2021年5月21日青海玛多M_(W)7.4地震及余震序列应力降时空分布与孕震环境  

Spatial-temporal evolution of stress drops in the 21 May 2021 M_(W)7.4 Madoi earthquake sequence and its seismgenic environment

作　　者：沈琳 赵连锋[1,3] 谢小碧[4] 何熹 姚振兴[1] SHEN Lin;ZHAO LianFeng;XIE XiaoBi;HE Xi;YAO ZhenXing(Key Laboratory of Earth and Planetary Physics,Institute of Geology and Geophysics,Chinese Academy of Scicences,Beijing 100029,China;Colloge of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;Heilongjiang Mohe Observatory of Geophysics,Institute of Geology and Geophysics,Chinese Academy of Sciences,Mohe Heilongjiang 165099,China;Institute of Geophysics and Planetary Physics,University of California at Santa Cruz,CA 95064,USA)

机构地区：[1]中国科学院地质与地球物理研究所地球与行星物理重点实验室,北京100029 [2]中国科学院大学,北京100049 [3]中国科学院地质与地球物理研究所黑龙江漠河地球物理国家野外科学观测研究站,黑龙江漠河165099 [4]美国加州大学圣克鲁兹分校地球物理与行星物理研究所,美国圣克鲁兹,CA 95064

出　　处：《地球物理学报》2023年第10期4111-4131,共21页Chinese Journal of Geophysics

基　　金：国家自然科学基金(U2139206,42104055,41974061,41974054);中国地震科学实验场(2019CSES0103)联合资助。

摘　　要：2021年5月21日发生在青藏高原巴颜喀拉块体内部的玛多M_(W)7.4地震是继2008年M_(W)7.9汶川地震之后在中国陆区发生的最大地震.由于玛多地震发生在板块内部滑移速率较缓慢的次级断裂上,该地震成为研究巴颜喀拉块体内部地震危险性的典型震例.通过计算2021年玛多地震序列中震级大于2.5的地震应力降,我们调查了该地震序列应力释放的时空演化规律.首先,利用已有的青藏高原及其周边地区宽频带Lg波衰减模型,对玛多地震序列产生的地震Lg波观测数据进行了传播路径衰减校正,获得119个地震事件的Lg波震源谱;然后,通过将理论震源函数与观测数据拟合,获得对Lg波标量地震矩、拐角频率和高频下降率的估计;最后,根据标量地震矩和拐角频率计算了2021年玛多地震序列的应力降.结果表明,2021年5月21日玛多地震主震应力降为22 MPa,余震序列的应力降分布范围为0.08~7.5 MPa、中位数为0.39 MPa,平均值为0.88 MPa.应力降与震级具有较强的正相关关系,说明该地区的地震活动可能并不遵从地震自相似理论.换言之,大小地震具有不同的破裂动力学性质.玛多地震序列应力降变化反映了断层面上的应力释放过程具有强烈的非均质性.主震发生之后余震应力降显著降低,但其间仍夹杂着少数具有较高应力降的事件.这些高应力降事件所在区域与主震后破裂面上的闭锁和应力集中区域相对应.The M_(W)7.4 Madoi earthquake,which occurred inside the Bayan Har block on the eastern edge of the Tibetan Plateau on May 21,2021,is the largest earthquake in the Chinese continent since the 2008 M_(W)7.9 Wenchuan earthquake.The 2021 Madoi earthquake sequence,located on a secondary fault inside the block with a slow slip rate,provides us an opportunity to understand the seismic risk for the Bayan Har block.By estimating the stress drops of the 2021 Madoi earthquake sequence for events with magnitudes larger than 2.5,we investigated the temporal and spatial evolution of the stress release of the earthquake sequence.We first used an established high-resolution broadband Lg-wave attenuation model for the Tibetan Plateau and its surrounding areas to correct the attenuation effect during wave propagation and obtained the Lg-wave source excitation spectra for 119 earthquakes in the 2021 Madoi earthquake sequence.Then,we modeled the seismic moment,corner frequency,and high-frequency fall-off rate by fitting the theoretical and observed source spectra,and finally estimated the stress drops.Our results show that the stress drop of the mainshock is about 22 MPa,and the range,median and average values of the stress drop of the aftershock sequence are 0.08~7.5 MPa,0.39 MPa,and 0.88 MPa,respectively.A strong positive dependence between the stress drops and the magnitudes was observed,indicating the earthquakes in this area may not follow the earthquake self-similarity theory.In other words,large and small earthquakes have different rupture dynamics.The spatial and temporal variations of stress drops reflect strong heterogeneity and a complex stress release process on the fault plane.Though the stress drops of these aftershocks decrease rapidly after the mainshock,there are several aftershocks with relatively high stress drops.The regions with high stress drop indicate the area of stress concentration on the fault plane after the mainshock.

关 键 词：2021年玛多地震序列 LG波 震源函数 应力降 衰减 

分 类 号：P315[天文地球—地震学]