The M_S 4.1 Reservoir-induced Hujiaping Earthquake in the Yangtze Three Gorges Reservoir Region

In this paper,based on the collected data and earthquake field investigation,characteristics of the MS4.1 Hujiaping earthquake of November 22,2008 at Guizhou town in Zigui county,Hubei Province and the geological and hydrogeological conditions and seismicity background of the area are analyzed,and the earthquake disaster is presented. Some scientific issues relating to earthquake precursors and the cause of the earthquake is discussed. The authors consider that the earthquake is a tectonic type reservoir-induced earthquake,occurring along the Xiannvshan fault under the joint action of reservoir water loading and water infiltration,and that there were certain suspected anomalies appearing in the gravity field before the earthquake. The cause of the earthquake may also be related to the effect of the Wenchuan earthquake on the local stress field.

The Upper Limit Size of Reservoir-Induced Earthquakes

We showed the relation between the magnitude of induced earthquake and the reservoir storage and dam height based on the global catalog from 1967 to 1989 compiled by Ding Yuanzhang(1989).By multiplying reservoir storage with dam height,we introduced a new parameter named E_E.We found that the cases with specific E_E and magnitude do not exceed a limit.Based on the discussion of its physics,we called E_E the equivalent energy.We considered this limit as the upper limit of magnitude for reservoir-induced earthquakes.The result was proved by the recent cases occurring in China.This size limitation can be used as a helpful consideration for reservoir design.

Induced Earthquake Monitoring of the Three Gorges Reservoir

The Three Gorges Project(TGP) on the Yangtze River(YR) is the largest water power station in the world;it is now attracting the worldwide attention. Possessing comprehensive utilization benefits mainly for flood control,power generation and navigation improvement,TGP will be a vital and backbone project in harnessing and developing of the YR. TGP has been commenced in 1993,the main channel of Yangtze was diverted on Nov.8th,1997 and whole project was completed in 2009. The Three Gorges(TG) reservoir has been formed since June 2003 and impounded to 175 m on Oct.26th,2010. The reservoir has a total length of 660 km and an average width of 1.0-1.5 km,with a total waters area of 1048 km2. In pace with the raised pool level,the enlargedstorage,the probability of reservoir earthquake would be enlarged. According to the magnitude records of historical maximum earthquake and properly weighted,defined the maximum reliable earthquake of TG reservoir would be ML6 magnitude,existed the probability of ML 5.0-5.8 induced earthquake around the Xiannvshan and Jiuwanxi fault zone(18 km upstream of the dam) . However,the highest intensity around the dam site would not exceed Degree VI,whereas the main structures of TGP were designed with an anti-seismic intensity of Degree VII,hence the reservoir induced earthquake would not form direct threat to the main structures of TGP. After the impoundment and operation of TG reservoir,the frequency and intensity of earthquake has been increased in some extent,yet the earthquake activities at TG region still kept in an original weak earthquake activities status. We should strengthen the TG reservoir induced earthquake monitoring and forecast,prevent the earthquake and geological calamity,ensure the safety of dam construction and operation,form the harmonious society as well as guarantee the long term security. This paper explained the mechanism,kinds,causes,development and calamities of the earthquakes in the world,collected a lot of TGP,China and World's earthquake and geology materials. Such as 105 year(Jan.1906-June2011) earthquake records in the world(Tab.1) ,13 main reservoir induced earthquake records in China(Tab. 2) ,19 main reservoir induced earthquake records in the world(Tab.3) ,14 year(1996-2009) reservoir earthquake monitoring records in TGP(Tab.4) . Analyzed the cause,calamities of the main earthquakes as well as its alarm and forecast. May it provide reference for readers and beg your guide.

