基于三重震相的青藏高原东缘岩石圈地幔波速结构

眭怡; 吴庆举; 张瑞青

doi:10.11939/jass.20180030

基于三重震相的青藏高原东缘岩石圈地幔波速结构

眭怡¹,
吴庆举^1,2, ,,
张瑞青¹

1.
中国北京 100081 中国地震局地球物理研究所
2.
中国北京 100081 中国地震局地震观测与地球物理成像重点实验室

基金项目: 中国地震局地球研究所基本科研业务费专项（DQJB16B09）、国家自然科学基金青年基金项目（41604073）和国家自然科学基金面上项目（41474089）共同资助

详细信息

通讯作者:
吴庆举: email： wuqj@cea-igp.ac.cn

中图分类号: P315.2
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出版历程
- 收稿日期: 2018-03-04
- 修回日期: 2018-05-14
- 网络出版日期: 2018-07-01
- 发布日期: 2018-08-31

Lithospheric velocity structure of eastern Tibet Plateau from triplication

1.
Institute of Geophysics，China Earthquake Administration，Beijing 100081，China
2.
Key Laboratory of Seismic Observation and Geophysical Imaging，Beijing 100081，China

摘要

摘要: 本文利用中国数字地震台网记录到的中国青海和缅甸弧发生的两次浅源地震的区域波形资料，在以Crust2.0改进AK135模型所构建的参考模型C2AK的基础上，通过三重震相波形拟合的方法，获得了青藏高原东部下方从莫霍面至上地幔顶部180 km深度范围内的P波和S波最佳拟合模型。最佳模型显示：松潘—甘孜地块（A和B剖面）下方的P波速度比C2AK模型高5%，而川滇地块（C剖面）下方上地幔顶部的P波速度要比参考模型低5%，且随深度逐渐增加，直至120 km处与C2AK模型值相同；松潘—甘孜地块下方的S波速度较C2AK模型要高3%。上述区域性速度结构差异表明，相对于松潘—甘孜地块，川滇地区的岩石圈地幔存在着更明显的挤出效应。
- 青藏东缘 /
- 岩石圈 /
- 地震三重震相 /
- 速度结构
Abstract: By comparing the synthetic and observed seismic triplications for two events from Qinghai and Myanmar Arc with the trial-and-error method, the velocity structures of P-wave and S-wave from Moho to the depth of 180 km are obtained. The P-wave velocity models for the profiles A and B beneath Songpan-Garze block are 5% higher than that in the model C2AK, which is based on the model AK135 with crust structure of Crust2.0. The P-wave velocity model for the profile C beneath Sichuan-Yunnan block, however, is 5% lower than that in the model C2AK at Moho depth, and then increases slowly down to the depth of 120 km. The S-wave velocity model beneath Songpan-Garze block is 3% higher than the model C2AK from Moho to 180 km. Such regional difference in velocity structure may indicate that the lithospheric mantle beneath Sichuan-Yunnan block has been extruded more obviously than that beneath Songpan-Garze block in the uplift of the Tibetan Plateau.
- eastern Tibetan Plateau /
- lithosphere /
- seismic triplication /
- velocity structure

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图 1 研究区域构造、所用地震及台站分布图

震源球为地震事件1和2的位置；黑线限定了A，B和C等3个剖面；三角形为所用台站；白点为三重震相拐点位置的地表投影

Figure 1. Tectonic settings and distribution of stations and events used in this study

Event locations for events 1 and 2 are represented by beach balls. The profiles A，B and C are confined by solid lines. Black triangles are for seismic stations，and white dots are for the projection position on the Earth’s surface of turning points of seismic triplications

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图 2 地震事件1的剖面A的S波理论与观测三重震相拟合测试

（a）观测S波形（黑线）与模拟波形（红线）的拟合对比。红色的折合走时曲线和模拟波形根据图（c）中红线模型给出；（b）观测S波形（黑线）与模拟波形（红线）的拟合对比。蓝色的折合走时曲线和模拟波形根据图（c）中蓝线模型给出；（c） SH速度模型，图中点划线为C2AK模型，而红色模型从莫霍面至130 km深度之间有3%的高速S波异常，而蓝线模型的3%高速异常存在于莫霍面至180 km之间

Figure 2. Match-testing of observed and synthetic seismic triplications for different velocity models of profile A for the earthquake event 1

（a） The observed S-wave triplications （black lines） and the synthetic ones （red lines） calculated for the model denoted by the red line in Fig.（c）；（b） The observed S-wave triplication （black lines） and the synthetic one （red lines） calculated for the model denoted by the blue line in Fig.（c）；（c） SH velocity model where the dash-dotted line represents C2AK model，the red model has 3% high velocity anomaly from Moho to 130 km，the blue model has 3% high velocity anomaly from Moho to 180 km

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图 3 地震事件1中剖面A的拟合波形与观测波形对比及相应的速度模型

