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

This Article Figures Only Full Text Full Text (PDF) Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Tusa, G. Articles by Musumeci, C. Search for Related Content GeoRef GeoRef Citation

Attenuation of Short-Period P Waves at Mount St. Helens

Dipartimento di Scienze Geologiche
Università di Catania
Corso Italia 55, 95129 Catania, Italy
gtusa{at}unict.it, gresta{at}unict.it
(G.T, S.G.)
Department of Earth and Space Sciences
Box 351310
University of Washington
Seattle, Washington 98195
steve{at}geophys.washington.edu
(S.D.M.)
Istituto Nazionale di Geofisica e Vulcanologia
Sezione di Catania
Piazza Roma 2, 95123 Catania, Italy
giampiccolo{at}ct.ingv.it, musumeci{at}ct.ingv.it
(E.G., C.M.)

Manuscript received 26 February 2003.

An increase of seismicity occurred at Mount St. Helens between May and July 1998, with more than 900 events (M_d <2.2) recorded by the Pacific Northwest Seismograph Network. This article describes an attempt to estimate the temporal and spatial variation in seismic attenuation using 200 microearthquakes that occurred before (January 1995-April 1998), during, and after (August-December 1998) the period of higher seismicity and recorded on three different one-component seismic stations. Epicentral distances of the studied events ranged between 0.5 and 15 km. We performed the analysis distinguishing the deep (depth > 5.5 km) from shallow (depth < 5.5 km) events. We used the frequency decay method to estimate the quality factor Q and station site correction S for P waves in the frequency bands 2-7 and 18-30 Hz. The results show that the attenuation varies from site to site systematically and decreases with depth. Lower Q_p values are obtained for focal depths less than 5.5 km. Moreover, the spatial variations of Q_p show minimum values (30) in the crater area that are interpreted as due to a low-density mass distribution under the crater. We find that Q_p was 30% higher before the period of high seismicity than after. This change may be attributed to an increase of pressure in the magma chamber producing new cracks and/or reopening of pre-existing cracks, which are the most viable mechanisms for increasing attenuation.

This article has been cited by other articles:

				E. Giampiccolo, S. D'Amico, D. Patane, and S. Gresta Attenuation and Source Parameters of Shallow Microearthquakes at Mt. Etna Volcano, Italy Bulletin of the Seismological Society of America, February 1, 2007; 97(1B): 184 - 197. [Abstract] [Full Text] [PDF]