1999 Summary: A1302: Pacific Northwest Seismograph Network Operations

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, 1998 - Sept. 30, 1999

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, 1998 and Sept. 30, 1999 the PNSN analyzed 4,564 events. Of these, 3,807 were earthquakes or blasts within the network (1,470 of which were too small to locate). Within the network area, 1,870 earthquakes were located west of 120.5 degrees west longitude (including 861 in the general vicinity of Mount St. Helens, which has not had a magmatic eruption since 1986), and 218 east of 120.5 degrees west longitude. The remaining events were blasts within the network, regional earthquakes (270) or teleseisms (487).

Between Oct. 1, 1998 and Sept. 30, 1999, 20 earthquakes were reported felt in Washington west of the Cascades, ranging in magnitude from 1.7 to 5.1. No earthquakes were reported felt east of the Cascades, and seven earthquakes (magnitudes 2.5 to 3.2) were reported felt in Oregon.

Network Operations

The Pacific Northwest Seismograph Network (PNSN) operates 114 short-period, broad-band, or strong-motion seismometer stations west of 120 degrees west longitude under this agreement, and 37 additional stations under other support. Some stations include up to 6 components. In addition, the PNSN records and assists with the maintenance of several other stations operated by the USGS. The USGS also operates four USNSN stations in Washington and Oregon. This year a new short-period station was installed at the summit of Mt. Rainier,

Figure 1. Seismograph stations operated by or recorded at the PNSN at the end of September, 1999. Red triangles indicate the locations of short-period seismometers, while green asterisks represent the locations of three-component broad-band seismometer installations. Purple hour-glass symbols show the locations of strong-motion stations.

A PNSN seismologist is always available, 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. PRELIMINARY information for earthquakes of M>=2.9 is sent out automatically by the event detection process. Emergency managers and other high-priority information users receive very rapid notification through the RACE pager-PC system, faxes and e-mail. Simultaneously, an automatic Web-site is created for the event (see http://www.geophys.washington.edu/SEIS/EQ_Special/lasteq.html ).

FINAL details are provided as soon as the duty seismologist analyzes the earthquake information. Final locations and magnitudes for earthquakes of M>=2.9 are also disseminated through the NOAA weather-wire. For all earthquakes, updates of information are posted to Web-pages each time the analyst finalizes a group of locations and magnitudes. In addition to ordinary phone lines, the PNSN has 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.

The PNSN Strong Motion Program: Since 1996, the PNSN has installed sixteen 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. Highlights this year include the upgrade of two stations to meet CREST (Consolidated Reporting of EarthquakeS and Tsunamis) standards, and installation of an EARTHWORM data acquisition node 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/

Special Events:

The PNSN, along with UW Geological Sciences and the USGS co-sponsored an Urban Hazards Workshop to review the current status of a variety of geologic mapping and geophysical exploration projects which are providing detailed geologic-hazards information that can be used for land-use and code planning. The invitation-only meeting was attended by about 200 people from the scientific, government and business communities.
The PNSN hosted the 94th Annual Meeting of the Seismological Society of America, held May 3-5 at the Seattle Center. More than 375 seismologists attended. The meeting had a special focus on current and ongoing work on the Pacific Northwest, including results from the 1998 SHIPS experiment. A special Public Forum on PNW Earthquake Hazards was attended by more than 250 scientists and members of the public.
The PNSN organized natural hazards information fairs for two "Disaster Saturday" presentations (Sponsored by Seattle Project Impact). USGS and UW scientists working in the Puget Sound region presented their work on earthquake hazards to the public.
The second phase of the U.S. Geological Survey's (USGS) SHIPS (Seismic Hazards in Puget Sound) active seismic experiment took place from September 20-22. This phase consisted of about 40 explosions at 33 shot-points along a 100 km long east-west line running from the Cascade foothills to the Olympic Peninsula. Seismic waves were generated by explosions in boreholes. Waves reflected from underground layers were recorded by about 1,000 seismic recorders spaced at 100 meter intervals along the same line, and also by the permanent stations of the PNSN.

Seismicity

Between Oct. 1, 1998 and Sept. 30, 1999, 20 earthquakes were reported felt in Washington west of the Cascades, ranging in magnitude from 1.7 to 5.1. Seven earthquakes (magnitudes 2.5 to 3.2) were reported felt in Oregon. No earthquakes were reported felt east of the Cascades, Table 1 gives the locations, depths and magnitudes of earthquakes reported felt, and Figure 2 shows earthquakes of magnitude 2.0 or larger located in Washington and Oregon during this reporting period.

