利用模板匹配方法研究稀疏台站地区地震活动性
发布时间：2018-09-01 09:32
【摘要】：地震目录是发震构造确认、地震活动性分析的基础资料。然而由于强震尾波的干扰、地震事件震级较小、台站分布稀疏等原因,会造成地震目录的严重缺失,从而影响以地震目录为基础的地震活动性分析等的可靠分析。目前,以互相关技术为基础的模板匹配方法是低信噪比情况下检测遗漏事件的有效方法,且已经得到了广泛应用。本文利用模板匹配方法,针对以下两个问题,进行了相关研究。一、2014年8月3日在云南省鲁甸县发生了Ms6.5地震。鲁甸地震之后,关于鲁甸地震是否由溪洛渡水库引起存在一些争议。根据前人研究表明,分析中强地震前后地震活动性可以为判断主震起源提供一定的依据。然而,由于鲁甸地震震中附近固定台站分布稀疏及主震后尾波干扰等因素的影响会造成地震目录的缺先从而可能影响地震活动性的可靠分析。本文采用模板匹配方法,以台网目录中的541个事件作为模板对鲁甸地震前后小地震进行了搜索和识别,得到以下结果：(1)在主震之前33天到主震后5天的连续波形中识别出991个未在目录中列出的地震,使余震的完备震级从1.8降低到1.3。并根据检测目录得到主震前33天内的b值为1.04±±0.18,余震的b值在震后5天内由0.5左右逐渐上升至0.9附近并保持稳定。(2)根据2009年到主震发生前的台网目录得到该区域的背景b值为0.93±0.04。即鲁甸地震前后区域地震活动b值均与背景b值接近,这与典型水库诱发的中强震具有的b值特征不相符。(3)通过进一步分析台网目录,未发现溪洛渡水库蓄水前后研究区域内的地震活动性存在明显变化,这也与典型水库诱发地震区域的地震活动性特征不相符。二、2015年4月15日在内蒙古自治区阿拉善左旗发生Ms5.8地震。由于台网目录中地震事件较少,且震中附近固定台站分布稀疏可能会造成台网目录所提供的震源位置误差偏大,因此很难从台网目录提供的震源位置判断发震构造。本文利用模板匹配方法,采用震中附近几个流动台的数据,以台网目录中的55个事件作为模板事件对阿拉善地震前后的遗漏事件进行了搜索和识别,并结合Hypo2000和HypoDD,对此次地震的发震构造进行了初步的分析。主要结论如下：(1)在主震之前10天到主震后10天的连续波形中识别出362个为遗漏事件；(2)采用Hypo2000对台网目录中的55个事件进行了重定位,重定位后震源位置的水平和垂直方向理论平均误差分别为2.50km和36.9km,理论平均走时残差为0.58s;(3)通过互相关技术提取遗漏事件P、S到时,结合HypoDD对遗漏事件进行了重定位。重定位后震中优势分布近东西向(最小二乘拟合得优势走向为261.4°),与USGS给出的震源机制解中节面Ⅱ的走向(262°)基本一致。另外从震源深度由浅及深的趋势可以看出,余震分布具有较大倾角的特征。通过参考不同研究机构和学者所得震源机制,我们认为2015年阿拉善Ms5.8地震的发震构造为一条走向约261°,高倾角的左旋走滑断层。
[Abstract]:Earthquake catalogue is the basic data for confirmation of seismogenic structure and analysis of seismicity. However, due to the interference of strong coda waves, small magnitude of earthquake events, sparse distribution of stations and other reasons, it will cause serious deficiency of earthquake catalogue, thus affecting the reliable analysis of seismicity based on earthquake catalogue. The template matching method based on this method is an effective method to detect missing events under low signal-to-noise ratio and has been widely used. In this paper, template matching method is used to solve the following two problems. First, the Ms6.5 earthquake occurred in Ludian County, Yunnan Province on August 3, 2014. After the Ludian earthquake, the Ludian earthquake is considered to be an earthquake. According to previous studies, the analysis of seismicity before and after moderate earthquakes can provide a certain basis for judging the origin of the main earthquake. However, due to the sparse distribution of fixed stations near the epicenter of the Ludian earthquake and the interference of coda waves after the main earthquake, the earthquake catalogue will be absent. In this paper, a template matching method is used to search and identify small earthquakes before and after the Ludian earthquake using 541 events in the catalogue of the network as templates. The following results are obtained: (1) 991 earthquakes not listed in the catalogue are identified from the continuous waveforms from 33 days before the main earthquake to 5 days after the main earthquake. The complete magnitude of the aftershocks was reduced from 1.8 to 1.3. According to the catalogue, the b value of the aftershocks was 1.04 (+0.18) within 33 days before the main shock, and the b value of the aftershocks gradually increased from 0.5 to 0.9 within 5 days after the earthquake and remained stable. (2) According to the catalogue of the seismic network from 2009 to the occurrence of the main shock, the background b value of the region was 0.93 (+0.04). The b values of regional seismicity before and after the impoundment of Xiluodu Reservoir are close to the background B values, which is not consistent with the b value characteristics of moderate and strong earthquakes induced by typical reservoirs. (3) Through further analysis of the network catalogue, it is not found that there are obvious changes in seismic activity in the study area before and after the impoundment of Xiluodu Reservoir, which is also consistent with the seismic activity in the typical reservoir-induced earthquake area. Second, the Ms5.8 earthquake occurred on April 15, 2015 in Alashan Zuoqi, Inner Mongolia Autonomous Region. It is difficult to judge the seismogenic structure from the source position provided by the network catalogue because of the few earthquake events in the network catalogue and the sparse distribution of fixed stations near the epicenter. In this paper, the missing events before and after the Alxa earthquake are searched and identified by using template matching method with the data of several mobile stations near the epicenter and 55 events in the network catalogue as template events. The seismogenic structure of the earthquake is preliminarily analyzed by combining Hypo2000 and HypoDD. 362 missing events were identified in the continuous waveforms from 10 days before the main earthquake to 10 days after the main earthquake; (2) 55 events in the network catalogue were relocated by Hypo 2000, and the theoretical average errors of the horizontal and vertical directions of the focal positions were 2.50 km and 36.9 km respectively, and the theoretical average travel time residuals were 0.58 s; (3) the cross-correlation technique was used to relocate the 55 events in the network catalogue. After the relocation, the predominant distribution of the epicenter is nearly East-West (the predominant trend of least square fitting is 261.4 degrees), which is basically consistent with the direction of nodal plane II (262 degrees) in the focal mechanism solution given by USGS. According to the focal mechanism obtained by different research institutes and scholars, we think that the seismogenic structure of the Alashan Ms5.8 earthquake in 2015 is a sinistral strike-slip fault with a strike of 261 degrees and a high dip angle.
