Body‐wave deconvolution for variable source parameters; application to the 1978 December 6 Kuriles earthquake

A method to determine the depth and mechanism of subevents in earthquakes with complex rupture is developed. Complex body‐waves are deconvolved using a damped Lanczos inversion to retrieve the source time function. Some constraints on the mechanism and depth of the first subevent are assumed, though not required. The data set is deconvolved using the Green's function for the first subevent to obtain a best‐fitting source time function. This source time function is then windowed in time around the first pulse and the corresponding synthetic seismogram is subtracted from the data. This process is repeated on residual data to determine mechanisms and depths of subsequent subevents. This method is applied to the 1978 December 6 Kuril Islands earthquake, a complex event which ruptured vertically from 100 to 220km in depth, and represents tearing of the Pacific plate as it subducts beneath the Kuril and Honshu arcs. Using long‐period WWSSN data, we found three main subevents with the mechanism ø= 150°, δ= 80°, and λ= 20° at depths of 120, 165, and 210km. In this particular case one nodal plane is very well constrained and there is some a priori evidence for significant vertical rupture.