Focal Mechanisms of Relocated Earthquakes and New Stress Orientations in the Charlevoix Seismic Zone

Session: Seismicity and Tectonics of Stable Continental Interiors
Type: Oral
Date: 4/30/2020
Time: 01:45 PM
Room: 240
Description: 

Focal mechanisms for the Charlevoix Seismic Zone (CSZ) were determined using a new processing package that determines focal mechanisms with wave polarities and amplitude ratios as constraints. The purpose was to understand the stress state of the seismic zone and to check past results of a significant clockwise rotation in the seismic zone relative to the first-order regional stress orientation. Our method was to determine the focal mechanisms of relocated earthquakes in a 3D model from previous tomography work using wave polarity and amplitudes ratios. We performed stress inversion with the focal mechanisms and determined new sets of stress orientations in the CSZ using different partitions of the earthquakes. The results show that stress changes across the seismic zone and with depth in systematic ways. We observed a significant stress clockwise rotation with respect to the regional stress orientation, which is consistent with the past study. Stress orientations within the impact structure, especially on the Northwest cluster, roughly align with the regional stress orientation but deviates in a clockwise sense for earthquakes outside of the impact structure. However, the results show that the degree of clockwise stress changes increases with depth, which is contrary to previous numerical stress modeling of the CSZ. These results suggest additional stress perturbation mechanisms at mid-crustal depths in the CSZ.

Presenting Author: Oluwaseun I. Fadugba

Authors