王俊^1,,
郑定昌²,
张金川¹,
詹小艳¹,
钱婷¹
1. 江苏省地震局, 南京 210014
2. 云南省地震局, 昆明 650224

基金项目: 中国地震局科技星火计划攻关项目（XH19014）资助


详细信息

作者简介: 王俊, 男, 2007年毕业于云南大学固体地球物理专业, 高级工程师, 主要从事数字地震监测及背景噪声源研究.E-mail:wangjun1099@qq.com

中图分类号: P315

收稿日期:2019-06-30
修回日期:2019-12-02
上线日期:2020-02-05

Seismic velocity changes in the epicentral region of the 2013 Lushan earthquake measured from ambient seismic noise

WANG Jun^1,,
ZHENG DingChang²,
ZHANG JinChuan¹,
ZHAN XiaoYan¹,
Qian Ting¹
1. Earthquake Administration of Jiangsu Province, Nanjing 210014, China
2. Earthquake Administration of Yunnan Province, Kunming 650224, China


MSC: P315

--> Received Date: 30 June 2019
Revised Date: 02 December 2019
Available Online: 05 February 2020


摘要
摘要:为探究芦山M7.0级地震后5年多来，震源区龙门山断裂带西南段介质波速的变化规律，本文基于2012年4月至2018年4月共6年的连续波形数据，运用移动窗互谱与频域偏振等分析方法，结合背景噪声源的特性，对不同深度范围内的相对波速变化以及震后的恢复过程与机制进行了研究.获得的主要认识包括：（1）年尺度而言，震源区周期为1~20 s的背景噪声场相对稳定，但成分复杂、2~10 s频带内至少存在2个能量相对稳定的噪声源；不同周期噪声的能量，在月变与季节性上的变化特征差异明显.（2）获得了长时间尺度、不同频带内介质相对波速的背景变化水平，1~2 s、2~4 s的波动幅度（约为±0.04%）与季节性变化规律强于4~10 s、10~20 s的，结合与降雨量相关的地下水位模型能很好地解释其变化规律.（3）震源区的同震波速降低现象清晰，降幅约为0.08%~0.1%；空间上，波速下降最为显著的区域主要集中在龙门山断裂带两侧约70 km范围内，其中四川盆地一侧平均约为0.1%，略高于青藏高原（0.08%）一侧；在断裂带内的降速不显著.对不同子频带进行测量的结果显示，震后除10~20 s外，其余3个子频带的相对波速在震后较短时间内（约20天左右）均出现较大幅度的波速降低现象，其中4~10 s的平均降速最大（约为0.08%），分析认为主震及大量余震的松弛效应是引起介质波速下降的主要原因.（4）震后大约1年左右，波速变化基本恢复到震前水平，且至2018年4月前未观察到大幅的波速变化现象，总体上各频带内的结果均沿零线小幅波动.
关键词: 龙门山断裂带西南段/
背景噪声互相关函数/
背景噪声源特性/
同震波速变化

Abstract:In order to investigate spatial and temporal changes of seismic velocity in the epicentral region of the M7.0 Lushan earthquake, located in the southwestern segment of the Longmenshan fault. We used the Moving-Window Cross-spectral and Frequency-dependent polarization technique to analyze the ambient noise during the time period from April 2012 to April 2018. Firstly, we investigated the variations of amplitude and polarization of the ambient noise in the period band of 1~20 s. Secondly, we measured the seismic velocity changes at different depth during and after the Lushan earthquake. Our results indicate that (1) The seismic noise field is stable on the annual scale. The seismic records indicate a complicated, multistate wavefield with at least two noise sources in the period band of 2~10 s. The monthly and seasonal variations of the noises are different at different frequency bands. (2) Clear seasonal seismic velocity changes are observed. The amplitude of velocity change at higher frequences (1~2 s and 2~4 s, about ±0.04%) are greater than velocity changes at longer periods (4~10 s, 10~20 s). This seasonal velocity changes can be explained by the precipitation induced groundwater level change. (3) The coseismic velocity changes are most prominent in the period band of 1~20 s, the coseismic velocity reduction is observed with amplitude up to 0.08%~0.1%. And significant coseismic velocity reductions mainly contrained within 70 km from Longmenshan fault. The velocity reduction was about 0.1% on the Sichuan Basin (east) side, which slightly higher than that on the Qinghai-Tibet Plateau side (0.08%). The reduction inside the Longmenshan fault was not obvious. The results in different frequency bands show that except for 10~20 s, the relative seismic velocity in the other three sub-bands showed a sudden significant reduction after main shock; the largest reduction (about 0.08%) was observed at the period band of 4~10 s. We suggest that the the post-seismic relaxation of the main shock and aftershocks are responsible for the observed velocity changes. (4) The seismic velocities recovery to the pre-earthquake value approzimatedly one year after the Lushan earthquake where only slight osscillations around the pre-earthquake level are obaserved until April 2018.
Key words:Southwestern Longmenshan fault/
Ambient noise cross-correlation funciton/
Ambient noise Properties/
Coseismic velocity change



PDF全文下载地址:

http://www.geophy.cn/data/article/export-pdf?id=dqwlxb_15336