固体地球物理学术报告通知-韦生吉

报告地点:腾讯会议ID:455 115 744

报告时间:2022-01-14 从 15:00 到 17:00

报告人:韦生吉

报告人简介:

Shengji works at the EOS and ASE as a PI and an assistant professor since 2014, and brings a broad range of research interests in seismology. He completed his PhD in 2009 at the University of Science and Technology in China, and spent his postdoc time the CalTech SeismoLab. He and his research team are investigating the following sub-topics: earthquake rupture process imaging, strong ground motion simulations, earthquake focal mechanism inversion, crustal to upper mantle scale velocity structure inversion, induced seismicity and rock mechanics, Southeast Asia seismology, and volcano seismology.

报告题目:Stepovers connecting a shallow, creeping Sumatran fault segment to its deep, locked Seulimeum branch revealed by a dense seismic array

报告内容简介

Earthquake is produced by shear dislocation of rocks across the fault, the frictional status and the area of locked/creeping patches on the fault thus govern the size and occurrence of damaging earthquakes. To better understand these fundamental earthquake physics issues, we deployed over 130 short period seismic nodal stations along the plate boundary type Sumatran fault in Aceh region to cover a segment that was reported to be creeping at various depths. We overcame enormous logistic difficulties, in particular those caused by the COVID-19 pandemic, and maintained deployment from Jan 2020 to July 2021.

A machine learning based earthquake detection algorithm was applied to the first 12-months of the dataset, which results in a high-resolution seismic catalog that has more than 4000 micro-seismic events. These events clearly delineate the subvertical creeping segment of the Sumatran fault and its Seulimeum branch to the northwest. The seismicity on the creeping segment is almost uniformly distributed from 3 to 12 km in depth, confirming the creeping nature of the fault segment as revealed by geodetic observations, but providing a much more accurate depth constraint. In contrast, the Seulimeum fault branch shows a much deeper seismicity at the depth range of 18 to 25 km, indicating the entire upper crust is fully locked. Sharp stepovers are observed along both strike (~10km) and strike-normal (~4km) directions between the seismicity on these fault segments. The creeping sections of the Sumatran fault, as defined by repeating earthquakes, agree well with the lenses of serpentinite, which has much smaller frictional coefficient that facilitates fault creep. However, two shallow Mw6 earthquakes occurred on the creeping segment in the last 25 years, suggesting a partially creeping/locked status on the fault. On the other hand, the active Seulimeum fault has been quiet of large earthquakes in the instrumental era, its deep locking depth (~25km) escalates the level of seismic hazard as larger earthquakes could be hosted, especially when the stepovers are overcome due strong rupture dynamic triggering. Further investigation of the dense array data would allow us to further quantify the key parameters that are critical for more accurate seismic hazard assessment.