Research status of earthquake forecasting in hydraulicfracturing induced earthquakes

In the new types of industrial activities including unconventional energy extraction associated with shale gas and hot dry rock,gas reservoir operations,CO2 geological storage,undergoing research on induced earthquake forecasting has become one of the forward positions of current seismology.As for the intense actual demand,the immature research on induced earthquake forecasting has already been applied in pre-assessment of site safety and seismic hazard and risk management.This work will review systematically recent advances in earthquake forecasting induced by hydraulic fracturing during industrial production from four aspects:earthquake occurrence probability,maximum expected magnitude forecasting,seismic risk analysis for engineering and social applications and key scientific problems.In terms of earthquake occurrence probability,we introduce statistical forecasting models such as an improved ETAS and non-stationary ETAS and physical forecasting models such as Seismogenic Index(SI)and hydro-mechanism nucleation.Research on maximum expected magnitude forecasting has experienced four stages of linear relationship with net injection volume of fluid,power exponential relationship and physical forecasting regarding fault parameters.For seismic risk analysis,we focus on probabilistic seismic hazard assessment and quantitative geological susceptibility model.Furthermore,this review is extended to key scientific problems that contain obtaining accurate fault scale and environmental stress state of reservoir,critical physical process of runaway rupture,complex mechanism of fault activation as well as physical mechanism and modeling of trailing effect.This work in understanding induced earthquake forecasting may contribute to unconventional energy development and production,seismic hazard mitigation,emergency management and scientific research as a reference.

The accurate location of the injection- induced microearthquakes in German Continental Deep Drilling Program

From August 21, 2000 to October 20, 2000,a fluid injection-induced seismicity experiment has been carried out in the KTB (German Continental Deep Drilling Program). The KTB seismic network recorded more than 2 700 events. Among them 237 events were of high signal-to-noise ratio, and were processed and accurately located. When the events were located, non KTB events were weeded out by Wadatis method. The standard deviation, mean and median were obtained by Jackknife's technique, and finally the events were accurately located by Gei-gers method so that the mean error is about 0.1 km. No earthquakes with focal depth greater than 9.3 km, which is nearly at the bottom of the hole, were detected. One of the explanation is that at such depths the stress levels may not close to the rocks frictional strength so that failure could not be induced by the relatively small perturbation in pore pressure. Or at these depths there may be no permeable, well-oriented faults. This depth may be in close proximity to the bottom of the hole to the brittle-ductile transition, even in this relatively stable interior of the in-teraplate. This phenomenon is explained by the experimental results and geothermal data from the superdeep bore-hole.

Quantitative assessment of the impact of earthquakeinduced geohazards on natural landscapes in Jiuzhaigou Valley

Many natural landscapes that lie in high mountain regions are highly susceptible to geological hazards, and their values and integrity are strongly threatened by the hazards. A preliminary framework was proposed to undertake a quantitative assessment of the impact of earthquake-induced geological hazards on the natural landscapes. Four factors reflecting the aesthetic value, ecological value, integrity of landscapes were selected to assess their vulnerability. The impact of earthquake-induced geological hazards on the landscapes is quantitatively expressed as the product of their vulnerability and resilience. The assessment framework was applied to Jiuzhaigou Valley which was severely struck by the Ms 7.0 earthquake on August 8, 2017. Field survey, satellite image interpretation, high-resolution DEM and unmanned aerial vehicle(UAV) reconnaissance were used to retrieve the values of the assessment factors. Twenty seven World Heritage Sites in the valley strongly influenced by the earthquakeinduced geohazards were evaluated. The impact values of two sites of them(Sparking Lake and Nuorilang Waterfall) are up to 8.24 and 4.65, respectively, and their natural landscapes were greatly damaged. The assessment results show a good agreement with the actual damages of the heritage sites.

