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
URL: http://www.geophys.washington.edu/SEIS/PNSN/
Key words: Seismology, Education-lay, Real-time earthquake information

Oct. 1, 1997 - Sept. 30, 1998

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, 1997 and Sept. 30, 1998 the PNSN analyzed 7,148 events. Of these, 6,258 were earthquakes or blasts within the network (1,906 of which were too small to locate). Within the network area, 3,831 earthquakes were located west of 120.5 degrees west longitude (including 2,621 in the general vicinity of Mount St. Helens, which has not had a magmatic eruption since 1986), and 232 east of 120.5 degrees west longitude. The remaining events were blasts within the network, regional earthquakes (301) or teleseisms (589).

Between Oct. 1, 1997 and Sept. 30, 1998, nine earthquakes were reported felt in Washington west of the Cascades, ranging in magnitude from 1.8 to 3.2. Four earthquakes (magnitudes 2.4 - 4.0) were reported felt east of the Cascades, and no earthquakes were reported felt in Oregon.

Network Operations

The Pacific Northwest Seismograph Network ( PNSN) operates 105 short-period, broad-band, or strong-motion seismometer stations west of 120 degrees west longitude under this agreement, and 43 additional stations under other support. Some stations include up to 6 components. In addition, the PNSN records and assists with the maintenance of 7 short-period or strong-motion stations operated by the USGS. The USGS also operates three USNSN stations in Washington and Oregon.

A PNSN seismologist is always on duty, and our standard procedure is to respond to pager messages 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 from the UW police. The automatic detection procedure 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 that includes an updated, 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 Emergency Operations Center. At the same time that pager messages 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 Program: Since 1996, the PNSN has installed eleven digital strong-motion instruments in the Puget Sound urban area. Continuous data from these stations are sent to the PNSN via Internet or lease-line modem, but the instruments also have a trigger set to record stronger events on-site. If continuous data transmission fails, the data will still be available via dial-up retrieval or site visit. Three additional dial-up stations are operated by the USGS in the Portland area.

  • Data Availability:All triggered network trace-data in raw unedited format, plus continuous telemetry from station TTW (3 component broad-band), and broadband data for each event, 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 archive the edited trace-data at the University 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.

  • Mt. St. Helens Seismicity: The most notable seismicity in the PNSN area was the increased number of very small earthquakes beneath the cone of Mt. St. Helens. Only 7 earthquakes of magnitude 2.0 or larger were located in the area, but the monthly number of well located (quality BB or better) earthquakes immediately beneath the cone of Mt. St. Helens (Latitude 46.23 - 46.17N, Longitude: 122.14 - 122.23W) rose from about 60 quakes/month during the `97-`98 winter to 168 events in May, 319 in June, and 445 in July. After mid-July the number of earthquakes declined; to 123 events in August, 145 in September, and 97 in October. All of the seismicity was located below the mountain at depths of more than 2 km.

    The May-July episode of seismicity was the most intense at Mt. St. Helens since 1986, when a dome-building eruption occurred, and likely reflected an episode of replenishment of the magma reservoir, located about 7 kilometers below the crater. However, the seismic energy was very low compared to eruptive periods. The low energy level indicated by the very small magnitudes of the earthquakes, and the lack of seismicity at depths shallower than 2 km, suggested that an eruption would be unlikely unless the activity became considerably more vigorous and moved to shallower depths.

    Three Information Statements describing the activity at Mt. St. Helens were issued in cooperation with the USGS Cascades Volcano Observatory; on June 2, July 1, and August 14. These are available on the PNSN web page for Mt. St Helens:

    http://www.geop hys.washington.edu/SEIS/PNSN/HELENS/

    The PNSN also provides frequently updated web pages on seismic activity at Mt. Rainier:

