The revised direct stiffness matrix method for seismogram synthesis due to dislocations: from crustal to geotechnical scale

Abstract

SUMMARY The seismograms for the multiscale crustal model due to dislocations are synthesized by a revised direct stiffness matrix method. By extracting the exponential growth terms related to wavenumber and layer thickness, the fast and accurate wavefield modelling can be achieved for the multiscale system with superficial fine layers (the layer thickness and velocity vary from metre level in the near-surface to kilometre level in deep crustal zones). This method allows relatively high-frequency cases of engineering interest (about 10 Hz) to be tackled without extra computations, linking the geophysics to the geotechnical earthquake engineering. The simulations considering superficial fine layers (5–50  m) show that the horizontal peak ground velocities can be amplified twice with superficial velocity decreasing from 0.4 to 0.15 km s–1. A case study using a realistic fine model in Tokyo metropolis elucidates that the displacements are localized within the epicentre distance about 5 km, predicting the displacement responses by factors up to 6.7, 1.1 and 6.7 for radial, tangential and vertical directions in comparison to the simplified model without superficial fine structures.