The Yarlung Tsangbo fault zone, one of the most important geological interfaces in the Yarlung Tsangbo suture zone which is a huge geotectonic boundary with nearly east-west-trending in southern Tibet Plateau, has undergone a long-term tectonic evolution. Studying this fault zone can help us understand the development and evolution history of the suture zone and the tectonic mechanism of subduction-collision about the Tibet Plateau, so it has always been a hot topic in the field of geology. Most of existing data suggest that the current tectonic activity in southern Tibet is given priority to the rift system with nearly north-south-trending, and the Yarlung Tsangbo fault zone with nearly east-west-trending has relatively weaker activity since late Quaternary. There are only some evidences of Holocene activity found in the Lulang town section near eastern Himalayan syntaxis, and there are few reports about the reliable geological evidences of late Quaternary activity of the section on the west of Milin County of the fault zone.
Based on image interpretation, field investigation and chronological method, we found several fault profiles along the Yarlung Tsangbo fault zone near the Angren Lake in this study. These profiles reveal that loose fault gouge has been developed on the fault plane which nearly extends to the surface and offsets the loess sediments and its overlying alluvial-proluvial gravels. The loess is characterized by coarser grains, higher content of fine sand and tiny small gravels. The results of the two OSL dating samples collected in the loess are(94.68±6.51)ka and(103.84±5.14)ka respectively, showing that the loess revealed at the Angren site should be the middle-late Pleistocene sand loess distributed on the high-terraces along the Yarlung Tsangpo River. Consequently, the Angren segment of the Yarlung Tsangpo fault zone is active since the late Quaternary. In addition, synchronous left-lateral offsets of a series of small gullies and beheaded gullies can be seen near the profiles along the fault, which are the supporting evidence for the late Quaternary activity of the fault.
However, the segment with obvious geomorphology remains is relatively short, and no evidence of late Quaternary activity have been found in other sections on the west of Milin County of the Yarlung Tsangpo fault zone. Existing data show that, in the southern Tibet, a series of near NS-trending rift systems are strongly active since the late Quaternary, cutting almost all of the near east-west-trending tectonic belts including the Yarlung Tsangpo fault zone. In addition, majority of the earthquakes occurring in southern Tibet are related to the NS-trending rift systems. Tectonic images show that the Angren segment locates between the Shenzha-Dingjie rift and the Dangreyong Lake-Gu Lake rift. These two adjacent rifts are special in the rift system in southern Tibet:Firstly, the two rifts are located in the conversion position of the trend of the whole rift system; Secondly, the size of the two rifts varies significantly between the north side and the south side of the Yarlung Tsangbo fault zone. Thirdly, the Shenzha-Dingjie rift seems to be of right-lateral bending, while the Dangreyong Lake-Gu Lake rift shows left-lateral bending. These characteristics may lead to the fact that the amount of absorption and accommodation of the rift activities in the north side of the Yarlung Tsangbo fault zone is larger than that in the south side during the migration of the plateau materials, leading to the differential movement of the block between the two sides of the fault zone. Therefore, the Yarlung Tsangbo fault zone possesses the accommodating tectonic activity, of course, the intensity of this accommodating activity is limited and relatively weaker, which may be the reason why it is difficult to find large-scale tectonic remains characterizing the late Quaternary activity along the fault zone. The scale of the rift system in southern Tibet is systematically different between the two sides of the Yarlung Tsangbo fault zone, so it cannot be ruled out that there are also weak activities similar to the Angren segment in other sections of the fault zone.

