Large thrust earthquakes and tsunamis: Implications for the development of fore arc basins

Abstract

Variations of the subduction regime around the Pacific are reflected in changes of both the lengths of rupture zones and the source areas for tsunamis associated with large shallow earthquakes. Crustal deformation occurring during the earthquake and related tsunamic activity play important roles in the development and maintenance of topographic features in the fore arc region. A regional comparison of the average length of upper slope basins and terraces with the maximum length of earthquake rupture zones shows that longer basins and terraces characteristically occur in regions with larger rupture zones. Examples from Japan, Alaska, and the Aleutians clearly show how these topographic features reflect the size and spatial distribution of seismic‐tsunamic source areas. In many areas this relationship may be explained by the coseismic reactivation of structural units within the fore arc region. The two principal areas of coseismic reactivation are the trench slope break and the frontal arc region. Thus upper slope basins, deep sea terraces, and other bathymetric features may serve as indicators of the tectonic regime and of seismic‐tsunamic risk along convergent margins. Variations of the dimensions of rupture zones also appear to be influenced by the blocklike behavior of the overthrust plate. In many instances the dimensions of upper slope basins and terraces are equivalent to those of the crustal blocks. Regions with basin or terrace lengths greater than 100 km have histories of large ruptures involving adjacent segments. Regions with basin or terrace dimensions less than 100 km tend to rupture independently of adjacent segments.