长岛震群b值随深度变化特征
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摘要
利用双差定位方法对2017年2月～2018年5月长岛震群进行重定位,根据重定位结果计算长岛震群地震集中活动区域b值在深度上的变化分布。结果显示:长岛震群重定位的结果主要表现为北、南两个地震活动区域。北部地震活动区域的地震数量多,时间跨度长;南部地震活动区域的地震数量较少,形成时间较晚,震源深度主要集中在地壳深度4～25 km之间;长岛震群北、南两个地震活动区域的b值总体上均随深度增大而减小,在8.5 km深度左右均存在转折上升的情况。长岛震群b值的深度变化特征表明,其应力主要受围岩静压力影响,受断裂活动影响较小。
The Changdao earthquake sequence from February 2017 to May 2018 was relocated by using the double difference location method. According to the result of relocation, the variation of b value with depth in the seismic activity concentrating area in Changdao earthquake sequence is calculated. The results obtained show that the earthquake sequences can be divided into north and south concentrated areas. There is more earthquakes in the northern concentrated area with long time span. The number of earthquakes in the southern concentrated area is relatively small, and the formation time is relatively late. The focal depth is mainly concentrated in the depth between 4 and 25 km. The b values of the north and south concentrated areas decrease with depth. There is an upward trend in depth around 8.5 km. It is inferred that the stress is mainly affected by static pressure of surrounding rock, and the fault activity is less affected.
The Changdao earthquake sequence from February 2017 to May 2018 was relocated by using the double difference location method. According to the result of relocation, the variation of b value with depth in the seismic activity concentrating area in Changdao earthquake sequence is calculated. The results obtained show that the earthquake sequences can be divided into north and south concentrated areas. There is more earthquakes in the northern concentrated area with long time span. The number of earthquakes in the southern concentrated area is relatively small, and the formation time is relatively late. The focal depth is mainly concentrated in the depth between 4 and 25 km. The b values of the north and south concentrated areas decrease with depth. There is an upward trend in depth around 8.5 km. It is inferred that the stress is mainly affected by static pressure of surrounding rock, and the fault activity is less affected.
引文
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[2]王辉,曹建玲,荆燕,等.川滇地区强震活动前b值的时空分布特征[J].地震地质,2012,34(3):531-543.
[3]朱艾斓,徐锡伟,甘卫军,等.鲜水河-安宁河-则木河断裂带上可能存在的凹凸体:来自背景地震活动性的证据[J].地学前缘,2009,16(1):218-225.
[4]易桂喜,闻学泽,苏有锦.川滇活动地块东边界强震危险性研究[J].地球物理学报,2008,51(6):1 719-1 725.
[5]李正芳,周本刚.利用断裂带上的低b值识别凹凸体方法的探讨---以龙门山断裂带和鲜水河断裂带为例[J].震灾防御技术,2014,51(6):1 719-1 725.
[6]Scholz C H.The frequency-magnitude relation of microfracturing in rock and its relation to earthquakes[J].Bull Seim Soc Am,1968,58(1):399-415
[7]Amitrano D.Brittle-ductile transition and associated seismicity:Experimental and numerical studies and relationship with the b value[J].J Geophys Res Sol Earth,2003,108(B1,2044).
[8]Schorlemmer D,Wiemer S,Wyss M.Variations in earthquake-size distribution across different stress regimes[J].Nature,2005,437:539-542.
[9]Mori J,Abererombie R E.Depth dependence of earthquake frequency-magnitude distributions in California:implications for the rupture initiation[J].J GeoPhys Res,1997,102:15 081-15 090.
[10]朱艾斓,徐锡伟,胡平,等.首都圈地区b值随震源深度的变化:对地震成核的意义[J].科学通报,2005,50(8):788-792.
[11]韩晓明,薛丁,赵星.内蒙古东部扎兰屯地区的b值时空变化特征[J].地震,2012,32(3):142-149.
[12]张洪艳,卢燕红,康建红,等.吉林前郭震群b值的深度变化特征分析[J].华南地震,2015,35(2):96-99.
[13]申金超,徐波,张斌.2013-2016年乳山震群b值深度变化特征及意义[J].地震地磁观测与研究,2018,39(2):25-32.
[14]Waldhauser F,Ellsworth W L.A double-difference earthquake location algorithm:method and application to the Northern Hayward fault California[J].Bull Seism Soc Amer,2000,90:1 353-1 368.
[15]Wiemer S,Wyss M.Minimum magnitude of completeness in earthquake catalogs:Examples from Alaska,the western US and Japan[J].Bull Seismol Soc Amer,2000,90:859-869.
[16]Wiemer S,Malone S.A software package to analyze seismicity:ZMAP[J].Seismological Res Letters,2001,72(2):374-383.
[17]葛孚刚,王志才,王纪强,等.山东省长岛第四纪断裂活动初步研究[J].防灾减灾学报,2010,26(4):13-21.
[18]于磊.渤海海峡地区微震监测与活动断层研究[D].北京:中国地质大学,2017:531-79.