Figure 2. Earthquakes magnitude 2.0 or larger between Oct. 1, 1998 and Sept. 30, 1999. Locations of a few cities are shown as white-filled diamonds. Earthquakes are indicated by red circles or green squares; red circles represent earthquakes at depths shallower than 30 km, and green squares represent earthquakes at 30 km or deeper.

The Mc 5.1 Benioff Zone Earthquake of July 3 (UTC) 1999

The largest earthquake in Washington or Oregon during this reporting period was a coda magnitude 5.1 earthquake on July 3 UTC (July 2 6:43 PM PDT). It occurred at a depth of about 41 km, about 8 km north of Satsop, WA. Location details are provided in Table 1.

Magnitude estimates for this earthquake varied considerably. The coda magnitude scale used by the PNSN has not been well calibrated for large and deep earthquakes in the Pacific Northwest since they occur so infrequently. The National Earthquake Information Center (NEIC) has assigned this earthquake a magnitude of 5.5 based on the body-wave scale and the surface-wave scale. NEIC gives a moment magnitude of 5.9 for this event.

The hypocentral depth indicates that this event is a Benioff Zone earthquake, occurring in the subducted Juan de Fuca plate. The PNSN's P-wave first-motion focal mechanism for this event is consistent with the moment-tensor focal mechanism determined by Oregon State University, and indicates normal faulting with a nearly horizontal T axis. No aftershocks were recorded immediately following the event, but on July 9 there were 3 small earthquakes with similar hypocentral coordinates occurring at 05:13UT (Mag 1.5), 07:45UT (Mag 2.3), and 08:07UT (Mag 2.3 - reported felt). Another aftershock occurred on August 11 at 17:37 UT (Mag 1.7). Both the focal mechanism and lack of sizable aftershocks are typical of Benioff Zone earthquakes.

The July 3 UTC earthquake was felt throughout most of western Washington and northwest Oregon, and in parts of southwest British Columbia, Canada. The strongest shaking corresponded to a level of about VI on the Modified Mercalli Intensity scale. Structural damage included cracked chimneys and broken windows. The three-story Grays Harbor County Courthouse, built in 1910 and located in Montesano (epicentral distance of about 15 km), suffered extensive structural damage to its cupola. Interior walls were also cracked. The Montesano fire station, built around 1979, also suffered structural damage. In Aberdeen (29 km epicentral distance), some structural cracks of walls and beams were reported. In addition, power outages and water main breaks occurred. The wood-framed roof of a furniture store collapsed. An engineering firm, EQE, has provided a summary of damage information at:

http://www.eqe.com/revamp/wash/index.html

Figure 3. Figure 3 shows a contour map of peak accelerations. Some were recorded by on-line (11 stations; data available on internet within an hour) or dial-up (2 stations, data available within a day or so) PNSN stations. Data from eighteen other sites, operated by various groups, were not available until much later.

Ground motions from this earthquake were recorded by 31 strong motion stations, including 11 real-time stations operated by the PNSN. Peak accelerations on PNSN stations, and a list of their locations is available at:

http://www.geophys.washington.edu/SEIS/EQ_Special/WEBDIR_99070301435p/strong_motion.html
The maximum acceleration recorded was 8%g at Wynoochee dam (see Fig. 3). The estimated acceleration at the epicenter is 17%g. The strongest horizontal ground acceleration recorded by the PNSN real-time stations was about 2%g, at station TBPA in Tacoma, at 88 km epicentral distance. Station UPS, also in Tacoma, and at 77 km epicentral distance, recorded 0.5%g horizontal ground motions. RWW, the nearest PNSN station with an accelerometer, at 14 km epicentral distance, was in the process of being upgraded to a CREST station, and was not functioning at the time that the earthquake occurred.

____________________________________________________________________________________________
		TABLE 1-- FELT EARTHQUAKES 10/1/98-9/30/99
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
____________________________________________________________________________________________

