Source parameters of the swarm earthquakes in West Bohemia/Vogtland

Abstract

The self-similarity of earthquake rupture scaling is a subject of ongoing debates. The output of multiple recent studies agrees on the fact that stress drops of earthquakes varies from 0.1 to 100 MPa over a broad range of seismic moments. We investigated the source parameters of 56 earthquakes in the magnitude range ML from 0.8 to 3.3 occurred during the 2000 and 2008 swarm in West Bohemia/Vogtland in order to learn if the source scaling of these, most-likely fluid triggered events, differ from the observations in other seismogenic regions around the world. We used two approaches to calculate the corner frequency in the frequency domain: inverting for the corner frequency fc of the displacement spectra and integrating of spectra by the method of Snoke. A single fc for all stations was determined with attenuation correction defined by inverting for an event-dependent Q-factor. Similar dependence of the corner frequency on seismic moment was observed in the form fc ∝ M0−0.2, which is a much weaker scaling than expected for a constant stress drop model. Accordingly, the stress drops vary from 1 to 130 MPa and appears to grow with seismic moment as Δσ ∝ M00.43. The non-self similarity of the swarm earthquakes is supported by rather wide span of apparent stress ranging between 0.3 kPa and 1.2 MPa.