Estimation of Strong Motion Generation Area for the 2004 Parkfield Earthquake Using Empirical Green’s Function Method

The empirical Green’s function (EGF) method is used to simulate the 2004 Parkfield earthquake (Mw = 6.1). The strong motion generation areas (SMGA) are estimated to reproduce near-source ground motions in a broadband frequency range of 0.25–10 Hz. In this simulation, the EGF uses the small events that occurred in 2005 (Mw = 4.5), 2012 (Mw = 4.4), 2010 (Mw = 4), and 2007 (Mw = 4). The source spectral ratio estimates the seismic moment ratio between large and small events whose corner frequencies obey the omega-squared scaling law. The estimated SMGA is 12 km in length by 8 km in width and is located near the large slip area of the waveform inversion. The result shows that the rupture propagates radially from the southeastern bottom part of the SMGA toward the northwestern shallow direction. In addition, a characterized source model comprising two asperities and a background slip area is proposed. The rupture propagates from asperity1 toward asperity2 with 2 s time delay. The characterized source model simulates more accurately than the single SMGA. The comparison between the 5% damped pseudo acceleration response spectra of our simulations verifies a better compatibility for more than 2 Hz.