Attenuation of peak ground acceleration in central california from observations of the 17 october, 1989 Loma Prieta earthquake

The strong ground motion produced by the 17 October, 1989 Loma Prieta earthquake in northern California was recorded at over 100 stations. Accelerograms were generated at sites with significantly different geology, including land fill and soft sedimentary soil sites. In this study, the attenuation characteristics of the peak vertical and horizontal ground accelerations are studied for freefield recording conditions within 100 km of the source by the application of a non-linear multi-regression procedure. Two sets of attenuation models for weighted and unweighted observations are compared with those reported by other investigators for this earthquake and for regional and worldwide data. The peak ground acceleration (PGA) observations for this earthquake exceed previous predictions of standard attenuation models, particularly beyond 30 km (approximately 60 percent at 50 km). Higher attenuation of the vertical component compared to the horizontal is confirmed. The regression considers site geology as an independent parameter. Soil sites display as much as 23 per cent amplification relative to rock sites for horizontal PGA and as much as 40 per cent for vertical PGA. Amplification of the ground motion at sites characterized by soft soil geology is examined by comparing the recorded PGA with the corresponding prediction at sites underlain by stiff soil. Eight of ten of the soft soil sites display significant amplification relative to stiff soil sites (as much as 300 per cent for horizontal and 200 per cent for vertical components). Particular attention is paid to the so-called anomalous observations at distances beyond 50 km. The anomalous observations between 50 and 80 km may be attributed to various factors such as geology, basic geometry, azimuthal dependence, source mechanism and normal scatter of observations.     

Macroseismic observations of earthquake in Yugoslavia (April 15, 1979, 06h21m gmt), on the territory of Czechoslovakia

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Modeling and simulating earthquake accelerograms using strong-motion data from the Istanbul, Turkey, region

In order to simulate earthquake ground motions for the Instanbul (Turkey) region, acceleration time series from western Turkey are modeled by transforming the series into a stationary one which can be described by an autoregressive moving-average (ARMA) process. The ARMA and other parameters used in the stationary transformation are related to physical parameters (e.g. magnitude, distance to epicenter, depth to hypocenter and duration) via a regression analysis. To create simulations for a given set of physical parameters, the modelling procedure is reversed.     

Simulation of accelerograms from simplified deterministic approach for the 23rd October 2004 Niigata-ken Chuetsu,Japan earthquake

A simple hybrid approach for the simulation of strong ground motion is presented in this paper. This approach is based on the deterministic modelling of rupture plane initially started by Midorikawa, Tectonophysics 218:287–295, (1993) and further modified by Joshi, Pure Appl Geophys (PAGEOPH) 8:161, (2004). In this technique, the finite rupture plane of the target event is divided into several subfaults, which satisfy scaling relationship. In this paper, simulation of strong ground motion due to a rupture buried in a earth medium consisting of several layers of different velocities and thicknesses is made by considering (1) transmission of energy at each layer; (2) frequency filtering properties of medium and earthquake source; (3) correction factor for slip of large and small magnitude earthquakes and (4) site amplification ratio at various stations. To test the efficacy of the developed technique, strong motion records were simulated at different stations that have recorded the 2004 Niigata-ken Chuetsu, Japan earthquake (M _s 7.0). Comparison is made between the simulated and observed velocity and acceleration records and their response spectra. Distribution of peak ground acceleration, velocity and displacement surrounding the rupture plane is prepared from simulated and observed records and are compared with each other. The comparison of synthetic with the observed records over wide range of frequencies shows that the present technique is effective to predict various strong motion parameters from simple deterministic model which is based on simple regression relations and modelling parameters.     

Field observations from the Aquila, Italy earthquake of April 6, 2009

On April 6, 2009 an earthquake of magnitude 6.2 (M_w) struck the Abbruzzo region of Italy causing widespread damage to buildings in the city of L??Aquila and surrounding areas. This paper summarizes field observations made by the Earthquake Engineering Field Investigation Team (EEFIT) after the event. The paper presents an overview of seismological and geotechnical aspects of the earthquake as well as a summary of the observed damage to buildings and infrastructure. A brief overview of the earthquake casualties is also reported.     

