利用近场高频GPS、 强地面运动和远场地震波形数据联合反演2008年汶川MS8.0地震的震源时空破裂过程

联合近场GPS测站1-Hz运动学位移、 强震仪加速度波形和全球台站P震相波形作为约束, 以时空滑动分布约束条件和ABIC模型参数选择方法, 结合先验的滑动方向变化范围, 反演2008年汶川M_S8.0地震的震源时空破裂过程, 给出了能够综合反映震源破裂过程的统一模型。 结果表明, 汶川地震总体上存在4个主要的破裂区, 最主要的一个破裂区位于震源东北40~120 km, 断层面上的最大位错量约为10 m, 主体滑动分布在2~20 km深度范围, 破裂达到地表; 第二个主体破裂区位于断层破裂带南段, 最大滑动量达到6 m; 另外2个主体滑动区位于断层破裂带北段, 但滑动破裂量小于断层南段破裂区的滑动量, 滑动破裂值最大值为4 m, 超过1 m的区域在走向上超过70 km。 反演得到的断层滑动模型的地震矩为9.5×10²¹ Nm, 相应的矩震级为M_W7.95。 汶川地震破裂表现为单侧破裂, 起始破裂在汶川下方16 km深度, 向东北方向一致性地传播, 过程持续~120 s。 在地震发生后0~10 s内, 破裂集中在震源起始破裂区, 滑动破裂值为~1.0 m, 之后破裂向东北方向扩展, 震后20~40 s是主要的破裂时段。 在40~60 s, 破裂跨越断层南段和北段。 在80~90 s破裂最大值开始下降, 在100~110 s时, 下降为~0.5 m, 在110~120 s时, 下降为~0.1 m。 加入近场GPS测站1-Hz 波形数据与近场强震仪波形和远场长周期体波联合反演, 提高了震源破裂模型的空间分辨率, 特别是浅部滑动破裂区的分辨率, 反演的最大滑动破裂值比不用1-Hz 波形数据反演的结果增大, 表明近场1-Hz GPS波形数据对于揭示汶川地震的时空破裂过程具有重要的作用。     

Parallel PSM/FDM Hybrid Simulation of Ground Motions from the 1999 Chi-Chi,Taiwan, Earthquake

-- A new technique for the parallel computing of 3-D seismic wave propagation simulation is developed by hybridizing the Fourier pseudospectral method (PSM) and the finite-difference method (FDM). This PSM/FDM hybrid offers a good speed-up rate using a large number of processors. To show the feasibility of the hybrid, a numerical 3-D simulation of strong ground motion was conducted for the 1999 Chi-Chi, Taiwan earthquake (M_w 7.6). Comparisons between the simulation results and observed waveforms from a dense strong ground motion network in Taiwan clearly demonstrate that the variation of the subsurface structure and the complex fault slip distribution greatly affect the damage during the Chi-Chi earthquake. The directivity effect of the fault rupture produced large S-wave pulses along the direction of the rupture propagation. Slips in the shallow part of the fault generate significant surface waves in Coastal Plain along the western coast. A large velocity gradient in the upper crust can propagate seismic waves to longer distances with minimum attenuation. The S waves and surface waves were finally amplified further by the site effect of low-velocity sediments in basins, and caused the significant disasters.     

远震反演中新的地壳异常体改正方法

近年来，远震走时层析成像方法有了长足的发展，在地下结构反演的研究中获得了众多成果。针对射线在台站下方覆盖率较差而导致远震反演方法对地壳速度约束不足的问题，本文提出了一种新的地壳异常体改正方法——对同一台站的相对走时残差进行求和平均去均值，消除了地壳中复杂的速度异常体对上地幔速度结构反演的干扰，反演结果具有更优的相对走时残差分布，同时反演得到的速度模型具有更小的数据方差。     

