The objective of our paper is to develop a workflow that allows us to calculate more
accurate hypocenter locations in seismic event clusters of aftershock sequences or
artificial events. Due to the increased sensitivity of the seismological instruments
and density of the network, we are able to record small natural and artificial events.
The discrimination of these events is necessary to investigate the recent tectonic
movements in the Pannonian Basin. As a first step, we performed a hierarchical cluster
analysis on the events in the Hungarian National Seismological Bulletin using the
spatial distances between the events to obtain event clusters. We selected 5 different
test clusters from the list of clusters where two clusters consist of quarry blasts,
another two consist of earthquakes, and the last one is a mixture of earthquakes and
anthropogenic events. In the second step, to prepare for the double-difference multiple
event location analysis, we manually revised the arrival time picks in the Hungarian
National Seismological Bulletin in order to increase the consistency and accuracy
of the arrival times. We obtained improved single-event locations with the iLoc algorithm
using the RSTT 3D global velocity model to provide initial locations for the double-difference
relocation. We applied waveform cross-correlation at every station to obtain the differential
times and correlation matrices. In order to discriminate the events in the mixed event
cluster, we repeated the hierarchical cluster analysis, but this time, we used the
correlation matrix as a distance metric. Examining the shape of the resulting dendrogram,
it is clear that certain subclusters are well separated. In these subclusters, the
coordinates of the events are close to the mines, where explosive quarrying takes
place. With this technique, we are able to identify explosions that were listed as
earthquakes in the catalogue.