用钻孔应变数据探测2011年日本Tohoku大地震激发的低频地球环型自由振荡及其谱峰分裂

地震激发的地球自由振荡中, 环型自由振荡(特别是低频环型自由振荡)的精确探测相比于球型自由振荡更加困难. 环型自由振荡对SH波速度结构更加敏感, 能更好地监测走滑断层运动, 因此精确估算环型自由振荡的谱峰参数可为地球内部大尺度SH波速度结构和大地震的震源机制提供更强约束. 本研究利用2011年日本Tohoku地震后四分量钻孔应变仪的观测资料, 提取了该地震激发的1.3 mHz以下低频环型和球型自由振荡信号, 与STS-1宽频带地震仪的结果相比较, 发现四分量钻孔应变仪对1 mHz以下的环型自由振荡具有更强的探测能力. 本研究还采用频率域自回归方法精确估计了₀T₂—₀T₆的简并频率, 结果与PREM模型理论值相差非常小, 平均相对误差仅为2.52×10^-4.此外还用钻孔应变仪观测资料探测到了₀T₂谱峰分裂现象. 研究结果表明, 钻孔应变仪能有效探测到大地震激发的低频地球环型自由振荡信号, 可为地幔大尺度各向异性结构研究提供高质量的基础数据.

     

A note on the L’Aquila earthquake of 6 April 2009: Permanent ground displacements obtained from strong-motion accelerograms

On 6 April 2009, 01:32 GMT, an M_w 6.3 earthquake hit the Abruzzi region of central Italy causing widespread damage in the City of L’Aquila and its nearby villages. The mainshock of this earthquake was recorded by 57 digital strong-motion instruments, four of which are located on the hanging wall of the Paganica Fault near L’Aquila. These stations are no more than 6 km from the epicentre. We use accelerometric data from these four stations to estimate permanent ground displacements caused by the mainshock. Our numerical results reveal south-east and downwards directed permanent co-seismic displacements which are in fair agreement with the outcomes of GPS and InSAR measurements reported in preliminary Istituto Nazionale di Geofisica e Vulcanologia (INGV) reports.     

1999年四川绵竹5.0级地震临震电磁辐射信号的准-静电磁场场强理论估算

1999年9月14日和11月30日在四川省绵竹县清平乡和汉源乡先后发生Ms5.0地震.本文通过都江堰电磁波ULF超低频观测仪震前接收到的电磁辐射信号,对观测场量的某些特征进行理论分析和估算.结果表明:理论估算是针对地下发射、空中接收的方式进行的,且针对ULF频段的磁场,与地下发射-地下接收方式的ULF频段的电场所计算的对比结果表明,此估算结果是合理的;两次地震辐射源峰值电流矩为108～106 A·m量级(平均为107A·m量级),表明两次地震的孕震体与孕震过程可能不是"独立"的.     

GNSS观测的2021年5月22日玛多MS7.4地震同震位移及其约束反演的滑动破裂分布

2021年5月22日青海省果洛州玛多县发生M_W7.4地震,此次地震产生的地表破裂在空间上表现出明显的分段特征.本文基于不同来源的GNSS连续观测网数据获取了此次地震的精细三维同震形变场,结果显示:观测到的最大水平位移量达到280 mm,最大垂直形变量仅为25 mm,暗示此次地震的逆冲分量较小;此次地震具有较为明显的左旋走滑特征,同震形变基本对称,在NW-SE向的影响范围更广,该方向上水平同震形变大于3 mm的震中距范围超过500 km.进而,本文以余震精定位结果和GNSS观测到的三维同震形变场为约束,构建了地表破裂线为折线、倾角为85°、倾向西南的断层模型,反演了滑动破裂分布.结果显示:滑动破裂分布在震中两侧不均匀,均破裂到地表,破裂深度达到15 km左右,最大滑移量为4.73 m,计算的矩震级为M_W7.37.该结果与余震精定位结果具有很好的一致性,破裂的极值区正好位于早期余震空区,推测该余震空区未来的发震风险性较低.最后基于反演结果模拟计算了震中区域形变和应变场,结合应变值在断层地表迹线东南侧呈现挤压特征和已有的研究成果,推测此次地震增强了巴颜喀拉块体在东部地区挤压应力的积累特征,导致东部地区发震危险性增强,值得后续跟踪研究.     

