Seismic network design to detect felt ground motions from induced seismicity

Human activities, such as fluid injection as part of the stimulation of an enhanced geothermal system (EGS) for heat and power production, can cause damaging earthquake ground motions. A difficulty in quickly settling or rejecting insurance claims to the policy of the EGS operator is the lack of ground truth on the observed shaking at sites of reported damage. To overcome this problem a local seismic network could be installed prior to injection to constrain the ground-motion field at points of potential damage. Since the installation and maintenance of seismometers are costly there is an incentive to keep the number of instruments to a minimum. In this short communication, ground-motion fields are simulated and receiver operating characteristic analysis is conducted to guide decisions on the number of sensors required to obtain a certain confidence in the rate of false alarms and missed detections. For densities of 10–20 instruments per km² the ability to estimate potentially damaging ground motions is reasonable but associated with a significant chance of missed detections and false alarms. If an EGS operator or regulatory authority does not want to accept such chances then network densities of 50–100 instruments per km² are required and even in this case the exceedance/non-exceedance of a certain ground-motion threshold cannot be completely constrained.     

利用地下流体异常预测强震危险区的标志与方法

在系统地研究了华北北部5次中强以上地震前地下流体异常空间演化过程的基础上，分析了地下流体动态异常的迁移特征，根据迁移特征和异常时间与震中距的关系提出了预测强震危险区的5个标志和3个步骤，并用几个震例进行了检验，结果表明，运用地下流体异常的空间演化特征能够对未来强震危险区作出有一定可信度的预测。     

注水诱发地震的研究进展

研究注水诱发地震的特征、发生机理和最大可能震级等对开展诱发地震的预防、危险性评价、减灾策略制定等方面的工作具有重要意义。文章系统地梳理了国内外关于注水诱发地震研究的主要认识和分歧。结果表明：(1)诱发地震的最大可能震级由断层大小和应力状态等地质条件决定,受注水压力和累积注水量等参数的影响;(2)识别诱发地震的可靠方法取决于地震和注水之间的时空相关性,统计模型的参数以及断层活化分析等一系列证据链条;(3)当断层与流体储层之间存在水力连接时,孔隙压力扰动是诱发地震的主要发生机制,反之岩石基质体积变形引起的孔隙弹性应力变化主导了诱发地震的过程。此外,注水诱发的稳定滑动传播到断层的孕震部分、流体的化学作用和小地震级联触发效应也可能在注水诱发地震中发挥重要的作用。研究结果将为注水诱发地震机理研究和减轻破坏性诱发地震灾害提供一定的科学参考。     

Triggered earthquakes and deep well activities

Earthquakes can be triggered by any significant perturbation of the hydrologic regime. In areas where potentially active faults are already close to failure, the increased pore pressure resulting from fluid injection, or, alternatively, the massive extraction of fluid or gas, can induce sufficient stress and/or strain changes that, with time, can lead to sudden catastrophic failure in a major earthquake. Injection-induced earthquakes typically result from the reduction in frictional strength along preexisting, nearby faults caused by the increased formation fluid pressure. Earthquakes associated with production appear to respond to more complex mechanisms of subsidence, crustal unloading, and poroelastic changes in response to applied strains induced by the massive withdrawal of subsurface material. As each of these different types of triggered events can occur up to several years after well activities have begun (or even several years after all well activities have stopped), this suggests that the actual triggering process may be a very complex combination of effects, particularly if both fluid extraction and injection have taken place locally. To date, more than thirty cases of earthquakes triggered by well activities can be documented throughout the United States and Canada. Based on these case histories, it is evident that, owing to preexisting stress conditions in the upper crust, certain areas tend to have higher probabilities of exhibiting such induced seismicity.     

北京五里营井流体前兆观测到的两次异常及讨论

In this paper, the precursor response characteristics of digital fluid caused by the Wenchuan M8.0 and Yushu M7.1 earthquakes are studied, and the response difference of the observations of Wuliying well to the two strong earthquakes is compared. The result shows that the abnormal fluid response has a certain relationship with earthquake size and epicenter distance. The greater the earthquake, and the closer it is to the epicenter from the observatory, the more sensitive the response will be to fluid anomalies. Abnormal Helium release was first observed before both strong earthquakes in the fluid precursor observation. The release intensity is related to earthquake magnitude; the larger the magnitude, the stronger the abnormal changes. The large change in He release in a short period after the Wenchuan earthquake may be related to the continuous activity of strong aftershocks and the structural adjustment after the earthquake. Helium release increased significantly after both earthquakes, as contributed by the abnormal deep-sited Helium release. However, this process may be connected to the annual change from July to September or the hot-reservoir type gas release in the Wuliying well. In the earthquake preparation process, a large number of deep-derived Helium is released into the geothermal system and the entire composition is changed. Temporally, this gas release appears later than fault-type gas release, and the disappearance time of this anomaly is also much later. The response difference of the fluid precursor to the two strong earthquakes may be related to differences of deep structural setting and dynamic mechanism. It also shows there is a stronger correlation between Wenchuan M8.0 earthquake in the North-South Seismic Belt and North China region than the Yushu M7.1 earthquake in the internal Qinghai-Tibetan plateau. Helium gas can be a sensitive indicator for monitoring abnormal deep-gas activity of the region where the observation station is located. Hence, observation and research should be strengthened in the future.     

