Abstrakt
The source scanning method allows for not only the automated determination of the earthquake locations but also the study of the earthquake source processes. It is based on shifting seismograms back in time by the travel times and capitalizes on summing them over the seismic stations.
In this way, it produces a brightness field. Using the results from synthetic seismogram tests, we show that the vector from the hypocenter to the brightspot equals a vector of the unilateral earthquake rupture propagation.
We apply source scanning to study rupturing of 12 natural West Bohemian (the Czech Republic, Central Europe) earthquakes in a magnitude range from 1.6 to 3.7 recorded by the WEBNET (up to 23 stations at epicentral distances of up to approximately 25 km). The travel times were calculated by the ray method and adjusted by adding the location arrival-time residuals.
The normalized envelopes of the vertical component of the direct P wave velocity seismograms were used for source scanning. We estimated the rupture direction and identified which nodal plane was the fault plane from the brightness field for each of the earthquakes.
The reliable outcomes of the rupture direction estimation had the rupture azimuth to be towards the north and the southeast. Upward rupturing was found for 11 earthquakes, whereas downward rupturing occurred in only 1 earthquake.
The method is useful as an auxiliary method for fault plane identification.