摘要
2010年4月14日青海玉树MS7.1地震发生在青藏高原东南部甘孜—玉树地震带,在震后7～10天内,我们快速建立了由15个GPS测站组成的跨地震破裂带观测剖面,包括1个连续站,3个半连续站和11个流动站,对所有站进行了240多天的观测,获取了该次地震的震后形变时空特征.采用欧拉矢量和位错模型解算了背景速度场,并从GPS观测的形变场中扣除该分量.采用分层黏弹性位错模型计算余震引起的地表形变,结果表明余震对部分测站的位移造成不可忽视的影响.采用对数模型拟合位移时间序列,表明特征衰减时间为6.7±1.2天.利用最速下降法反演震后余滑时空分布,反演结果表明震后断层活动以左旋滑动为主,断层南盘具有少量的抬升.在空间分布上,余滑主要位于同震破裂区的两侧,西北侧的余滑几乎达到地表,而东南区的余滑基本在同震破裂区的下方,余滑最大的区域位于结古镇东南下方10～20km的深度范围.随着震后离逝时间的增加,2个余滑区在空间上保持不变,余滑区的面积逐渐扩大.余滑的矩释放为（1.5～5.1）×10^18 Nm,相当于1个MW6.1～6.4地震释放的能量.分层岩石圈黏弹性模型计算的地壳孔隙弹性反弹形变与地表观测值相差较大,不能解释观测到的震后变形.采用麦克斯维尔流变体模型计算下地壳和上地幔松弛引起的地表形变,显示出其对地表形变的贡献较小.GPS观测得到的震后形变所具有的快速衰减特征,以及余滑模型能够较好地拟合GPS地表形变,表明2010年玉树MS7.1地震后早期阶段的地壳形变主要是由余滑机制决定的.
The Yushu M_S7.1earthquake occurred on April 14 th,2010in the southeasternTibetan Plateau,China.The seismic event ruptured the Yushu segment of the pre-existing Garzê-Yushu fault.We established 15 GPS stations over 7～10days following the earthquake,which constituted a～360 km long transection across the rupture trace,encompassing 1continuously operating,3semi-continuous and 11survey-mode sites.Most of the sites were observed for more than 240 days to capture the spatiotemporal changes of postseismic deformation.The secular deformation of the 15 sites was corrected using Euler vectors and a dislocation model.A layered visco-elastic dislocation model was employed to calculate aftershockinduced deformation,showing that aftershocks contributed considerably to the deformation of near-field sites.A logarithmic function was used to fit the post-seismic displacements,yielding a characteristic decay parameter of 6.7±1.2days.The Steepest Decrease Method of optimization was employed to invert for spatiotemporal changes of afterslip.Afterslip was found mostly at the northwestern and southeastern flanks of coseismic slip.The afterslip patch at the northwestern flank almost reaches the surface,and the other one being directly beneath the major cosesimic slip patch.Maximum afterslip is located at 10～20km depth range southeast of Gyêgu town.With the time lapse after the mainshock,the 2domains of major afterslip were stationary in space,but their area was significantly increased.The moment released by the afterslip is（1.5～5.1）×10^18 Nm,equivalent to an earthquake of MW6.1～6.4.Deformation due to poroelastic rebound cannot explain the observed surface deformation.The contribution to observed postseismic deformation from relaxation of lower crust and upper mantle is not significant,calculated using a Maxwell visco-elastic model.The rapid decay of postseismic deformation and the good fit of the after slip model suggest that the dominant source in the early stage of postseismic process is most likely ascribed to afterslip.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2016年第12期4570-4583,共14页
Chinese Journal of Geophysics
基金
国家自然科学基金(4117004,41461164004)
国家国际科技合作项目(2015DFR21100,2010DFB20190)
2010年玉树7.1级地震科学考察(0210660)
中国地震局地震预测研究所基本科研业务费专项重点项目(2014IES010102)
俄罗斯远东联邦大学项目(14-08-01-05_m)联合资助
关键词
玉树7.1级地震
震后形变
构造活动
余震活动
震后余滑
Yushu MS7.1 earthquake
Postseismic deformation
Tectonic movement
Aftershock activity
Postseismic afterslip
