On February 6, 2023, two destructive earthquakes struck southern and central Turkey and northern and western Syria. The epicenter of the first event(M_W7.8)was 37km west-northwest of Gaziantep. The earthquake had a maximum Mercalli intensity of Ⅻ around the epicenter and in Antakya. It was followed by a M_W7.7 earthquake nine hours later. This earthquake was centered 95km north-northeast from the first one. There was widespread damage and tens of thousands of fatalities. In response to these catastrophic events, in March 2023, a seismic scientific expedition led by China Earthquake Administration(CEA)was promptly organized to investigate the surface ruptures caused by these earthquakes. Here, we focus on the surface ruptures of the second earthquake, known as the Elbistan earthquake. The post-earthquake field survey revealed that the Elbistan earthquake occurred on the East Anatolian fault zone's northern branch(the Cardak Fault). This event resulted in forming a main surface rupture zone approximately 140km long and a secondary fault rupture zone approximately 20km long, which is nearly perpendicular to the main rupture.

We combined the interpretation of high-resolution satellite imagery and geomorphic investigations along the fault to determine the fault geometry and kinematics of the second earthquake event. The Elbistan earthquake formed a main surface rupture zone approximately 140km long, which strikes in an east-west direction along the Cardak Fault. The main rupture zone starts from Göksun in the west and extends predominantly eastward until the western end of the Sürgü Fault. It then propagates northeast along the southern segment of the Malatya fault zone. The entire Cardak Fault and the Malatya fault zone's southern segment are considered seismic structures for this earthquake. The overall surface rupture zone exhibits a linear and continuous distribution. Secondary ruptures show a combination of left-lateral strike-slip or left-lateral oblique-thrust deformation. Along the rupture zone, a series of en echelon fractures, moletracks, horizontal fault striations, and numerous displaced piercing markers, such as mountain ridges, wheat fields, terraces, fences, roads, and wheel ruts, indicate the predominance of pure left-lateral strike-slip motion for most sections. The maximum measured horizontal displacement is(7.6±0.3)m. According to the empirical relationship between the seismic moment magnitude of strike-slip faulting earthquakes and the length of surface rupture(SRL), a main rupture zone of 140km in length corresponds to a moment magnitude of approximately 7.6. Based on the relationship between the seismic moment magnitude and the maximum coseismic displacement, a maximum coseismic displacement of(7.6±0.3)m corresponds to a moment magnitude of about 7.5. The magnitudes derived from the two empirical relationships are essentially consistent, and they also agree with the moment magnitude provided by the USGS. Besides the main surface rupture zone, a secondary fault rupture zone extends nearly north-south direction for approximately 20km long. Unfortunately, due to the limited time and traffic problem, we did not visit this north-south-trending secondary fault rupture zone.

According to the summary of the history of earthquakes, it is evident that the main surface rupture zone has only recorded one earthquake in history, the 1544 M_S6.8 earthquake, which indicates significantly less seismic activity compared to the main East Anatolian Fault. Moreover, the “earthquake doublet” will inevitably significantly impact the stress state and seismic hazard of other faults in the region. Seismic activity in this area remain at a relatively high level for years or even decades to come. The east-west striking fault, which has not been identified on the published active fault maps at the western end of the surface rupture zone, and the north-east striking Savrun Fault, which did not rupture this time, will experience destructive earthquakes in the future. It remains unknown why the east-west striking rupture did not propagate to the Sürgü Fault this time. More detailed paleoearthquake studies are needed to identify whether it is due to insufficient energy accumulation or because this section acts as a barrier. If the Sürgü Fault, about 40km long, was to rupture entirely in the future, the magnitude could reach 7 based on the empirical relationship.

Considering the distribution of historical earthquakes along the East Anatolian fault zone, as well as the geometric distribution of the surface ruptures from the recent “earthquake doublet” and the surrounding active faults, it is believed that the future earthquake hazards in the northeastern segment of the East Anatolian fault zone, the northern segment of the Dead Sea Fault, and the Malatya Fault deserve special attention.

