讲座预告 | 名师讲座第315讲：Some new observations on the frictional roles serpentinites play on strike-slip and megathrust faults
主讲题目：Some new observations on the frictional roles
serpentinites play on strike-slip and megathrust faults
主 讲 人：韦生吉 副教授（南洋理工大学）
时 间：2023年7月20日（周四）10:30-12:00
地 点：中山大学（南校区）梁銶琚第二会议室
主 持 人：冯万鹏 副教授
南洋理工大学新加坡地球观象站研究员和亚洲环境学院副教授
兼助理院长。本科和博士毕业于中国科学技术大学，加州理工学院
地震 实 验 室 博 士 后 。担 任 BSSA，GeoscienceLetters副 主 编 和
Tectonophysics编委。研究方向集中在地震震源和地球速度结构，
目的是为了更好的理解地震震源物理，板块构造以及地球动力学过
程。其研究团队所用方法包括利用测地学、地质学和地震学数据综
合约束地震的基本几何参数和运动学(破裂)过程，并致力于开发波
形反演和模拟的方法并应用于和地震灾害更密切相关的高频 (比如
>1Hz)波形研究。
报告内容简介：
It is commonly believed that serpentinites are frictionally weak,therefore they were
considered to be direct evidences of a creeping fault. Here we provide new observations on a
strike-slip fault and a megathrust fault that serpentinites are playing critical roles during
large seismic events. The strike-slip fault case is the Aceh segment of the Sumatran fault that
was reported to be creeping at various depths.We deployed 140 short period seismic nodes
along the fault to acquire data from Jan 2020 to July 2021. This dense network data was
used to derive in a high-resolution seismic catalog of ~8000 events. The seismicity is very
active and almost uniformly distributed from 3 to 12 in depth, which is in line with the
creeping nature of the fault segment. The similar earthquake families,considered as indirect
evidencof a creeping fault, agrees well with the lenses of serpentinite. However,
the
2013 Mw6.1 earthquake occurred exactly in the middle of the creeping segment, with the
rupture extended from 12 km depth to the surface, suggesting a partially creeping/locking or
conditionally stable frictional status on the entire seismogenic depth range of the fault.
The subduction zone case is associated with the 2021 M8.1 Kermadec megathrust, which radiated
high frequency (HF) energy mostly from its up dip rupture. We resolve its rupture using
finite fault inversion and a path calibrated back-projection (BP) method. In particular,
the calibration established from refined
earthquake locations reduces BP location
uncertainties to < 20 km. The model shows a slip patch at 20-45km depth, elongating ~100 km
along strike, while HF sources are distributed along the up-dip edge of the slip, coinciding
with the forearc Moho depth and bursting within a belt of background events, aftershocks,
mainshock epicenter and triggered HF sources from the M7.4 foreshock.
Strong heterogenous
friction promoting the up-dip HF
radiation is likely caused by the beginning of
serpentinization in the overriding mantle wedge. Both cases show that large seismic slip on
the serpentinized faults, which urges a re-evaluation of seismic hazards in conventionally
considered aseismic area.
