乳山震群震源谱参数的稳健反演  

Robust inversion of seismic-source spectral parameters for the 2013—2015 Rushan swarm

作　　者：郑建常[1] 王鹏[1] 徐长朋[1] 许崇涛 刘凯 李冬梅[1] 李翠芹[1] ZHENG Jian-Chang WANG Peng XU Chang-Peng XU Chong-Tao LIU Kai LI Dong-Mei LI Cui-Qin(Earthquake Administration of Shandong Province, Jinan 250014, China Wulian Seismic Station, Shandong Wulian 262300, China Dezhou Seismic Station, Shandong Dezhou 253000, China)

机构地区：[1]山东省地震局,济南250014 [2]五莲地震台,山东五莲262300 [3]德州地震台,山东德州253000

出　　处：《地球物理学报》2016年第11期4100-4112,共13页Chinese Journal of Geophysics

基　　金：中国地震局星火计划项目(XH15026);山东省科技发展计划项目(2014GSF120007);山东省地震局重点项目(SD1250501)联合资助

摘　　要：本文引入截止频率f_(max)提出基于Brune模型的高频截止(High-Cut)模型,采用两步反演的方法来拟合求解震源谱的特征参数,并给出其误差范围;实际应用显示该模型的理论谱对观测谱有很好的拟合,可明显改善拐角频率识别的准确度.将该方法应用于2013—2015年的乳山震群,计算了乳山震群25次M_L≥3.0事件的震源参数(地震矩、破裂半径、应力降等),进一步对乳山震群的震源破裂特性进行了讨论.结果显示:拐角频率、应力降与震源尺度大小明显相关;高频衰减系数γ与震源破裂区的复杂程度以及破裂性质有关,当观测记录中混杂有其他事件的波形或微破裂时,高频衰减系数大于2,并且不确定性增大;截止频率f_(max)与地震大小存在一定相关性;使用Beresnev(2001)给出的震源半径计算公式,得到的乳山震群的结果显示与华北地区的经验关系较为一致;乳山震群的应力降明显偏小(最大不超过0.15 MPa),一方面反映了震中区域的构造应力水平,另一方面可能还意味着此次震群是一个相对非耗散型的脆性破裂过程,属于低摩擦应力的断层作用.Based on the Brune′s model,we propose a high-cut model by introducing the cut-off frequency-f_（max）.We use a two-step inversion method to fit the observed seismic-source spectra and resolve its characteristic parameters,i.e.corner frequency,low-frequency level,attenuation coefficient.Additionally,95% confidence level is given by aparticle swarm nonlinear optimization algorithm.Tests on real data show that this method can improve the accuracy of spectra parameters significantly.This method is applied to the 2013—2015 Rushan swarm which has continued for over two years,including more than 10000 aftershocks recorded.Source parameters,such as scalar moment,rupture radius,and stress drop for 25 M_L≥3.0 events of this swarm are calculated using the method aforementioned.The results show that（1）the corner frequency and stress drop are evidently correlated with the source scale or event size.（2）Theattenuation coefficientγ,which implies the deviation to the Brune′s circular model,is related with the complexity and features of the rupture area.Examples show that if records are contaminated by other events or mixed with micro cracks,the high-frequency attenuation coefficientγis greater than 2with larger uncertainty.（3）The cut-off frequency f_（max） might be connected with micro cracks of an event,and also has correlation with the event size.（4）The source radius derived from Beresnev′s formula（2001）is more suitable in North China,which is in agreement with previous study.（5）The Rushan swarm has obviously lower stress drops,implying this swarm is a relatively non-dissipative brittle rupture process,or a faulting with low frictional stress.

关 键 词：震源参数 拐角频率 破裂半径 应力降 高频衰减系数 

分 类 号：P315[天文地球—地震学]