Grid dispersion in generating finite-differences synthetic seismograms

Ｇｒｉｄｄｉｓｐｅｒｓｉｏｎｉｎｇｅｎｅｒａｔｉｎｇｆｉｎｉｔｅ－ｄｉｆｆｅｒｅｎｃｅｓｓｙｎｔｈｅｔｉｃｓｅｉｓｍｏｇｒａｍｓＡｂｄｏｌｒａｈｉｍＪａｖａｈｅｒｉａｎ（ＩｎｓｔｉｔｕｔｅｏｆＧｅｏｐｈｙｓｉｃｓ，ｔｈｅＵｎｉｖｅｒｓｉｔｙｏｆＴｅｈ...     

The algorithms for calculating synthetic seismograms from a dipole source using the derivatives of Green’s function

The problem of calculating complete synthetic seismograms from a point dipole with an arbitrary seismic moment tensor in a plane parallel medium composed of homogeneous elastic isotropic layers is considered. It is established that the solutions of the system of ordinary differential equations for the motion–stress vector have a reciprocity property, which allows obtaining a compact formula for the derivative of the motion vector with respect to the source depth. The reciprocity theorem for Green’s functions with respect to the interchange of the source and receiver is obtained for a medium with cylindrical boundary. The differentiation of Green’s functions with respect to the coordinates of the source leads to the same calculation formulas as the algorithm developed in the previous work (Pavlov, 2013). A new algorithm appears when the derivatives with respect to the horizontal coordinates of the source is replaced by the derivatives with respect to the horizontal coordinates of the receiver (with the minus sign). This algorithm is more transparent, compact, and economic than the previous one. It requires calculating the wavenumbers associated with Bessel function’s roots of order 0 and order 1, whereas the previous algorithm additionally requires the second order roots.     

An explicit finite element－finite difference method for analyzing the effect of visco－elastic local topography on the earthquake motion

Ａｎｅｘｐｌｉｃｉｔｆｉｎｉｔｅｅｌｅｍｅｎｔ－ｆｉｎｉｔｅｄｉｆｆｅｒｅｎｃｅ　ｍｅｔｈｏｄｆｏｒａｎａｌｙｚｉｎｇｔｈｅｅｆｆｅｃｔｏｆｖｉｓｃｏ－ｅｌａｓｔｉｃ　ｌｏｃａｌ　ｔｏｐｏｇｒａｐｈｙ　ｏｎ　ｔｈｅ　ｅａｒｔｈｑｕａｋｅ　ｍｏｔｉｏｎ...     

The characteristics of tectonic stress field about strike slip earthquake－generating structure in the Chinese mainland

（环文林，汪素云，宋昭仪）Ｔｈｅｃｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆｔｅｃｔｏｎｉｃｓｔｒｅｓｓｆｉｅｌｄａｂｏｕｔｓｔｒｉｋｅｓｌｉｐｅａｒｔｈｑｕａｋｅ－ｇｅｎｅｒａｔｉｎｇｓｔｒｕｃｔｕｒｅｉｎｔｈｅＣｈｉｎｅｓｅｍａｉｎｌａｎｄ￥Ｗｅｎ－Ｌｉｎ...     

The quasi－static solutions of two kinds of the thermo－elastic problem and the time spacedistributionfeatureoftheseismicprecursorfields

Ｔｈｅｑｕａｓｉ┐ｓｔａｔｉｃｓｏｌｕｔｉｏｎｓｏｆｔｗｏｋｉｎｄｓｏｆｔｈｅｔｈｅｒｍｏ┐ｅｌａｓｔｉｃｐｒｏｂｌｅｍａｎｄｔｈｅｔｉｍｅｓｐａｃｅｄｉｓｔｒｉｂｕｔｉｏｎｆｅａｔｕｒｅｏｆｔｈｅｓｅｉｓｍｉｃｐｒｅｃｕｒｓｏｒｆｉｅｌｄｓＹＯＮ...     

Smoothing the source time function – a tool to soften inadequate modelling of the medium during inversion of local waveforms?

The inconsistency of records of local earthquakes and synthetic seismograms due to noise contamination of the data and/or to improper Green function because of an inexact structural model often results in high frequency oscillations of the source time function, which prolongs it spuriously. A priori limit on the roughness of the source time function turned out to reduce the spurious oscillations but it keeps its spurious extension unchanged. Thus, it may yield a severe distortion of the seismic moment. However, it reduces the spurious volumetric component of the mechanism resulting from improper modelling of the structure and, thus, may help decide whether the retrieved volumetric component is real or false. The demand for the smoothness is incorporated as a penalty function in the minimization of the least square residuals, which allows us to decide about the degree of the smoothness. The minimization is performed with a simple genetic algorithm, which offers the advantage of a detailed exploration of the model space reducing the danger of being trapped in local minima.     