1999年台湾集集地震震源破裂过程

使用GPS同震位移资料和远场P波记录,研究了1999年台湾集集地震震源破裂过程．根据地质构造和余震分布引入了一个由弯曲断层面构造的三段“铲状”断层模型．在使用静态GPS位移资料反演集集地震的断层破裂滑动分布时,由于集集地震断层北部近地表破裂的复杂性,在位错模型中考虑拉张分量对地表同震位移的贡献,可更好地同时拟合GPS观测资料的水平和垂向分量．而纯剪切位错弹性半空间模型和分层地壳模型都无法同时拟合水平和垂向GPS观测资料．在此基础上,同时使用静力学同震位移资料和远场地震波形记录,反演集集地震的震源破裂过程．结果表明,一种垂直于断层面的“挤压性”(负)拉张分量几乎集中分布于地震断层的浅部和北部转折处,而这一带地表破裂远较没有(负)拉张分量出现的南部断层复杂．“冒起构造”的数字模拟表明,这种在集集地震破裂转折处及北部断裂带广为出现的典型破裂造成的地表位移可以用具有负拉张分量(挤压)的逆冲断层更好地模拟．而这种负拉张分量(挤压)的分布正是地震破裂性质和几何复杂性的综合反映,震源破裂过程也显示北部转折处破裂在空间和时间上的复杂性.高滑区域与余震分布表现为负相关.     

Validation and Joint Inversion of Teleseismic Waveforms for Earthquake Source Models Using Deep Ocean Bottom Pressure Records: A Case Study of the 2006 Kuril Megathrust Earthquake

The importance of accurate tsunami simulation has increased since the 2004 Sumatra-Andaman earthquake and the Indian Ocean tsunami that followed it, because it is an important tool for inundation mapping and, potentially, tsunami warning. An important source of uncertainty in tsunami simulations is the source model, which is often estimated from some combination of seismic, geodetic or geological data. A magnitude 8.3 earthquake that occurred in the Kuril subduction zone on 15 November, 2006 resulted in the first teletsunami to be widely recorded by bottom pressure recorders deployed in the northern Pacific Ocean. Because these recordings were unaffected by shallow complicated bathymetry near the coast, this provides a unique opportunity to investigate whether seismic rupture models can be inferred from teleseismic waves with sufficient accuracy to be used to forecast teletsunami. In this study, we estimated the rupture model of the 2006 Kuril earthquake by inverting the teleseimic waves and used that to model the tsunami source. The tsunami propagation was then calculated by solving the linear long-wave equations. We found that the simulated 2006 Kuril tsunami compared very well to the ocean bottom recordings when simultaneously using P and long-period surface waves in the earthquake source process inversion.     

利用1-HzGPS波形数据反演2011年日本北大地震震源破裂过程

利用1-Hz GPS数据反演2011年3月日本东北大地震的时空破裂过程,通过理论波形图与观测波形图的拟合,以及ABIC准则的判定,反演得到滑移分布的稳定估计.结果表明:破裂集中在震源附近,并在震中以下30 km处达到最大位错量,约72 m,在岩手和福岛靠近海岸线处有两个较小的破裂区,断层的南半段破裂很小,同时也是余震最为密集的地方.整个破裂过程由3个破裂阶段组成,发震后断层从震源向周围缓慢破裂,在50～60 s破裂延伸至地表(海沟);60～90 s在震中下方迅速发生强烈破裂,形成了最大位错区,这一阶段主要是倾向上的双边破裂;90～120 s在断层最北西处和断层南半段发生较小破裂,整个破裂过程持续大约120 s.反演得到的地震矩为3.8×1022 Nm,相应的矩震级为MW 9.0.     