Patterns of Seismicity Associated with USGS Identified Areas of Potentially Induced Seismicity

A systematic review across U.S. Geological Survey (USGS) identified potentially induced seismic locations was conducted to discover seismic distance patterns and trends over time away from injection disposal wells. Previous research indicates a 10 km (6 miles) average where the majority of induced seismicity is expected to occur within individual locations, with some areas reporting a larger radius of 35 km (22 miles) to over 70 km (43 miles). This research analyzed earthquake occurrences within nine USGS locations where specified wells were identified as contributors to induced seismicity to determine distance patterns from disposal wells or outward seismic migration over time using established principles of hydrogeology. Results indicate a radius of 31.6 km (20 miles) where 90% of felt earthquakes occur among locations, with the closest proximal felt seismic events, on average, occurring 3 km (1.9 miles) away from injection disposal wells. The results of this research found distance trends across multiple locations of potentially induced seismicity.     

增强型地热系统研究开发:以美国新墨西哥州芬登山为例

增强型(或工程)地热系统是指从地壳深部低孔渗的干热岩体中,采用人工工程方法形成储层,经济地采出具有相当数量的热能.这种早期被称之为干热岩的技术首次在美国新墨西哥州芬登山得到示范.本文以芬登山增强型地热系统为例,通过综述其发展历程,论述了增强型地热系统钻井与储层激发、工质流动与储层测试、储层性能评价等关键问题,总结了从芬登山增强型地热系统研究中获得的认识和启示.芬登山地热项目发展的经验表明,增强型地热储层是通过重新打开本来存在、但被密封的、多重连通的节理组,或通过水力压裂创造新的流动通道和换热面,利用复杂裂隙网络中的流循环,从储层系统中开采热能.芬登山实践表明,在稳态条件下增强型地热系统的持续运行是可能的,芬登山地热项目对世界和我国深层地热发展具有重要指导意义.     

Study on the relationship between geothermal exploitation and seismic activity in Xi''''an region

IntroductionGeothermal energy is a new and clear energy resource. It is very useful in heating and generating electricity and medical treating. The Assembly of International Environmental Protection in 1992 predicted that the usage and development of geothermal energy would exceed the traditional energy such as oil and coal, and its developmental prospect will be very bright.There are great geothermal resources in Weihe basin. The average value of heat flow in Weihe basin is 7.88(10(2 W/m2…     

A Preliminary Study of the Types of Volcanic Earthquakes and Volcanic Activity at the Changbaishan Tianchi Volcano

INTRODUCTIONThe Changbaishan volcano is located in Jilin Province , along the border of China and NorthKorea .It isthelargest nature reservein China .Changbaishan belongstothe northeastern Asian activebelt in the eastern margin of the Euro-Asia plate . The Changbaishan volcano is a gigantic ,polygenetic ,central volcano,and has been active since Holocene .The early eruption started in thePliocene andformedthe basaltic shield. Duringthe middle and late Pleistocene ,the volcanic cone …     

基于数值模拟的设定地震场地谱时程拟合方法

本文将确定性数值模拟方法与地震动预测方程相结合,提出了一种重大水电工程场址设定地震的地震动时程生成方法。该方法基于场址设定地震,首先采用地震动预测方程确定场址的场地相关反应谱;其次建立包含震源和场址的场地模型,通过确定性数值模拟方法生成场址地震动时程;最后对生成的场址地震动时程进行调整,使其反应谱与设计谱相一致,用于工程抗震分析。这一方法生成的地震动时程既考虑了震源机制、传播路径以及局部场地效应等物理背景,又与场地相关的设计地震反应谱保持一致,为重大工程抗震分析与评价提供了一种新的思路。     