The calibration of measuring equipment for the observation of seismo－electromagnetic emission

Ｔｈｅｃａｌｉｂｒａｔｉｏｎｏｆｍｅａｓｕｒｉｎｇｅｑｕｉｐｍｅｎｔｆｏｒｔｈｅｏｂｓｅｒｖａｔｉｏｎｏｆｓｅｉｓｍｏ－ｅｌｅｃｔｒｏｍａｇｎｅｔｉｃｅｍｉｓｓｉｏｎＱｕａｎ－ＸｉＺＨＡＮＧ（张全喜），Ｘｉｎ－ＭｉｎＬＩ（李新民）ａｎｄＭｉｎｇ－Ｃａ...     

Mechanical model of precursory source proces for strong earthquakes in western Yun－nanarea——conceptandnumericalsimula┐tion

Ｍｅｃｈａｎｉｃａｌｍｏｄｅｌｏｆｐｒｅｃｕｒｓｏｒｙｓｏｕｒｃｅｐｒｏ┐ｃｅｓｆｏｒｓｔｒｏｎｇｅａｒｔｈｑｕａｋｅｓｉｎｗｅｓｔｅｒｎＹｕｎ┐ｎａｎａｒｅａ——ｃｏｎｃｅｐｔａｎｄｎｕｍｅｒｉｃａｌｓｉｍｕｌａ┐ｔｉｏｎＹＯＵ－ＪＩＮＳＵ（苏有...     

Source time functions of the Gonghe，China earthquake retrieved from long－period digital waveform data using empirical Green＇s function technique

ＳｏｕｒｃｅｔｉｍｅｆｕｎｃｔｉｏｎｓｏｆｔｈｅＧｏｎｇｈｅ，Ｃｈｉｎａｅａｒｔｈｑｕａｋｅｒｅｔｒｉｅｖｅｄｆｒｏｍｌｏｎｇ－ｐｅｒｉｏｄｄｉｇｉｔａｌｗａｖｅｆｏｒｍｄａｔａｕｓｉｎｇｅｍｐｉｒｉｃａｌＧｒｅｅｎ＇ｓｆｕｎｃｔｉｏｎｔｅｃｈｎｉｑ...     

基于频率-慢度域叠前地震记录的合成与并行方法研究

正演模拟是叠前弹性波反演的基础.采用慢度法计算层状介质的叠前地震记录,分别对频率和慢度进行积分变换得到时-空域的地震道集,并对在慢度积分过程中产生的计算噪音提出了解决方案.为得到高精度合成地震记录,需将地层细分,但地层层数很多时,计算量较大;而对地层粗分虽然会大大加快运算速度,但合成记录会丢失很多信息,文中给出了地层的划分原则.该方法能够计算出包括转换波和多次反射在内的全地震响应.但在提高合成记录精度的同时,也导致计算量增大、计算效率降低,因此,本文对基于慢度法全波场模拟进行了并行算法设计,采用计算域分割、工作池并行技术,建立了慢度法全波场正演模拟的并行算法,使得弹性波正演问题求解更加高效,为充分利用叠前地震资料进行叠前反演提供了研究基础.     

横向不均匀介质中Kirchhoff-Helmholtz积分合成地震图

本文将Kirchhoff-Helmholtz积分方法应用于横向非均匀介质的合成地震图计算.与反射率方法及二维有限差分方法进行了比较.表明KH积分方法能很好的模拟反射波震相,且精度较高.KH 积分方法能够计算复杂界面的反射波,且其计算效率明显大于有限差分.     

Determination of source-time function of intermediate and small earthquakes from empirical Green’s functions

The regularization method was used to invert the source-time function of four larger aftershocks of the Luquan, Yun-nan,M _s = 6.1 earthquake of April 18, 1984. Near-field digital accelerograms were used in the inversion. Instead of calculating synthetic seismograms theoretically, an accelerogram of smaller earthquake was used as an empirical Green’s function. The results obtained showed that the source-time function of smaller aftershock was usually a simple pulse, while that of larger events was more or less complicated. The rupture velocities and the average particle velocities of the aftershocks were determined. All the results were in good agreement with the result estimated from the present seismic source theory. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 22–31, 1993. This study is supported by the Western Yunnan Experimental Site for Earthquake Prediction and the Chinese Joint Seismological Science Foundation.     