The Longling-Lancang seismotectonic belt in southwestern Yunnan is critical for accurately defining the boundaries of active blocks and evaluating seismic risks. Using pre- and post-earthquake high-spatial-resolution satellite imagery to study strong earthquakes retrospectively proves to be a practical method in such study. Strong earthquakes frequently cause secondary effects such as coseismic landslides, collapses, and debris flows, which lead to considerable loss of life and property. These secondary effects, often as the most dramatic manifestations of an earthquake, show geologic signatures providing evidence of historic or prehistoric seismic activities. The use of satellite imagery captured shortly after historic earthquakes to interpret these secondary effects is particularly beneficial in determining the intensity and influence radius of earthquakes, thereby helping study on seismogenic faults of earthquakes.

On May 29, 1976, two strong earthquakes with M_S7.3 and M_S7.4 occurred in Longling county, southwest China, followed by intense aftershocks. The seismogenic structure of these earthquakes still remains undetermined to present. These earthquakes triggered numerous coseismic landslides in the regolith of the granitic rock mass. The seismic zone, located in subtropical regions, is characterized by high precipitation and dense vegetation. Apart from the ancient landslides in the northwest and southeast, no records of landslides and debris flows persisted in the epicenter zone for a century, making the occurrence of substantial landslides post the main earthquakes unexpected. Currently, these landslides have undergone reshaping by land surface processes and re-vegetation, which makes them indistinguishable in recent remote sensing images. Using Keyhole satellite images with a resolution of 0.6~1.2m offers a useful means to identify the coseismic landslides of the Longling mainshocks. In this study, we employ these images for a comprehensive visual interpretation of the coseismic landslides. To ensure the accuracy and reliability of the results, we used images captured in 1981(the most recent following the earthquakes)to extract coseismic landslides and substantiated them with images from 1974, field investigation photos from 1976, and relevant records. Finally, we have compiled an exhaustive database of coseismic landslides triggered by the 1976 Longling cases.

Our results are summarized as follows: 1)A total of 14 448 landslides were interpreted, encompassing an overall area of 17.2km². The area of individual landslides primarily ranged from several hundreds to one thousand m², and most were superficial slides in the surface regolith with short sliding distances. The regional stratigraphy is complex, with 70.9% of the landslides occurring in the regolith of granitic rock mass, 15.3%in sandstones or siltstones, and a mere 13.8%in other areas such as limestones. Consequently, these landslides were relatively small compared to those in other regions like the Loess Plateau in north China, where the surface sediment is extremely loose. 2)A strong correlation exists between the intense area of coseismic landslides and the earthquake sequence, which tends to migrate from south to north. Notable aftershocks(e.g., M_S6.2 on June 9 and M_S6.6 on July 21)particularly exhibited the general NNW distribution direction of the earthquake sequence and triggered scattered landslides outside the epicenter zone. Through synthesizing field surveys, combining other records and the findings of this study, we believed that the two main earthquakes triggered numerous coseismic landslides, and the continuous strong aftershocks led to the destabilized regolith of the granitic rock mass creeping successively, resulting in subsequent landslides. 3)The concentration areas of coseismic landslides do not match the high-earthquake-intensity areas, instead, they are all located on one side of active faults, which suggests that the seismogenic fault is neither the Longling-Ruili Fault nor the Wanding Fault. The spatial distribution of the landslides suggests that the scope of the surface rupture zone is about 30km. The conjugated strong earthquake ruptures in southwestern Yunnan may limit the spatial scale of single strong earthquakes, so it is crucial to pay more attention to the intersection zone of NE and NW trending active faults when assessing regional strong earthquake risk in the future.