长白山天池火山地震活动机理研究

对1999年以来长白山火山观测站记录到的火山地震活动进行了研究,发现在西北太平洋5.0级以上中深源地震发生前后,均有火山地震活动发生变化。我们统计发现有以下三种情况:第一种是深源地震发生后火山地震随之增强;第二种是火山震群活动结束后发生中深源地震;第三种是深源地震前后火山地震活动频繁,在火山地震活动较少时发生中深源地震。本文通过对近年来长白山火山地震活动与西北太平洋俯冲板块的中、深源地震关系以及火山玄武岩地幔性质和长白山地热活动等资料并参考前人研究成果,建立了长白山地幔柱模型,对长白山火山地震活动机制进行了初步探讨。     

Earthquake loss estimation for the New York City Metropolitan Region

This study is a thorough risk and loss assessment of potential earthquakes in the NY–NJ–CT Metropolitan Region. This study documents the scale and extent of damage and disruption that may result if earthquakes of various magnitudes occurred in this area. Combined with a detailed geotechnical soil characterization of the region, scenario earthquakes were modeled in HAZUS (Hazards US), a standardized earthquake loss estimation methodology and modeling program. Deterministic and probabilistic earthquake scenarios were modeled and simulated, which provided intensities of ground shaking, dollar losses associated with capital (the building inventory) and subsequent income losses. This study has also implemented a detailed critical (essential) facilities analysis, assessing damage probabilities and facility functionality after an earthquake. When viewed in context with additional information about regional demographics and seismic hazards, the model and results serve as a tool to identify the areas, structures and systems with the highest risk and to quantify and ultimately reduce those risks.     

Analysis of the Microseismicity Induced by Fluid Injections at the EGS Site of Soultz-sous-Forêts (Alsace, France): Implications for the Characterization of the Geothermal Reservoir Properties

In June/July 2000, a hydraulic stimulation experiment took place at the geothermal EGS site of Soultz-sous-Forêts (Alsace, France) in order to enhance the permeability of the fractured granitic massif at 5 km depth. As it is well known that fluid injections tend to induce microseismic events, a downhole and a surface seismological network have been installed to monitor the seismic activity during the stimulation test. 23400 m³ of fluid have been injected in the rock volume through the open-hole section (4400 m–5000 m) of the well GPK2 at increasing rates of 30 l.s⁻¹, 40 l.s⁻¹ and then 50 l.s⁻¹. More than 7200 microseismic events in the magnitude range –0.9 to 2.6 have been precisely located through a simultaneous inversion of the seismic velocity structure and location parameters. The analysis of the behavior of the seismicity relative to the hydraulic parameters gives important information about the geothermal reservoir. It appears that the evolution of the seismicity strongly depends on the variations of the injection rate: An increase or a decrease leads to changes of the velocity structure, the number and magnitude of microseismic events. This involves different hydro-mechanical processes between the fluid flow and the fracture planes, which will control the final shape of the microseismic cloud. Moreover, the study of the variations of the b-value with time suggests that the stimulation experiment produces a large proportion of small earthquakes, but records of events of magnitude higher than 2 indicate that fluid injection could reactivate structures whose dimensions allow the generation of such earthquakes.     

基于F-D曲线法的中国大陆地区地震灾害经济可接受风险研究

合理的地震灾害经济可接受风险水平可以有效管理防灾减灾的投入。基于1991～2020年中国大陆地区地震灾害经济损失数据,利用F-D曲线法(Frequency-Damage curve),建立不同震级(M_S<5.0、M_S5.0～5.9、M_S6.0～6.9和M_S≥7.0)和不同灾情等级(微灾、小灾、中灾、大灾和巨灾)的地震灾害经济可接受风险曲线,并以此为标准讨论30年间由地震产生直接经济损失事件的可接受风险等级。研究结果表明：中国大陆地区地震灾害造成0.020亿元直接经济损失的灾损率不超过1.29×10^-2/a为可接受经济风险,直接经济损失超过14.763亿元其灾损率为任意值均是不可接受经济风险。由此判断,30年间有18.07%的地震灾害属于不可接受经济风险事件。同理,不同震级和不同灾情等级地震灾害的可接受经济风险水平也被确定,并得到M_S<5.0、M_S5.0～5.9、M_S6.0～6.9和M_S     

长白山天池火山地震类型及火山活动性的初步研究

2002年以来，长白山天池火山区出现了地震活动增强、地形变加剧和多种地球化学异常等现象，火山口附近发生的多次有感地震在社会上产生了较大影响。本文利用2002年以来的流动地震观测资料，采用频谱分析、时频分析和多台站资料对比的方法，对火山区地震事件的类型进行了分析；对火山活动的危险性进行了初步研究。结果表明，目前天池火山区出现的大量地震活动仍然属于火山构造地震，少量台站地震记录中表现出的低频特征主要是由于局部介质影响造成的，排除了长周期地震引起的可能。尽管长白山天池火山地震活动明最增强，震群活动较为频繁，但仍属于岩浆活动的早期阶段，短期内发生火山喷发的危险性较小。     