Characteristics of amplitude and duration for near fault strong ground motion from the 1999 Chi-Chi, Taiwan Earthquake

A great number of free-field ground motion records are obtained during the 1999 Chi-Chi, Taiwan, earthquake. Records from 130 near fault free-field stations within 55 km to the causative fault surface are used as database, and characteristics of earthquake peak ground acceleration, velocity, displacement and duration are analyzed. According to this study, near fault ground motions are strongly affected by distance to fault, fault rupture directivity, site condition, as well as thrust of hanging wall. Compared with empirical strong ground motion attenuation relations used in China, US and Japan, the PGAs and PGVs recorded in this earthquake are not as large as what we have expected for a large earthquake as magnitude 7.6. However, the largest PGV and PGD worldwide were recorded in this event, which are 292 cm/s and 867 cm, respectively. Caused by nonlinear site effects of soil, peaks and corresponding ratios on E-class site were markedly different from those on other sites. Just as observed in historic earthquakes, fault rupture directivity effects caused significant differences between peaks of ground motion of two horizontal components, but took very slight effects on the duration of ground motion. The significant velocity pulses associated with large PGVs and PGDs, as well as large permanent displacements, which may result from the large thrust of the hanging wall, became the outstanding character of this event. Based on this study, we point out that 3D waveform modeling is needed to understand and predict near fault ground motion of large earthquakes.     

Estimation of Nonlinear Soil Behavior During the 1999 Chi-Chi, Taiwan, Earthquake

The 1999 Chi-Chi, Taiwan, earthquake (M_w = 7.6) was one of the strongest earthquakes in recent years recorded by a large number of strong-motion devices. Though only surface records are available, the obtained strong-motion database indicates the variety of ground responses in the near-fault zones. In this study, accelerograms of the Chi-Chi earthquake were simulated at rock and soil sites, and models of soil behavior were constructed at seven soil sites (TCU065, TCU072, TCU138, CHY026, CHY104, CHY074, and CHY015), for which parameters of the soil profiles are known down to depths of at least ~70 m and at 24 other soil sites, for which parameters of the soil profiles are known down to 30–40 m; all the sites were located within ~50 km from the fault. For reconstructing stresses and strains in the soil layers, we used a method similar to that developed for the estimation of soil behavior based on vertical array records. As input for the soil layers, acceleration time histories simulated by stochastic finite-fault modelling with a prescribed slip distribution over the fault plane were taken. In spite of the largeness of the earthquake’s magnitude and the proximity of the studied soil sites to the fault plane, the soil behavior at these sites was relatively simple, i.e., a fairly good agreement between the spectra of the observed and simulated accelerograms and between their waveforms was obtained even in cases where a single stress-strain relation was used to describe the behavior of whole soil thickness down to ~70–80 m during strong motion. Obviously, this is due to homogeneity in the characteristics of soil layers in depth. At all the studied sites, resonant phenomena in soil layers (down to ~40–60 m) and nonlinearity of soil response were the main factors defining soil behavior. At TCU065, TCU110, TCU115, CHY101, CHY036, and CHY039 liquefaction phenomena occurred in the upper soil layers, estimated strains achieved ~0.6–0.8%; at other stations, maximum strains in the soil layers were as high as 0.1–0.4%, according to our estimates. Thus, valuable data on the in situ soil behavior during the Chi-Chi earthquake was obtained. Similarity in the behavior of similar soils during the 1995 Kobe, 2000 Tottori (Japan), and Chi-Chi (Taiwan) earthquakes was found, indicating the possibility of forecasting soil behavior in future earthquakes. In the near-fault zones of the three earthquakes, “hard-type” soil behavior and resonant phenomena in the upper surface layers prevail, both leading to high acceleration amplitudes on the surface.     

Inversion of Source Parameters for Moderate Earthquakes Using Short-Period Teleseismic P Waves

In this paper, we introduce a new method for estimating the source parameters of moderate earthquakes (M _w ~5.0) by modeling short-period teleseismic waveforms. This method uses a grid-search algorithm to minimize misfits between observed data and synthetic seismograms in depth, magnitude, and mechanism domain in a relative high-frequency range of 0.8–2.0 Hz, similar to the traditional cut-and-paste method used in regional modeling (Zhu and Helmberger, Bull Sesimol Soc Am 86:1634–1641, 1996). In this frequency range, a significant challenge is determining the initial P-wave polarity because of a low signal-to-noise ratio (SNR). Therefore we first determine source properties for a master earthquake with a relative strong SNR. Both the travel time and amplitude corrections are developed relative to the reference 1D model along each path used in inverting the master event. We then applied these corrections to other earthquakes clustered in the same area to constrain the initial P polarities. Thus the focal mechanisms can be determined reasonably well. We inverted focal mechanisms for a small set of events beneath Qeshm Island in southern Iran and demonstrate the importance of radiation pattern at short periods.     

