Inversion of long-period P-waves from great earthquakes along subduction zones

Abstract

Long-period P-waves from subduction zone earthquakes in the moment range from 7×10 27 to 8×10 29dyn · cm are analyzed using an iterative deconvolution method. In addition to discrete subevents which effectively contribute to the observed seismograms, the long-period component of the moment rate function is derived with the constraint that the total seismic moment is equal to the moment determined from long-period surface waves. It is shown that great earthquakes can be described by several subevents with a duration of about 10 s. which changes little from earthquake to earthquake in the above moment range. The long-period component of the moment rate function becomes larger for a greater earthquake. The greatest earthquakes of M w ~ 9 additionally involve subevents with another duration scale (much longer than 10 s). It is also shown that the local stress drop is 1 order of magnitude larger than the stress drop averaged over the entire fault plane. The constancy of the local stress drop as well as the average stress drop holds among various magnitudes of earthquakes. These observations suggest an essential similarity in the mode of dislocation distribution.