in comparison with gentle slopes. Moreover, the slope stability decreases when loading a seismic force and it varies with the slope angle. Firstly, the Fs decreases when the slope angle increasing, and when the slope angle reaches 45°, the Fs then becomes greater with the slope angle increasing.

On August 3, 2014, an M_W6.5 earthquake occurred in Ludian County, Yunnan Province, which triggered significant landslides and caused serious ground damages and casualties. Compared with the existing events of earthquake-triggered landslides, the spatial distribution of co-seismic landslides during the Ludian earthquake showed a special pattern. The relationship between the co-seismic landslides and the epicenter or the known faults is not obvious, and the maximum landslide density doesn't appear in the area near the epicenter. Peak ground acceleration (PGA), which usually is used to judge the limit boundary of co-seismic landslide distribution, cannot explain this distribution pattern. Instead of correlating geological and topographic factors with the co-seismic landslide distribution pattern, this study focuses on analyzing the influence of seismic landslide susceptibility on the co-seismic distribution. Seismic landslide susceptibility comes from a calculation of critical acceleration values using a simplified Newmark block model analysis and represents slope stability under seismic loading. Both DEM (SRTM 90m)and geological map (1 ︰ 200^￣￣000)are used as inputs to calculate critical acceleration values. Results show that the most susceptible slopes with the smallest critical accelerations are generally concentrated along the banks of rivers. The stable slopes, which have the larger critical accelerations and are comparably stable, are in the places adjacent to the epicenter. Comparison of the distribution of slope stability and the real landslides triggered by the 2014 M_W6.1 Ludian earthquake shows a good spatial correlation, meaning seismic landslide susceptibility controls the co-seismic landslide distributions to a certain degree. Moreover, our study provides a plausible explanation on the special distribution pattern of Ludian earthquake triggered landslides. Also the paper discusses the advantages of using the seismic landslide susceptibility as a basic map, which will offer an additional tool that can be used to assist in post-disaster response activities as well as seismic landslides hazards zonation.

The Ganzi-Yushu Fault, the boundary of Bayan Har active tectonic block, Qiantang active tectonic block and Sichuan-Yunan active tectonic block, is a sinistral strike-slip fault zone with intensive Holocene activity. Thus, the study of activity characteristics and rupture behavior of paleoearthquakes in the late Quaternary on the Ganzi-Yushu Fault is of fundamental importance for understanding the future seismic risk of this fault. The southeast section of Ganzi-Yushu Fault is made up of three segments of Ganzi, Manigange and Dengke, where a M_S7.3 earthquake in 1866, a M_S7.7 earthquake in 1854 and a M_S7.3 in 1896 occurred, respectively. There is still lack of in-depth study on the active features and the cascading rupture possibility of these segments, which hindered the evaluation of seismic risk for the southeast section of Ganzi-Yushu Fault. By the means of field geological survey and micro topography measurement, this paper studied the geological and geomorphological features of the southeast section of the Ganzi-Yushu Fault. The results show that the Ganzi and Dengke segments show obvious extension movement, in addition to the left-lateral movement. For Manigange segment, the characteristics of the movement are mainly left-lateral strike-slip and thrusting, and the maximum vertical displacement of the Holocene strata is greater than 2m. In part areas, the movement is normal faulting, which perhaps relates to the left stepping zone in the local stress environment. Therefore, combining the research results such as the fracture distribution in different motion characteristics, rupture behavior of paleoearthquakes, and the distribution of historical earthquake surface ruptures, we divide the southeast section of Ganzi Yushu Fault into Ganzi, Manigange and Dengke segment, and consider the Yakou and the Dengke Basin as the stepovers and the segments' boundaries. As the small scale of impermanent barriers including Dengke Basin and the ridge near Yakou, of which the width is about 1~2km, they may be broken through in great earthquake rupture in future. A trench was excavated in Zhuqing township to investigate the paleoearthquakes on the Manigange segment, radiocarbon dating was employed and 3 paleoseismic events were revealed in the Zhuqing trench, which are the seismic events occurring respectively at 3875~3455BC, after 775BC, and the latest one that ruptured the surface. Compared with the previous results of paleoseismology in the southeast section of Ganzi-Yushu Fault, it is found that the paleoseismic events in the Manigange segment are obviously different with that in Ganzi segment and Dengke segment. Due to the lack of sufficient data on the southeast section of the Ganzi-Yushu Fault, it still needs further discussion whether the cascade-rupturing between these segments exists.