Evaluation model of landslide hazards induced by the 2008 Wenchuan earthquake using strong motion data

Landslides induced by the 2008 Wenchuan earthquake in the Longmenshan area were relatively well instrumented, which makes it possible to investigate the landslides using ground motion records. Firstly, this paper analyzes the data from Wenchuan earthquake on both regional and local site scale. The analyses show that the Newmark accumulative displacement calculated from the ground motion recorded in a particular geological hazard zone corresponds to the hazard intensity in that zone; the larger the displacement, the more serious the geologic hazard. The calculated result also shows that the displacement is related to the Arias intensity, which represents the total energy released during the earthquake at the observation site. Secondly, this paper constructs an evaluation model of Newmark displacement calculated with Arias intensities to estimate the subsequent slope failure resulting from the earthquake. The calculated results based on the model fit well with the distribution of actual landslides, suggesting that this method is useful for hazard evaluation. Therefore, this type of model can be used for estimating regional-scale distribution of earthquake-induced landslides and their associated hazards immediately after an earthquake.

A Hazard Assessment Method for Potential Earthquake-Induced Landslides – A Case Study in Huaxian County, Shaanxi Province

The hazard assessment of potential earthquake-induced landslides is an important aspect of the study of earthquake-induced landslides. In this study, we assessed the hazard of potential earthquake-induced landslides in Huaxian County with a new hazard assessment method. This method is based on probabilistic seismic hazard analysis and the Newmark cumulative displacement assessment model. The model considers a comprehensive suite of information, including the seismic activities and engineering geological conditions in the study area, and simulates the uncertainty of the intensity parameters of the engineering geological rock groups using the Monte Carlo method. Unlike previous assessment studies on ground motions with a given exceedance probability level, the hazard of earthquake-induced landslides obtained by the method presented in this study allows for the possibility of earthquake-induced landslides in different parts of the study area in the future. The assessment of the hazard of earthquake-induced landslides in this study showed good agreement with the historical distribution of earthquake-induced landslides. This indicates that the assessment properly reflects the macroscopic rules for the development of earthquake-induced landslides in the study area, and can provide a reference framework for the management of the risk of earthquakeinduced landslides and land planning.

Relationships between ground motion parameters and landslides induced by Wenchuan earthquake

The MS8.0 Wenchuan earthquake induced severe landslide hazards.For the first time in China,large numbers of strong motion records were obtained during the Wenchuan earthquake,providing the opportunity to study the relationships between ground-motion parameters and the earthquake-induced landslides.Nearly 40 groups of records from the main shock distributed along the Longmenshan fault lines were used to carry out this study.The results appropriate to the Longmenshan area are as follows：1 The threshold of the peak ground acceleration（PGA） is about 0.7 m/s2.When the PGA reaches 2 m/s2,the landslide hazards are very serious; 2 The threshold of the peak ground velocity（PGV） is about 0.5 m/s.When the PGV reaches 1.5 m/s,severe landslide hazards will be induced; 3 The threshold for the Arias intensity（Ia） is about 0.2 m/s.When the Ia in one horizontal direction reaches 2 m/s,landslide hazards will be very serious; 4 As for the relevance order of the parameters to earthquake-induced landslides,Ia is the leading parameter,followed by PGV,and finally PGA.The results presented in this paper are consistent with the results from other studies,indicating that the threshold of the ground motion parameters for strong earthquakes is of the same order of magnitude as that of moderate earthquakes.Landslide density of local sites fluctuated with the increase of ground motion intensity if the thresholds were reached.When the upper limits are exceeded,the landslide density remains at a certain level with relatively little variation.

Factor analysis of earthquake-induced geological disasters of the M7.0 Lushan earthquake in China

The seismic intensities, lithologic characteristics and terrain features from a 3000 km2-region near the epicenter of the Lushan earthquake are used to analyze earthquake-induced geological disaster. The preliminary results indicate that secondary effects of the earthquake will affect specific areas, including those with glutenite and carbonate bedrock, a seismic intensity of IX, slopes between 40° and 50°, elevations of less than 2500 m, slope change rates between 20° and 30°, slope curvatures from - 1 to -0.5 and 0. 5 to 1, and relief between 50 and 100 m. Regions with susceptibility indices greater than 0.71 are prone to landslides and collapses. The secondary features are mainly distributed on both sides of the ridges that extend from Baosheng to Shuangshi and from Baosheng to Longxing. Other features are scattered on both sides of the ridges that extend from Qishuping to Baosheng and from Masangping to Lingguan. The distribution of the earthquake-related features trends in the NE direction, and the area that was most affected by the Lushan earthquake covers approximately 52.4 km^2.

