IMPROVED RESOLUTION OF EARTHQUAKE SOURCE PARAMETERS FROM LONG-PERIOD SURFACE-WAVE INVERSIONS

Source centroid location optimization improves moment tensor inversions of long-period fundamental mode surface wave spectra. Joint inversions of Rayleigh and Love wave spectra are used to find source moment tensors for the 18 October 1989 Loma Prieta, California, earthquake (M(w) = 6.9) and the 22 April 1991 Valle de la Estrella, Costa Rica, earthquake (M(w) = 7.6). For the Loma Prieta event, the focal mechanism at the optimal centroid location is consistent with that at the epicenter, and both agree with independent information. For the Costa Rica event, the solution at the optimal centroid location is consistent with geodetic and body wave observations, whereas the solution found for the epicenter is not. We conclude that optimizing for centroid location in spectral inversions is possible and improves the determination of long-period surface wave source parameters.