NEW_Accomplishments.indd - IRIS

2006 IRIS 5-YEAR PROPOSAL EARTHQUAKES
Exploring Subduction Zone Earthquake Rupture
Susan L. Bilek • New Mexico Institute of Mining and Technology
Thorne Lay • University of California, Santa Cruz
Larry J. Ruff • University of Michigan
Subduction zone earthquakes generate significant amounts of moment in great earthquakes, such as the 2004 Mw 9.0 Sumatra-Andaman
event. In addition, events such as these can have tragic results, as ground shaking and tsunami can results in
large numbers of casualties. We need to increase our understanding of subduction zone earthquake proceses and the important
tectonic conditions that can lead to the devastating events. Some of our research has explored the rupture characteristics of
subduction zone earthquakes, both large and small magnitude, to understand variable rupture and tsunami earthquake occurrence.
For example, tsunami earthquakes such as the 1992 Nicaragua event can be very devastating, and models sugggest
shallow rupture (up to the trench in some cases) though low-rigidity materials can produce the observed tsunami data. Using
seismic waveforms obtained through IRIS, we have examined rupture processes of hundreds of earthquakes in 14 global subduction
zones to find a depth-dependent behavior of rupture characteristics. These results, summarized below, suggest a depth
dependence of frictional properties along the megathrust, which may impact tsunami earthquake generation. Indeed, these
results suggest heterogeneous conditions along the megathrust, but that shallow portions of the fault may contain patches of
conditionally stable material, as suggested by tsunami models.
Bilek, S.L., Lay, T., and Ruff, L.J., J. Geophys. Res., 109, B09308, doi:10.1029/2004JB003039, 2004.
Bilek, S.L. and Lay, T., Geophys. Res. Lett. 29, 1673, doi:10.1029/2002GL015215, 2002
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