远震体波有限破裂过程反演敏感性测试及其在汶川地震上的应用

本文利用远震P和SH波反演得到2008年5月12日汶川大地震(M_W=7.9)的一系列有限破裂模型。使用一种基于小波变换的模拟退火非线性反演方法, 我们将主断层划分成若干个子断层, 在反演时同时确定每个子断层上的滑移量、 滑动角、 上升时间(rise time)以及平均破裂速度。我们首先根据一个假定的破裂模型生成理论地震图, 将该理论地震数据作为输入进行反演, 对该有限破裂反演方法进行了一系列测试, 以验证反演对断层倾角、 平均破裂速度、 最大破裂深度等参数的敏感性。然后我们采用4个不同倾角的断层面来对汶川地震远震体波记录进行反演。结果表明, 若对只在一个断层面上模拟该地震, 30°倾角是个较为合适的值。反演的结果还表明, 此次地震有两个主要的能量释放区域, 并且主断层面存在倾角变化的可能性。在将来的研究中, 可以结合GPS, InSAR测地学以及强震等数据, 来对强震的破裂过程做更细致的研究。     

The k -2 Rupture Model Parametric Study: Example of the 1999 Athens Earthquake

We employ a realistic finite-extent k ^-2 stochastic source model with k-dependent rise time, introduced by Bernard et al. (1996) and extended by Gallovi and Brokeová (2004), to synthesize the strong ground motions in near source distances. For a given magnitude, this rupture model involves a number of free parameters (fault dimensions, slip roughness, maximum rise time, slip velocity function). We study their influence on the peak ground acceleration (PGA) maps (parametric study) for an example of the 1999 Athens earthquake of M _w = 5.9. The observed macroseismic intensities serve us as a rough constraint on the simulated PGA's to find a set of suitable k ^-2 models. These models agree with empirical source scaling relations.     

Characteristics of Soil Response in Near-Fault Zones During the 1999 Chi-Chi, Taiwan, Earthquake

Distribution of parameters characterizing soil response during the 1999 Chi-Chi, Taiwan, earthquake (M _w = 7.6) around the fault plane is studied. The results of stochastic finite-fault simulations performed in Pavlenko and Wen (2008) and constructed models of soil behavior at 31 soil sites were used for the estimation of amplification of seismic waves in soil layers, average stresses, strains, and shear moduli reduction in the upper 30 m of soil, as well as nonlinear components of soil response during the Chi-Chi earthquake. Amplification factors were found to increase with increasing distance from the fault (or, with decreasing the level of “input” motion to soil layers), whereas average stresses and strains, shear moduli reduction, and nonlinear components of soil response decrease with distance as ~ r ^?1 . The area of strong nonlinearity, where soil behavior is substantially nonlinear (the content of nonlinear components in soil response is more than ~40–50% of the intensity of the response), and spectra of oscillations on the surface take the smoothed form close to E(f) ~ f ^?n , is located within ~20–25 km from the fault plane (~ 1/4 of its length). Nonlinearity decreases with increasing distance from the fault, and at ~40–50 km from the fault (~ 1/2 of the fault length), soil response becomes virtually linear. Comparing soil behavior in near-fault zones during the 1999 Chi-Chi, the 1995 Kobe (M _w = 6.8), and the 2000 Tottori (Japan) (M _w = 6.7) earthquakes, we found similarity in the behavior of similar soils and predominance of the hard type of soil behavior. Resonant phenomena in upper soil layers were observed at many studied sites; however, during the Chi-Chi earthquake they involved deeper layers (down to ~ 40–60 m) than during lesser-magnitude Kobe and Tottori earthquakes.     

