Abstract

This paper demonstrates the usefulness of a novel technique for analysis of single-site, three-component seismogram records for reliable epicenter determinations for even small seismic events at any distance. Parameters that may be extracted by this technique are P-phase identifications in terms of x2 probabilities and the associated slowness vectors. Using data from short-period and broadband seismometers installed in the new NORESS (Norway) array, single-site event locations are demonstrated: azimuth estimates are found directly from the slowness vector, while epicenter distance estimates are derived from differential arrival times between Pn, Pg, Sn, and Lg (Sg). Simultaneous inversion for crustal model and hypocenter data indicate a crustal thickness beneath NORESS of 33.5 km. If Sn and/or Lg are well-recorded, focal depth estimates are often accurate to within a few kilometers. Locating teleseisms is problematic, since secondary phases are not fully readily identifiable, and hence distance can be estimated only by conversion of the measured apparent phase velocity.

For distances out to approximately 1000 km, event location errors as compared to network solutions seldom exceed 50 km and are due mainly to errors in azimuth estimates. With Sn phases available, focal depth errors appear to be of the order of 4 km. For teleseismic P waves (short-period), location errors occasionally exceeded 7° and were due mainly to poor distance estimates. Using broadband records from relatively strong events, location errors were about 1°. Further refinements seem feasible by using seismicity information and/or recognition of stationarity in the P-wave decomposition pattern for events within the same region. At least in certain cases, such approaches reflect genuine location refinements as demonstrated.

First Page Preview

First page PDF preview
You do not currently have access to this article.