Rupture Process of Subduction Zone Earthquakes.

There are large variations in temporal and spatial seismic moment release associated with large underthrusting earthquakes at subduction zone plate boundaries. The rupture process is characterized for several large underthrusting earthquakes in the Colombia-Ecuador, Cotabato (Philippines), Kurile Isl and s, and central Peru subduction zones. The fault heterogeneity of the earthquake process is interpreted in the framework of the asperity/barrier model. The Colombia-Ecuador subduction zone has failed in 3 adjacent underthrusting earthquakes in 1942 (M$\\sb{\\rm W}$ = 7.6), 1958 (M$\\sb{\\rm W}$ = 7.7) and 1979 (M$\\sb{\\rm W}$ = 8.1). The 1979 Colombia earthquake had a smooth rupture and failed with one dominant asperity between $\\approx$60-120 km NE of the epicenter. In contrast, the 1942 and 1958 earthquakes had dominant asperities near their epicenters. The entire zone failed in 1906 in a great earthquake presumably as a multiple asperity earthquake. The 1976 Mindanao earthquake (M$\\sb{\\rm W}$ = 8.1) occurred along the Cotabato trench in the north Celebes Sea, a relatively young subduction zone in a region of rapidly evolving plate boundaries. In contrast to the smooth rupture of the 1979 Colombia earthquake, the 1976 Mindanao earthquake (M$\\sb{\\rm W}$ = 8.1) had a very jagged moment release with no dominant asperity. The rupture of this earthquake was abruptly truncated by a geometric barrier. The 1963 Kurile Isl and earthquake is an excellent example of a multiple asperity event. This earthquake failed with 3 dominant asperities and a total fault length of 250 km. The area of moment release for the 1963 main shock did not overlap with its large (M $\\approx$ 7) foreshock and aftershock. The central Peru subduction zone had three large underthrusting earthquakes in 1974 (M$\\sb{\\rm W}$ = 8.1), 1940 (M = 8), 1966 (M$\\sb{\\rm W}$ = 8.1) along adjacent segments. The 1966 and 1940 earthquakes had dominant asperities near their epicenters. The historic earthquake record suggests that the entire segment of the central Peru zone may have failed as one multiple asperity earthquake in the past similar to the 1906 Colombia-Ecuador earthquake. The 1963 Kurile Isl and earthquake has a center to center asperity distance of $\\approx$100 km which is smaller than the distance between the single asperity earthquakes along the rest of the Kurile Isl and s trench. This distance may be important in determining whether the failure of one asperity will trigger the adjacent asperity and result in a multiple asperity rupture. (Abstract shortened with permission of author.)PhDGeophysicsUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/161629/1/8801278.pd