An M_S 7.0 earthquake attacked southern segment of the Longmenshan Fault zone on 20 April 2013, in Lushan County, Sichuan Province, southwest of China. The seismic intensity of the meizoseismal area of the Lushan event is Ⅰ Ⅹ(the Chinese Seismic Intensity Scale). The meizoseismal area strikes NE, and is approximately 24km long and 11km wide. In the post-earthquake emergency scientific survey, some members found a series of co-seismic surface rupture signs at Longmen Township, one of the most damaged areas by this quake, north of Lushan County. The reported typical surface rupture signs include intensive shear-fissures along the channel at Zhanghuo Group, rotation of bricks near a white tower at Wanghuo Group, and lots of extensive cracks. On the basis of analyzing such surface rupture signs, Han et al., (2013)deduced that there might be a blind fault along Lushan County and Longmen Township(named the Lushan-Longmen presumed blind fault), and this fault probably was the seismogenic fault. Therefore, to confirm whether there is a potential seismogenic fault along Lushan and Longmen is very important not only to research of seismogenic fault for this earthquake but also to the reconstruction in the disaster-hit areas. Through surface ruptures surveying and trench excavating, we conclude that: there are no co-seismic surface ruptures at Longmen. Meanwhile, artificial seismic prospecting outcome, which shows nonexistence of the Lushan-Longmen presumed blind fault at least 800m below the ground surface, also supports our idea. Consequently, the reported shear-fissures and extensive cracks are not produced by the seismogenic fault, but most likely by ground shaking during the earthquake.

The groundwater monitoring network in the reservoir area of cascade hydroelectric stations in the lower reaches of Jinshajiang(abbreviation: Jinshajiang groundwater observation network)is the second groundwater observation network in China constructed by enterprise exclusively for earthquake precursor monitoring and study in reservoir areas.In this paper,distribution of the observation network,observational technologic system,basic characteristics of observation well and aquifer,and basic result of trial observation are presented,and the monitoring capability of earthquake precursor are discussed with respect to the conditions of observation well and aquifer and characteristics of multi-monthly,monthly,daily behaviors of water level and temperature in well.

The temperature and its gradient is measured carefully in 6 wells of Jinshajiang groundwater observation network.The result shows that the influence depth of sun-radiation heat is 50～125m.The average water temperature gradient is different in deferent wells,the minimum value is 0.11℃/hm,the maximum is 2.81℃/hm,and the general is 1～2℃/hm.The temperature gradient diversity in deferent depth sections in one well is very obvious,with values being in decimal fraction of ℃/hm,and the larger ones being 4～5℃/hm.Lithology of stratum and completeness of rockmass,particularly the high-angle fault crush zone,play a major role in affecting the influence depth of sun-radiation heat and temperature gradient of each well.The micro-behavior characteristics of water temperature in well,e.g.co-seismic effect,tide effect and anomalies before an earthquake etc,depend largely on the temperature gradient of the depth section where the temperature sensor is fixed.

Violent blowouts occurred in Chagan Well when the M_S 8.7 Sumatra earthquake happened on Dec.26,2004,with the eruptive fountain up to 60m high.The result of investigation and analysis of Chagan well indicates that blowout occurred in the condition of special hydrogeology.The water of monitoring layer was rich of CO₂.When the aquifer of monitoring was disturbed by the earthquake wave,a large number of absorbed gases were released.On the other hand,free bubble was broken by the earthquake wave and the groundwater was gasified,leading to the rapid increase of the pore pressure.

Based on the analysis of fluid anomaly data and investigation of macro precursor of the M_S 8.0 Wenchuan earthquake,and having taken careful consideration of the difficulty and ability of predicting earthquake,we found that the failed prediction of the M_S 8.0 Wenchuan earthquake doesn't mean that earthquakes can't be predicted.There were,though not much in quantity,a certain amount of underground fluid anomalies and remarkable macro anomalies occurring before the earthquake.Though it is difficult to predict the earthquake basing on them,it is possible to be aware of the impending earthquake.To improve the ability of earthquake prediction,the paper proposes to innovate the present work and administrative systems,in which,earthquake monitoring,prediction and research are separate each other,and professional and local forces are separate each other,to change the present work state of computer-replacing-human brain and the work mode of the too early use of formality and standardization,and to attach greater importance to investigation and confirmation of precursory anomalies and to monitoring and studying macro anomalies.

