Pacific Northwest Seismograph Network Operations
1434-95-A-1302
S.D. Malone, R.S. Crosson, and A.I. Qamar, P.I.s
Dept. of Earth and Space Sciences, University of Washington
Seattle, WA 98195
Phone:(206)543-8020 FAX:(206)543-0489
e-mail: steve, bob, tony, or ruth@geophys.washington.edu
Key words: Seismology, Education-lay, Real-time earthquake information

Oct. 1, 1996 - Sept. 30, 1997

Non-technical Summary

The Pacific Northwest Seismograph Network ( PNSN) operates seismograph stations in Washington and Oregon, and collects and analyzes earthquake data. Between Oct. 1, 1996 and Sept. 30, 1997 the PNSN analyzed 3,798 events Of these, 3,074 were earthquakes or blasts within the network (1,025 of which were too small to locate). Within the network area, 1,588 earthquakes were located west of 120.5 degrees west longitude (including 511 near Mount St. Helens, which has not erupted since 1986), and 189 east of 120.5 degrees west longitude. The remaining events were blasts within the network, regional earthquakes (224) or teleseisms (500). Twenty-three earthquakes were reported felt in Washington west of the Cascades, ranging in magnitude from 0.8 to 4.9. Five earthquakes (magnitudes 2.6 - 4.6) were reported felt east of the Cascades, and four earthquakes were reported felt in Oregon.

Network Operations

The Pacific Northwest Seismograph Network ( PNSN) operates 85 short-period or broad-band seismometer stations west of 120 degrees west longitude under this agreement, and 51 additional stations under other support. Some stations are 3-component.

A PNSN seismologist is always on duty, and our standard procedure is to respond to beeper pages from our automatic earthquake detection process (initiated for any earthquake within our network of magnitude 2.9 or larger), or from Washington or Oregon emergency management agencies, or the UW police. Automatic detection generates PRELIMINARY faxes and electronic mail to emergency managers and other high-priority information users for earthquakes that it judges M>=2.9. We follow-up with phone calls, faxes, and e-mail with the manually analyzed solution. In addition to ordinary phone lines, we have a radio link to the Washington State Dept. of Emergency Services, and an independent direct phone link to the City of Seattle EOC. At the same time that beeper pages and faxes are sent, an automatic process creates a Web-site for the event (see http://www.geophys.washington.edu/SEIS/EQ_Special/lasteq.html ) Frequent automated updates of information are posted to Web-pages each time the analyst finalizes locations and magnitudes.

  • The PNSN Strong Motion Progam: In May, 1996 the US Geological Survey (USGS) funded the Pacific Northwest Seismograph Network (PNSN) to begin a pilot project of modern strong-motion instrumentation in the Puget Sound urban area. Three sites were funded under this agreement, and funds for three additional stations were provided by the USGS under special contract 1434-HQ-96-GR-02714.

  • Data Availability:All triggered network trace data in raw unedited format, plus continuous telemetry from station TTW (3 component broad-band), and other non-continuous event-by-event broadband data, are backed up on a network archive tape. Edited event trace data are archived on large disks, and kept on 2.1 GByte exabyte tape. We also archive the edited trace data on high-speed, high-capacity (20 GByte) digital linear tape (DLT) cartridges and at the IRIS Data Management Center (DMC) in SEED format, where they can be retrieved by any investigator via the standard IRIS data request mechanisms.

  • Education and Outreach: Staff from the PNSN provide an educational outreach program to better inform the public, policy makers, and emergency managers about seismicity and natural hazards. In addition to information sheets, lab tours, workshops, and media interviews, we have an audio library with several tapes, including a frequently updated message on current seismic activity. Similar, more comprehensive, information is available via Internet on the World-Wide-Web (WWW): http://www.geophys.washington.edu/SEIS/

    Seismicity

    Figure 2 shows earthquakes of magnitude 2.0 or larger located in Washington and Oregon during this reporting period. Table 1 gives the locations, depths and magnitudes of earthquakes reported felt.

    Three geographically separated magnitude 4.5+ earthquakes occurred within a 24 hour period on June 23 and 24. The first, and largest, earthquake occurred within the Puget basin near Bremerton. The second earthquake was east of the Cascade crest near Okanogan, and the third was located in British Columbia's Georgia Strait between Vancouver Island and the mainland.

