2:30 PM - 2:45 PM
[SSS06-04] Joint earthquake source inversion method using P-wave spectra and focal mechanism solutions
Keywords:rupture directivity, source spectra analysis, focal mechanism
Improving characterizations of small earthquake sources advances our understanding of fault structures and seismic mechanics. Traditional methods for determining focal mechanisms, stress drops, and rupture directivities are limited by ambiguities in nodal plane identification and the neglect of rupture directivity, which impedes in-depth analyses and comparisons between earthquakes of varying magnitudes. To address these challenges, we introduce an innovative adjoint source inversion method that integrates focal mechanism solutions with P-wave spectra. Initially, we determine the apparent P-wave corner frequencies for the target event by analyzing the source spectral ratio between the target event and its surrounding Empirical Green's Function (EGF) events. We then synthesize corner frequencies with all potential fault plane orientations derived from the focal mechanism solutions and select the optimal fault plane orientation and 3D rupture directivity that best correspond with the observed azimuthal variations of P-wave corner frequencies.
Validated using a synthetic dataset and 2634 events with magnitude larger than 1.5 around the Parkfield locked patch, our findings indicate significant unilateral rupture directivity in 88% of the earthquakes. Of these, 53% occur along the main fault with various dipping angles, and 47% exhibit high angle to the main fault with near-vertical dips. Events above the locked patch predominantly show NE dipping planes with SE directivity, while those below exhibit SW dipping with NW directivity, suggesting consistent earthquake rupture direction with the hanging wall's slip direction. Incorporating directivity effects, 84% of events exhibit larger corner frequency, indicating higher stress drops than those previously estimated without directivity corrections. The proposed method can help to solve unprecedented detailed spatiotemporal variation of small earthquake properties, including fault orientation, 3D rupture directivity, and stress drop, which offers new perspectives on fault geometry, kinematics, and dynamics.
Validated using a synthetic dataset and 2634 events with magnitude larger than 1.5 around the Parkfield locked patch, our findings indicate significant unilateral rupture directivity in 88% of the earthquakes. Of these, 53% occur along the main fault with various dipping angles, and 47% exhibit high angle to the main fault with near-vertical dips. Events above the locked patch predominantly show NE dipping planes with SE directivity, while those below exhibit SW dipping with NW directivity, suggesting consistent earthquake rupture direction with the hanging wall's slip direction. Incorporating directivity effects, 84% of events exhibit larger corner frequency, indicating higher stress drops than those previously estimated without directivity corrections. The proposed method can help to solve unprecedented detailed spatiotemporal variation of small earthquake properties, including fault orientation, 3D rupture directivity, and stress drop, which offers new perspectives on fault geometry, kinematics, and dynamics.