Spring water is strongly related to earthquake, and groundwater within fault zone carries a large amount of information about the water-rock response and tectonic activity. Meanwhile, hydrogeochemical monitoring in the area of strong seismic activity could well obtain the precursor information related to earthquake. Therefore, it is essential to analyze the sources and characteristics of hydrogeochemistry in areas of strong earthquakes. The Bayankara Block is a rectangular active block in the east-central part of the Tibetan plateau. In recent years, the perimeter of the block is undergoing a period of moderate to strong seismic activity and has become the major area of seismicity in mainland China. However, due to the tough geological conditions surrounding the Madoi area, little has been reported on water chemistry, and the geochemical background fields have yet to be established and identified.
On 22 May 2021, an earthquake of M_S7.0 struck Madoi County, Qinghai Province, the largest magnitude earthquake in China since the 2017 Jiuzhaigou M_S7.4 earthquake. After the earthquake, a near NWW-SEE surface rupture zone was formed, with a rupture area of about 70km, along which tension fissures, sand liquefaction, sand blasting and water bubbling can be seen, and there are cold springs upwelling near the surface rupture zone. One day after the earthquake, 21 water chemistry samples were taken. They are the water bubbling from the earthquake rupture zone and the hot springs near the East Kunlun fault zone, as well as 4 sandy soil samples from post-earthquake sandblasting and water bubbling sites. The ordinary and minor ionic components of spring water and stable isotopes of δD, δ¹⁸O and ⁸⁷Sr/⁸⁶Sr were analyzed. Percentage of oxides in sand particles was also analyzed. The sources and characteristics of spring water and sandy soils were researched, and the differences between the groundwater in surface rupture zone and the geothermal water near the East Kunlun Fault are discussed. The results show that: 1)The range of TDS of the 21 springs is 113.2~1 264.6mg/L, pH values range from 7.6 to 8.3, conductivity ranges from 200.3 to 865.7μs/cm, and temperatures range from 3 to 49℃. The spring water samples near the surface rupture zone are all from cold springs(3 to 11℃). The degree of water-rock reaction is weak. The chemistry types of spring water are Ca·Mg-HCO₃, Ca·Mg·Na-HCO₃, Ca-HCO₃, Na·Ca·Mg-HCO₃·Cl, Ca·Na·Mg-HCO₃·SO₄, Ca·Na·Mg-HCO₃·SO₄ and Ca·Na-HCO₃. Calcium, magnesium and bicarbonate ions are the main ions of the spring. 2)The range of spring water average recharge elevation in the region is 0.8~2.8km. There is an abnormal hydrogen isotope value(δD=-59‰)in the spring water near the epicenter in the surface rupture zone, and Na⁺, Cl^-, $SO_{4}^{2-}$ and other ions have high values. 3)Overall, the springs do not contain high concentrations of elements such as Ca and Sr, and most elements have EF<1, which may be related to the weak degree of water-rock reaction in the springs. Lithium in springs near the East Kunlun fault zone(maximum value of 2 014μg/L)is much greater than in springs around the surface rupture zone(6.56~43.0μg/L); and metallic trace elements of Pb, Ba, Cu, and Zn are more enriched in springs around the surface rupture zone. 4)The source of the spring water is meteoric water, and the spring water near the surface rupture zone is mixed with the surrounding water, and the results of water temperature, γNa/γCl, and elements from mantle in the East Kunlun fault zone reveal that the hot spring water circulation is deeper in the East Kunlun fault zone, with faults cutting deeply and deeper elemental recharge. The Cl^- and(Na⁺+K⁺)concentrations in the spring near the surface rupture zone are significantly higher than those near the East Kunlun fault zone, where the springs are more enriched in δD and δ¹⁸O.
The hydrochemical characteristics and sources of the samples are discussed and the fluid geochemical differences between the two areas are compared, and the sources of the sand samples that emerged after the earthquake are analyzed. The paper concludes that it is of great significance for earthquake risk assessment of the East Kunlun Fault to carry out hydro-geochemical monitoring and further study of hot springs in the East Kunlun Fault in the future. The paper fills the gap of background groundwater data in the region, meanwhile, discusses the response of water chemistry after the earthquake and the characteristics and sources of water chemistry in the middle Bayan Kara block.