  • The Bremerton earthquake, June 23 19:13 UTC, M 4.9 The magnitude 4.9 Bremerton earthquake occurred at a depth of about 8 km on June 23, 1997 at 19:13 UTC (12:13 PM PDT). The epicenter was approximately 5.7 km east-northeast of Bremerton, Washington. The earthquake, and several aftershocks, were widely felt throughout the greater Seattle area. A total of 80 events, including the mainshock, were located within a rectangular area 10 km square centered on the mainshock location, including two felt earthquakes about 3 minutes apart on July 11 (UTC). (see Table 1). After the end of July, aftershock activity diminished considerably.

  • The Okanogan earthquake, June 24 14:23 UTC, M 4.6 A magnitude 4.6 earthquake centered between Okanogan and Twisp, Washington, occurred at 14:23 UTC (7:23 AM PDT) on June 24, 1997 (Figure 11). It had a depth of about 11 km, and was widely felt in north-eastern Washington. A moderate aftershock (M 3.6), also felt, occurred 12 minutes after the mainshock. Nine more aftershocks, none larger than magnitude 2.7, were recorded and located.

  • The Georgia Strait earthquake, June 24 14:41 UTC, M 4.6 The second magnitude 4.6 earthquake on June 24 occurred beneath the Strait of Georgia at 14:41 UTC (7:41 AM PDT). Although out of the area normally covered by this report, this event was felt in northwestern Washington. A foreshock, magnitude 3.1, was felt on June 13. One aftershock, magnitude 1.5, was located nearby. 

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		TABLE 1-- FELT EARTHQUAKES 10/1/96-9/30/97
DATE-TIME is in Universal Time (UTC) which is PST + 8 hours.
Magnitudes are reported as local magnitude (Ml).
QUAL is location quality A-good, D-poor
____________________________________________________________________________________________
DATE-(UTC)-TIME      LAT(N)  LON(W)   DEP  MAG  QUAL  COMMENTS
yy/mm/dd hh:mm:ss    deg.      deg.   km   Ml
96/10/27 07:53:28    47.75N  121.85W  5.4  2.6  B    9.5 km E of Duvall
96/11/13 06:12:00    47.75N  121.85W  5.0  2.3  B    9.6 km E of Duvall
97/01/19 18:03:48    45.03N  122.61W 16.0  2.4  C    22.0 km ESE of Woodburn, OR
97/02/01 10:10:56    46.63N  121.66W  0.0  0.8  A    21.9 km NW of Goat Rocks
97/02/01 11:31:56    46.63N  121.65W  1.0  1.4  B    21.6 km NW of Goat Rocks
97/02/06 22:17:18    47.55N  121.81W  3.3  2.3  B    5.2 km ESE of Fall City
97/02/10 04:26:58    47.55N  122.28W  6.8  3.5  B    5.3 km SSE of Seattle
97/03/22 06:05:34    45.18N  120.06W  0.8  3.9  C    79.7 km E of Maupin, OR
97/03/26 03:10:36    45.98N  118.35W  4.7  2.6  B    9.7 km S of Walla Walla
97/05/03 23:49:44    48.48N  121.70W  0.0  3.1  C    6.3 km SSE of Concrete
97/05/18 08:28:08    48.66N  122.35W 12.7  3.2  C    14.2 km SE of Bellingham
97/05/22 10:35:21    44.05N  122.51W  6.8  2.3  C    45.6 km E of Eugene, OR
97/05/22 13:57:10    44.05N  122.51W  8.1  2.6  C    45.4 km E of Eugene, OR
97/06/13 13:44:37    49.23N  123.56W 25.7  3.1  C    40.0 km WNW of Vancouver, BC
97/06/14 20:18:07    48.11N  121.58W 12.0  2.6  C    14.6 km S of Darrington
97/06/23 19:13:27    47.58N  122.56W  7.7  4.9  B    5.6 km NE of Bremerton
97/06/23 19:30:09    47.60N  122.55W  1.2  2.6  B    6.9 km NE of Bremerton
97/06/23 21:46:24    47.60N  122.55W  0.9  3.1  B    6.9 km NE of Bremerton
97/06/24 14:23:13    48.35N  119.88W 11.2  4.6  B    23.0 km W of Okanogan
97/06/24 14:36:02    48.36N  119.86W  8.3  3.6  C    22.5 km W of Okanogan
97/06/24 14:40:58    49.25N  123.61W 15.7  4.6  B    44.1 km WNW of Vancouver, BC
97/06/24 20:40:10    47.58N  122.55W  1.1  2.6  B    6.9 km ENE of Bremerton
97/06/26 07:11:04    47.60N  122.55W  0.3  1.2  A    7.0 km NE of Bremerton
97/06/27 05:30:49    47.60N  122.58W  1.5  3.1  C    5.4 km NE of Bremerton
97/06/27 10:47:49    47.58N  122.55W  0.9  3.9  D    6.9 km ENE of Bremerton
97/07/03 22:54:43    47.75N  121.80W  0.0  1.7  A    13.9 km E of Duvall
97/07/04 10:45:38    47.70N  120.03W  8.6  3.7  C    14.1 km S of Chelan
97/07/11 01:26:01    47.58N  122.53W  1.0  2.2  B    7.2 km ENE of Bremerton
97/07/11 01:28:55    47.58N  122.53W  6.1  3.5  B    7.0 km ENE of Bremerton
97/08/01 12:55:03    47.30N  123.73W  0.0  3.4  C    36.5 km N of Aberdeen
97/09/03 17:17:26    47.68N  120.26W  0.6  3.3  C    4.9 km NW of Entiat
97/09/24 06:10:22    48.60N  123.08W 10.0  3.4  C    10.9 km NW of Friday Harbor, San Juan Is.
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    Publications

