A strong earthquake with magnitude M_S6.2 hit Hutubi, Xinjiang at 13:15:03 on December 8th, 2016(Beijing Time). In order to better understand its mechanism, we performed centroid moment tensor inversion using the broadband waveform data recorded at stations from the Xinjiang regional seismic network by employing gCAP method. The best double couple solution of the M_S6.2 mainshock on December 8th, 2016 estimated from local and near-regional waveforms is strike:271°, dip:64ånd rake:90° for nodal plane I, and strike:91°, dip:26ånd rake:90°for nodal plane Ⅱ; the centroid depth is about 21km and the moment magnitude(M_W)is 5.9. ISO, CLVD and DC, the full moment tensor, of the earthquake accounted for 0.049%, 0.156% and 99.795%, respectively. The share of non-double couple component is merely 0.205%. This indicates that the earthquake is of double-couple fault mode, a typical tectonic earthquake featuring a thrust-type earthquake of squeezing property.The double difference(HypoDD)technique provided good opportunities for a comparative study of spatio-temporal properties and evolution of the aftershock sequences, and the earthquake relocation was done using HypoDD method. 486 aftershocks are relocated accurately and 327 events are obtained, whose residual of the RMS is 0.19, and the standard deviations along the direction of longitude, latitude and depth are 0.57km, 0.6km and 1.07km respectively. The result reveals that the aftershocks sequence is mainly distributed along the southern marginal fault of the Junggar Basin, extending about 35km to the NWW direction as a whole; the focal depths are above 20km for most of earthquakes, while the main shock and the biggest aftershock are deeper than others. The depth profile shows a relatively steep dip angle of the seismogenic fault plane, and the aftershocks dipping northward. Based on the spatial and temporal distribution features of the aftershocks, it is considered that the seismogenic fault plane may be the nodal plane I and the dip angle is about 271°. The structure of the Hutubi earthquake area is extremely complicated. The existing geological structure research results show that the combination zone between the northern Tianshan and the Junggar Basin presents typical intracontinental active tectonic features. There are numerous thrust fold structures, which are characterized by anticlines and reverse faults parallel to the mountains formed during the multi-stage Cenozoic period. The structural deformation shows the deformation characteristics of longitudinal zoning, lateral segmentation and vertical stratification. The ground geological survey and the tectonic interpretation of the seismic data show that the recoil faults are developed near the source area of the Hutubi earthquake, and the recoil faults related to the anticline are all blind thrust faults. The deep reflection seismic profile shows that there are several listric reverse faults dipping southward near the study area, corresponding to the active hidden reverse faults; At the leading edge of the nappe, there are complex fault and fold structures, which, in this area, are the compressional triangular zone, tilted structure and northward bedding backthrust formation. Integrating with geological survey and seismic deep soundings, the seismogenic fault of the M_S6.2 earthquake is classified as a typical blind reverse fault with the opposite direction close to the southern marginal fault of the Junggar Basin, which is caused by the fact that the main fault is reversed by a strong push to the front during the process of thrust slip. Moreover, the Manas earthquake in 1906 also occurred near the southern marginal fault in Junggar, and the seismogenic mechanism was a blind fault. This suggests that there are some hidden thrust fault systems in the piedmont area of the northern Tianshan Mountains. These faults are controlled by active faults in the deep and contain multiple sets of active faults.

The large river systems are the major transfer of continental masses to the ocean and basin, playing significant roles in global geochemical cycles. The Tibetan plateau is the birthplace of many huge rivers flowing through eastern and southern Asia, in which the fluvial deposits kept not only closely relate to the geological evolution information from the source areas, but also record the river itself building process. The low-temperature thermochronology method of detrital minerals (zircon and apatite, etc.) can be used to constrain the river's source areas, establishing its source-sink system. It can also combine regional tectonic deformation analysis to determine the potential source region of the river and the formation time of the plateau geomorphology, which is a focused issue in recent years. In this study, we have summarized the research results from the large rivers in the Tibetan plateau in recent years, suggesting that the low-temperature thermochronology analysis of the detrital minerals should be focused on the river's key locations in the upstream, midstream and downstream, respectively, combining the small tributaries analysis which can give a more detailed thermal evolution history in the whole drainage basin. On the conditions of the bedrock, it is shown that in the same river's different place we should use the same low-temperature thermochronology, while in different river's places we should take several low-temperature thermochronology methods (apatite and zircon, etc.)at a same position, so we get a complete time series related to the river incision. Combining the valley bedrock and detrital river minerals with the low-temperature thermalchronology on the Tibetan plateau, together with the chronology, structure analysis and other sedimentary studies, we can obtain detailed structures and river's evolution processes.