【学位授予单位】：中国地震局地球物理研究所
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P315.5
本文编号：2216778
[Abstract]:Earthquake catalogue is the basic data for confirmation of seismogenic structure and analysis of seismicity. However, due to the interference of strong coda waves, small magnitude of earthquake events, sparse distribution of stations and other reasons, it will cause serious deficiency of earthquake catalogue, thus affecting the reliable analysis of seismicity based on earthquake catalogue. The template matching method based on this method is an effective method to detect missing events under low signal-to-noise ratio and has been widely used. In this paper, template matching method is used to solve the following two problems. First, the Ms6.5 earthquake occurred in Ludian County, Yunnan Province on August 3, 2014. After the Ludian earthquake, the Ludian earthquake is considered to be an earthquake. According to previous studies, the analysis of seismicity before and after moderate earthquakes can provide a certain basis for judging the origin of the main earthquake. However, due to the sparse distribution of fixed stations near the epicenter of the Ludian earthquake and the interference of coda waves after the main earthquake, the earthquake catalogue will be absent. In this paper, a template matching method is used to search and identify small earthquakes before and after the Ludian earthquake using 541 events in the catalogue of the network as templates. The following results are obtained: (1) 991 earthquakes not listed in the catalogue are identified from the continuous waveforms from 33 days before the main earthquake to 5 days after the main earthquake. The complete magnitude of the aftershocks was reduced from 1.8 to 1.3. According to the catalogue, the b value of the aftershocks was 1.04 (+0.18) within 33 days before the main shock, and the b value of the aftershocks gradually increased from 0.5 to 0.9 within 5 days after the earthquake and remained stable. (2) According to the catalogue of the seismic network from 2009 to the occurrence of the main shock, the background b value of the region was 0.93 (+0.04). The b values of regional seismicity before and after the impoundment of Xiluodu Reservoir are close to the background B values, which is not consistent with the b value characteristics of moderate and strong earthquakes induced by typical reservoirs. (3) Through further analysis of the network catalogue, it is not found that there are obvious changes in seismic activity in the study area before and after the impoundment of Xiluodu Reservoir, which is also consistent with the seismic activity in the typical reservoir-induced earthquake area. Second, the Ms5.8 earthquake occurred on April 15, 2015 in Alashan Zuoqi, Inner Mongolia Autonomous Region. It is difficult to judge the seismogenic structure from the source position provided by the network catalogue because of the few earthquake events in the network catalogue and the sparse distribution of fixed stations near the epicenter. In this paper, the missing events before and after the Alxa earthquake are searched and identified by using template matching method with the data of several mobile stations near the epicenter and 55 events in the network catalogue as template events. The seismogenic structure of the earthquake is preliminarily analyzed by combining Hypo2000 and HypoDD. 362 missing events were identified in the continuous waveforms from 10 days before the main earthquake to 10 days after the main earthquake; (2) 55 events in the network catalogue were relocated by Hypo 2000, and the theoretical average errors of the horizontal and vertical directions of the focal positions were 2.50 km and 36.9 km respectively, and the theoretical average travel time residuals were 0.58 s; (3) the cross-correlation technique was used to relocate the 55 events in the network catalogue. After the relocation, the predominant distribution of the epicenter is nearly East-West (the predominant trend of least square fitting is 261.4 degrees), which is basically consistent with the direction of nodal plane II (262 degrees) in the focal mechanism solution given by USGS. According to the focal mechanism obtained by different research institutes and scholars, we think that the seismogenic structure of the Alashan Ms5.8 earthquake in 2015 is a sinistral strike-slip fault with a strike of 261 degrees and a high dip angle.
【学位授予单位】：中国地震局地球物理研究所
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P315.5
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