The North Beijing Geothermal Field includes Xiaotangshan and Shahe sub-geothermal fields, distributing as a triangle in plan. It borders Huangzhuang-Gaoliying Fault on the southeast, Nankou-Sunhe Fault on the southwest, and Asuwei-Xiaotangshan Fault on the north. The thermal reservoirs are the fissure aquifers of carbonate karsts among Wumishan Formation and Tieling Formation of Jixian System, and Cambrian-Ordovician System. The cover rocks of thermal reservoir are impermeable strata of sandstone and shale of Qingbaikou system, sandstone and shale of Carboniferous-Permian and volcanic rocks of Jurassic. Its plane characteristic of geo-temperature is marked by two hyper thermal areas in Xiaotangshan and Tang11. The vertical characteristic is such that the temperature increases with depth at the rate being lower in the thermal reservoirs and higher in the cover rocks. The compositions of δD-δ¹⁸O in rainwater, groundwater and geothermal water are almost on the Craig Atmosphere Precipitation Line in the area. The diagram shows that the natural rainfall is the geothermal water source. In hydrochemical diagram of geothermal water in Beijing area, the geothermal water is under urban thermal water. It shows that the North Beijing geothermal water is closer to cold water replenished area than the urban geothermal water. The distributing of ³H in geothermal water is higher in the north and lower in the south, and the dating of ¹⁴C of geothermal water is increasing from north to south. So we can conclude that the geothermal water flows from north to south. This shows that the atmosphere precipitation infiltrating underground from the northern mountain area flows from the karst area of Ming Tombs-Taoyukou, striding over Asuwei-Xiaotangshan Fault, then circulating in the deep and being heated by geothermal. At last it flows into and is stored in the North Beijing area, forming a geothermal field. Based on the above-mentioned characteristics, the genetic model of North Beijing geothermal system is built and defined as a mid-low temperature convective type geothermal system in North Beijing.

Much interference has been found in seismic subsurface fluid behaviors. The interference of subsurface water resource exploitation is very universal, and that of hot water exploitation is severe. It affects the observation on subsurface fluid. So, the influence of ground water exploitation on subsurface fluid behaviors should be observed, investigated and researched. Based on hydro-geological settings, exploitation history and actualities of the Jingbei geothermal field, the influences of hot water production on subsurface fluid behaviors in observation wells, which have different hydro-geological settings and different intervals from exploitation wells, are analyzed. Discrepancies of the influence on different observation items are also discussed. Our result shows that disturbance distance of hot water exploitation on subsurface fluid behaviors is within 5km in the Jingbei geothermal field, and the influence on behaviors of the observation wells nearby the water-transmitting fault is most notable. As for the effects on observation items, those on water level and temperature rank first, the escape gas (Rn, Hg) comes second, and that on soil gas (CO₂) is inconspicuous.

It is well known that the appearance of a vast amount of macro-anomalous phenomena is an important sign of strong activity of crust and is often followed by the occurrence of strong earthquake.Some examples of successful short-impending prediction of strong earthquake depended greatly on the appearance of a vast amount of macro-anomalous phenomena.The most famous examples are the cases of Haicheng,Longling and Songpan strong earthquakes.During the crucial moment of the prediction of these earthquakes,macro-anomalous phenomena had played an important role,which might not be replaced by microa-nomalous phenomena.It may indicate that the successful prediction of strong earthquake would not come true without macro-anomalous phenomena. However,in the period from May to June of 2002,after a vast amount of reliable macro-anomalous phenomena coming forth in Xichang area,Sichuan Province,the expected earthquake did not occur.The analysis has shown that these anomalous phenomena are controlled by tectonic structure,and their distribution bears a close relation with fault structure,and especially the anomaly of ground water has a notable tectonic attribute. This fact may indicate that the macro-anomalous phenomena are not equivalent to earthquake precursor,and they posses duality.On the one hand they can be regarded as an important short-impending earthquake precursor,and on the other hand they may reflect the anomaly of tectonic activity,rather than the precursor of earthquake.During the development of earthquake prediction,therefore,the observation,analysis and study of the macro-anomalous phenomena should be greatly enhanced,so that earthquake precursor can be distinguished from the anomaly of tectonic activity.In this way,the macro-anomalous phenomena will play a more and more important role in earthquake prediction.