  • Reports and Articles

    Quarterly bulletins from the PNSN provide operational details and descriptions of seismic activity in Washington and Oregon. These are available from 1984 through the third quarter of 1997. PNSN Quarterly Reports since 1994 have included moment-tensor focal mechanisms for earthquakes larger than magnitude 3.5 provided by Dr. John Nabelek of Oregon State University (OSU) under support from USGS NEHRP Grant 1434-93-G-2326. Final published catalogs are available from 1970, when the network began operation, though 1989. A 1990-1994 catalog is in preparation.

    Ludwin, R.S., A.I. Qamar, S.D. Malone, R.S. Crosson, S. Moran, G,C. Thomas, and W.P. Steele (in preparation), Earthquake Hypocenters in Washington and Oregon, 1990-1994, Washington State Dept. of Natural Resources Information Circular

    Malone, Steve, 1997,"Near" Realtime Seismology Seismological Research Letters V67, N6, 52-54.

    Malone, Steve, 1997, The Electronic Seismologist goes to FISSURES, Seismological Research Letters V68, N4, 489-492.

    Thomas, G.C. and R.S. Crosson, (in preparation) The 3 May 1996 M5.4 Duvall, Washington Earthquake: Structure and Tectonic Implications, to be submitted to BSSA

    Univ. of Wash. Dept. of Earth and Space Sciences, 1997, Quarterly Network Reports; 96-D, 97-A,97-B, and 97-C; Seismicity of Washington and Oregon

  • Abstracts

    Crosson, R.S., 1996, Seismic root structure of the Cascade Volcanic Arc of Washington: evidence for deep crustal magmatism, EOS, V. 77, No. 46, p. F514.

    Malone, Steve and Anthony Qamar, 1997, Stress Conditions in the United States Pacific Northwest: Focal Mechanisms, Tectonics, and Geodesy, Geophysical Meeting on earthquakes fault-plane solutions, databases, derived parameters, and geodynamic inferences, Taormina-Messina, Italy, Feb. 1997. (invited)

    Thomas, G.C., R.S. Crosson, B. Cohee, T. Qamar, and P. Lombard, 1996, The May 2, 1996, Duvall, Washington earthquake and aftershock sequence, EOS, V. 77, No. 46, p. F523.

    Symons, N.P. and R.S. Crosson, 1996, P-wave Tomography in the Puget Sound Region, Washington: preliminary results, EOS, V. 77, N. 46, p. F466

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