A new BIEM for rupture dynamics in half-space and its application to the 2008 Iwate-Miyagi Nairiku earthquake

Abstract

SUMMARY We developed a code for dynamic rupture propagation on arbitrarily shaped faults embedded in half-space using boundary integral equation method (BIEM). It is based on an existing code for the full-space case, in which virtual free surface elements were introduced. Computations in half-space are definitely necessary for the modelling of shallow dipping fault ruptures. First, we describe the implementation and conduct some validation tests that demonstrate the accuracy of the code. The validation tests are carried out by comparing the BIEM results both with the analytical static solution and with the seismic wavefield obtained by a discrete wavenumber method. Then, we apply the code to the study of the 2008 Iwate-Miyagi, Japan, earthquake (Mw 6.9) rupture dynamics. The average stress drop was estimated to be rather large (16 MPa) in the asperity area, while the average strength excess was 5 MPa. The average fracture energy inside the asperity was found to be 36 MJm −2 . Finally, the free surface effect examination showed that the stress drop and the fracture energy were overestimated at shallow depth in the full-space computation.