合成地震图的广义反射透射系数矩阵方法

简述了在均匀层状介质中，合成地震图的广义反射透射系数矩阵方法，并通过与有人的计算结果对比，检验了经过修改调试后的合成地震图的计算程序。计算与对比表明，经修改调试后的程序对于各种因素，包括震源类型、震源深度、震中、频率和慢度都有较好的普适性，适用于实际的地震波形研究。     

Synthetic seismograms in heterogeneous media by one-return approximation

When reverberations between heterogeneities or resonance scattering can be neglected but accumulated effects of forward scattering are strong, the Born approximation is not valid but the De Wolf approximation can be applied in such cases. In this paper, renormalized MFSB (multiple-forescattering single-backscattering) equations and the dual-domain expression for scalar, acoustic and elastic waves are derived by a unified approach. Two versions of the one-return method (using MFSB approximation) are given: One is the wide-angle dual-domain formulation (thin-slab approximation); the other is the screen approximation. In the screen approximation, which involves a small-angle approximation for the wave-medium interaction, it can be seen clearly that the forward scattered, or transmitted waves are mainly controlled by velocity perturbations; while the backscattered or reflected waves, by impedance perturbations. The validity of the method and the wide-angle capability of the dual-domain implementation are demonstrated by numerical examples. Reflection coefficients of a plane interface derived from numerical simulations by the wide-angle method match the theoretical curves well up to critical angles. For the reflections of a low-velocity slab, the agreement between theory and synthetics only starts to deteriorate for angles greater than 70°. The accuracy of the wide-angle version of the method could be further improved by optimizing the wave-number filtering for the forward propagation and shrinking the step length along the propagation direction.     

合成地震记录制作中的质量控制方法研究

合成地震记录制作中的质量控制将最终决定地震地质层位标定的精度,为此,在分析合成地震记录原理基础上,从三个环节对合成地震记录制作进行质量控制:①通过测井数据精确计算反射系数;②提取与地震资料频谱一致、波形和相位稳定的地震子波;③在获得高精度速度场的基础上,从波组、波形、振幅、频率和相位特征等方面进行匹配调整等,通过对各个环节的研究分析,提出了一整套行之有效的质量控制方法,提高合成地震记录的精度,达到层位标定对合成地震记录精度的要求.     

A study of crust and upper mantle structure in Northeastern region of China by means of synthetic seismograms

In this paper, structure models of the crust and upper mantle beneath each station have been obtained by way of fitting synthetic seismograms with P waveforms of deep focus teleseismic records from the 11 stations in the Northeastern Region of China. We have studied the structure in the region based on those models. Our results show that the medium of the crust and upper mantle is a layered structure with alternate high and low velocity layers within about 100 km under the region. The crustal thickness is about 31.8–35.8 km. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 471–479, 1991. This work is one part of the project funded by the State Seismological Bureau of China.     

Complete synthetic seismograms for high-frequency multimodeSH-waves

We present an efficient scheme to compute high-frequency seismograms (up to 10 Hz) forSH-waves in a horizontally stratified medium with the mode summation method. The formalism which permits the computation of eigenvalues, eigenfunctions and related integral quantities is discussed in detail. Anelasticity is included in the model by using the variational method. Phase velocity, group velocity, energy integral and attenuation spectra of a structure enable the computation of complete strong motion seismograms, which are the basic tool for the interpretation of near-source broad-band data.Different examples computed for continental structures are discussed, where one example is the comparison between the observed transversal displacement recorded at station IVC for the November 4, Brawley 1976 earthquake and synthetic signals. In the case of a magnitudeM _L =5.7 earthquake in the Friuli seismic area we apply the mode summation method to infer from waveform modeling of all three components of motion of observed data some characteristics of the source.On leave from Institute of Geophysics, ETH, Zürich, Switzerland.     

A simple source inversion scheme for displacement seismograms recorded at short distances

We have implemented and tested a simple inversionscheme to retrieve source parameters of small andmoderate earthquakes recorded at close distances. Theinversion assumes that such events may be approximatedby a point-source shear dislocation, and the mediummay be considered an infinite space. Theoreticalseismograms used in the inversion include near- andintermediate-field contributions. The effect of freesurface is approximately taken into account bymultiplying the infinite-space synthetics by two. Thelocation of the event is assumed to be known. Based onan examination of the data, the user chooses thelength of the record and the weight of each trace tobe used in the inversion. The shape of the source-timefunction is estimated from the observed seismograms.A grid search is performed to determine the focalmechanism and the seismic moment which minimizes theerror between the observed and the syntheticseismograms. For two or more recordings, the inversiongives a solution which is consistent with thefirst-motion data and/or the moment tensor inversionof regional seismic waves. If only a singlethree-component recording is available then theinversion yields more than one equally acceptablefocal mechanisms. In such cases, the first-motionpolarities or a prior knowledge of the tectonics ofthe region is essential to constrain the solution. Thetest of the method on near-source broadband recordingsof small and moderate earthquakes in Mexico and theaftershock sequence of 1997 Umbria-Marche, Italy showsthat it gives fast, and surprisingly robust andreliable estimation of source parameters.