Physics
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992pepi...75...25b&link_type=abstract
Physics of the Earth and Planetary Interiors, Volume 75, Issue 1-3, p. 25-38.
Physics
1
Scientific paper
The `master event relocation' and `hypocentroid' techniques are compared in an effort to determine their relative performance in evaluating the location of epicenters in a region hampered with recording station location bias and a poorly understood seismic velocity structure. The study areas chosen are the Explorer and Gorda plates, two small lithospheric subplates of the oceanic Juan de Fuca plate, which show a high degree of apparent intraplate seismicity. Previous studies have indicated systematic eastward errors in the location of epicenters due to the lack of recording stations to the west.
Both techniques produce similar results in defining plate boundary vs. intraplate seismicity; however, noteworthy differences exist. The selection of a well-constrained master event has a clear effect on the alignment of relocated epicenters with plate boundaries. An event on the Gorda plate located by ocean bottom seismometer allows for a relocation of epicenters about the Gorda Rise. Using a more widely recorded master event on the Explorer plate produces parallelism of the events with the plate boundaries but an additional uniform shift in the relocated epicenters is required to align seismicity with the boundaries.
Location of the master event, with respect to tectonic features of the plate, appears to affect the results, probably owing to differences in lithospheric conditions and their effect on wave travel paths through the plate. A comparison of results of the two techniques on intraplate seismicity on the Gorda plate shows opposing direction vectors for the relocations.
The hypocentroid technique is less affected by changing conditions within the plate as events are clustered according to location. The relocations are still affected by the station location bias, as the events are relocated in relation to the weighted center of the event cluster. The technique produces greater definition of the trends of the relocated epicenters; however, in this situation an additional shift of the epicenters is required for alignment with the boundaries.
Bebel D. J.
Stoddard Paul R.
Woods Mark T.
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