地震地质 ›› 2025, Vol. 47 ›› Issue (1): 306-324.DOI: 10.3969/j.issn.0253-4967.2025.01.018

• 研究论文 • 上一篇    下一篇

基于背景噪声成像研究北京地区三维S波速度结构

吉宇1)(), 张广伟2,3),*(), 任俊杰2), 何静2), 王肖薇2)   

  1. 1) 中国科学院大学, 北京 100049
    2) 应急管理部国家自然灾害防治研究院, 北京 100085
    3) 中国矿业大学安全工程学院, 徐州 221116
  • 收稿日期:2023-11-10 修回日期:2024-08-06 出版日期:2025-02-20 发布日期:2025-04-09
  • 通讯作者: 张广伟
  • 作者简介:

    吉宇, 女, 1995年生, 现为中国科学院大学应急管理科学与工程学院计算机技术专业在读硕士研究生, 主要研究方向大数据处理及地下结构反演, E-mail:

  • 基金资助:
    国家自然科学基金(42074102); 国家自然科学基金(U2139201); 应急管理部国家自然灾害防治研究院基本科研业务专项(ZDJ2020-09)

HIGH-RESOLUTION S-WAVE VELOCITY STRUCTURE OF BEIJING AREA USING AMBIENT NOISE TOMOGRAPHY

JI Yu1)(), ZHANG Guang-wei2,3),*(), REN Jun-jie2), HE Jing2), WANG Xiao-wei2)   

  1. 1) University of Chinese Academy of Sciences, Beijing 100049, China
    2) National Institute of Natural Hazards, Ministry of Emergency Management of China, Beijing 100085, China
    3) School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China
  • Received:2023-11-10 Revised:2024-08-06 Online:2025-02-20 Published:2025-04-09
  • Contact: ZHANG Guang-wei

摘要:

特大城市地下三维速度结构对分析潜在灾害源和评价地震危险性具有重要的研究意义。文中利用北京地区28个宽频带地震台和109个短周期地震台的波形资料, 采用背景噪声成像方法反演了北京地区上地壳和昌平南口-孙河断裂带周边浅部的三维S波速度结构。研究结果揭示北京的地下速度结构具有显著的横向非均匀性, 断裂主要位于高、低波速异常的过渡带, 其中凹陷区的低速异常反映了较深的沉积盖层, 而构造隆起区的高速异常则反映了相对坚硬的古老岩层。基于小尺度密集台阵的反演结果显示, 南口-孙河断裂断层面倾角较为陡立, 控制了沙河凹陷的北侧边界, 且沙河凹陷的沉积厚度远远深于上庄凹陷; 另外, 精细的三维速度模型为东北旺-小汤山隐伏断裂的存在提供了直接的地震学证据。文中研究表明, 利用城市背景噪声可高效经济地获取地下三维速度结构, 在识别主要地质构造单元和隐伏断裂等方面具有广阔前景。

关键词: 背景噪声成像, 三维速度结构, 北京地区, 南口-孙河断裂, 沙河凹陷

Abstract:

Beijing is located at the intersection of the Yanshan Mountains, Taihang Mountains, and the northwestern part of the North China Basin. This region has experienced multiple periods of crustal movement, forming a series of Cenozoic Basins exhibiting alternating uplifts and depressions. The intense tectonic activity has resulted in a relatively complex fault system, with the main directions of the faults being NE and NW. Notably, the Xixiadian Fault in the NE direction experienced an earthquake with a magnitude of 8 in 1679. Meanwhile, the NW-oriented Nankou-Sunhe Fault offsets multiple NE-oriented faults and directly passes through urban residential areas, making it an important active fault in Beijing. Although these intersecting faults have not experienced earthquakes of magnitude 4 or higher in recent decades, small seismic events(M<4.0)still occur frequently. Furthermore, the thickness of Quaternary sedimentary layers in the Beijing area varies significantly. These relatively low-velocity sedimentary layers can cause seismic site effects such as amplitude amplification of seismic waves and increased vibration duration. Therefore, disaster detailed study of the three-dimensional velocity structure of the upper crust and depression areas in Beijing is of great significance for analyzing potential disasters and assessing seismic hazards.

This study utilized continuous waveform data from 28 permanent seismic stations. The stations are distributed across the Beijing area, with an average inter-station distance of approximately 30km. This study's continuous constant waveform data spans from April 2022 to October 2022. For the Nankou-Sunhe Fault in the Changping area, we employed 109 short-period temporary seismic stations located around the fault zone. The seismic data is recorded from July 2, 2022, to August 3, 2022, over 33 days, with an average inter-station distance of approximately 2km. By applying the ambient noise tomography method, we successfully inverted the three-dimensional S-wave velocity structures of the upper crust for the Beijing region and the near-surface for the Nankou-Sunhe fault zone.

Our results reveal that the velocity structure beneath the Beijing area exhibits significant lateral heterogeneity. The Yanshan uplift in the north, the Jingxi uplift in the west, and the Daxing uplift in the southeastern part of the study area present obvious high-velocity anomalies, reflecting a relatively dense crystalline basement. In the Dachang depression and Shunyi depression areas, the structures from shallow to 7km depth show characteristics of low-velocity anomalies, indicating a relatively deep sedimentary layer in this area. Meanwhile, the distribution of low-velocity anomalies within the study area mainly presents a NE direction, consistent with the dominant strike direction of fault zones. Based on the results of small-scale dense seismic array inversion, it shows that the dip angle of the Nankou-Sunhe Fault is quite steep, controlling the northern boundary of the Shahe depression, and the sedimentary thickness of the Shahe depression is much deeper than that of the Shangzhuang depression. Overall, the significant low-velocity anomaly in the depression reflects the direction of the fault controls the deep sedimentary layer, and the boundary of the depression. The velocity structure in the uplift area shows a high-velocity anomaly, which reflects the relatively old rock stratum.

Additionally, the inversion results based on a small-scale dense array reveal that the fault plane of the Nankou-Sunhe Fault is relatively steep, which controls the northern boundary of the Shahe depression. The thickness of the sedimentary layer in the Shahe Depression varies significantly along the fault strike, and the deepest layer is up to 1.5km, which is much deeper than that of the Shangzhuang Depression. Furthermore, the detailed three-dimensional velocity structure model in this study provides direct seismological evidence for the existence of the Dongbeiwang-Xiaotangshan buried fault in Beijing. In summary, this study shows that seismic tomography using urban ambient noise can efficiently and economically obtain the three-dimensional velocity structure, as well as has broad prospects in identifying geological structural units and hidden faults.

Key words: Ambient noise tomography, 3-D S-wave velocity structure, Beijing area, Nankou-Sunhe Fault, Shahe depression