Characteristics and failure mechanism of an ancient earthquake-induced landslide with an extremely wide distribution area

The Lamuajue landslide is located in Lamuajue village on the right bank of the Meigu River,Sichuan Province, China. This landslide is an ancient landslide with an extremely wide distribution area,covering an area of 19 km^2 with a maximum width of5.5 km and an estimated residual volume of 3×10~8 m^3.The objectives of this study were to identify the characteristics and failure mechanism of this landslide. In this study,based on field investigations,aerial photography, and profile surveys, the boundary,lithology, structure of the strata, and characteristics of the landslide deposits were determined. A gently angled weak interlayer consisting of shale was the main factor contributing to the occurrence of the Lamuajue landslide. The deposition area can be divided into three zones: zone A is an avalanche deposition area mainly composed of blocks,fragments, and debris with diameters ranging from0.1 m to 3 m; zone B is a residual integrated rock mass deposition area with large blocks,boulders and "fake bedrock"; and zone C is a deposition zone of limestone blocks and fragments. Three types of failure mechanism were analyzed and combined to explain the Lamuajue landslide based on the features of the accumulation area. First, a shattering-sliding mechanism caused by earthquakes in zone A. Second,a sliding mechanism along the weak intercalation caused by gravity and water in zone B. Third,a shattering-ejection mechanism generated by earthquakes in zone C. The results provide a distinctive case for the study of gigantic landslides induced by earthquakes, which is very important for understanding and assessing ancient earthquakeinduced landslides.

Experiment on Hydraulic Fracturing in Rock and Induced Earthquake

Experiment on rock hydraulic fracturing strength under different confining pressures was conducted on a series of test specimens with various pre-cracks prepared from 7 types of rock. Combining the data of an actual reservoir-induced earthquake with the experimental results of the contemporary tectonic stress field according to the theory of rock strength and the principle and method of rock fracture mechanics, the authors tentatively investigated the earthquakes induced by pore-water pressure in rock and obtained the initial results as follows: （1） One type of induced earthquake may occur in the case of larger tectonic stress on such weak planes that strike in similar orientation of principle tectonic compressional stress in the shallows of the rock mass; the pore-water pressure σp may generate tensile fracture on them and induce small earthquakes; （2） Two types of induced earthquake may occur in the case of larger tectonic stress, i.e.,① on such weakness planes that strike in similar orientation of principle tectonic compressional stress, σ1, in the shallows of the rockmass, the pore-water pressure, σp, may generate tensile fracture on them and induce small earthquakes; ② When the tectonic stress approximates the shear strength of the fracture, the pore-water pressure σp may reduce the normal stress, σn, on the fracture face causing failure of the originally stable fracture, producing gliding fracture and thus inducing an earthquake. σp may also increase the fracture depth, leading to an induced earthquake with the magnitude larger than the previous potential magnitude; （3） There is a depth limit for each type of rock mass, and no induced earthquake will occur beyond this limit.

Earthquake-induced collapse mechanism of two types of dangerous rock masses

As the economy of China develops, an increasing number of key traffic projects have been undertaken in the west of China, where there are high, steep rock slopes. The collapse of dangerous rock masses, especially following a strong earthquake, is one of common geological disasters known in rock slope engineering. Therefore, it is important to study the collapse mechanism of dangerous rock masses induced by an earthquake and the analysis approach of its stability. This study provides a simple and convenient method to determine the collapse mechanisms of two types of dangerous rock masses （i.e. cantilever and upright） associated with the definition and calculation of the safety factor, which is based on the flexure theory of a constant-section beam by combining with the maximum tensile-stress criterion to depict the process of crack propagation caused by seismic waves. The calculation results show that there are critical crack depths in each form of the dangerous rock masses. Once the accumulated depth of the crack growth during an earthquake exceeds the critical depth, the collapse will occur. It is also demonstrated that the crack extension amount of each step is not a constant value, and is closely associated with the current accumulated crack depth. The greater the cumulative crack depth, the more easily the crack propagates. Finally, the validity and applicability of the proposed method are verified through two actual engineering examples.

