采用体波谱振幅相关系数方法研究地震序列的震源机制变化过程

发生在同一震源区的两个地震, 当地震之间的距离远小于地震到台站之间的距离时, 同一个台站的直达P波、 S波零频观测谱值之比与其辐射图型因子之比线性相关, 而辐射图型因子取决于震源机制解的几何特性。 利用同一震源区两次事件的相同台站的波形记录计算谱振幅相关系数, 该系数可认为是震源机制异同的归一化的数值描述; 据此对地震序列事件进行聚类分组以及计算序列事件的滑动平均相关系数时序曲线。 对2001年雅江和2003年大姚强震序列, 以及2002年漾濞和2003年洱源小震序列进行分析的研究结果表明: ① 强震序列与小震序列的滑动平均相关系数时序曲线形态存在明显差异; ② 某些强震序列的初期震源机制有从散乱到一致的过程。 分析认为, 孕震应力场的应力强度对孕震区内地震的破裂方向有明显的约束作用。     

福建水口及仙游地震序列的谱振幅相关系数变化特征

利用福建省数字地震台网记录的波形数据,计算了水口和仙游地震序列的谱振幅相关系数,结果显示水口序列谱振幅相关系数在0.90-0.98之间变化,相关系数高,序列地震震源机制解相似程度高;仙游序列谱振幅相关系数在0.72-0.81之间变化,相关系数略低,震源机制解整体相似程度不高。结合福建地区同期地震活动背景水平分析认为,较高的谱振幅相关系数与福建地区较高的背景应力积累水平存在一定相关性。水口和仙游序列谱振幅相关系数时序变化显示,序列最大地震发生前的谱振幅相关系数存在上升变化,显示较大地震发生前震区应力水平有增强迹象。     

新源、和静交界M_L6.8地震序列的应力降和震源机制研究

采用新疆区域台网记录的2012年6月30日新源、和静交界M_L6.8地震序列的数字波形资料,研究分析了余震序列应力降的变化特征及其地震序列震源机制的相关性。采用波谱分析方法和Brune震源模型,计算了新源、和静交界M_L6.8地震序列震源参数、地震序列中不同事件在相同台站的体波零频震源谱值、地震谱振幅相关系数;并对地震序列震源机制解进行聚类分组。结果表明:①在余震序列平静阶段,应力降呈平稳态势,强余震前应力降出现升高-回落变化过程;②滑动平均谱振幅相关系数在主震后发散,表明余震的震源机制解与主震的相关性降低;③震源机制解聚类分组结果显示,M_L6.8地震序列主要以走滑型地震为主,主压应力轴呈近NS向,与近NS向的构造应力场结果基本一致,一定程度上显示了地震前天山中段受NS向水平挤压应力作用明显;④震级、震源机制演化表明,强余震前震源机制解表现较好的一致性,显示了区域应力场控制作用增强,对后续强余震发生具有预测意义。     

小金地震序列的震源区应力场

用Ｐ波和Ｓ波最大振幅比方法测定了１９８０年９月２２日小金Ｍｓ６．６级地震前后的１１７个小震的震源机制。根据小金地震序列中３次最大地震和１１７个小震震源机制解，了震源区应力场的基本特征的变化形态。对小震机制解进行系统聚类分析，小震机制解的优势取向和３次最大地震的震源机制一致。由小震机制主要类型的平均解和３次最大地震的震源机制反演得到的应力场方向与区域应力场相符。和主震相近的优势走滑类型及逆倾滑动类型     