Statistical study of earthquakes in the past, due to the small-medium size magnitude earthquake associated with surface rupture are rare, considers that only the earthquakes beyond magnitude 6 1/2 could produce surface ruptures in the most cases. Identification of paleoseismic events is also often based on this assumption. In this paper, we summarized 56 historical moderate size earthquakes worldwide, which have clearly documented about surface ruptures from 1950 to 2014.Results show that the magnitude lowest limit of the earthquake associated with surface rupture may be lower than the 6 1/2 , probably is about 5, even can be as low as 3.6 under extreme conditions. Additionally, from the view of theory and practice, this paper explored the effect of control factors on surface rupture, so as to indicate that the shallow focal depth is one of the most important factors for small-medium size earthquake associated with surface rupture, also included are the high heat flow values, tensile tectonic environment and active fault with weak friction strength. Although the probability that small magnitude earthquake produces surface rupture is low, it is not impossible. In the interpretation of paleoearthquake events, it also cannot overgeneralize that the corresponding earthquake magnitude must be 6.5 or greater as long as the fracture appeared, while ignoring the possibility of some moderate size earthquakes.

Using Ne(electron density) and Te(electron temperature) data of Langmuir Probe onboard DEMETER(Detection of Electro-magnetic Emissions Transmitted from Earthquake Regions) satellite,the paper studies the variations of electron density and electron temperature associated with strong earthquakes.The specific scientific objectives of Langmuir Probe are to map the bulk plasma parameters and to study their variations associated with seismic activity,volcanism and human activity and other sources of perturbations.Langmuir probe sweeps in voltage allow to obtain a current-voltage(Ⅰ-Ⅴ) characteristic every second.Bulk plasma parameters are obtained from the analysis of the Ⅰ-Ⅴ characteristics.The work principle,data format of Langmuir Probe onboard DEMETER is briefly introduced.We mainly studied the 2006 M_W 7.9 Tonga earthquake and the M_W 7.1 Taiwan earthquake in this paper.For each earthquake,we choose the orbits which passed over the area about 2000km around epicenter,including four months data before and two months data after the earthquakes.There are mainly three steps to reprocess the raw data,in order to avoid disturbances resulting from solar activities and geomagnetic activities.The result on the M_W 7.9 Tonga earthquake shows that at the equatorial region the electron density was relatively low before 28 April,while it began to increase from 28 April,and got the highest at 2 May one day before the earthquake.Until 4 May after the main shock,Ne began to decline.Based on comparison between revisited orbits,the orbit 097681(before shock) and 098721(after shock) observed certain disturbance.To further investigate the features of the preearthquake ionospheric anomalies,using 5 days as time window and 1 day as step size,we examined the temporal and spatial evolution of electron density within the area of 2000km around epicenter.Results show that the normal distribution of Ne kept at a relatively high level,except a relatively sharp reduction of Ne from 29 April to 2 May.The result on the M_W 7.1Taiwan earthquake shows that Ne changed randomly,while Te kept at a relatively high level,but dropped gradually before the quake.Currently we have no evidence to conclude that these changes are the results from the seismic activity,but based on data reprocessing,we can exclude the disturbances induced by solar activity and magnetic field at certain degree.If these changes of Ne/Te really resulted from earthquake,we may prudently conclude that ionospheric disturbance associated with seismic activity may possibly occur in a short time impending an earthquake with a short duration.

Based on the IDP data from French DEMETER satellite,the global distribution is shown,which corresponds to three precipitation zones:auroral precipitation zone,mid-high latitude precipitation zone and South Antarctic precipitation zone.Then the Chili earthquake with M8.8 on February 27,2010 is taken as an example.The IDP fluxes from repeated orbits are compared and the results show that there is a clear enhancement on February 26,just one day ahead of the Chili earthquake.In the south zone with L = 2.1 ～ 2.7,the flux on February 26 is higher than that on other days before.While in the north zone with L = 2.1 ～ 2.7,there is no clear change in the day time but a great enhancement during the night,which is close to the earthquake occurrence time.At the same time,the flux on February 26 over the epicenter is far lower than that on other days before during the day time while it reaches the peak at night.

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.

The Wanyaogou Fault dislocates the Jurassic sandstone.The tilted bedrock becomes a natural barrier to the groundwater,and a water-rich stratum formed in the footwall which caused obvious resistance difference between the two walls of the fault.The electrical imaging is an effective way to detect the fault on this condition.The experimental electrical resistivity tomography survey was conducted to detect the Wanyaogao Fault.The results of 2-D resistivity inversion indicate that the electrical structures on both sides of the fault present obvious difference,the resistivity of the hanging wall is high,while that of the foot wall is low.And the interface of the high and low resistance regions inclines to the low resistance region.The electrical resistivity tomography survey was also conducted to detect other faults in Urmuqi which have similar tectonic characteristics with Wanyaogou Fault.And the electrical structures appear the similar abnormality.So the abnormal characteristic is an important indicator and basis for identification of fault in the Urumqi region.The faults in Urmuqi are almost all high-obliquity reverse faults.After comparing the electrical imaging with the trench section,we find the fault is not coincident with the borderline between the high and low resistance,but lies in the high resistance region.The fault inclination is reverse to the gradient direction of isolines.The fault location is near to the inflexion of the upper isolines.

