15 Fakultätsübergreifend / Sonstige Einrichtung

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Author: search.filters.author.Schulte-Theis, HartwigSubject: search.filters.subject.550

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    Master-event correlation of weak local earthquakes by dynamic waveform matching
    (1993) Joswig, Manfred; Schulte-Theis, Hartwig
    Dynamic waveform matching (DWM) performs a non-linear correlation between two seismograms that are similar in shape but may be squeezed or stretched relative to each other. It extends the application of master-event comparisons to seismograms of greater spatial distance and retains the high-timing resolution of correlation techniques that act on the original time series. The DWM approach is applied to data recorded by a small array being part of the BOCHUM UNIVERSITY GERMANY (BUG) network which monitors the mining-induced seismicity in the Ruhr basin of NW Germany. The observed epicentres occur in clusters and therefore display only a limited number of seismogram waveform types. In one application an automatized cluster association with DWM obtains a resolution of about 100 metres at an epicentral distance of 200 to 40 km, using 10-20 defined master events for each region. These results are confirmed both by seismograms from a near-site station for mining-induced events from the Hamm region and by blast reports for a quarry region near Wuppertal. In another application of DWM, array traces from the BUG array are correlated to yield azimuth and slowness for epicentre location. as for the master event application, this approach is tuned for high performance on weak local events using a priori information about the approximate epicentral region. The implemented processes are shown to be capable of locating events with a rate of success equal to the performance of an experienced seismologist when processing all seismogrmas of four years BUG registration.
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    Clustering and location of mining induced seismicity in the Ruhr Basin by automated master event comparison based on dynamic waveform matching (DWM)
    (1993) Schulte-Theis, Hartwig; Joswig, Manfred
    Most of the local seismicity in the Ruhr Basin can be separated into characteristic clusters of similar, mining induced earthquakes. Each cluster can be represented by a strong master event. Therefore, it is possible to associate weak events to the corresponding clusters by master event comparison. The seismic signal matching is performed by a nonlinear correlation termed DWM for the entire seismogram length. DWM permits stretchings and shortenings between the two signals and overcomes the ambiguities in phase correlation by a consistent matching path. The automatic cluster association searches for the best DWM-correlation between the actual event and all master events of the appropriate epicenter region. Knowing the P- and S-onsets of the master event, they can be transposed to the actual event by the correlation path with one sample accuracy. The method has been applied to all BUG small array recordings 1987–1990 of local events from the Hamm-region to investigate spatial and temporal clustering. Within the clusters, a high percentage of weak events could be located relative to its master event. The temporal clustering resolved seismic activities that typically last a few months per cluster, but single aftershocks occur in the following years.