【作者】 李宇彤；

【导师】 吴忠良；

【作者基本信息】 中国地震局地球物理研究所 ， 固体地球物理学， 2012， 博士

【副题名】1999年岫岩地震序列及辽宁区域台网的应用研究

【摘要】 波形相关意义的“重复地震”在自然界中普遍存在,据Schaff和Richards(2004a)对中国大陆及邻区的研究表明,其比例约占地震总数的10%甚至更多。近年来随着数字地震观测技术的普及和发展,有关“重复地震”的研究引起越来越多的关注,“重复地震”已被广泛应用于检测地壳介质性质变化、评估地震台网的定位精度、地震“复发”和断层深部滑动速率的估算；在提高定位和震相识别精度、断层结构、震源物理及地震预测研究等方面都显示出值得关注的应用潜力。本研究根据Schaff和Richards(2004a)对“重复地震”的定义,利用波形相关技术识别辽宁及邻区(38～44°N,119～126°E)1999年6月～2006年12月底发生的“重复地震事件”。共选出满足三个以上台站具有清晰的直达P波的地震事件2024例,采用每个地震与其周围20km范围内的已选地震进行两两组合,共组成570374个“地震对”,对于宽频带和短周期地震记录,分别采用0.5-5.0Hz、1.0-5.0Hz频带滤波,每个“地震对”利用波形记录逐台进行波形相关计算,最后得到满足三个以上台站相关系数不小于0.8的地震对共787对,由497个地震组成,约占总数的24.6%。这些“重复地震”又组成了多组数量不同的“多重地震”组(multiplets),可以确定124个分组,包括71组由两个地震构成的重复地震对(double)和53组由两个以上地震构成的多重地震对(multiplets)。利用辽宁台网三个以上台站波形相关系数大于等于0.8的阈值作为识别条件,发现两组有代表性的“多重地震”其中一组57-plet分布在1999年岫岩地震附近,另一组19-plet分布在1975年海城地震附近。在岫岩地区识别的一组“多重地震”(57-plet)中属于1999年岫岩Ms5.4地震前震序列的地震22个,对其中每个地震进行了滑动量的计算,通过对比两组重复序列累积滑动量发现,1999年岫岩Ms5.4地震前在震源附近的57-plet表现出明显的矩释放加速现象,包括清晰的震前加速和震后松驰过程。在Schaff和Richards(2004a)给出的“重复地震”中有23对位于辽宁区域地震台网监测能力覆盖范围内,这些地震主要属于1999年辽宁岫岩Ms5.4地震序列,利用辽宁区域台网监测范围内的“重复地震对”重新进行了波形相关计算,结果表明远震波形相关意义上的“重复地震”与区域台网波形相关意义上的“重复地震”是有一定差别的,它们只有部分交集,但在评估台网震相拾取误差和定位精度方面并无实质差别,Pg震相的走时差均有约有94%落在±1秒之间,Sg震相的到时差均有约有88%落在±1秒之间,在区域台网观测报告中这些“重复地震对”之间的表观距离在5km之内,平均2km。更多还原

【Abstract】 ’Reneatina earthnuakes’,identified by cross-correlation of seismic waveforms are found to be much more abundant in nature than conventionally expected. Using the data of GSN, Schaff and Richards (2004) found that in China about10%of earthquakes were repeating events. In recent years, with the development of digital seismic networks, waveform correlation and ’repeating earthquake’have caused much attention in measuring crustal media variation; estimating the location precision and fault slip rates at depth or earthquake recurrence.Taking the definition of waveform correlation by Schaff and Richards (2004a), we cross-correlated the seismic waveforms in Liaoning and its surrounding regions using records from Liaoning Regional Seismograph Network (LRSN). There are totally2,024events selected with clear P phase pickings at no less than3stations for the period June1999to December2006within the spatial range38～44°N,119～126°E. The2,024events can make up570,374pairs with bulleting reported separation distance less than20km. Considering the frequency response and the level of background noise, the data are filtered before the cross-correlation. For broadband recordings the pass band is taken as0.5～5Hz, and for short-period recordings the pass band is1.0～5Hz. Cross-correlating the waveforms of these preliminary pairs there are497events recognized as ’repeating events’, consist of787repeating pairs, being24.6%of the whole events, with three or more stations having the cross-correlation coefficients larger than0.8. Based on the data, we also identified multiplets. Two ’multiplets’ located near the seismogenic fault of the1999Xiuyan MS5.4earthquake and the February4,1975, Haicheng Ms7.3earthquake, respectively, were investigated. For the ’multiplet’ occurred before and after the1999Xiuyan earthquake, apparent pre-shock accelerating-like slip behavior, clear immediate-post-seismic change, and relaxation-like post-seismic change can be observed.There were23’repeating pairs’ identified by Schaff and Richards (2004a), by teleseismic waveform cross-correlation, located in Liaoning Province. These events were cross-correlated using the waveforms recorded at Liaoning Regional Seismograph Network. The result shows that ’repeating events’ in the sense of teleseismic waveform cross-correlation and those in the sense of regional waveform cross-correlation have significant differences, with some overlap. However, the overall assessment of the location precision and the phase pick errors of Liaoning Regional Seismograph Network by using these two sets of ’repeating events’, respectively, provide similar results, Assuming that the separation between the ’repeaters’ is less than1km, uncertainty of the routine location practice of Liaoning Regional Seismograph Network can be estimated as below5km, with the average of2km, and the errors of the phase picking of Pg and Sg, respectively, in the observational bulletins, can be estimated as94%and88%, respectively, within±1s.更多还原