At 02:04 a.m. on May 22, 2021, a M_S7.4 earthquake occurred in the Maduo County, Qinghai Province, China. Its epicenter is located within the Bayan Har block in the north-central Tibetan plateau, approximately 70km south of the eastern Kunlun fault system that defines the northern boundary of the block. In order to constrain the seismogenic fault and characterize the co-seismic surface ruptures of this earthquake, field investigations were conducted immediately after the earthquake, combined with analyses of the focal parameters, aftershock distribution, and InSAR inversion of this earthquake.
This preliminary study finds that the seismogenic fault of the Maduo M_S7.4 earthquake is the Jiangcuo segment of the Kunlunshankou-Jiangcuo Fault, which is an active NW-striking and left-lateral strike-slip fault. The total length of the co-seismic surface ruptures is approximately 160km. Multiple rupture patterns exist, mainly including linear shear fractures, obliquely distributed tensional and tensional-shear fractures, pressure ridges, and pull-apart basins. The earthquake also induced a large number of liquefaction structures and landslides in valleys and marshlands.
Based on strike variation and along-strike discontinuity due to the development of step-overs, the coseismic surface rupture zone can be subdivided into four segments, namely the Elinghu South, Huanghexiang, Dongcaoarlong, and Changmahexiang segments. The surface ruptures are quite continuous and prominent along the Elinghu south segment, western portion of the Huanghexiang segment, central portion of the Dongcaoarlong segment, and the Huanghexiang segment. Comparatively, coseismic surface ruptures of other portions are discontinuous. The coseismic strike-slip displacement is roughly determined to be 1~2m based on the displaced gullies, trails, and the width of cracks at releasing step-overs.

Located in the intervening zone between Tibetan plateau and surrounding blocks, the Lintan-Dangchang Fault(LDF)is characterized by north-protruding arc-shape, complex structures and intense fault activity. Quantitative studies on its new activity play a key role in searching the seismogenic mechanism, building regional tectonic model and understanding the tectonic interaction between Tibetan plateau and surrounding blocks. The LDF has strong neotectonic activities, and moderate-strong earthquakes occur frequently(three M6~7 earthquakes occurred in the past 500 years, including the July 22nd, 2013, Minxian-Zhangxian M_S6.6 earthquake), but the new activity of the fault is poorly known, the geological and geomorphological evidence of the Holocene activity has not been reported yet. Based on remote sensing interpretation and macro-landform analysis, this paper studies the long-term performance of LDF. Based on the study of fault activity, unmanned aircraft vehicle photogrammetry and differential GPS, radiocarbon dating, etc., the latest activity of LDF is quantitatively studied. Then the research results, historical strong earthquakes and small earthquake distribution are comprehensively analyzed for studying the seismogenic mechanism and constructing regional tectonic models. The results are as follows: Firstly, the fault geometry is complex and there are many branch faults. According to the convergence degree of the fault trace and the fault-controlled macroscopic topography, the LDF is divided into three segments: the west, the middle and the east. The west segment contains two fault branches(the south and the north)and the south Hezuo Fault. The south branch of the west segment mainly dominates the Jicang Neogene Basin, and the south Hezuo Fault controls the south boundary of Hezuo Basin. The middle segment has more convergent and stable trace, consisting of the main fault and south Hezuo Fault, and these faults separate the main planation surface of the Tibetan plateau and Lintan Basin surface geologically and geomorphologically. The fault traces in the east segment are sparsely distributed, and the terrain is characterized by hundreds of meters of uplifts. The branch faults include the main fault, Hetuo Fault, Muzhailing Fault and Bolinkou Fault, each controlling differential topography. Secondly, the motion property of the LDF is mainly left-lateral strike-slip, with a relative smaller portion of vertical slip. The left-lateral strike-slip offset the Taohe River and its tributaries, gullies and ridges synchronously, and the maximum left-lateral displacement of the tributary of Taohe River can reach 3km. Meanwhile, the pull-apart basins and push-up ridges associated with the left-lateral fault slip are also developed in the fault zone. The performance of vertical slip includes tilting of the main planation surface, vertical offsets of the boundary and interior of Neogene basin and hundred meter-scale differential topography. The vertical offset of the Neogene is 300~500m. Thirdly, one fault profile was newly discovered in Gongqia Village, revealing a complete sequence of pre-earthquake-coseismic-postseismic deposition, and this event was constrained by the radiocarbon ages of pre-earthquake and post-earthquake deposition. The event was constrained to be 2090~7745aBP(confidence 2σ), which for the first time confirmed the Holocene activity of the fault. Fourthly, a gully with two terraces at least on the west side of Zhuangzi Village in the east segment of the main fault retains a typical faulted landform. The T2/T1 terrace riser of the gully has a left-handed dislocation of 6.3~11.8m, and the scarp height on terrace T2 is 0.4~0.7m, the radiocarbon age of the terrace T2 is7170~7310aBP, so the derived left-lateral strike-slip rate since the early Holocene in the east segment of the main fault is 0.86~1.65mm/a, and the vertical slip rate is 0.05~0.10mm/a. The derived slip rates are in line with the regional tectonic model proposed by the predecessors, so the LDF plays an important role in the internal deformation of the West Qinling. The clockwise rotation of the middle to east segments of the LDF acts as an obstacle to the left-lateral strike-slip motion, which inevitably leads to the redistribution and rapid release of stress, so earthquakes in the middle-east segment of the LDF are unusually frequent.