Study on the relationship between geothermal exploitation and seismic activity in Xi＇an region

Based on the analysis of the induced earthquakes in China and abroad, we get some ideas about earthquakes induced by pumping water out of a well or injecting water into a well. The induced earthquakes usually occur near the well, and they are generally small earthquakes. The earthquake sources are shallow, and they belong to the main shock-after shock type of earthquake or the swarm-type of earthquake. The magnitude and the quantity of the induced earthquakes obviously depend on the pressure and the quantity of water pumped or injected. These earthquakes happen as soon as pumping or injecting occurrence, or after ten or twenty days, they may occur at the time of injecting mud or injecting high pressure water when a well is being drilled, or at the time when the ground water is being normally exploited. A large quantity of hot water has been exploited since 1990 in Xi＇an, and the quantity of water exploited has been increasing year by year, as a result the groundwater level has been dropping with the water pumped out and the water level is high in summer and low in winter. The earthquakes in Xi＇an region belong to the solitary-type and they spread outside Xi＇an city where the wells are concentrated but no earthquake happens.The seismic frequency and the energy released have no relation with the quantity of water exploitation or the water level in the well. It is considered that geothermal exploitation does not induce earthquakes in and around Xi＇an because of its specially geological condition.     

强震近震中区地电阻率变化速率的各向异性

用归一化月速率方法处理了６次强震前近震中区11个台的地电阻率数据，得到在孕震中短期至短临阶段，与主压应力方向正交（或近于正交）测向的地电阻率下降变化的速率大于平行（或近于平行）主应力方向的变化速率．产生变化速率各向异性的原因可能是:在孕震后期的扩容阶段，裂隙走向沿主压应力方向优势排列，导电流体活动产生真电阻率变化速率的各向异性，表现为地表视电阻率变化速率的各向异性．本文为视电阻率各向异性的实验结果提供了震例支持，物理解释比较清晰，可能成为研究某些强震孕育晚期震源区及其附近地壳应力状态的参考依据．      

工业开采诱发地震（二）:监测技术和危险性研究

随着页岩气和地热等能源开采过程中可能诱发地震并造成灾害等问题的关注度的提高,及时总结分析国际上已经实施开展的针对可能的诱发地震的监测、危险性分析、风险评价和风险管理工作,对有针对性地预防和减轻此类地震灾害、实现有效的社会治理等均具有重要意义。本文重点对国际上公开发表的学术出版物进行了调研,对目前已有的针对可能的诱发地震的监测系统建设、地震危险性分析和风险评价、风险管理等方面的研究和工作进行了归纳,以期为诱发地震减灾工作提供参考。      

地下流体异常性质定量判别方法探索与地震预报

采用异常频次累加法和异常频次变化速率法研究了中强地震前后一定范围内地下流体群体异常随时间的演化特征．结果表明：地震前后地下流体异常频次累加曲线和变化速率曲线变化特征表现为“平稳（零值波动）—加速（连续正值）—恢复（连续负值）”３个阶段;地震与异常的关系表现为“加速（连续正值）—地震”的形式．利用该方法可以对地下流体异常性质（即非震异常、震前异常和震后异常）进行一定程度的定量判别．     

Study on the relationship between geothermal exploitation and seismic activity in Xi’an region

Based on the analysis of the induced earthquakes in China and abroad, we get some ideas about earthquakes induced by pumping water out of a well or injecting water into a well. The induced earthquakes usually occur near the well, and they are generally small earthquakes. The earthquake sources are shallow, and they belong to the main shock-after shock type of earthquake or the swarm-type of earthquake. The magnitude and the quantity of the induced earthquakes obviously depend on the pressure and the quantity of water pumped or injected. These earthquakes happen as soon as pumping or injecting occurrence, or after ten or twenty days, they may occur at the time of injecting mud or injecting high pressure water when a well is being drilled, or at the time when the ground water is being normally exploited. A large quantity of hot water has been exploited since 1990 in Xi’an, and the quantity of water exploited has been increasing year by year, as a result the groundwater level has been dropping with the water pumped out and the water level is high in summer and low in winter. The earthquakes in Xi’an region belong to the solitary-type and they spread outside Xi’an city where the wells are concentrated but no earthquake happens. The seismic frequency and the energy released have no relation with the quantity of water exploitation or the water level in the well. It is considered that geothermal exploitation does not induce earthquakes in and around Xi’an because of its specially geological condition. Foundation item: Project sponsored by the Landslide Office of Shaanxi Province and Society of Disaster Reduction of Shaanxi Province.