Injection-induced Microseismicity in Colorado Shales

—Imperial Oil Resources Limited uses cyclic steam stimulation to recover oil from their Cold Lake oil field in Alberta. This operation, in particular situations, can be associated with the failure of well casings in the Colorado shales above the oil-bearing formation. A number of fluid injection operations was undertaken at this site and the associated microseismicity was detected using two three-component geophones and fifteen hydrophones. The purpose of this experiment was to simulate the occurrence of a casing failure, determine the feasibility of monitoring in a shallow environment, and characterize the microseismic activity. A calibration survey provided values of 1786 ± 108 m/s for P-wave velocity, 643 ± 56 m/s for S-wave velocity and 0.428 ± 0.017 for Poisson’s ratio in the shale formation. Estimates of the quality factor Q _P were 15 for the horizontal direction and 38 for the vertical direction, corroborating the evidence of velocity anisotropy. Calibration shots were located to within 10 m of the actual shot points using triangulation and polarization techniques. Several hundred microseis mic events were recorded and 135 events were located. The results showed that microseismic activity was confined to depths within 10 meters of the injection depth. The experiment clearly established the feasibility of detecting microseismicity induced by fluid injection rates typical of casing failures in shales at distances over 100 m.     

Microseismicity and tectonics of Sinai

Five microearthquake seismographs were used at 11 sites in northern Sinai in the period February 1987 to February 1988 to study the microseismicity of the area around the Maghara coal mine for mine-development studies. A total of 270 events were recorded on 850 records. The magnitude, epicenter and depth of each event were calculated using suitable software for an Egyptian Geological Survey and Mining Authority's (EGSMA) XT computer. The interpretation of the seismic activity in the area is given in view of plate tectonics, the Sinai subplate boundary follows the Gulf of Aqaba and the Dead Sea. The plate and subplate boundaries are presently active, and there seems to be a diffuse zone of deformation between “NW Africa” and “Nubia” affecting the Cairo-Suez district.     

Parameters of Tsunami Source Versus Earthquake Magnitude

This study employs an empirical-analytical approach in combination with Monte-Carlo method to establish relationships between earthquake moment magnitude and upper limits of tsunami source parameters: double-amplitude of vertical bottom deformation, displaced water volume, and potential energy of initial elevation. The approach is based on the Okada solution for a finite rectangular fault and empirical scaling laws for earthquake sources. Results are compared to empirical and theoretical relationships published previously. Parameters of some recent tsunami sources, those for which USGS provides slip distribution data, are considered in light of the established relationships.     

红河断裂带两侧地块地震震源参数研究

利用云南区域数字地震遥测台网资料,采用Brune圆位错模型对1998年12月至2006年8月云南境内M≥3地震和越南北部M>2地震测算震源参数。结果表明,红河断裂两侧活动块体的地震活动和震源参数存在较为明显的差异。就地震矩与震级的标度关系而言,滇西南块体与美国加州圣安德列斯断层和滇西实验场及其周边地区的结果一致,但与华南块体和越南北部地区有差异;从应力降的测算结果看,华南块体西缘的云南及越南北部地区的年均值为7.29MPa,滇西南块体为4.48MPa,两块体北部地震的应力降大于南部地区,应力降由北向南逐渐减小;就地震位错年均值而言,华南块体为12.3mm/a,滇西南块体为6.6mm/a。     

长岛震群震源谱参数反演和震源参数特征

采用高频截止(High-Cut)震源模型,以均方根误差最小原则稳健地求解震源谱参数,并由此推算震源尺度和静态应力降。实际应用显示,该模型的理论谱对观测谱有很好的拟合,可明显改善拐角频率识别准确度。计算了长岛震群内71次M_L≥2.5地震事件的震源参数,结果表明：(1)拐角频率处于2～10 Hz范围,与震级大小存在一定的相关性,截止频率范围处于10～30 Hz之间,与地震大小的相关性不明显;(2)地震矩M₀分布在10¹²～10¹⁴ N·m,与震级M_L存在正相关关系：logM₀=0.977M_L+10.186;M_L与矩震级M_W之间的关系为：M_W=0.651M_L+0.766;(3)根据相对应力降时域演化发现,自2017年3月3日M_L4.5地震之后应力快速释放,应力降水平在均值附近波动,而且多数M_L≥3.5地震发生于...     

