← Back to Sessions

Adjoint Earthquake Source Inversion Method Using P-Wave Spectra and Focal Mechanism Solutions

Description: 

Comprehensive and accurate characterization of small earthquake sources helps illuminate fine-scale fault structure and understand earthquake physics. In the past decades, seismologists developed methods for estimating small earthquake focal mechanism, stress drop, and rupture directivity, which constrains the radiation pattern and rupture dynamics of small earthquakes, respectively. However, focal mechanism solutions provide two nodal planes instead of one; stress drop estimations usually stack spectra from all stations without considering the rupture directivity effect; and rupture directivity estimations usually ignore vertical directivities due to limited station coverage. These limitations prevent effective interpretations of the obtained source properties and the comparisons between small- and large-magnitude earthquake source properties. Therefore, we propose an adjoint source inversion method combining focal mechanism solutions and P-wave spectra to solve these problems. We first solve the apparent P-wave corner frequencies of the target event and its neighboring Empirical Green’s Function (EGF) events at each individual station using the source spectra ratio between the target event and its EGF events. We then combine the solved apparent P-wave corner frequencies at all stations and all possible fault plane orientations from the focal mechanism solution to find the best-fitting fault plane orientation, and 3D rupture directivity that can minimize the differences among the corrected P-wave corner frequencies from all stations after removing the rupture directivity effect. The obtained corrected P-wave corner frequencies at all stations are further stacked and used to estimate the stress drop, radiated seismic energy and apparent stress. We validate our method using events in the Parkfield area. The results illustrate unprecedented, detailed spatiotemporal variation of high-quality small earthquake properties, including fault orientation, 3D rupture directivity, and stress drop, which provides a great opportunity to study fault geometry, kinematics, and dynamics.

Session: Earthquake Source Parameters: Theory, Observations and Interpretations [Poster]

Type: Poster

Date: 4/18/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Yifang Cheng

Student Presenter: No

Invited Presentation: 

Authors