HIGHER-ORDER INTERRELATIONS BETWEEN SEISMOGENIC STRUCTURES AND EARTHQUAKE PROCESSES

To advance our understanding of higher-order (smaller-scale) interrelations between the fault zone structure and the earthquake process we start with the observation that the source parameters of major California earthquakes deviate systematically from the self-similarity. This departure from the self-similarity is interpreted in terms of both the specific barrier model and the asperity model. The asperity model, however, is found to be inconsistent with the following observations: (1) sharp impulsive displacements waveform in the direction perpendicular to the fault trace; (2) the complementary relationship between fault slip and aftershock; and (3) existence of barriers in the creeping segment of the San Andreas fault. The application of the specific barrier model, on the other hand, leads to a predominant subevent crack size of a few hundred meters in the creeping segment. This result is consistent with the negative correlation between coda Q-1 and b-value observed in the Stone Canyon area for 1.5 < M < 4, and suggests that the creeping brittle region may be the source of temporal change in coda Q-1. The existence of an extensive creeping brittle zone under southern California with the same predominant crack size can explain the observed strong positive correlation between the coda Q-1 and b-value for M > 3. Temporal increase in coda Q-1 is sometimes accompanied by an increase in the rate of surface deformation, but not always so. This is attributed to the erratic coupling between the creeping brittle region and the overlying brittle region. The applicability of the conclusions obtained from California earthquakes to other regions is investigated using the observed scaling laws of seismic source spectra, and it is suggested that the crack size of the creeping brittle zone may vary regionally from a few hundred meters to a few kilometers. As an alternative to the widely held view that the aseismic creep in the plate boundary may occur as a giant slow earthquake, our result suggests that it may be occurring as small fractures with scale lengths from a few hundred meters to a few kilometers.