小湾水库近场区地震震源参数初步研究

利用小湾电站水库诱发地震监测台网11个子台自2005年5月21日开始观测至2006年9月所记录的数字波形资料,在已知非弹性衰减系数和场地响应的条件下,用遗传算法反演了小湾水库近场328个中小地震的地震矩、应力降和拐角频率等震源参数,并对近场区及库区地震震源参数之间的关系进行了初步讨论。结果表明,小湾库区应力水平明显低于其周边区域。     

Discrete Element Modeling of Stick-Slip Instability and Induced Microseismicity

Using Particle Flow Code, a discrete element model is presented in this paper that allows direct modeling of stick-slip behavior in pre-existing weak planes such as joints, beddings, and faults. The model is used to simulate a biaxial sliding experiment from literature on a saw-cut specimen of Sierra granite with a single fault. The fault is represented by the smooth-joint contact model. Also, an algorithm is developed to record the stick-slip induced microseismic events along the fault. Once the results compared well with laboratory data, a parametric study was conducted to investigate the evolution of the model’s behavior due to varying factors such as resolution of the model, particle elasticity, fault coefficient of friction, fault stiffness, and normal stress. The results show a decrease in shear strength of the fault in the models with smaller particles, smaller coefficient of friction of the fault, harder fault surroundings, softer faults, and smaller normal stress on the fault. Also, a higher rate of displacement was observed for conditions resulting in smaller shear strength. An increase in b-values was observed by increasing the resolution or decreasing the normal stress on the fault, while b-values were not sensitive to changes in elasticity of the fault or its surrounding region. A larger number of recorded events were observed for the models with finer particles, smaller coefficient of friction of the fault, harder fault surroundings, harder fault, and smaller normal stress on the fault. The results suggest that it is possible for the two ends of a fault to be still while there are patches along the fault undergoing stick-slips. Such local stick-slips seem to provide a softer surrounding for their neighbor patches facilitating their subsequent stick-slips.     

微震研究与应用进展

随着地震观测台站密度的不断增加以及地震检测技术的快速发展,微震研究受到了地震学界的广泛关注.与发震周期较长的大地震相比,微震复发周期短、发生频次高,可以获得更高分辨率的地壳内部介质物性和应力状态等变化信息.微震在许多领域具有广泛的应用,如研究断层几何形态、前震与地震成核的关系、余震时空演化特征及余震触发机理、远程动态触...     

马尔康地震序列震源参数研究

利用马尔康台记录的数字地震波资料，使用波谱分析方法计算了马尔康地震序列93次ML2．5～5．0地震的震源参数，并对其进行了初步分析。结果表明：马尔康地震序列的地震距（M0）与震级（ML）有较好的相关性，关系式为log10M0=0．92ML＋10．24，相关系数R为0．86；地震应力降与震级的关系不明显，二者基本无关。     

Use of Microseismic Source Parameters for Rockburst Hazard Assessment

—Since 1994 Noranda’s Brunswick #12 Mine has complemented their MP250/Queen’s Full Waveform seismic systems with an ISS (Integrated Seismic System). Time histories of ISS source parameter information form a component of the daily ground control decision-making. This paper discusses a methodology for microseismic hazard assessment, which filters ISS data using energy, apparent stress and seismic moment criteria to identify those events that are relevant for the assessment and decision-making process. Seismic events are classified into four groups (1) no or minor hazard; (2) seismically-triggered, gravity-driven hazards; (3) stress-adjustment-driven hazards resulting in bulking due to rock mass fracturing; and (4) deformation-driven hazards exploiting existing rock mass damage. Three case histories from 1994–1996, for the 1000 Level South and the 850 Level at Brunswick Mine, are analyzed using this technique to calibrate and verify the proposed methodology.     