2007年8月15日秘鲁M_W8.0地震的破裂震相记录特征

对2007年8月15日秘鲁近海MW8.0地震在全球数字地震仪台网(GSN)83个台的宽频带数字记录进行分析,在短周期(SP)、中长周期(SK)和长周期(LP)记录上均识别出在震源破裂过程中由主要破裂激发出的破裂震相。由破裂震相分析结果可以看出:该地震是一个由4次主要破裂构成的地震事件,第2次破裂、第3次破裂和第4次破裂与第1次破裂之间的时间间隔平均约9.1 s、48.5 s和63.3 s,与震源破裂时间函数的结果一致。4次主要破裂激发的破裂震相在GSN台站可识别的震中距范围为1.4°—153.8°。本文给出的破裂震相记录特征,为分析识别其他地震的破裂震相提供了参考。从地震记录图上直接识别破裂震相有助于快速判断震源破裂过程,有助于快速判断震灾损失。     

Source rupture model of the 2018 Mw6.7 Iburi,Hokkaido earthquake from joint inversion of strong motion and InSAR observations

The 2018 Mw6.7 Iburi earthquake shocked the eastern Iburi region to the west of the Hidaka Collision Zone in Hokkaido,which is a destructive inland earthquake.We resolved the kinematic rupture process of the event by combining strong motions(SM)and synthetic aperture radar(SAR)images in a joint inversion.The results reveal that the duration of the whole rupture is about 17s,yielding a total seismic moment of 1.4×1019 N·m(Mw=6.7).The main slip area is located at a depth of approximately 24 km with a peak slip of～0.8m above the hypocenter.The comparison with the regional velocity model shows the earthquake was initiated in the upper mantle,while the majority of slips are located in the lower crust,which is an"aseismic"domain in the typical sandwich model.The location of the major slip area is consistent with a high-conductivity volume.We proposed a mechanism of low frictional property(＜0.3)produced by high pore pressure to explain the abnormal high dip angle and centroid depth located in the ductile lower-crust.Aftershocks are distributed in areas where the Coulomb frictional stress increases due to co-seismic displacement with a mechanism conjugating to the mainshock.     

地球物理研究所15年来关于地震预测问题的基础研究

地震预测首先是一个科学问题 ,地震预测的实现只能以科学研究为基础。十五年来 ,在中国地震局有关部门和国家自然科学基金会等机构的支持下 ,地球物理研究所科研人员围绕与地震预测的有关的科学问题 ,开展了多方面的基础研究和应用研究。这些研究工作可以概括为 3个方面。1　地震活动性分析及其在地震预测研究中的应用我国有着丰富的历史和现代地震目录。地震活动性研究是我所地震预测研究中最重要的工作之一 (许绍燮等 ,1 989,1 990 ;许绍燮 ,1 993 ;Wang等 ,1 996;郑秀芬等 ,1 998;王林瑛 ,1 999)。地震活动性的经验性研究包括强地震活动…     

日本熊本M_W 7.0地震的长周期地震动

利用日本K-NET和KiK-net强震动台网获取的距离发震断层100 km以内136个强震动台站的三分量加速度记录,研究熊本M_W7.0地震地震动的长周期特性.基于残差分析研究不同周期地震动的空间分布差异,将观测分析结果与美国NGA经验模型、汶川和芦山地震观测结果进行对比,揭示此次熊本地震近场强震动的长周期特点及其形成机理.研究结果表明:(1)虽然总体上此次地震的近场地震动水平与美国NGA-West2经验模型的预测结果接近,但周期2 s以上地震动的分布在断层不同方位有系统性差异,在断层的北东方位,周期2.0～10.0 s的反应谱高于NGA-West2经验模型的预测结果,在西南方位,谱值低于经验预测模型.(2)我们认为此次地震2.0～10.0 s的长周期地震动的空间分布差异主要受破裂方向性的影响,在破裂传播的正前方,周期T=2.0 s,3.0 s,5.0 s,7.5 s和10.0 s的加速度谱被放大到整体观测平均水平的1 4～2.0倍.从周期T=2.0 s到10.0 s,破裂向前方向的放大作用和破裂反方向的减弱作用均有所增强,此次地震观测到的速度大脉冲记录均位于断层的东北方位,这与方向性脉冲的产生机理相吻合,速度大脉冲对加速度反应谱有显著的长周期放大作用,放大倍数值可以超过4.0,放大作用的影响主要位于脉冲的特征周期T_p附近.(3)近断层记录在建筑结构敏感的周期(0.5～2.0 s)的反应谱达到芦山地震的3～6倍,虽然与芦山地震震级接近,此次地震近断层地震动破坏力大大超过了芦山M_W6.8地震,甚至超过了汶川W_W7.9地震,这种长周期特点应该引起工程抗震设计和相关研究人员的重视.     

