Implications of the GreatMw 9.0 Tohoku‐Oki Earthquake on the Understanding of Natural Hazard in Taiwan and New Zealand

Abstract

Estimating the hazard resulting from great earthquakes on active subduction megathrusts is plagued with difficulties, yet it is necessary in populated areas proximal to active subduction. In practice, we are increasingly including knowledge of the physical fault system and mechanics into estimations of seismic hazard, aided by rapid advances in understanding the diverse spectrum of megathrust behavior. In general, statistical approaches to estimating hazard are hampered by the paucity of observed data and deterministic approaches involve large uncertainty. In Taiwan and New Zealand, megathrust‐hazard estimates are further complicated by the relatively short history of seismic observations and lack of any historical, local, or regional great earthquakes to use as analogs. Thus, it is useful to consider what insights can be gained from observations of the 2011 M w 9.0 Tohoku‐Oki earthquake, Japan. Tectonic similarities in Japan, Taiwan, and New Zealand (Fig. 1), including the complexity of subduction geometry, rapid convergence, and similarity in age and temperature of the incoming plate, make the comparison of these three subduction zones appealing. It is worth noting that unless complicated linking of multiple and disparate faults is invoked, rupture extent in all three regions is clearly limited on one side by local changes in the geometry of the convergent margins. Perhaps the most striking similarity between Tohoku and the southern Hikurangi (Fig. 1) is the distribution of interseismic coupling as determined from the inversion of Global Positioning System (GPS) data (Nishimura et al. , 2004; Wallace et al. , 2004; Suwa et al. , 2006; Hashimoto et al. , 2009). Similarities include both the down‐dip extent of locking and strong along‐strike variations. Figure 1. Tectonic maps of (a) Japan, (b) New Zealand, and (c) Taiwan. Shading on (a) and (b) shows interseismic plate coupling. Green contours in (a) show slip distribution from Tohoku‐Oki in 8 m intervals. Green contours in (b) show Tohoku‐Oki slip overlain …