HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) References Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Husebye, E. S. Articles by Dainty, A. M. Search for Related Content GeoRef GeoRef Citation

Robust and reliable epicenter determinations: Envelope processing of local network data

Institute of Solid Earth Physics University of Bergen, Allégt. 41, N-5007 Bergen, Norway
Earth Science Division Phillips Laboratory, 29 Randolph Rd., Hanscom AFB, Massachusetts 01731-3010

Abstract

Local event recordings are complex in the sense that relevant P and S phases vary in an unpredictable manner even between closely spaced stations; thus, manual analysis of such records is still commonplace. Our approach to solving this long-standing problem of observational seismology is to bandpass filter (3 to 6 Hz) to ensure good signal-to-noise ratio SNR and then form envelopes to ensure simple signals across a seismograph network. The physical basis is that Pg and Lg are crustal wave-guide phases reflecting P- and S-energy propagation. Extensive tests on envelope analysis of local records from different areas found that arrival times of the maxima of Pg and Lg envelopes increase very consistently with distance even in different tectonic regimes, typical velocities being 6.1 and 3.5 km/sec, respectively. These arrival-time parameters are easy to extract in a semi-automatic manner and are highly suitable for local epicenter determinations. Extensive tests on locating mining explosions were conducted, and on average, the "envelope" location errors relative to "true" locations were similar to those in bulletins that are based on conventional phase pickings. Occasionally, the Pg/Pn envelope may be very weak but can be replaced by the easily pickable (non-envelope) Pn phase. Additional advantages with envelope locations are transportability (not overly sensitive to details of crustal structure), and that envelope amplitudes can be directly converted to ground motion and magnitudes. For modern stations, envelopes can be formed in situ with low sampling rates of 1 to 2 Hz, thus greatly reducing transmission costs.

Footnotes

^* Present address: Defense Special Weapons Agency, Special Programs Division, 6801 Telegraph Road, Alexandria, Virginia 22310-3398.