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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, B09308, doi:10.1029/2004JB003039, 2004

Radiated seismic energy and earthquake source duration variations from teleseismic source time functions for shallow subduction zone thrust earthquakes

S. L. Bilek

Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA


T. Lay

Department of Earth Sciences, University of California, Santa Cruz, California, USA


L. J. Ruff

Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, USA


Abstract

Earthquake source time functions deconvolved from teleseismic broadband P wave recordings are used to examine rupture variations for 417 underthrusting earthquakes located on the interplate interface in circum-Pacific subduction zones. Moment-scaled duration of significant moment release varies with depth, with longer-duration events occurring in the shallowest 20 km of the megathrusts. The source time functions are also used to estimate radiated seismic energy. Two estimates are obtained: a simple scaled triangle substitution for the moment release history provides a minimum estimate, while integration of the time function shape provides an estimate limited only by the bandwidth of the teleseismic deconvolutions. While these energy calculations underestimate total energy, they enable systematic comparisons of rupture process within and between subduction zones. We do not find significant depth dependence for radiated energy overall, but some regions do show mild trends of increasing energy/seismic moment ratios (E/M o ) with increasing source depth that correspond to rupture duration variations in those regions. The observations of longer rupture duration at shallow depth with moderate E/M o may be due to heterogeneous friction and structural features on the shallow plate interface.

Received 24 February 2004; accepted 19 July 2004; published 25 September 2004.

Keywords: radiated energy; shallow subduction; source parameters.

Index Terms: 7215 Seismology: Earthquake parameters; 7230 Seismology: Seismicity and seismotectonics; 8164 Tectonophysics: Stresses—crust and lithosphere.

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Citation: Bilek, S. L., T. Lay, and L. J. Ruff (2004), Radiated seismic energy and earthquake source duration variations from teleseismic source time functions for shallow subduction zone thrust earthquakes, J. Geophys. Res., 109, B09308, doi:10.1029/2004JB003039.