反投影远震P波记录法在1996年丽江7.0级地震破裂过程中的运用

选取1996年丽江7.0级地震27个台站的地震记录,运用反投影远震P波记录法对该次地震的破裂过程进行研究。结果显示丽江7.0级地震震源破裂主要沿北南向的玉龙雪山东麓断裂发展,震源破裂时间约为30s,空间破裂尺度约40km。表明反投影远震P波记录法能在震后较短时间内得到震源破裂过程,可为地震速报工作提供重要补充,从而为震后应急救援工作提供依据。     

基于敏感性迭代拟合算法反演汶川Mw 8.0地震InSAR同震形变场

基于单一断层模型,运用敏感性迭代拟合算法反演了汶川地震InSAR同震形变场,获得了断层滑动分布及部分震源参数.结果表明,倾角线性变换的单断层模型模拟的同震形变场与InSAR形变场吻合较好,且残差较小,平均残差为0.11 m;反演的滑动分布主要集中于地下0～20km,其中,汶川地区在震源深度附近有较大的滑动量,10～15 km深度最高可达7 m,地表滑动量却相对较小,平均值仅为2.5 m,平均滑动角均值约为121°;北川地区最大滑动量可达到10 m,平均滑动角均值约为109°;而青川地区10～15 km深度滑动量最高也达8 m,平均滑动角均值约为135°;滑动矢量图显示,沿SW-NE走向断层面的滑动方向以强烈的逆冲为主,兼有一定右旋走滑分量.反演矩张量为1.0×1021 N·m,矩震级达Mw8.0.     

地震频发区域背景噪声提取格林函数的反褶积方法研究

针对云南这一地震频发区域记录到的地震背景噪声数据,设计了一种"最大值均一化"算法,该算法能有效地消除背景噪声中的地震信号、畸变信号及其它干扰信号。应用此算法对记录到的背景噪声数据进行预处理,对处理后的数据利用多窗谱反褶积计算方法可获得其具有较高信噪比和保留了相对幅值信息的格林函数。     

基于实时观测数据快速判定地震破裂方向的方法研究

针对地震烈度速报工作中快速评估大震断层破裂方向的需求,使用我国西部多个地震的观测资料,根据有限移动源理论,利用趋势面分析方法探讨了震中一定范围内台站初始P波参数的方向差异特征,提出一种利用初始P波快速判定地震破裂断层方向的方法。并通过断层距模型和最小二乘法,统计回归最优拟合参数以确定地震断层破裂方式。通过实际震例对比分析了根据所提方法获得的判定结果与实际地震断层破裂分布的吻合度,证实了方法的可用性。本研究为利用地震实时监测资料快速进行地震断层破裂方向判定提供了新思路,可为地震烈度速报中破裂方向的快速判定和动态修正提供参考。     

根据GPS和水准资料反演2008年汶川地震同震破裂模型

通过分析2008年汶川8.0级地震前后的GPS观测资料和1983～2010年的精密水准观测资料,得到地表同震位移场。结合野外地质调查,反演了汶川地震同震断层几何模型和断层面上滑动分布。反演结果表明:北川—映秀断裂是一个铲形断层,长度为180km,地表倾角为62°,随指数函数形式逐渐变缓,深度18km,断层面滑动以逆冲为主;青川断裂长为120km,倾角为58°,断层面上走滑分量由南向北逐渐增加;灌县—江油断裂为纯逆冲断层,长度为80km,倾角35°。整个断层模型中最大错动量达到7.6m,对应破坏最严重的北川地区。本次地震释放的地震矩为7.62×1020N·m,相应矩震级为MW7.9。反演所得模型对于近场的水准观测资料和GPS观测资料拟合很好。