2008年盈江地震序列的震源参数和震源机制相关系数研究

基于云南数字地震台网记录的2008年盈江地震序列的数字波形资料,采用波谱分析方法和Brune震源模型,得到盈江地震序列的震源参数。利用两次地震事件的相同台站的震源谱参数（零频振幅）计算谱振幅相关系数,据此对地震的震源机制进行聚类分组,并收集和对比地震序列已知的震源机制解结果,发现每组内震源机制解P轴的相关性较好,且相关系数越大,P轴的方位角就越接近。将盈江地区划分为三个研究区,联合震源参数的应力降和聚类分组中每组的平均震源机制解结果研究地震序列发生过程中应力的释放水平和应力场方向变化特征。结果表明：不同阶段震源机制解类型的变化和转化特征一定程度上反映了孕震过程中区域应力场随时间的变化特征,并且地震震源机制解类型在时间段上的集中并向区域构造应力场方向转换的现象可能是发生强震的标志。震源机制解分组类型和对应类型的地震的应力降有一定依赖关系,震源机制解类型反映的应力场与区域应力场接近的地震应力降高,震源机制解类型反映的应力场与区域应力场差距较大的地震应力降普遍较低。     

2008年盈江地震序列的震源参数和震源机制相关系数研究

基于云南数字地震台网记录的2008年盈江地震序列的数字波形资料, 采用波谱分析方法和Brune震源模型, 得到盈江地震序列的震源参数。 利用两次地震事件的相同台站的震源谱参数(零频振幅)计算谱振幅相关系数, 据此对地震的震源机制进行聚类分组, 并收集和对比地震序列已知的震源机制解结果, 发现每组内震源机制解P轴的相关性较好, 且相关系数越大, P轴的方位角就越接近。 将盈江地区划分为三个研究区, 联合震源参数的应力降和聚类分组中每组的平均震源机制解结果研究地震序列发生过程中应力的释放水平和应力场方向变化特征。 结果表明: 不同阶段震源机制解类型的变化和转化特征一定程度上反映了孕震过程中区域应力场随时间的变化特征, 并且地震震源机制解类型在时间段上的集中并向区域构造应力场方向转换的现象可能是发生强震的标志。 震源机制解分组类型和对应类型的地震的应力降有一定依赖关系, 震源机制解类型反映的应力场与区域应力场接近的地震应力降高, 震源机制解类型反映的应力场与区域应力场差距较大的地震应力降普遍较低。     

体波谱振幅相关系数计算程序的开发与实现

序列地震的体波谱振幅相关系数是地震序列震后快速判定的重要依据.体波谱振幅相关系数计算程序是在地震序列发生后,读取其地震波形数据,快速计算其相关系数,绘制滑动相关系数的时序图或聚类图,判定震源机制一致性程度,为地震序列的震后判定提供依据.     

2013年吉林前郭强震群序列的谱振幅相关系数变化特征

使用吉林省数字地震台网记录的波形数据,计算了2013年吉林前郭强震群序列ML≥2.5地震的谱振幅相关系数.结果表明:前郭强震群序列的谱振幅相关系数总体较高,在0.85~0.95之间波动,说明该序列具有很强的震源机制一致性,区域应力场强度较高,分析认为可能是该震群序列一直持续发生的原因.研究发现,在2013年11月23日MS5.8强余震发生之前,谱振幅相关系数升高,震后,则明显降低,与前人研究结果一致,即强震前小震震源机制趋于一致,强震后,则发散.     

2013年左贡-芒康MS6.1地震序列震源机制变化过程研究

2013年8月12日西藏自治区昌都地区左贡县、芒康县交界发生6.1级地震,地震序列为前-主-余型,在主震发生前9h内发生了7次ML≥2.0中小地震,最大震级为ML 4.7。本文采用体波谱振幅相关系数方法,基于区域测震台网记录的数字地震波形资料研究左贡-芒康6.1级地震序列震源机制变化过程。结果显示,主震前的中小地震相关系数较高,均值为0.86,表明其震源机制相似程度较高,是具有震兆意义的小震序列;余震的相关系数较低,表明震源机制相似程度较低。     

2013年左贡-芒康M_S6.1地震序列震源机制变化过程研究

2013年8月12日西藏昌都地区左贡县、芒康县交界发生6.1级地震,地震序列为前-主-余型,在主震发生前9h内发生了7次ML≥2.0中小地震,最大震级为ML4.7。本文采用体波谱振幅相关系数方法,基于区域测震台网记录的数字地震波形资料研究左贡-芒康6.1级地震序列震源机制变化过程。结果显示,主震前的中小地震相关系数较高,均值为0.86,表明其震源机制相似程度较高,是具有震兆意义的小震序列;余震的相关系数较低,表明震源机制相似程度较低。     