A new fault rupture scenario for the 2003 Mw 6.6 Bam earthquake,SE Iran: Insights from the high-resolution QuickBird imagery and field observations

The December 26, 2003 M_w 6.6 Bam earthquake is one of the most disastrous earthquakes in Iran. QuickBird panchromatic and multispectral satellite imagery with 61 cm and 2.4 m ground resolution, respectively provide new insights into the surface rupturing process associated with this earthquake. The results indicate that this earthquake produced a 2–5 km-wide surface rupture zone with a complex geometric pattern. A 10-km-long surface rupture zone developed along the pre-existing Bam fault trace. Two additional surface rupture zones, each 2–5 km long, are oblique to the pre-existing Bam fault in angles of 20–35°. An analysis of geometric and geomorphic features also shows that movement on the Bam fault is mainly right-lateral motion with some compressional component. This interpretation is consistent with field investigations, analysis of aftershocks as well as teleseismic inversion. Therefore, we suggest that the 2003 Bam earthquake occurred on the Bam fault, and that the surface ruptures oblique to the Bam fault are caused by secondary faulting such as synthetic shears (Reidel shears). Our fault model for the Bam earthquake provides a new tectonic scenario for explaining complex surface deformations associated with the Bam earthquake.     

基于GPS、水准和强震动观测资料联合反演2013年芦山7.0级地震同震滑动分布

为了更好理解2013年四川芦山M_S7.0级地震的发生过程及其与发震构造和地表多种观测资料的动力学关联,本文综合重新定位的余震分布与地质、地球物理信息构建3D发震构造模型,采用水平层状介质模型,并以震区GPS、水准、强震动等同震位移/形变观测资料为约束,联合反演了芦山主震的同震滑动分布.其中,断层解译结果表明震源区包含5条相关断层F1-F5,通过对所有可能的断层组合模型进行反演分析,显示采用F1+F3+F4+F5的组合模型反演效果相对最好,是最可能的发震断层模型.反演得到的芦山主震矩震级为M_W6.5,其中同震滑动主要分布在NW倾的主断层F1的断坡周围,最大值为0.86 m,滑动角92.88°,纯逆冲型;F1上方反倾的次级断层F3上最大滑动量为0.37 m,滑动角119.92°,表现出以逆冲为主兼右滑的斜向反冲作用;而沿另一条反倾的次级断层F4的最大滑动量为0.40 m,滑动角97.98°,几乎为纯逆冲作用.此外,震区还存在一个NW缓倾深度为5~8 km的浅部滑脱面F5,它分隔了浅部沉积盖层与深部变质基底,限制了其下方F1、F3及F4等断层的同震破裂继续向更浅部扩展.主震时深部F1和F3断层夹持的冲起构造发生了上冲运动,除了使浅层和地表产生响应运动及变形外,还引起冲起构造顶面即F5底面的NE段和SW段分别产生了NE和SWW向调节滑动,最大值0.25 m.总之,基于文中构建的F1+F3+F4+F5的发震断层模型,反演结果能很好拟合地表多种观测资料,还能解释地表GPS观测的同震"左旋"运动与地震学观测的震源断层逆冲运动的"不协调性".     

