Dependency of Near-Field Ground Motions on the Structural Maturity of the Ruptured Faults

Little work has been undertaken to examine the role of specific long-term fault properties on earthquake ground motions. Here, we empirically examine the influence of the structural maturity of faults on the strong ground motions generated by the rupture of these faults, and we compare the influence of fault maturity to that of other source properties (slip mode, and blind versus surface rupturing). We analyze the near-field ground motions recorded at rock sites for 28 large (M(w) 5.6-7.8) crustal earthquakes of various slip modes. The structural maturity of the faults broken by those earthquakes is classified into three classes (mature, intermediate, and immature) based on the combined knowledge of the age, slip rate, cumulative slip, and length of the faults. We compare the recorded ground motions to the empirical prediction equation of Boore et al. (1997). At all frequencies, earthquakes on immature faults produce ground motions 1.5 times larger than those generated by earthquakes on mature faults. The fault maturity appears to be associated with larger differences in ground-motion amplitude than the style of faulting (factor of 1.35 between reverse and strike-slip earthquakes) and the surface rupture occurrence (factor of 1.2 between blind and surface-rupturing earthquakes). However, the slip mode and the fault maturity are dependent parameters, and we suggest that the effect of slip mode may only be apparent, actually resulting from the maturity control. We conclude that the structural maturity of faults is an important parameter that should be considered in seismic hazard assessment.