Reservoir induced earthquakes (RIE) are caused by impoundment of reservoir,with the characteristics of small magnitude and shallow focal depth,but they can also lead to not only economic loss,but also many serious secondary disasters,such as dam destruction,landslide,producing greater damages far more than the damages directly produced by earthquakes.So study on RIE is quite significant in the field of dam construction,thus more attentions should be paid to RIE.There are many factors to induce reservoir earthquakes,such as geological condition,rock mass mechanical index,state of crustal stress,pore pressure distribution,all of which are extremely difficult to measure due to the presence of many randomness;even if applying most advanced methods to measure them,the values fluctuate in great range,without a certain value in time and space.The great variety of these parameters gives rise to troubles to analyze RIE by deterministic approaches.How to handle the randomness of these factors has become vital problem in the field of RIE research.In this study,based on probability theory,and taking the main influence factors as stochastic variables,a new method to analyze probability of RIE was proposed by applying reliability theory.Firstly,the factors inducing reservoir earthquakes were analyzed,of which pore pressure in fault caused by water impounding of reservoir plays a vital role in triggering earthquakes.Then,taking these factors,including attitude,friction coefficient,cohesion of fault plane,stress state of fault plane and pore pressure in fault,as stochastic variables,performance function of triggering earthquakes was established by applying Coulomb stress on the fault plane,and reliability theory was used to analyze probability of earthquake induced by main factors.A special case analysis showed that:(1) The probability of induced earthquakes dramatically increases as pore pressure in fault increases;under the condition of equal pore pressure at triggering earthquakes area,probability of induced earthquakes obviously rises with enlarging of variation of pore pressure;(2) those faults with strike approximately parallel to horizontal maximum principal stress direction or with steep dip angle about more than 60° are prone to inducing earthquake;(3) as horizontal minimum principal stress increases,which has greater effect on induced earthquakes than horizontal maximum principal stress,probability of induced earthquakes becomes lower and fault keeps in more stable condition;(4) probability of induced earthquakes gradually decreases with the increase of friction coefficient and cohesion of fault plane;However,the effect of friction coefficient on induced earthquakes is much greater than the cohesion of fault plane.

Since the Wenchuan earthquake,the seismic hazard of the northeastern segment of the Longmenshan Fault zone as well as the Hanzhong Basin has drawn more and more concerns. However,the essential data needed for further analysis on the seismic hazard in this region is scarce at present time,hence there is an urgent need for an in-depth study on the activities of faults around the basin. The faults around the Hanzhong Basin include five main faults,namely,the northern margin fault of Hanzhong Basin,the southern margin fault of Hanzhong Basin,the Qingchuan Fault,the Chaba-Lin'ansi Fault and the southern margin fault of Liangshan. Based on several detailed field investigations on the geometric distribution,movement nature and active ages of the five faults,and with consideration of previous work,our study shows that the late-Quaternary tectonic activity in the basin is relatively intense in west and weak in east. The west section of the north-margin fault of the Hanzhong Basin(east of Baohe)was active in early late Pleistocene,while its eastern section(west of Baohe)was active in middle Pleistocene. The south-margin fault of the basin was also active in middle Pleistocene. And the three faults in the southwest of the basin were all active in late Pleistocene. This activity pattern of high in the west and low in the east is also demonstrated by the difference in thickness of Quaternary system and the distribution of small earthquakes.