The Hongtong earthquake occurring on 25 September 1303 in both Linfen Basin (LFB)and Taiyuan Basin (TYB)in Shanxi Graben is the first M8.0 earthquake based on the Chinese literature in China mainland, 392 years later, the Linfen M7.5 earthquake occurred on 18 May 1695 in Linfen Basin with its macro-epicenter distance of only 40km south of the Hongtong earthquake. Due to their close macro-epicenter distance and shortly interval of 392a, it attracted continuous attention to the geoscientists around Southern Shanxi Graben, southeastern Orods Plate. This paper combines the historical documents and interpreting the coseismic triggered disasters in study area. The results show that:1)the number of building damaged in the southern TYB and Lingshi Uplift (LSU)during 1303 Hongtong earthquake is similar to that of the LFB, indicating that the TYB and LSU maybe suffered the same or even worse earthquake disaster losses during the 1303 Hongtong earthquake. While the 1695 Linfen earthquake is confined within the LFB and south of Hongtong County; 2)More than 11 000 loess landslides were triggered by the 1303 Hongtong earthquake event between LFB and TYB, which is consistent with the literature records. We suggested the macro-epicenter of the 1303 Hongtong earthquake should move about 60km northward from the present location (36.3°N, 111.7°E)near Hongtong County to the new location (36.8°N, 111.7°E) between Huozhou City and Lingshi County, the new macro-epicenter location can reasonably explain the large-scale centralized earthquake-triggered landslides during the event. The landslides had aggravated the severity of the loss; 3)Our result helps to understand the spatial distribution of the two strong earthquakes and the relationship between them, especially the distribution map of earthquake-induced loess landslides by 1303 Hongtong earthquake extracted using the Google Earth images, which supports the amendment of the macro-epicenter.