On the basis of systematically checking up nearly ten years observation data of 11 water temperature observation wells in the Capital Circle, the behaviors of well water temperature are divided into several types, such as perennial tendency, annual, monthly and daily behaviors. The mechanisms and characteristics of these behaviors are then analyzed. The perennial tendency can be sub divided into smooth, ascending, descending, fluctuate and composite subtypes; the annual behaviors can be sub divided into smooth-stepwise, ascending, descending and fluctuate subtypes; the monthly behaviors can be sub divided into smooth, smooth-stepwise, smooth-fluctuate, descending-fluctuate, ascending fluctuate and composite subtypes; the daily behaviors are mostly fluctuate types, but 5 wells have tidal effects and most wells posses stepwise or pulsed changes. Up to now, the main factors that have been found to have influence on the behaviors of water temperature include the infiltration recharge of atmospheric water, lateral recharge of groundwater, groundwater exploration in adjacent area, and water turbulence in the observation wells, etc. In addition, the instability of observation instruments has great impact on water temperature behaviors. After the normal behaviors are recognized and all kinds of interference factors are eliminated, water temperatures are found to have good reflection on seismic event. Relatively distinct short imminent term anomalies have been found before some moderate-strong earthquakes, and remarkable co seismic anomalies can be recognized while distant strong earthquakes occur. Moreover, some pre seismic anomalies are also identified before the occurrence of a few distant strong earthquakes. Therefore, the further study on the behaviors of water temperature, and the elimination of all kinds of interference factors including stepwise or pulsed variation caused by the instability of observation instruments, will remarkably enhance the capacity and effectiveness of the reflection of water temperature behavior on seismic event. This will also help to improve the capability of short imminent term earthquake predication in our country.

A trial geochemical prospecting for active faults in urban area through the survey of soil gases has been conducted in Fuzhou City, China. This paper demonstrates the principal methodology and results of the trial prospecting. As compared with field investigation of active fault, the detection of buried active faults in urban area is more complicated since there are additional unfavorable environment and conditions such as road, constructions, refilled soils, rubbish dumps and soil/water pollution etc. The trial is aimed at the assessment of the effectiveness of soil gases survey for buried fault prospecting in urban area, and the identification of the surface locations of two buried faults in Fuzhou City. The trial includes the following comparative surveys: 1)different types of sites(soils); 2)different radon detectors and 3)different detecting items(adsorbed mercury, free mercury and radon in soil). Totally, 18 traverses of free mercury gas surveying have been conducted, along with 8 traverses of free radon gas and 1 traverse of adsorbed mercury surveying. The anomalies of different items are basically accordant, but it seems that radon gas is more sensitive to the influence of environmental factors such as groundwater level. The locations of two buried faults determined by soil gases are in good accordance with those determined by seismo-geologic investigation. The results of soils gases survey have also been compared with those of shallow seismic exploration. The comparison shows that the anomalies detected by the two different prospecting techniques are fairly coincident(the "fitting ratio" is about 70%); the false soil gas anomalies seem to occur in such a site as bridge side, abandoned construction bases and rubbish dumps.

Recently, remarkable rare gas anomalies have been observed in the water of Baolong and Tai-ping-zhuang wells in Beijing area, and Xialiao No.1 well in Xiaxian County, Shanxi Province. All these three wells are located in North China. According to the characteristics of rare gas anomalies in the three wells and the relationship between the anomalies and groundwater levels, theoretical analysis and experimental study have been carried out to gain an insight into the genesis of the anomalies. The results of experiments show that the volume of gases in the pores and fractures varies significantly with the evolution of groundwater dynamic condition. We find that the gas volume will expanse about 0.009 0% when the water level drops for 100mm. This may indicate that the anomalies of rare gases in these three wells are resulted from the expansion of gas volume and escape of gases due to the drop of groundwater level and the decrease of pore fluid pressures. It is proposed, therefore, that the rare gas anomalies discussed in this paper should not be earthquake precursor, but are anomalies caused by interference factors.