（a）观测P波三重震相（黑线）与P波速度最佳拟合模型MAP的理论三重震相（蓝线）对比；（b）观测S波三重震相（黑线）与S波速度最佳拟合模型MAS的理论三重震相（红线）对比；（c） P波（蓝线）和S波（红线）速度结构最佳拟合模型，点划线为参考模型C2AK的P波和S波速度结构；（d）最佳拟合模型中P波和S波速度比v_P/v_S模型MAR （红线）及参考模型C2AK的v_P/v_S比值模型C2AKR （黑线）

Figure 3. Fitting of the synthetic and observed seismic triplications and the related velocity models of profile A for the earthquake event 1

（a） The observed P-wave triplications （black lines） and the synthetic ones （blue lines） calculated for the best-fitting model MAP in Fig.（c）；（b） The observed S-wave triplications （black lines） and the synthetic ones （red lines） calculated for the best-fitting model MAS in Fig. （c）；（c） The best-fitting of P- （blue line） and SH-wave （red line） velocity models of profile A，where the dotted-dashed lines are for C2AK model；（d） The v_P/v_S ratio of best-fitting model MAR （red line） and C2AKR for reference model C2AK （black line）

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图 4 地震事件1中剖面B的拟合波形与观测波形对比及相应的速度模型

（a）观测P波三重震相（黑线）与P波速度最佳拟合模型MBP的理论三重震相（蓝线）对比；（b）观测S波三重震相（黑线）与S波速度最佳拟合模型MBS的理论三重震相（红线）对比；（c） P波（蓝线）和S波（红线）最佳拟合模型，点划线为参考模型C2AK相应的P波和S波速度结构；（d）最佳拟合模型中的P波与S波速度比v_P/v_S模型MBR （红线）及相应的参考模型C2AK的v_P/v_S比值模型C2AKR （黑线）

Figure 4. Fitting of the synthetic and observed seismic triplications and the related velocity model of the profile B for earthquake event 1

（a） The observed P-wave triplications （black lines） and the synthetic ones （blue lines） calculated for the best-fitting model MBP in Fig.（c）；（b） The observed S-wave triplications （black lines） and the synthetic ones （red lines） calculated for the best-fitting model MBS in Fig. （c）；（c） The best-fitting of P- （blue line） and SH-wave （red line） velocity models of profile B，where the dotted-dashed lines are for C2AK model；（d） The v_P/v_S ratio of best-fitting model MBR （red line） and C2AKR for reference model C2AK （black line）

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图 5 地震事件2中剖面C的拟合波形与观测波形对比及相应的速度模型

（a）观测P波三重震相（黑线）与P波速度最佳拟合模型MCP的理论三重震相（蓝线）对比；（b） P波（蓝线）最佳拟合模型，点划线为相应的参考模型C2AK的P波速度结构

Figure 5. Fitting of the synthetic and observed seismic triplications and the related velocity model of the profile C for the earthquake event 2

（a） The observed P-wave triplications （black lines） and the synthetic ones （blue lines） calculated for the best-fitting model MCP in Fig. （c）；（b） The best-fitting of P-wave velocity model （blue line） of profile C. The dotted-dashed line is for the reference model C2AK

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图 6 各剖面v_P，v_S，v_P/v_s对比

（a） v_P模型对比，蓝线为剖面A和B的P波速度模型MAP和MBP，绿线为剖面C的P波速度模型MCP；（b） v_S模型对比，蓝线为剖面A的S波速度模型MAS，红线为剖面B的S波速度模型MBS；（c） v_P/v_S对比，蓝线为剖面A的v_P/v_S比值结构模型MAR，红线为剖面B的v_P/v_S比值结构模型MBR。各子图中的黑色虚线为相应的参考模型C2AK相关结构：P波速度结构C2AKP，S波速度结构C2AKS和v_P/v_s比值C2AKR

Figure 6. Comparison of the best-fitting structures of v_P，v_S，v_P/v_S for three profiles

（a） v_P velocity model comparison. The dashed line represents P-wave velocity model of C2AKP，the blue one repre-sents P-wave velocity model for profiles A and B，and the green one represents P-wave velocity model for profile C；（b） v_S velocity model comparison. The dashed line represents S-wave velocity model of C2AKS，the blue one represents S-wave velocity model for profile A，and the red one represents S-wave velocity model for profile B；（c） v_P/v_S comparison. The dashed line represents v_P/v_S ratio of C2AKR，the blue one represents v_P/v_S ratio model MAR for profile A，and the red one represents v_P/v_S ratio model MBR for profile B

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表 1 本文所用两次地震的震源参数

Table 1 Focal parameters of two events used in this study

序号	发震日期		北纬/°	东经/°	M_W	走向/°	倾向/°	滑动角/°	震源深度/km
序号	年-月-日	时:分:秒	北纬/°	东经/°	M_W	走向/°	倾向/°	滑动角/°	震源深度/km
事件1	2009-08-31	10:15:34.10	37.59	95.86	5.8	277	33	90	12
事件2	2012-11-11	10:54:42.30	22.60	96.05	5.9	91	75	14	12
注：震源参数来自于国际地震中心（ISC）目录，震源机制来自于全球矩张量（GCMT）目录。

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