基于背景噪声的滇西地区瑞利面波相速度成像

doi:10.12196/j.issn.1000-3274.2023.01.010

摘要/Abstract

摘要： 利用中国地震科学台阵第一期(2011年1月—2014年6月)在青藏高原东南缘布设的流动地震台阵中的190个流动站和云南省区域台网的35个宽频带固定台所记录到的两年半的连续地震记录, 运用噪声成像方法反演得到滇西(21.0°N～29.5°N, 97°E～103.5°E)的相速度分布图像。反演结果揭示研究区地壳及上地幔速度结构存在明显横向不均匀性。短周期6～12 s的相速度分布图像反映上地壳的速度结构与地表地质构造单元存在较大的相关性。腾冲火山区及其南侧的低速异常与该地区上地壳存在的岩浆囊或部分熔融体有关, 且在深度上的形态不一。在程海断裂和普渡河断裂之间存在高速异常, 这与体波走时反演得到攀西呈现大面积高速异常的结果较为一致, 可能与该地区的玄武岩隆起有关。 14～25 s周期的相速度图像显示在川滇菱形块体内部及腾冲火山区呈现低速异常, 暗示了该区下地壳流的存在。由14～40 s图像对比发现, 受地壳厚度差异的影响, 南部地区高速异常逐渐增大。此外, 腾冲火山区的低速异常从地表一直延伸至上地幔, 但似乎并不与川滇菱形块体内部的低速异常相连, 这可能是地幔热流的通道。腾冲断裂和龙陵断裂的交会区域似乎为高低速异常的分界处, 该区下方可能就是1976年两次7级以上地震的震源区。

关键词: 背景噪声层析成像, 滇西地区, 相速度, 地壳结构

Abstract: In this paper, the phase velocity distribution images of Southwest Yunnan (21.0°N~29.5°N, 97.0°E~103.5°E) are obtained with continuous seismic records at 190 mobile stations in the first periods of ChinArray (2011-01—2014-06) and 35 broadband permanent stations of Yunnan regional network. The ChinArray was setup in the southeast of the Qinghai-Xizang Plateau. Inversion results reveal significant lateral heterogeneity in the velocity structure of the crust and upper mantle in the study area. Short period images (6~12 s) indicate a strong correlation between upper crust velocity and surface geological structures. The low velocity anomaly in Tengchong volcanic area and its southern side is related to the magmatic sac or partial melt in the upper crust, and the shape is different in depth. A high-velocity anomaly is observed between Chenghai fault and Puduhe fault, consistent with the body wave travel time inversion results. The inversion indicates a large high-velocity anomaly in Panxi area, potentially related to basalt uplift in this area. Phase velocity images with periods of 14~25 s reveal low-velocity anomalies in the Sichuan-Yunnan rhombic block and Tengchong volcanic area, suggesting the presence of lower crustal flow. Comparing 14~40 s images, due to variations in crustal thickness, the high-velocity anomaly gradually increases in the southern region. Furthermore, the low-velocity anomaly in the Tengchong volcanic area extends from the surface to the upper mantle, but it does not appear to be continuous with the low velocity anomaly in the Sichuan-Yunnan rhombic block. This low velocity anomaly may be a channel of mantle heat flow. The intersection of the Tengchong fault and Longling fault appears to be the boundary between high and low-velocity anomalies. Two M≥7 earthquakes in 1976 may occurred beneath this area.

Key words: Ambient noise tomography, Southwest Yunnan Area, Phase velocity, Crustal structure

中图分类号:

P315.7

张艺, 郭震, 朱培育, 朱佳苗, 戴乐翔. 基于背景噪声的滇西地区瑞利面波相速度成像[J]. 地震, 2023, 43(1): 124-136.

ZHANG Yi, GUO Zhen, ZHU Pei-yu, ZHU Jia-miao, DAI Le-xiang. Rayleigh Wave Phase Velocity Maps of Southwest Yunnan Based on Ambient Noise Tomography[J]. EARTHQUAKE, 2023, 43(1): 124-136.

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