| The Vienna Basin in Eastern Austria is a region of low to moderate
seismicity, and hence the seismological network coverage is relatively
sparse. Nevertheless, the area is one of the most densely populated and most
developed areas in Austria, so accurate earthquake location, including depth
estimation and relation to faults is not only important for understanding
tectonic processes, but also for estimating seismic hazard. Particularly
depth estimation needs a dense seismic network around the anticipated
epicenter. If the station coverage is not sufficient, the depth can only be
estimated roughly. Regional Depth Phases (RDP) like sPg, sPmP and sPn have
been already used successfully for calculating depth even if only observable
from one station. However, especially in regions with sedimentary basins
these phases prove difficult or impossible to recover from the seismic
records.
For this study we use seismic array data from GERES. It is 220 km to the
North West of the Vienna Basin, which – according to literature – is a
suitable distance to recover PmP and sPmP phases. We use array processing on
recent earthquake data from the Vienna Basin with local magnitudes from 2.1
to 4.2 to reduce the SNR and to search for RDP. At the same time, we do
similar processing on synthetic data specially modeled for this application.
We compare real and synthetic results to assess which phases can be
identified and to what extent depth estimation can be improved. Additionally,
we calculate a map of lateral propagation behavior of RDP for a typical
strike-slip earthquake in our region of interest up to 400 km distance.
For our study case RDP propagation is strongly azimuthally dependent. Also,
distance ranges differ from literature sources. Comparing with synthetic
seismograms we identify PmP and PbP phases with array processing as strongest
arrivals. Although the associated depth phases cannot be identified at this
distance and azimuth, identification of the PbP phases limits possible depth
to less than 20 km. Polarization analysis adds information on the first
arriving Pn wave for local magnitudes above 2.5. |