Seismic waveform attributes before and after the Loma Prieta earthquake: Scattering change near the earthquake and temporal recovery

During 1987-1995 several clusters of nearly identical seismic events (multi plets) occurred near the Loma Prieta source region. These multiplets allow us to investigate and demonstrate spatial and temporal changes in seismic w ave character associated with the 1989 Loma Prieta main shock. For seismogr am pairs we use a moving window technique to compute coherencies depending on lapse time and frequency. Post-Loma Prieta events have reduced coherenci es with pre-Loma Prieta events in a spatially limited region close to the L oma Prieta hypocenter, while other paths remain nearly unaffected. These ch anges gradually recover within a time interval of 5 years after the Loma Pr ieta earthquake. A possible explanation for the time dependence is coseismi cally opened cracks which cause scattering increase for wavefields after th e Loma Prieta event. Postseismic relaxation processes such as crack healing , fluid diffusion, or after deformations lead to progressive closure of the se cracks with time after the main shock. Thus the scattering properties of the local crust approach the pre-main shock state.