Earthquakes induced by deep penetrating bombing

The data of M≥5 earthquakes occurred in one year before and after 4 deep penetrating bombs in the region within 500 km and 1 000 km from the shooting site are presented. The 4 bombs are those happened in 1999 Kosovo of Yugoslavia, the 1991 Baghdad of Iraq, the 2001 Tora Bora of Afghanistan, and the 2003 Kirkuk of Iraq, respec-tively. The data indicate that the deep penetrating bombs may have remotely triggered some earthquakes. The deep penetrating bombs in seismically active regions should be forbidden.

Liquefaction Susceptibility of Soils With Clay Particles from Earthquake-induced Landslides

The main reason for earthquake-induced landslides is liquefaction of soil,a process considered to occur mostly in sandy soils.Liquefaction which occurs in clayey soils has also been reported and proven in the recent liters- ture,but liquefaction in clayey soils still remains unclear and there are many questions that need to be addressed.In order to address these questions,an depth study on the liquefaction potential of clayey soils was conducted on the ba- sis of field investigation and a series of laboratory tests on the samples collected from the sliding surface of the land- slides.The liquefaction potential of the'soils was studied by means of undrained cyclic ring-shear tests.Research re- sults show that the liquefaction potential of sandy soils is higher than that of clayey soils given the same void ratio; the soil resistance to liquefaction rises with an increase in plasticity for clayey soils;relation between plasticity index and the liquefaction potential of soil can be used in practical application to estimate the liquefaction potential of

Effects of mining－induced earthquakes on water table in deep wells

Based on the systematical collection and processing of data on the influence of mining-induced earthquakes on water table regime in deep well Lu-15 in Taozhuang Coal Mine since 1980, we study the characteristics of coseismic effect of water table in deep well in this paper. We have found precursory phenomena of water table in deep well before mining-induced earthquake. Here we discuss the physical mechanism of coseismic effect of mining--induced earthquake on water table in deep well.

Permanent displacement models of earthquake-induced landslides considering near-fault pulse-like ground motions

The permanent displacement of seismic slopes can be regarded as an effective criterion for stability estimation. This paper studied the characteristics of permanent displacements induced by velocity pulse-like ground motions and developed an empirical model to readily evaluate the stability of seismic slopes in a near-fault region. We identified 264 velocity pulse-like ground motions from the Next Generation Attenuation(NGA) database using the latest improved energy-based approach. All selected ground motions were rotated to the orientation of the strongest observed pulse for considering the directivity of the pulse effect, so that the most dangerous condition for slopes was considered. The results show the velocity pulse-like ground motions have a much more significant effect on permanent displacement of slopes than non-pulse-like ground motions. A regression model based on a function of peak ground velocity(PGV), peak ground acceleration(PGA) and critical acceleration(ac), was generated. A significant difference was found by comparing the presented model with classical models from literatures. This model can be used to evaluate the seismic slope stability considering the effects of nearfault pulse-like characteristics.

