Source Volume Heterogeneity of the Ms = 6.6 Kaoiki l983 Earthquake: Precursors and Mainshock

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Recently we found evidence which suggests that the Kaoiki earthquake is repeated every 10.4 years. The location and recurrence interval appear to be very stable. However, the magnitude varies between 5.5 and 6.6. We propose to study precursors and mainshock source heterogeneities of the last (Nov. 1983) Kaoiki earthquake in order to develop a physical model which may allow a detailed prediction of the next mainshock in this area. The parameters which we will analyze for the years 1979 to 1983 within the Kaoiki source volume are: (1) attenuation (coda decay rate), (2) b-values, (3) the frequency content of local earthquakes, and (4) seismic velocity variations using earthquake doubles. Our analysis of the seismicity rate in this volume revealed the most outstanding precursory quiescence reported to data, with the rate change varying from 0% near the hypocenter to 90% east of it. Preliminary results suggest that this heterogeneity of the source volume is also reflected in the coda decay rate: Stronger attenuation is observed in the volume which contains the highest background seismicity rate as well as the greatest precursory rate decrease. We plan to determine whether frequency content and b values also vary as a function of space and how any of these spatial differences may relate to the complexities of the mainshock rupture.