青藏高原东南缘地壳结构及云南鲁甸、景谷地震深部孕震环境

doi:10.3969/j.issn.0253-4967.2014.04.021

摘要/Abstract

摘要：

通过联合解释青藏高原东南缘地区Rayleigh波群速度频散和固定地震台站的远震接收函数, 构建了青藏东南缘3维地壳剪切波速度模型.结果表明研究区地壳结构具有强烈的横向不均一性.该区地壳厚度变化强烈(30～65km), 其总体趋势是东南浅、西北深.研究显示该区存在2个明显的壳内低速异常带, 其中中地壳(15～20km)低速带主要分布在腾冲、川滇菱形块体内部;而25～40km深度范围的中、下地壳低速带主要出现在研究区的北部, 而在四川盆地和研究区南部则普遍缺失.鲁甸地震所在地震带的上地壳表现为高速异常, 中、下地壳范围内存在2个显著的壳内低速带.鲁甸地震主震及其多数余震分布在高速的上地壳之中.与之不同, 景谷地震序列及其所在思茅-普洱地震带下方没有显著的壳内低速带的出现, 但其上地壳则表现为S波低速异常, 该上地壳低速异常可能与地壳强烈破碎及断层/微裂隙中的流体有关.

关键词: 青藏高原东南缘, 地壳结构, 联合反演, 接收函数, Rayleigh波频散

Abstract:

A detailed 3D crust S-wave velocity model is derived from joint analysis of Rayleigh wave group velocity and teleseismic P-wave receiver functions at permanent stations on the southeast margin of Tibet plateau and its surrounding area. Our new models show the velocity structure in the crust beneath SE Tibet is strongly heterogeneous. There are strong lateral variations in crustal thickness, which increases gradually from 30km in the south and east of Yunan to～65km in the SE Tibetan Plateau. Two obvious low velocity zones (LVZs) are revealed at various depths in the crust. The shallower LVZ in the middle crust (15～20km depth) are limited in the Tengchong volcano and Sichuan-Yunnan (Chuan-Dian) rhombus block. Another LVZ in the middle-to-lower crust varies between 25 and 40km and it shallows toward the east and southeast and is absent in the Sichuan Basin and the southern part of this study area. Our shear velocity model clearly shows an upper crustal high-velocity body and two LVZs in the middle crust and middle-to-lower crust (30～40km depth) across the source area of the 2014 Ludian earthquake. Ludian earthquake sequences and the neighbouring Yongshan-Daguan seismic zone are distributed in the upper crustal high-velocity body. In contrast, no obvious intra-crustal low velocity zones (IC-LVZs) appear beneath the Jinggu earthquake and its adjacent areas. But low velocity anomalies are found in the upper crust beneath the Jinggu earthquake and its neighbouring Simao-Pu'er seismic zone, which may be due to a highly fractured and fluid-filled rock matrix that may have initiated the nucleation of the Jinggu earthquake.

Key words: southeast edge of Tibet plateau, crust structure, joint inversion, receiver function, Rayleigh wave dispersion

中图分类号:

P315.63

李永华, 徐小明, 张恩会, 高家乙. 青藏高原东南缘地壳结构及云南鲁甸、景谷地震深部孕震环境[J]. 地震地质, 2014, 36(4): 1204-1216.

LI Yong-hua, XU Xiao-ming, ZHANG En-hui, GAO Jia-yi. THREE-DIMENSIONAL CRUST STRUCTURE BENEATH SE TIBETAN PLATEAU AND ITS SEISMOTECTONIC IMPLICATIONS FOR THE LUDIAN AND JINGGU EARTHQUAKES[J]. SEISMOLOGY AND GEOLOGY, 2014, 36(4): 1204-1216.

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