落锤震源不同参数激发的数值模拟研究

本文通过研究落锤震源的物理模型,利用有限元方法,对震源激发到子波形成的全过程进行数值模拟研究。从激发参数角度,分别对软地表（土壤）和硬地表（岩石）条件下的不同落锤震源参数的激发进行数值模拟,分析不同震源参数对子波能量和频谱的影响,并比较不同地表岩性介质对震源参数变化的响应。同时将模拟结果同已有的数据采集研究和实验研究进行对比,以说明其有效性。研究结果显示落锤震源的激发效果同重锤质量、冲击速度、基板大小和基板材料的关系,为浅地表地震勘查中落锤震源参数的选择提供了参考依据。     

湖北地区地震震源参数研究

为了研究湖北地区地震震源参数特征,本文基于湖北数字地震台网记录到的S波观测振幅谱,通过遗传算法获得湖北地区的介质品质因子和台站场地响应,并在此基础上计算了湖北地区地震震源参数。结果显示,湖北地区介质品质因子Q值随频率f变化的关系式为Q(f)=501.8·f~(0.309);对于大部分台站获得了与其岩石基底相符的场地响应,没有出现明显放大效应;地震震级与地震矩对数间呈线性关系,即lg M_0=10.06+1.093M_L;震源半径与应力降间呈双对数线性关系,即lgΔσ=10.52-2.01lgr;地震矩与拐角频率间整体上呈反相关;地震矩与应力降间关系不显著。     

利用近代微震资料研究地震危险性

利用１９７０～１９９３年华北地区ＭＬ≥２．０的微震资料，根据其地震活动特点，从中挑选了一些有代表性的区域，做其Ｇ－Ｒ关系曲线，由该曲线可得到每个震级的年频次，同时，由该区域的历史地震（１３００－１９９３年）可得到较大震级的实际年频次，两者对比，发现具有很好的一致性。因此，当选取合适的区域时，利用近代微资料可以推测出该区域较大地震的活动情况，但同时有两点注意：（１）利用微震资料进行统计时，得到的得一     

紫坪铺水库库区震源波谱参数研究

利用紫坪铺水库数字地震台网和成都区域数字台网中的油榨坪台2004年8月到2008年5月12日汶川大地震前的地震波形资料,采用遗传算法反演计算了紫坪铺库区261次1.6级以上地震的震源波谱参数.结果表明紫坪铺库区中小地震的地震矩Mo在1.35×1012～5.98×1014 N·m之间;应力降随着震级的增加而升高;库区小震震源谱拐角频率与地震矩、震级的依赖关系不明确,这可能与紫坪铺水库蓄水后库区压力增加,且水体沿着龙门山断裂方向扩散和渗透有关.     

Microseismicity and active deformation of Messinia,SW Greece

By deploying a 30 3-component digital seismic array in the Messiniakos gulf and the surrounding region, we recorded for a period of 45 days the microseismic activity. With a minimum of six records per event, we located 1121 earthquakes corresponding to an average of 20 events per day. For the hypocenter location we used a local velocity model adopted to two controlled source seismic experiments. Within the array, traveltime residuals were within ± 0.2 s and the epicentral accuracy in the order of ± 2 km, while the hypocentral one is twice this value. Correlation of the seismicity with the tectonic elements indicated that most of the NW-SE oriented faults are active with strike-slip movement along this orientation and extension perpendicular to it. The neogene basins of Messini, Meligalas and Megalopolis are seismically very active and their eastern flanks are delineated by higher seismic activity than their western ones. This indicates that the basins are asymmetric with master faults defining their eastern-northeastern flanks. This hypothesis is supported by the asymmetric structure mapped at the offshore Messiniakos basin as densely spaced high resolution reflection seismic profiles have revealed. The western margins of the basins are less deformed and the seismic activity is dispersed over several minor NW-SE faults. Since the NW-SE striking faults onshore are truncated by major NE-SW oriented ones, their overall length is shortened, reducing their seismic potential and capacity to store large stresses that could produce events above Ms6.1. Offshore western Messinia, in the Ionian Sea, the size and activity of the faults is significantly larger and prone to develop events of larger magnitudes. Subcrustal seismicity indicates a deepening of the foci to the east-northeast.Part of this work was presented at the CIESM Conference, Monaco, 2001, and in the EGS General Assembly, Nice, 2001.     