A complete understanding to the disasters triggered by giant earthquakes is not only crucial to effectively evaluating the reliability of existing earthquake magnitude, but also supporting the seismic hazard assessment. The great historical earthquake with estimated magnitude of M8.5 in Huaxian County on the 23^rd January 1556, which caused a death toll of more than 830 000, is the most serious earthquake on the global record. But for a long time, the knowledge about the hazards of this earthquake has been limited to areas along the causative Huashan piedmont fault(HSPF) and within the Weihe Basin. In this paper, we made a study on earthquake triggered landslides of the 1556 event along but not limited to the HSPF.
Using the high-resolution satellite imagery of Google Earth for earthquake-triggered landslide interpretation, we obtained two dense loess landslides areas generated by the 1556 earthquake, which are located at the east end and west end of the HSPF. The number of the interpreted landslides is 1 515 in the west area(WA), which is near to the macro-epicentre, and 2 049 in the east area(EA), respectively. Based on the empirical relationship between the landslide volume and area, we get the estimated landslide volume of 2.85~6.40km³ of WA and EA, which is equivalent or bigger than the value of ~2.8km³ caused by Wenchuan earthquake of M_W7.9 on 12^th May 2008. These earthquake triggered landslides are the main cause for the death of inhabitants living in houses or loess house caves located outside of the basin, such as Weinan, Lintong, Lantian(affected by WA) and Lingbao(affected by EA). Our results can help deeply understand the distribution characteristics of coseismic disaster of the 1556 Huaxian earthquake to the south of Weihe Basin, and also provide important reference for the modification of the isoseismals.

The Huoshan piedmont fault is a small watershed region in Shanxi Province. We utilized the high-resolution DEM data and the stream-power incision model which describes the relationship between the tectonic uplift and fluvial incision to analyze the S-A double-log graph, concavity index (θ)and steepness index (logk_s) of the 64 channels across this fault and discuss their responses to the tectonic movement of the fault. The results show that (1)the S-A double-log graphs all exhibit an obvious convex form, which is the direct expression of the response to the situation that the bedrock uplift rate is higher than the fluvial incision rate. (2)All of the concavity index (θ)values of 64 channels are lower than 0.35 with an average value of 0.223, much lower than the empirical value (0.49)of the rivers in steady state. These low values are the quantitative reflections of the channels' slightly concave profiles. Meanwhile they imply that these channels across the fault are very young. There is no enough time for them to adjust the profiles through the fluvial incision to the steady state because of the fault's frequent and strong tectonic movements. (3)The steepness index values of the channels located in the Laoyeding Mt. are highest, while they are lower in the northern and southern mountains. Moreover, the steepness index values of the channels in the northern mountains, on average, are higher than those of the channels in the southern mountains. To a certain extent, this distribution of the steepness index corresponds to the difference in the uplift rates of the Huoshan piedmont fault. It means that the uplift rate of the middle fault segment in the Laoyeding Mt. is highest, and the uplift rate of the northern segment is higher than that of the southern segment.

Two earthquakes with magnitude larger than 7.0 occurred in 2008 and 2014 on the southwestern end of the Altyn Tagh Fault, which is located in the northwestern borderland of Tibetan plateau. Occurrences of these two earthquakes provide important insights into regional geodynamics and potential seismic risk. Layered viscoelastic model is employed in the paper to study the interaction between these two events. We find that most of aftershocks were triggered by coseismic stress produced by the 2008 Yutian earthquake, and the effect of this earthquake is insignificant on the occurrence of the 2014 Yutian earthquake. However, stress transfer by viscoelastic relaxation of postseismic deformation is in favor of occurrence of the 2014 Yutian earthquake. The coseismic and postseismic stress transfer produced by the 2014 Yutian earthquake leads to stress increasing on the western segment of the Altyn Tagh Fault. Since the occurrence time of the last major earthquake on the western segment of the Altyn Tagh Fault is tens of years ago, it should have accumulated large moment deficit on the fault segment. The Altyn Tagh Fault should be considered as a fault with high potential seismic risk.