    http://www.geophys.washington.edu/SEIS/PNSN/RAINIER/

  • Offshore Earthquakes and Axial Seamount Eruption: Although the PNSN has no sensors offshore, it recorded several large earthquakes associated with underwater volcanic activity on the Juan de Fuca ridge, offshore of Washington. Beginning at 1200 GMT on 25 January 1998, the National Oceanographic and Atmospheric Administration (NOAA), using the U.S. Navy's SOund SUrveillance System (SOSUS); detected intense seismicity on the summit and southern flank of Axial Seamount on the central Juan de Fuca Ridge near 45.9 degrees north latitude and 130 degrees west longitude; approximately 300 miles west of Cannon Beach, Oregon. Over 8,000 earthquakes were recorded by SOSUS, including 3 of magnitude 4.5 or larger which were also recorded by the PNSN. Seismic activity dropped to background levels by early February. See the NOAA web page for more details:
    http://www.pmel.noaa.gov/vents/oceanseis.html 

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		TABLE 1-- FELT EARTHQUAKES 10/1/97-9/30/98
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
____________________________________________________________________________________________

97/10/14 18:20:49  47.58N    122.60W   6.5 2.3  A    3.8 km  NE of Bremerton, WA
97/10/19 23:06:19  47.76N    121.85W   5.4 3.1  B    9.5 km ENE of Duvall, WA
97/11/18 01:53:06  46.13N    120.46W  15.6 3.9  B   50.4 km   S of Yakima, Wa
97/11/26 00:05:34  47.78N    123.06W  46.6 3.7  B   32.7 km WNW of Poulsbo, WA
97/12/23 20:22:45  47.21N    123.88W   0.0 1.7  D   27.8 km NNW of Aberdeen, WA
98/01/22 23:37:03  47.18N    121.93W  16.5 2.0  B    3.1 km ESE of Enumclaw, WA
98/02/12 00:15:39  47.66N    122.48W  29.8 3.0  B   13.1 km ESE of Poulsbo, WA
98/02/15 15:14:53  46.85N    121.96W   9.3 3.2  A   16.2 km   W of Mount Rainier
98/03/03 04:19:02  49.15N    118.35W   0.6 4.0  D   76.4 km NNW of Colville, WA
98/04/27 07:00:16  48.73N    123.16W  57.8 3.0  C   26.1 km NNW of Friday Harbor, WA
98/06/24 15:53:17  47.75N    121.88W   4.0 2.5  A    7.9 km ENE of Duvall, WA
98/06/28 07:35:33  46.50N    116.90W  31.4 3.8  C   32.3 km  SE of Pullman, WA
98/06/29 01:36:42  47.56N    120.81W   8.4 2.4  C   41.9 km WNW of Wenatchee, Wa
    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 1998. 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, S.D., Of cathedrals, bazaars, and worms, 1998, Seismological Research Letters V69, N5, 407-409.

    Malone, S.D., and A.I. Qamar, Stress Conditions in the United States Pacific Northwest: Focal Mechanisms, Tectonics, and Geodesy, Jan. 1998 (invited), Earthquake Fault Plane Solutions: Databases, derived parameters, Geodynamic Inferences, Proceedings , Taormina-Messina, Italy, Editors: G. Neri and C. Eva

    Qamar A.I., S.D. Malone, and R.S. Ludwin, 1997, Rapid Earthquake notification in the Pacific Northwest, Washington Geology V25, N4 33-36, 1997

    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, 1998, Quarterly Network Reports; 97-D, 98-A,98-B, and 98-C; Seismicity of Washington and Oregon

  • Abstracts

    Oppenheimer, D., A. Bittenbinder, B. Bogaert, L. Dietz, W. Ellsworth, E. Jensen, W. Kohler, J. Van Shaack, R. Buland, H. Benz, R. Hansen, C. Weaver, S. Malone, and P. Okubo, 1997 CREST: Consolidated Reporting of EarthquakeS and Tsunamis, EOS V. 78, No. 46, p. F46.

    Malone, S., and S.C. Moran, Deep long-period earthquakes in the Washington Cascades, 1997, EOS, V. 78, No. 46, p. F438.

    Gee, L., S. Malone, D. Neuhauser, D. Oppenheimer, and R. Buland, 1998, The CNSS Composite Catalog. Seis. Res. Let. V69, n2, 166.

    Malone, S.D., The Council of the National Seismic System - The first five years, 1998, Seis. Res. Let. V69, n2, 164.

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