2017年12月15日青海泽库MS4.9地震序列分析

2017年青海泽库M_S4.9地震的震中位于走向南北的日月山断裂附近,而小震优势排列和震源机制解却和日月山断裂矛盾。本文通过活动断裂遥感解译和野外考察,在震中附近发现了EW走向和NW走向的断裂,它们属于夏河断裂西端构造,EW走向断裂倾向N,其运动性质兼具左旋走滑和逆冲。同时,我们使用双差定位方法对泽库M_S4.9地震开展重定位,发现小震排列也呈NW和EW两段,横跨EW走向段的小震指示倾向N的断层面。通过对比夏河断裂西端构造和地震排列特征,我们发现夏河断裂的三维几何和运动性质与小震排列和震源机制具有良好的对应关系。因此,我们推测夏河断裂是泽库M_S4.9地震的发震断裂。结合区域构造背景分析,我们认为夏河断裂可能是西秦岭北缘断裂西端帚状散开的分支之一,此次地震可能代表西秦岭北缘断裂西端的构造活动,同时也可能受到日月山断裂右旋剪切的影响。本文研究结果进一步凸显了鉴定构造活跃区次级先存断裂新活动特征、完善区域活动构造图像的意义。

     

2022年1月8日青海门源MS6.9地震GNSS同震形变场及其断层滑动分布

2022年1月8日在青海省海北州门源县发生M_S6.9地震,本次地震是继2016年门源M_S6.4地震后冷龙岭断裂周边发生的又一次强震。确定本次地震的破裂分布对分析该地区震害风险具有重要意义。通过收集震中及周边12个GNSS连续站点和震后加密观测的17个流动站点观测资料,获取了震中100 km范围内29个测站的GNSS静态同震形变场,并以此为约束反演了本次地震同震滑动分布。结果显示,近场GNSS观测到的最大形变量可达1.3 m。反演的最优破裂模型显示该地震主破裂区深度位于0～10 km,滑动破裂出露地表,最大滑动量为4.07 m,地震矩释放能量约1.1×10¹⁹ N·m,对应矩震级M_W6.7。门源地震破裂至地表是造成该地区基础设施破坏的直接原因。     

Time-clustering behavior of spreading-center seismicity between 15 and 35°N on the Mid-Atlantic Ridge: observations from hydroacoustic monitoring

An earthquake catalog derived from the detection of seismically-generated T-waves is used to study the time-clustering behavior of moderate-size (?3.0 M) earthquakes between 15 and 35°N along the Mid-Atlantic Ridge (MAR). Within this region, the distribution of inter-event times is consistent with a non-periodic, non-random, clustered process. The highest degrees of clustering are associated temporally with large mainshock-aftershock sequences; however, some swarm-like activity also is evident. Temporal fluctuations characterized by a power spectral density P(f) that decays as 1/f^α are present within the time sequence, with α ranging from 0.12 to 0.55 for different regions of the spreading axis. This behavior is negligible at time scales less than ∼5×10³ s, and earthquake occurrence becomes less clustered (smaller α) as increasing size thresholds are applied to the catalog. A power-law size-frequency scaling for Mid-Atlantic Ridge earthquakes also can be demonstrated using the distribution of acoustic magnitudes, or source levels. Although fractal seismic behavior has been linked to the structure of the underlying fault population in other environments, power-law fault size distributions have not been observed widely in the mid-ocean ridge setting.     

Assessing CPT-based methods for liquefaction evaluation with emphasis on the cases from the Chi-Chi, Taiwan, earthquake

In the early morning (1:47 Taiwan time) of September 21, 1999, the largest earthquake of the century in Taiwan (M_w=7.6, M_L=7.3) struck this island country. The earthquake killed more than 2400 people and caused great destruction to buildings, bridges, dams, highways, and railways. One of the causes for heavy damages to the structures is soil liquefaction and ground settlement during the earthquake. In this paper, investigation of soil liquefaction and case histories of liquefaction are presented. Three CPT-based simplified methods, the Robertson method, the Olsen method, and the Juang method, are examined using the case histories derived from the Chi-Chi earthquake. The results of the comparison show that the Juang method is more accurate than the two methods in predicting liquefaction potential of soils based on the cases derived from the Chi-Chi earthquake, although all three methods are quite comparable in accuracy.     

2013年4月22日科尔沁左翼后旗M5.3地震的发震构造初探

2013年4月22日内蒙古通辽市科尔沁左翼后旗、辽宁阜新市彰武县交界发生5.3级地震.研究发现,该地震序列震中分布、震源机制及烈度考察极震区长轴方向均为近东西方向,与横贯震区的养畜牧河断裂走向一致,综合判定该断裂是5.3级地震的发震构造.