摘要：The propagation of a seismic rupture on a fault introduces spatial variationsin the seismic wave field surrounding the fault. This directivity effectresults in larger shaking amplitudes in the rupture propagation direction.Its seismic radiation pattern also causes amplitude variations between thestrike-normal and strike-parallel components of horizontal ground motion. Weinvestigated the landslide response to these effects during the 2016 Kumamotoearthquake (Mw 7.1) in central Kyushu (Japan). Although thedistribution of some 1500 earthquake-triggered landslides as a function ofrupture distance is consistent with the observed Arias intensity, thelandslides were more concentrated to the northeast of thesouthwest–northeast striking rupture. We examined several landslidesusceptibility factors: hillslope inclination, the median amplificationfactor (MAF) of ground shaking, lithology, land cover, and topographicwetness. None of these factors sufficiently explains the landslidedistribution or orientation (aspect), although the landslide head scarps havean elevated hillslope inclination and MAF. We propose a new physics-basedground-motion model (GMM) thataccounts for the seismic rupture effects, and we demonstrate that thelow-frequency seismic radiation pattern is consistent with the overalllandslide distribution. Its spatial pattern is influenced by the rupturedirectivity effect, whereas landslide aspect is influenced by amplitudevariations between the fault-normal andfault-parallel motion at frequencies <2 Hz. This azimuth dependenceimplies that comparable landslide concentrations can occur at differentdistances from the rupture. This quantitative link between the prevalentlandslide aspect and the low-frequency seismic radiation pattern can improvecoseismic landslide hazard assessment.
