利用面波直接反演方法研究滇西北地殼三維S波速度結構

摘要： 我國滇西北地區（25°～27°N，99°～101°E）是川滇菱形地塊西邊界所在區域，由于構造運動活躍，是我國地震災害比較嚴重的地區，非常有必要深入研究其孕震結構。文章利用該地區69個短周期流動臺站2020年記錄的連續波形，通過背景噪聲互相關計算和時頻分析方法，提取所有臺站對Rayleigh面波相速度頻散曲線，采用基于射線追蹤的面波頻散直接反演方法，得到研究區地下三維S波速度結構。研究結果表明，研究區域上地殼速度結構存在明顯差異，特別是大型斷裂帶的分段特征明顯。如維西—喬后斷裂帶淺層5 km內整體表現為西北部高速，東南部低速;程海斷裂帶北段高南段低，在賓川盆地存在厚度約5 km的低速異常，說明賓川盆地存在較厚的沉積層。地殼淺層波速和地形起伏有較好的對應關系，在盆地區域整體表現為低速，高山區域為高速。2021年漾濞MS6.4地震發生在S波高低速過渡區域，研究區中下地殼內存在不同程度的低速區，可能為地震的發生提供了孕震環境。

關鍵詞： 滇西北地區; 背景噪聲; 面波直接反演方法; 地殼S波速度結構; 孕震環境

中圖分類號： P315.2""""" 文獻標志碼：A"" 文章編號： 1000-0844（2025）02-0458-10

DOI：10.20000/j.1000-0844.20231121004

Three-dimensional S-wave velocity structure of the crust in Northwest

Yunnan using the surface wave direct inversion method

CHA Wenjian^1，2， WANG Weijun3， ZHANG Yuanyuan4， HEI Hetang^1，2

（1. Dali Center， China Seismic Experimental Site， Yunnan Earthquake Agency， Dali 671000， Yunnan， China;

2. Northwestern Yunnan Crustal Tectonics Observatory of CEA， Dali 671000， Yunnan， China;

3. Institute of Earthquake Forecasting， CEA， Beijing 100036， China;

4. Kaiyuan Earthquake Agency， Honghe 661600， Yunnan， China）

Abstract：

The northwestern region of Yunnan Province （25°—27°N， 99°—101°E） lies along the western boundary of the Sichuan—Yunnan rhomboid block， a zone marked by active tectonic movements. This region is among the most seismically hazardous in China， requiring a comprehensive understanding of its seismogenic structures. In 2020， we analyzed continuous waveforms from 69 short-period stations in the area. We extracted Rayleigh surface-wave phase-velocity dispersion curves using cross-correlation of ambient noise and time-frequency analysis. We derived the Dl S-wave velocity structure beneath the study area using the direct inversion method of surface-wave dispersion based on ray tracing. The results reveal significant variations in the crustal velocity structure， particularly in segmented features along major fault zones. For example， at a depth of 5 km beneath the Weixi—Qiaohou fault zone， high velocities are observed in the northwestern section， whereas low velocities dominate the southeastern section. Similarly， the Chenghai fault zone exhibits high velocities in its northern segment and low velocities in the southern segment. In the Binchuan Basin， a low-velocity anomaly of approximately 5 km suggests the presence of a substantial sedimentary layer. Shallow crustal wave velocity correlates closely with terrain relief， with low velocities observed in basin areas and high velocities in mountainous regions. The 2021 Yangbi M6.4 earthquake occurred in a transition zone between high and low S-wave velocities. In addition， low-velocity zones of varying extents are identified in the middle and lower crust， potentially providing a seismogenic environment for the earthquake.

Keywords：

Northwest Yunnan; ambient noise; direct inversion method of surface wave; crustal S-wave velocity structure; seismogenic environment

0 引言

滇西北地區位于川滇菱形塊體的西部邊緣構造區，是印支塊體、揚子準地臺和松潘—甘孜褶皺帶的交匯部位。該地區構造運動強烈、地質結構復雜，正斷和左旋走滑斷裂構成Z型張扭性復合變形帶;NW走向的維西—喬后—巍山斷裂、紅河斷裂以及NS走向的程海斷裂等深大斷裂區內縱橫交錯。……