Time-Dependent Earthquake Tomography in Southern California

Date: 4/24/2019

Time: 06:00 PM

Room: Fifth Avenue

Temporal changes of seismic velocities have been determined through analysis of earthquake and ambient noise data in Southern California and other place, but there is limited understanding about the spatial distribution and amplitudes of these changes. In this study, we apply a new time-dependent earthquake tomography algorithm to monitor systematically 3-D velocity perturbations in the Southern California crust. The employed time-lapse double-difference tomography method utilizes differential times between two nearby earthquakes that occurred at different times. We use P picks of earthquake arrival times from 2000 to 2016 recorded at 285 stations in a region spanning longitudes 242o – 246o and latitudes 32o – 35o. The 16 year time span is separated into 98 intervals, each containing 1000 events, and velocity changes are monitored between successive time intervals. We first perform standard double-difference tomography at each time period to obtain a 3D P-wave velocity model using the CVM-H15.1 as the initial model. To analyze velocity changes between subsequent intervals, we use the inverted 3-D P-wave velocity model and associated relocated earthquakes of the earlier interval as initial model and event locations. Through trial and error, we find that horizontal grid size of 10 km and a depth grid setting of 0, 4, 7, 10, 13, 20, and 40 km lead to robust results. The obtained models include significant apparent velocity changes in the source region of the 2010 Mw 7.2 El Mayor – Cucapah earthquake, both before and after the event. We plan to incorporate differential times between station pairs in the time-lapse algorithm to increase the resolution of shallow structures. These and other updates will be presented in the meeting.

Presenting Author: Jing Hu

Authors