As an important technology to paleoseismologic research, trenching has been used to identify paleo-earthquakes recorded in strata, combined with dating technology. However, there have been some bigger uncertainties and limitations. For instance, subtle strata in loess sediment cannot be interpreted only by naked-eye, which seriously affects identifying paleo-earthquake horizon and time. Therefore, how to improve the accuracy and reduce the uncertainty of paleo-earthquake identification is the important problem we are currently facing. Dongyugou loess section, located in the northeastern corner of Linfen Basin, Shanxi Province, cuts across the Huoshan piedmont fault. The section exposes not only the well-developed loess sequence, but also several obvious faulting events. Thus, this loess section is a better site to make a high resolution study to improve the accuracy and reduce the uncertainty of paleo-earthquake identification. Based on the high-resolution grain size and magnetic susceptibility analysis, and associated with visual interpretation by naked-eye, we made a high-resolution stratification of Dongyugou loess section, including high-resolution thickness of each stratum and its upper and bottom boundaries. Based on the high-resolution stratification and their comparison between two fault walls, we identified three earthquake events, which occurred after formation of u5-7, u4 and u2, corresponding to their stratification depth of 7.1m, 4.7m and 2.9m in hanging wall. Based on results of OSL dating and average sedimentation rate of hanging wall, we estimated that the three events occurred around 45.8ka(between (48.1±1.5)～(43.2±2.5)ka), 32.8ka(between (35.0±2.4)～(30.6±1.3)ka) and 23.3ka(between (26.4±0.8)～(20.9±0.7)ka). According to the thickness difference of three loess-paleosol sedimentary cycles between two fault walls, we calculated the coseismic vertical displacements of the three events as 0.5m, 0.4 and 1.3m, respectively. Compared with other segments of the Huoshan piedmont fault zone, we found the southernmost segment is the weakest, with longer recurrence interval of about 11ka and lower vertical slip rate of 0.048mm/a. The high-accuracy grain size and magnetic susceptibility analysis offers an effective method for reducing the uncertainties of the paleo-earthquake research in loess area.

The quantitative analysis of morphologic characteristics of bedrock fault surface is a useful approach to study faulting history and identify paleo-earthquake. It is an effective complement to trenching technique, especially to identify paleo-earthquakes in a bedrock area where the trenching technique cannot be applied. In this paper, we calculate the 2D fractal dimension of three bedrock fault surfaces on Huoshan piedmont fault in Shanxi graben, China using the isotropic empirical variogram. Taking average fractal dimensions of every horizontal tape and plotting them along the vertical axis, we find the fractal dimension presents pronounced segmentation in vertical direction. This step change of the average fractal dimensions demonstrates obvious segmentation of the fault surface morphology. Then, the segmentation of fault surface morphology, showing different exposure duration of each segment, is caused by periodic faulting earthquake, but not continuous erosion. Therefore, taking best normal fitting of average fractal dimensions of each segment as a characteristic value to describe the surface morphology of the fault surface segment, the characteristic value can be used to estimate the exposure duration of the fault surface segment and then the occurrence time of the faulting earthquake that made the segment exposed. The width of each fault surface segment can also be regarded as an approximate vertical coseismic displacement. Based on the segmentation of quantitative morphology of the three fault surfaces on the Huoshan piedmont fault, we identify three faulting earthquake events. Combined with trenching results reported by previous researches, we attempt to fit an empirical relationship between the exposure time and the morphological characteristic value on the fault. The co-seismic vertical displacement of a characteristic earthquake on the Huoshan piedmont fault is estimated to be 3.5m(3~4m), the average width of all middle fault surface segments. Moreover, the small gap of average 0.5~1m width between two adjacent segments, where fractal value increases gradually with the increased fault surface height, is inferred to be caused by erosion between two faulting earthquakes.

