雷军,
北京大学地球与空间科学学院, 北京 100871
基金项目: 国家自然科学基金（41674053）资助
详细信息
作者简介: 陈聪, 男, 1994年生, 硕士研究生, 从事地震学研究.E-mail:chencong@pku.edu.cn
通讯作者: 雷军, 男, 1960年生, 副教授, 从事各向异性横波分裂研究.E-mail:leij@pku.edu.cn
中图分类号: P315收稿日期:2018-03-23
修回日期:2018-07-05
上线日期:2019-01-05
Estimating lithospheric anisotropy parameters in the Haida Gwaii region of North America using time-delays of shear waves
CHEN Cong,LEI Jun,
School of Earth and Space Science, Peking University, Beijing 100871, China
More Information
Corresponding author: LEI Jun,E-mail:leij@pku.edu.cn
MSC: P315--> Received Date: 23 March 2018
Revised Date: 05 July 2018
Available Online: 05 January 2019
摘要
摘要:本文收集到北美夏洛特皇后群岛VIB和DIB台站2005年1月1日至2014年12月31日2700余条近震三分量横波观测记录.经严格筛选提取到55条35°横波窗内的快慢波到时差值.通过建立到时差与多界面横波分裂路径关系，实现了对横波不同深度分裂界面的可靠识别和深度确定.依据对横波到时差及归一化到时差的分析结果，确认地处俯冲带的夏洛特皇后群岛的地震各向异性分别存在于该地区的上层陆壳、中层洋壳俯冲带及俯冲带底部或下层岩石圈顶部附近.发现除地幔岩石圈外，上两个分层的各向异性强度由北向南减弱，同时向西运动的洋壳俯冲带向南加深.不仅如此，归一化到时差结果显示该地区2012年M7.8强震前后各向异性强度减弱，但在3个各向异性层存在较大差异.无论在分层界面较浅的北部格雷厄姆岛附近还是在分层界面较深的南部莫尔兹比岛附近，强震后最上层的陆壳和最下层地幔岩石圈的各向异性强度均没有变化.M7.8后各向异性减弱全部发生在中层洋壳俯冲带内.并且，距离强震震中越近各向异性强度减弱越大，在一定程度上揭示出强震前后应力变化的空间分布特征.表明该地区洋壳俯冲是引起M7.8强震和现今构造运动的主要动力源.
关键词: 各向异性/
多层界面深度/
夏洛特皇后群岛/
横波分裂/
归一化到时差
Abstract:We collected more than 2700 three-component shear-wave data of stations VIB and DIB in the Haida Gwaii region (formerly the Queen Charlotte Islands) recorded from January 1, 2005 to December 31, 2014 and obtained 55 shear wave splitting time-delays of fast-slow shear waves in a 35° shear wave window. Establishing the relationship between the time-delays and the shear wave paths in multiple anisotropic layers, the shear wave splitting interfaces were recognized and the anisotropy interface depths were determined. Analysis of the time-delays and normalized time-delays shows that the seismic anisotropy exists within the whole Haida Gwaii subduction zone that incudes, from top to bottom, the continental crust, the subducting oceanic crust, and the bottom of the subduction zone or near the top of lithosphere. With the exception of the mantle lithosphere, the strength of anisotropy of the upper two layers weakens in general from north to south, while the westward motion of the oceanic crust subduction zone has a trend to deepen southwards. In addition, the normalized time-delays show that the strength of anisotropy of the region after the M7.8 earthquake in 2012 has weakened, but there are big differences in the three anisotropic layers. The strength of anisotropy in the continental crust and the mantle lithosphere of the northern Graham Island has no change, where the interface is shallow and near the southern Moresby Island. All changes of the strength of anisotropy after the M7.8 earthquake caused in the subducting oceanic crust. In addition, the closer to the epicenter of the M7.8 earthquake, the greater the decrease of anisotropy, revealing the spatial distribution of stress changes before and after major earthquakes. This in turn indicates that the subduction of the oceanic crust in this area is the main source of power for the M7.8 magnitude earthquake and the current tectonic movement.
Key words:Seismic anisotropy/
Multi interface depth/
Haida Gwaii/
Shear wave splitting/
Normalized time-delays
PDF全文下载地址:
http://www.geophy.cn/data/article/export-pdf?id=dqwlxb_14825
