Pre-seismic anomalies in seismicity and crustal deformation: case studies of the 2007 Noto Hanto earthquake of M6.9 and the 2007 Chuetsu-oki earthquake of M6.8 after the 2004 Chuetsu earthquake of M6.8

Abstract

SUMMARY If aseismic slip occured on a fault or its deeper extension, both seismicity and crustal deformation around the source would be affected. Such anomalies are determined from earthquake occurrence data and geodetic records during the periods leading up to the 2007 March Noto Hanto earthquake of M6.9 and the 2007 July Chuetsu-oki earthquake of M6.8, which successively occurred after the 2004 October Chuetsu earthquake of M6.8 on the Japan Sea coast. Assuming such aseismic slips, seismic zones corresponding to negative and positive increments of the Coulomb failure stress show seismic quiescence and activation, respectively, relative to the rate predicted by the epidemic type aftershock sequence model. These interpretations are further supported by transient crustal movements around the sources preceding the ruptures, for example, the time-series of baseline distances between permanent Global Positioning System stations deviated from their long-term linear trends in a manner that is consistent with the assumed slip. In particular, this paper emphazes on the investigation of the interacting tectonic processes within such a narrow area and a short period, considering the precursory slow slips on the focal faults or their downdip extensions based on the observed anomalies in seismicity and crustal movement.