Source Parameters for 1999 North Anatolian Fault Zone Aftershocks

We develop a data set of aftershock recordings of the 1999, M = 7.4 Izmit and M = 7.2 Duzce (Turkey) earthquakes to study their source parameters. We combined seismograms from 44 stations maintained by several sources (organizations) to obtain a unified data set of events (2.1 ≤ M_w ≤ 5.5). We calculate source parameters of these small earthquakes by two methods that use different techniques to address the difficulty in obtaining source spectra for small earthquakes subject to interference from site response. One method (program NetMoment (NM), Hutchings, 2004) uses spectra of direct S waves in a simultaneous inversion of local high-frequency network data to estimate seismic moment, source corner frequency (f_c), site attenuation (k) and whole-path Q. This approach takes advantage of the source commonality in all recordings for a particular earthquake by fitting a common Brune source spectrum to the data with a and individual k. The second approach (Mayeda et al., 2003) uses the coda method (CM) to obtain “nonmodel-based” source spectra and moment estimates from selected broadband recording sites. We found that both methods do well for events that allow the comparison with seismic moment estimates derived from waveform modeling. Also, source spectra obtained from the two methods are very closely matched for most of the events they have in common. We use an F test to examine the trade-off between k and f_c picks identified by the direct S-wave method. About half of the events could be constrained to have less than a 50% average uncertainty in f_c and k. We used these source spectra solutions to calculate energy and apparent stress and compare these to estimates from the selected “good quality” source spectra from CM. Both studies have values mutually consistent and show a similar increase in apparent stress with increasing moment. This result has added merit due to the independent approaches to calculate apparent stress. We conclude that both methods are at least partially validated by our study, and they both have usefulness for different circumstances of recording local small earthquakes. CM would work well in studies for which there is a broad magnitude range of events and NM works well for local events recorded by band-limited recorders.     

胶东半岛地区震源波谱参数研究

利用山东数字地震台网记录到的胶东半岛及附近地区2010年以来的地震波形资料,采用Brune模型,并结合遗传算法反演了本区134次2.0级以上地震的震源波谱参数.结果表明胶东半岛地区中小地震的地震矩在9.76×1011～5.9×1014N·M之间;应力降范围在0.017～25MPa之间,均值是0.97MPa;视应力范围在0.06～10.2MPa,平均应力水平在0.396MPa.地震矩、应力降和视应力都与震级呈正相关关系,拐角频率与震级的关系不是很明显;地震矩和拐角频率成负相关关系.根据本区震源参数和震级的定量统计关系,去除震级影响,通过应力降和视应力随时间的变化得到目前正处于应力的释放时期.     

Study on the Source Parameters of the Barkam Earthquake Sequence

INTRODUCTIONAn earthquake ofML5·0 occurredin Barkamcounty,Aba Prefecture ,Sichuan Province onJan.1 ,2005 ,and was located at the northwest of the Songganfault ,an area betweenthe Songgangfault ,Yukefault , Darlag fault and Madoi-Gad毢fault . TheML5·0 earthquake is the biggest one in AbaPrefecture since theM6·6 Xiaojinearthquake of 1989 and alsothe biggest oneinthe area betweentheSonggangfault ,Yuke fault ,Darlagfault and Madoi-Gad毢fault since Nov.8 ,1970·Since the commencem…     

云南姚安地震序列震源参数研究

2000年1月15日云南姚安发生5.9级和6.5级地震,利用布设在震中附近的6个流动数字地震台所记录的地震波资料,采用波谱分析和Brune理论的方法,得到姚安地震序列震源谱参数和震源参数。结果表明:地震序列的地震矩在108～1014N·m之间,应力降在0.005～10MPa之间,震源半径分布在50～660m之间,并得到地震矩M0和震级ML的关系为:lgM0=8.24+1.4ML。随着地震矩增大应力降增加,拐角频率反而减小;随震级的增大震源半径变大,但震源半径与应力降之间不存在明显的相关关系。