On April 20,2013,a strong earthquake of M_S 7.0 struck the Lushan County,Sichuan Province of China. In this paper,basic information of the April 20,2013 Lushan earthquake,historical earthquakes in the Lushan earthquake struck area and associated historical earthquake-triggered landslides were introduced firstly. We delineated the probable spatial distribution boundary of landslides triggered by the Lushan earthquake based on correlations between the 2008 Wenchuan earthquake-triggered landslides and associated peak ground acceleration(PGA).According to earthquake-triggered landslides classification principles,landslides triggered by the earthquake are divided into three main categories: disrupted landslides,coherent landslides,and flow landslides. The first main category includes five types: rock falls,disrupted rock slides,rock avalanches,soil falls,and disrupted soil slides. The second main category includes two types of soil slumps and slow earth flows. The type of flow landslides is mainly rapid flow slides. Three disrupted landslides,including rock falls,disrupted rock slides,and soil falls are the most common types of landslides triggered by the earthquake. We preliminary mapped 3883 landslides based on available high-resolution aerial photographs taken soon after the earthquake. In addition,the effect of aftershocks on the landslides,comparisons of landslides triggered by the Lushan earthquake with landslides triggered by other earthquake events,and guidance for subsequent landslides detailed interpretation based on high-resolution remote sensing images were discussed respectively. In conclusion,based on quick field investigations to the Lushan earthquake,the classifications,morphology of source area,motion and accumulation area of many earthquake-triggered landslides were recorded before the landslide might be reconstructed by human factors,aftershocks,and rainfall etc. It has important significance to earthquake-triggered landslide hazard mitigation in earthquake struck area and the scientific research of subsequent landslides related to the Lushan earthquake.

The co-seismic surface rupture signs of the "4.20" Lushan M_S7.0 earthquake are found at Longmen Township,Lushan County. The sites of rupture signs have a linear distribution with a 2～3km length and N40°～50°N strike. The maximum shortening of the rupture is about 8cm,uplifting is about 1～2cm. Strike-slip component is not observed,but the dynamic process of the earthquake is characterized by compression from northwest to southeast. The observed co-seismic surface ruptures can be oblique shear-fissure,or thrusting crack,however most of them are extensive fissures,which can be explained by the local extensive stress-field on the top of the thrust bending. Although these ruptures have different geometric shapes or variant mechanic features,they similarly reflect the northwest-southeast compression and the surface lift-bending on the top of a thrusting seismogenic structure. Comparing with Dachuan-Shuangshi Fault(frontal fault)and Dayi-Mingshan Fault(piedmont fault),Lushan-Longmen presumed blind fault is more likely the seismogenic fault,which is also consistent with the results of the Lushan earthquake sequence relocations and the seismic intensity contours. As the seismogenic fault of the Lushan earthquake has surpassed the frontal fault of Longmen Shan,it may be a new-generated tectonics,which implies that it is important to re-evaluate the seismic risk at the piedmont area of the Longmen Shan. However,the conclusions are still very primary and geophysical survey is needed to demonstrate the existence of the Lushan-Longmen presumed blind fault.

Hepu-Beiliu Fault starts from Beibuwan sea area in the southwest,extends northeastwards continually though Hepu,Bobai. The total length of the fault exceeds 400 kilometers and the general strike of the fault is 40°～60°. The Hepu-Beiliu Fault comprises two branches-the east branch and the west branch. The west branch stretches from the southwest of the Hepu Basin lying in the lower reaches of the Nanliu River towards the northeast. This paper discusses the activity of the fault segment in the Hepu Basin in the west branch of Hepu-Beiliu Fault from the following three aspects. Firstly,in view of the geological topography,fault-scarps develop widely in the Hepu Basin segment of the west branch and the linear feature of the scarp distribution is notable; Secondly,some exact locations that the fault crosses are investigated by high-resolution seismic reflection profiling; Finally,in order to evaluate the activity and their times of the Hepu Basin segment of the Hepu-Beiliu Fault,borehole drilling is carried out to find out the dislocated stratum of the fault and take samples for laboratory dating to define the latest activity time of the fault. Based on the fault chronology results,the latest active era of this segment(the Hepu Basin segment of the Hepu-Beiliu Fault)is concluded in the late era of the lower Pleistocene. The fault slip displacement is about 10 meters. This fault is covered by the strata of the middle to upper of mid-Pleistocene,which means that the activity level of this segment became lower,or it has been inactive since the late eva of mid-Pleistocene.