摘要
本文从误差解析公式及数值模拟计算两种途径讨论了利用常用地方震相Pg,Sg,Pm P,Pn,s PL测定震源深度的误差问题,结果表明,两种途径获取的误差值相当。对于上地壳的地震而言,当直达波走时误差处于0.1 s的量级时,若要将误差控制在3 km左右,则应选用震中距为30 km以内的台站;当走时误差处于0.2 s的量级时,若要控制同等误差,则应选用震中距为20 km以内的台站;如果地震位于下地壳,震中距可适当放宽,然而当震中距更大或走时误差更大时,震源深度的误差则近乎成倍增长。Pm P,Pn,s PL对上地壳的震源深度测定误差要小于下地壳,同时对误差的控制较好,不会随震中距的增大而快速增大,震中距处于90 km范围以内且走时误差小于0.1 s时的深度误差基本均能控制在3.5 km以内。此外,本文还通过"棋盘格"的方式定量地分析了速度扰动对走时的影响,并以首都圈地区台网布局为基础,分析了加入首波对震源深度测定的改善效果。这两项数值对比结果均表明,在2%的速度扰动下,只要下地壳和莫霍面的速度参数不同时出现过大或过小现象,加入首波后对震源深度的测定误差则基本能控制在3 km以内,且一致性明显地高于单独使用直达波。
In this paper,both analytic and numerical simulation methods were used to discuss the focal depth error resulted from the local seismic phases of Pg,Sg,Pm P,Pn,s PL. The result shows the two above methods produced very close error estimation. For the epicenter in the upper crust,on the condition of travel time error within 0.1 s,in order to ensure the depth error is less than 3 km,we should select these direct wave phases recorded within epicentral distance of 30 km to locate. If the travel time error is up to 0.2 s,we should select these direct wave phases within 20 km to locate on the above same condition. When the hypocenter in the lower crust,the limit of epicentral distance could be broaden a bit. As the epicentral distance or travel time error becomes larger,the error of depth location becomes practically several fold increase.Whereas,the seismic phases of Pm P,Pn,s PL can make a better error constrain when the hypocenter in the upper crust,and without an obvious enlarging effect on error as the epicentral distance increases. For these three mentioned phases,they also can ensure the depth error within 3.5 km when travel time error is set within 0.1 s and epicentral distance is less than 90 km.Furthermore,by the chessboard mode we analyzed the quantitative effect of travel time resulted from the velocity disturbance. And based on the capital seismic network,we analyzed the improvement of depth location after adding head wave phases. The above analyses result show that,within 2% velocity disturbance and without simultaneously too large or too small velocity deviation for the lower crust and Moho interface,adding head wave phases can effectively produce a reliable focal depth within 3 km,and also produce a more homogeneity result than only direct wave phases used.
作者
刘双庆
梁建宏
朱元清
于俊谊
谢静
Liu Shuangqing;Liang Jianhong;Zhu Yuanqing;Yu Junyi;Xie Jing(Tianjin Earthquake Agency, Tianjin 300201, China;China Earthquake Networks Center, Beijing 100045, China;Shanghai Earthquake Agency, Shanghai 200062, China;Zhejiang Earthquake Agency, Hangzhou 310013, China)
出处
《地震学报》
CSCD
北大核心
2018年第2期143-159,共17页
Acta Seismologica Sinica
基金
中国地震局地震科技星火计划(XH17003Y)
经常性项目"国家自动速报中心(CSN/GSN)运维及系统优化"
中国地震局震情跟踪项目(2017010128)联合资助
关键词
深度震相
震源深度
误差分析
地震定位
depth phase
focal depth
error analysis
earthquake location