Daliangshan Fault zone constitutes an important part of the eastern boundary of Sichuan-yunnan active block. The studies of slip rate along the fault is not only significant to the crust movement and deformation pattern on the southeast edge of Tibetan Plateau,but also has great value in seismic hazard assessment and mid-and long-term forecasting of earthquake of the Daliangshan region. Through detailed field work along the south segment of Daliangshan Fault zone,namely the Butuo Fault and the Jiaojihe Fault,and based on accurate RTK(GPS)survey for the alluvial fans and activity dating,we suggest that left-lateral slip rate of the south segment of the fault zone is between 2.5～4.5mm/a,and the slip rate of Jiaojihe Fault is slightly higher than that of the Butuo Fault. Due to partitioning of part of the strike-slip component on the Daliangshan Fault zone,there is an obvious deficit in the displacement and slip rate on the Anninghe-Zemuhe Fault,compared to the Xianshuihe and Xiaojiang Faults. Comparing to the slip rates between Daliangshan Fault and Anninghe-Zemuhe Fault,it is found that they have similar horizontal slip rate,indicating the seismicity level of the Daliangshan Fault will not be lower than that of Anninghe-Zemuhe Fault. As the Daliangshan Fault gradually replaces the role of Anninghe-Zemuhe Fault in the Xianshuihe-Xiaojiang Fault system,the seismicity on the Daliangshan Fault zone will increase,and the Dalianghan region will have a higher risk of earthquake damage.

When a reach of a stream is steepened with respect to the adjoining reach,it defines a topographic knickpoint.A knickpoint is supposed to be a response to the base-level changes,and the base-level of a drainage basin is influenced by the fault movement.The formation of a knickpoint on a gully long-profile,whose base-level is the footslope of the fault scarp,is associated very closely with the vertical movement of a fault,therefore,the ages of paleo-earthquake events can be estimated by the knickpoint series along the longitudinal profile of a gully.We have made a case study of the Huoshan Mts.Piedmont Fault,and extracted tens of gullies across the fault based on the high-resolution DEM data and identified out knickpoints in 23 gullies.There are 5 gullies with only one knickpoint which are laid on the fault.And there are two gullies having two knickpoints with the latest one laid on the fault.The positions of these knickpoints and their higher height ranging from 4～9m imply that there are several knickpoints superposed together and the knickpoints have not migrated upstream.The other 16 gullies respectively have 2～3 knickpoints.The latest knickpoints have been migrated upstream to a distance of 40～70m from the fault.The knickpoints of intermediate ages are at a distance of 150～150m upstream from the fault and the oldest ones at a distance of 300～500m.Under the conditions that the latest knickpoints are associated with the 1303 M_W8.0 Hongdong earthquake(Event Ⅲ)and that the gullies keep the same rate of headward erosion during the Holocene,Event Ⅱ is estimated to take place during 3336～2269a B.P. and Event Ⅰ is estimated to take place during 3336～2269a B.P. , respectively.The recurrence of events is about 1500～2600a.These results are consistent with those obtained through the trench investigations.

As the most important fault of Late Pleistocene in the Lhasa area,the Nalinlaka Fault is a left-lateral thrust fault,striking NWW,dipping SSW with a high dip angle,and extending over 33km.According to the studies on the latest strata on the Nalinlaka Fault zone,this fault zone has been obviously active since Late Pleistocene and the movement left behind some geomorphologic phenomena on the earth's surface,especially at the sites of the gully west of Cijiaolin and around Xiecun village.For example,some rivers,ridges and terraces are dislocated,forming beheaded gullies,fault escarps and so on.The horizontal displacements since Late Pleistocene at the above two places are 54～87m and 20～67m,respectively.Based on the studies on the 4 trenches along the fault using progressive constraining method,we conclude that there might have occurred 5 paleoearthquake events along the Nalinlaka Fault since 70ka BP,the ages of each paleoearthquake are 8.53,54.40,<41.23,21.96,and 9.86 ka BP,and the average recurrence interval is 14.67ka.Because of the limits of trenches and earthquake events exposed by each trench,no single trench revealed completely all the 5 events.So,there may be some errors in determining the upper and lower limits of some events in this article.