体波谱振幅相关系数法在肥东地震序列震后判定中的应用

地震直达体波记录的观测谱包含震源、传播路径和台站信息,而发生在同一震源区的不同地震,如:序列地震,在同一地震台站的记录,受传播路径影响基本相同,地震台站的场地响应、仪器响应也完全相同。因此,序列地震体波观测零频谱的相关系数直接反映震源辐射图型因子的相似性,即震源机制解的相似性。将该方法用于2009年安徽肥东地震序列,与传统方法计算的震源机制解作比较,结果显示,谱振幅相关系数法能反映序列地震震源机制解的变化过程。     

Study of effects of focal depth on the characteristics of Rayleigh waves using finite difference method

This paper presents a relationship between the focal depth in terms of Rayleigh-wave wavelength and the dominant frequency of Rayleigh waves generated in a homogeneous half-space. Rayleigh waves were simulated using a (2, 4) staggered grid P-SV wave finite difference algorithm with VGR-stress imaging technique as a free surface boundary condition. VGR is an acronym for vertical grid-size reduction. The simulated seismic responses using P-wave and SV-wave sources at different focal depths revealed Rayleigh-wave generation up to certain focal depth only for the considered frequency bandwidth. A shift of normalized spectral shape of Rayleigh wave towards lower frequency with increasing focal depth was inferred. Largest spectral amplitude was obtained in the wavelength for which the ratio of focal depth to the wavelength of Rayleigh wave was around 0.17 in the case of P-wave source and 0.9 in the case of SV-wave source. An exponential decrease of spectral amplitude of Rayleigh wave with the departure of the ratio of focal depth to Rayleigh wave wavelength from the above mentioned values was obtained.     

构造应力方向与震源机制解

本文根据二维模型实验的结果,探讨了地震波辐射图型、震源机制解以及构造应力方向之间的关系.地震波辐射图型取决于地震时震源介质运动的方式.它不但与震前存在的应力有关,而且依赖于震源区的地质条件等因素.根据岩石力学实验和我们实验的结果,可以认为,构造应力的主压应力方向要比震源机制解推断的释放主压应力方向更偏近断层面一些.      

comprehensive study on the changing process of focal mechanisms of the 2014 huoshan ms4.3 earthquake sequence

In this paper, the focal mechanisms of Huoshan M_S4.3 earthquake sequence since October 2013 are calculated with the method developed recently by Snoke, which combines the use of first motion of P, SV and SH waves and their amplitude ratios(referred to as Snoke method). We estimate the difference(also referred to consistency parameter θ)between the stress axis direction of focal mechanism solution and the mean stress tensor on one hand, and get the relative changes of focal mechanisms rather than the focal mechanisms themselves on the other hand, by using methods of correlation coefficient of body-wave spectral amplitudes, first motions and amplitude ratios of vertical P wave of single station, as limited by the network layout and density of observation points, focal mechanism solutions of small earthquakes are not easy to obtain. We studied the changing process of focal mechanisms of Huoshan M_S4.3 earthquake sequence since October 2013 with many methods such as consistency parameter, correlation coefficient of body-wave spectral amplitudes, first motion and amplitude ratio of vertical P wave of single station, to determine the type of the sequence. The result shows that: before Huoshan M_S4.3 earthquake of April 20, 2014, the consistency parameter of the earthquake sequence was lower than the mean for a long period, correlation coefficient of body-wave spectral amplitudes was always at high values(about 0.9), odds ratio of first motions of vertical P wave of single station near the epicenter, defined as the ratio of predominant number to contrast number of first motions, was up to 13.8 at station SJH, 3.8 at BZY and 3.6 at LNA, respectively; first motions of vertical P wave of single station showed an obvious predominant distribution as a whole, and the amplitude ratios of vertical P were consistent, which suggests that before Huoshan M_S4.3 earthquake, focal mechanisms were consistent, so the earthquake sequence before Huoshan M_S4.3 earthquake is the foreshock sequence. After Huoshan M_S4.3 earthquake, correlation coefficient of body-wave spectral amplitudes was lower(about 0.6), first motions and amplitude ratios of vertical P wave of single station were in disorder, which suggest that the focal mechanisms are inconsistent after the Huoshan M_S4.3 earthquake, so the earthquake sequence after Huoshan M_S4.3 earthquake is the aftershock sequence, and subsequent larger earthquakes are not likely to occur. The focal mechanisms in Huoshan region during the period of Huoshan M_S4.3 earthquake experienced a process from scattering to convergency and to scattering again.     

