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GEOPHYSICAL RESEARCH LETTERS, VOL. 29, NO. 14, 1673, doi:10.1029/2002GL015215, 2002

Tsunami earthquakes possibly widespread manifestations of frictional conditional stability

S. L. Bilek

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


T. Lay

Institute of Geophysics and Planetary Physics and Earth Sciences Department, University of California, Santa Cruz, Santa Cruz, CA, USA


Abstract

Tsunami earthquakes, shallow events that produce larger tsunamis than expected given their surface wave magnitudes (Ms), typically have long durations and a source spectrum depleted in short period energy. Seven cases of underthrusting tsunami earthquakes provide information on the rupture processes, but little constraint on geographic distribution or frequency. We compare their rupture characteristics with smaller magnitude earthquakes on circum-Pacific interplate thrust faults. Comparable moment release time histories are found for large tsunami earthquakes and for many smaller shallow subduction zone earthquakes, with significantly longer durations and additional source complexity than for events deeper than 15 km. Thus, very shallow interplate earthquake ruptures are scale invariant, with variable frictional properties on the plate interface controlling the depth dependent rupture process. Widespread occurrence of small shallow interplate earthquakes with long durations suggests that many subduction faults have frictional properties that may enable large tsunami-generating earthquakes to occur; fortunately, large shallow ruptures are infrequent.

Published 20 July 2002.

Index Terms: 7215 Seismology: Earthquake parameters; 7230 Seismology: Seismicity and seismotectonics; 8123 Tectonophysics: Dynamics, seismotectonics.

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Citation: Bilek, S. L., and T. Lay (2002), Tsunami earthquakes possibly widespread manifestations of frictional conditional stability, Geophys. Res. Lett., 29(14), 1673, doi:10.1029/2002GL015215.