In the eastern mainland of China there are few cross sections of faults where dislocation of Quaternary strata can be observed. However,recently we found such a profile about 2km away from the Nanling county,Anhui Province(30°55'456″N,118°177'74″E),west to the highway from Nanling to Fanchang. This fault has been identified on the satellite image,but its trace is confined to the southern side of the Nanling Basin. Our field investigation indicates that the northwestern end of this fault lies at the Xiaodanyang-Fangshan Fault. It is only 20km long,striking in NW,dipping to southwest. From observations on the profile,it consists of two small fractures and has two periods of activity at least. The first active period is before middle Pleistocene time,or probably in early Pleistocene. And the second active period is in or after middle Pleistocene. Its latest motion is of thrust with an amount of dislocation of 40cm. This fault cross section shows that the NW-trending faults in the eastern Mainland of China have new activities,though on small scales in general.

The Altyn Tagh,Kunlun and Haiyuan Faults are three major left-lateral strike-slip faults with high geologic and GPS-derived horizontal slip rates as well as frequent surface-rupturing earthquakes in the northern Tibetan Plateau.There exist local structures,such as pull-apart basins in stepovers and sag ponds,where fine-grained and/or organic interfaulting sediments have been continuously filled and co-seismic faulting traces have been well preserved in those sediments.Trenching across the strike-slip faults and those local structures,stratum-logging of the trench walls and structural-stratigraphic examination can uncover basic features of the permanent and cumulative geologic deformation zone of a strike-slip fault that has experienced several surface-rupturing earthquake cycles.The geologic section of the Banguoba trench 9km east of Old A'kesai Town across the recent traces of the Altyn Tagh Fault records 7 paleoearthquake events with a co-seismic left-lateral slip of 7±1m for the latest event and its cumulative geologic deformation zone is only 8m in width.The geologic section of the western Old A'kesai trench across a pull-apart basin of the Altyn Tagh Fault records at least 4 paleoearthquake events and its permanent and cumulative geologic deformation zone is only 13m in width.The geologic section of the Xidatan trench across the Kunlun Fault reveals 5 paleoearthquake events and their cumulative geologic deformation zones are 12～13m in width.The Maqin trench across a pull-apart of the Kunlun Fault also reveals 5 paleo-earthquake events and most of the structural deformation,about 15m wide,is concentrated in the pull-apart,while the widest structural deformation,including the associated distortion nearby the boundary fault of the pull-apart,is less than 35m.Two trenches excavated across the southern and northern boundary faults of the Songshan pull-apart basin along the Maomaoshan-Laohuashan segment of the Haiyuan Fault show up 6 paleoevents and their permanent geologic deformation zones are less than 10m wide for single boundary fault.Of course,as a extensional jog,the pull-apart basin over a hundred meters wide will experience severe tensional and transtensional surface ruptures during an earthquake,and the pull-apart basin itself may be taken as one part of the permanent geologic deformation zone.Thus,the repeatedly faulting of the Altyn Tagh,Kunlun,and Haiyuan Faults during the past several surface-rupturing earthquake cycles is localized along their strike and the width of their permanent geologic deformation zone for a single strike-slip fault is over 10 meters,but less than 30 meters in general.

Calcite is a common matter in the fault zone and it is often related with fault movement,so its dating is of vital significance for studying the time of fault movement.At present,ESR method is one of the ways for measuring the age of calcite,but there are no final conclusions regarding the ESR signals and measurement conditions of calcite.The samples used in this article were picked from the east of Erhai,Yunnan.According to the preliminary study of the samples,we found that calcite was liable to generate unstable short-lived signal when it was artificially exposed.So before measuring,the samples were kept under the room temperature condition for at least 5 days to eliminate the jamming signals.Generally,in natural calcite,there are many ESR signal centers,among them,the ones,g=2.0040 and g=2.0023,respond well to absorbed dose,and can be used in the dating.Growth curves of these two signals indicate a linear growth at least in the range of 1500Gy.But it is indicated with the artificially fixed known dose method that different microwave powers have to be taken for g=2.0040 and g=2.0023 signals.If we consider the deviation of ED value is smaller than 5%,then the microwave power should be 0.8 or 2mW for the g=2.0040 signal,and the microwave power be 2mW or 5mW for the g=2.0023 signal.

Based on the collection of six kinds of empirical relationships between magnitude and rupture parameters, the ranges of coefficients a_i and b_i(i=1,2,3,4,5,6) and their relationships are analyzed systematically.It is found that a_i and b_i are of more or less negative correlation, and the coefficients of different types have stable ranges while the stability and convergence degree are different.It suggests that more rupture parameters are involved in statistical relations, the coefficients are more stable.In the end, theoretical expression of a_i and b_i are derived from dislocation model of fault to explain the relationships between a_i and b_i and ranges of value of some parameters are presented as well.