Effect of earth structure and source time function on inversion of single-station regional surface waves for rupture mechanism and focal depth

Özcan Çakir and Murat Erduran

Department of Geophysics, Black Sea Technical University, 61080, Trabzon, Turkey

(Received 6 April 2000; accepted 15 January 2001)

Abstract: A single-station inversion using regional surface waves is tested to determine the rupture mechanism and the focal depth of an earthquake in a more like statistical manner throughout both synthetic seismograms and the actual records. The method works efficiently if the underground velocity structure and the source time function are chosen reasonably correctly. The Love-wave observed group velocities, which are affected least by the source phase shift, might be effectively used to predict the velocity structure. The minimum wave-period of surface waves used in the inversion is an important factor that significantly affects the stability of the method. It should be chosen slightly greater than the minimum of the observed Love-wave periods. The selected source time function should not have significant amount of time shift (e.g. 2 s) relative to the actual one. Otherwise, the method easily breaks down. An impulse or a simple triangular pulse properly located in time generally suffices. Synthetic seismogram modeling at the end of the inversion process should be used to check the validity of the model parameters. There is a trade-off between small and large wave-periods. Large periods guarantee stability in the solution while the small ones are necessary to increase the precision. The user of the method should be careful in handling this delicacy between stability and precision.

Key words: Surface Waves, Rupture Mechanism, Focal Depth, Source Time Function, Single-Station Inversion.