Changes in source and site effects compared to codaQ −1 temporal variations using microearthquakes doublets in California

We analyse spectral ratio of the coda of doublets of microearthquakes. Our purpose is to find evidence for temporal changes of the attenuation in the crust before a large magnitude earthquake. A Moving Window Cross Spectral analysis of the coda of doublets gives a plot of the spectral ratio as a function of lapse time along the seismogram, for several frequency bands (SR(T, f) plot). From a certain pattern in theSR(T, f) plot, we should infer a temporal change in coda attenuation. Several doublets recorded in Central California by the USGS network are analysed.Using events very close in time from one another, we show that the radiation pattern can be different enough to induce important variations in the spectral ratio of the first arrivals and of the coda.Another doublet exhibits a strong variation of the low frequencies for stations in the region of Hollister (California), wherePhillips andAki (1986) have noted a strong amplification of low frequencies, that they attribute to site effects on unconsolidated sediments in the fault zone. These variations could be related to slight changes in local conditions (creep, or water table).On the other hand, some doublets, in the vicinity and close in time to the August 1979 Coyote Lake Earthquake (M=5.9), show no variation inSR(T, f) related to this earthquake: this proves that there was no major change in attenuation in the crust preceding this large shock. If a change occurred, it should have been confined to a very limited region, which was not sampled by the many paths we studied.The employed method probably provides today the most accurate estimation of spectral ratio in the coda of microearthquakes. It shows that there are numerous kinds of variations and that it is not straightforward to relate them to coda attenuation changes only. Also, we must be circumspect when dealing with the coda of microearthquakes in relation to forecasting earthquakes.     

应用地震干涉法定位四川九寨沟7.0级地震震源位置

利用地震干涉法对2017年8月8日九寨沟M7.0主震及部分余震进行定位.地震干涉法在可控源地震勘探领域有着广泛应用,但由于震源机制和震源辐射花样的复杂性,在天然地震研究中,地震干涉震源成像应用较少.本研究将地震干涉震源成像技术应用到了天然地震定位中,通过计算原始地震波形记录的特征函数,消除了由于震源辐射花样不同而引起的初动方向不一致性.通过对干涉波形进行偏移叠加,选择互相关型和卷积型两种偏移核函数,分别对震源水平位置和深度进行偏移成像,确定了九寨沟M7.0主震及11次M > 3.5余震的震源位置参数.结果显示,这次地震发生在一个之前未被关注的无名断裂（现已命名为树正断裂）上,研究分析推测,树正断裂与虎牙断裂存在连接的可能性.     

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.     

姚安地震序列的震源参数研究

利用昆明区域数字遥测台网记录的姚安地震序列资料，结合姚安震区流动数字化台网的近震源观测资料，使用波谱分析法测算婉安地震序列的震源力学参数，给出S波的计算结果，并进行讨论。同时，对区域数字遥测台网和震区流动为流动数字化台网同时记录的39个地震采用同一模式计算出的震源参数进行了对比讨论。     

不同应力状态和摩擦系数对综合P波辐射花样影响的模拟研究

为研究不同应力状态(包括主应力相对大小)和摩擦系数对大量地震P波初动辐射花样(综合P波辐射花样)的影响,首先给出了不同应力状态下的剪应力、摩擦应力和库仑破裂应力在断层面法向上的三维分布.表明即使在不考虑摩擦的情况下,剪应力在不同取向断层面上的分布也有很大差别,摩擦应力也在不同取向断层面上造成一定影响.其次,根据库仑破裂...