Research of the Activity of Earthquakes Induced by Water Injection of Salt Mining in Changning County,Sichuan Province

According to information from on-the-spot investigations, the tectonics of salt mining areas and digital seismic records, we studied the activity of earthquakes induced by water pumping in and out of the salt mines in Shuanghe town, Changning county, Sichuan Province. The study found that the rates of water injection and extraction in the Shuanghe salt mining region were evenly matched before April 2006 and earthquake activity was stable. On the other hand, shallow small and moderate earthquake numbers increased sharply after the water injection rate became much larger than the water extraction rate. Large injection over a long time may causes the permeation of water through pre-existing small fractures and micro-cracks in the Changning anticlinal and accelerate the rupture of micro tectonic formations in nearby regions, inducing small earthquake swarm activity. The Q value calculated by using digital earthquake records indicates a relatively inhomogeneous medium in this area. The results of the accurate location of small earthquakes show that sources are relatively shallow and are concentrated at a depth of 2km to 3km. Focal mechanism solutions reveal a normal dip-slip character of shallow earthquakes. All of these show certain characteristics of earthquake activity induced by water injection.

Intensive Observation of Reservoirinduced Seismicity and Preliminary Analysis on the Causes of Earthquakes in the Three Gorges Reservoir Area,Yangtze River

根据第 11 五年的计划的国家关键技术 RD 节目的要求，由 26 个地震车站组成的一个使增加密度的地震网络在 2009 年 3 月 21 短时期的地震计在湖北省的节在三个峡水库区域被建立， 5 宽带数字地震计。从三月到 2009 年 12 月， 2,995 ML -0 的一个总数。8 - 2。9 地震在从 145 m 三朵峡水库水水平玫瑰扣押到 172.8m 的试用期间被检测。用双差别地震地点算法， 2,837 地震精确被重定位。小本地地震的模式聚集在三个峡水库区域的结果表演呈现了线性分布或像团的簇分发，事件的像团的簇通常在从水滨的 5 km 的距离以内，并且地震的线性分发能被扩大到 16 km 的距离离开水滨。在三座峡水库的湖北节，地震主要在 Xiangxihe 河附近在 Xiannvshan 和 Jiuwanxi 差错的北结束被集中，并且沿着在在 Badong 区域的北河岸上的 Xietan 镇区和 Shenlongxi 区域的西方的长江的河岸，与焦点的深度不到 10km ，和 4km 在平均。在水库区域的地震频率与水库水水平变化有积极关联，显示 seismicity 属于水库导致的地震。沿着在水库区域的 Shenlong 河，地震在北 Badong 县显示出三线性分布，并且根据石灰岩地区常见的地形散布了分发。在碳酸盐阶层有地下的河。当水库被扣押时，水渗入了进地下的河，因此导致地震。在 Xiannvshan 的 crossriver 片断上的区域的地震指责， Jiuwanxi 差错并且在 Xietan ， Shazhen 和 Xizhen 的区域西方，可能与弄软断绝有关 Xiannvshan 差错，或床上用品例如 Nukou 差错，连接，它将导致岩石群众的失败因此，导致地震。然而，关于被触发的机制的有说服力的结论仍然需要进一步的学习。另外， Zigui 县并且在 Badong 县的 Rangkou 镇东方的 Wenhua 和 Yanglin 向南接近区域， mininginduced 地震在水库的岸是的附近，并且上的矿发生了一些倒塌地震。

Three-Gorges Reservoir Area on the Yangtze River Faced with Risk of Induced Destructive Earthquakes

The Three-Gorge Water Conservancy Project on the Yangtze River started to impound water by locking gates on June 1, 2003. A swarm of more than 2000 small earthquakes suddenly occurred densely along the river section in Xinling Town north of Badong, Hubei Province, on June 7. This caused grave concern in the following years, but, with the completion of the second- and third-phase engineering construction, the water level in the reservoir will rise up to 156 m and 175 m respectively, no matter whether it can induce larger and stronger earthquakes. After an analysis of the distribution of active faults in the eastern part of the reservoir area, their intersections and capability to generate earthquakes from a seismo-tectonic viewpoint, we consider that after the reservoir impounding, two potential focal zones existing in Badong and Zigui counties may generate M 5.5 earthquake, the seismic intensity of which may reach Ⅷ. It will induce landslide bodies in the reservoir area to be reactivated and slide. The evidence is the large-scale landslide occurring on the Shazhenxi Creek river in Zigui County on June 12, 2003.