98/10/10 07:55:12  48.90N   122.19W   0.1 1.7  CD  9.4 km   N of Deming, WA
98/11/03 22:40:48  47.52N   122.77W  23.4 3.1  BA 11.4 km WSW of Bremerton, WA
98/11/20 17:39:20  48.84N   122.18W   1.6 2.0  CC  3.3 km  NE of Deming, WA
99/01/04 15:10:37  47.20N   122.27W  22.2 3.2  CA 12.5 km ESE of Tacoma, WA
99/01/11 13:48:46  45.32N   121.65W   7.5 2.5  CB  6.5 km SSE of Mount Hood, OR
99/01/11 16:54:11  45.32N   121.65W   7.0 3.0  BB  6.6 km SSE of Mount Hood, OR
99/01/11 22:04:14  45.31N   121.65W   6.9 3.2  BB  7.0 km SSE of Mount Hood, OR
99/01/14 11:56:47  45.33N   121.66W   7.6 3.2  CB  5.4 km SSE of Mount Hood, OR
99/01/14 16:13:42  45.32N   121.66W   5.9 3.0  BB  6.2 km SSE of Mount Hood, OR
99/01/31 11:33:32  42.77N   124.68W  25.0 2.6  CD 76.4 km SSW of Coos Bay, OR
99/02/24 16:45:17  45.13N   122.66W  35.7 2.7  BB 14.6 km   S of Canby, OR
99/03/16 13:39:49  48.48N   121.80W   0.0 1.8  BD  7.3 km  SW of Concrete, WA
99/04/03 17:29:22  48.35N   123.24W  46.3 3.1  BA 11.4 km  SE of Victoria, BC
99/04/11 00:05:37  48.19N   122.75W  20.3 2.6  AB 39.5 km  SW of Mount Vernon, WA
99/04/17 07:31:09  46.86N   121.95W   9.8 3.6  BA 15.2 km   W of Mount Rainier
99/06/29 04:51:43  48.94N   123.05W  19.6 2.7  BD 20.6 km   S of Vancouver,BC
99/06/29 13:31:46  48.91N   123.05W  20.1 2.2  BD 23.4 km   S of Vancouver,BC
99/07/02 05:22:19  47.36N   122.39W  27.1 3.1  CA 14.9 km   N of Tacoma, WA
99/07/03 01:43:54  47.07N   123.46W  40.7 5.1  BA  8.0 km   N of Satsop, WA
99/07/09 07:45:42  47.06N   123.46W  39.8 2.1  BA  6.8 km   N of Satsop, WA
99/07/16 05:58:24  45.65N   122.77W  19.7 2.3  AA 17.7 km  NW of Portland, OR
99/07/16 05:59:59  45.65N   122.77W  18.9 2.3  BA 17.7 km  NW of Portland, OR
99/07/16 21:34:03  45.64N   122.76W  18.1 3.1  AA 17.2 km  NW of Portland, OR
99/08/25 17:48:43  47.75N   121.86W   7.4 2.0  CB  9.5 km ENE of Duvall, WA
99/09/03 07:16:18  47.50N   123.12W   0.0 2.9  BC 38.2 km   W of Bremerton, WA
99/09/05 18:01:36  47.16N   123.12W  46.5 2.8  BA 22.3 km  NW of Olympia, WA
99/09/20 11:16:54  47.60N   121.76W  16.9 2.8  BA 10.4 km ENE of Fall City, WA

Publications

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 1999. PNSN Quarterly Reports from 1994-1998 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 printed catalog is in preparation.

Reports and Articles

Giampiccolo E., C. Musumeci, S. Malone, S. Gresta, E. Privitera, 1999, Seismicity and stress tensor inversion in the Central Washington Cascade Mountains (USA), Bull. Seis. Soc. Am. V89 811-821.

Khazaradze, G., A. Qamar, and H. Dragert, Tectonic deformation in western Washington from continuous GPS measurements, Geophys. Res. Lett., 26 (20), 3153-3156, 1999.

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

Johnson, J.B., J.M. Lees, E.I. Gordeev, 1998, Degassing explosions at Karymsky Volcano, Kamchatka, Russia, Geophysical Research Letters, V. 25, N. 21, pp. 3999-4042.

Malone, Steve, 1999, Seismic Network Recording and Processing Systems -I, Seismological Research Letters V70, N2, 175-178.

Malone, Steve, 1999, Seismic Network Recording and Processing Systems (continued), Seismological Research Letters V70, N4, 432-434.

Malone, Steve, 1999, U.S. Seismic Networks: A time for change, Opinion editorial in Seismological Research Letters V70, N5, 475-477.

Malone, Steve, 1998, Of cathedrals, bazaars, and worms, Seismological Research Letters V69, N5, 407-409.

Moran, S.C., J.M. Lees and S.D. Malone, 1999, P-wave velocity structure in the greater Mount Rainier area from local earthquake tomography, Jour. Geophys. Res 104, 10,775-10,786.

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, 1999, Quarterly Network Reports; 98-D, 99-A,99-B, and 99-C; Seismicity of Washington and Oregon

Abstracts

Crosson, R.S., 1999, Review of Instrumentally observed seismicity with tectonic implications for the central Cascadia subduction zone, Seismological Research Letters, V. 70, N. 2., p. 209.

Jacob, Stephen, David Oppenheimer, Robert Simpson, Steve Malone, 1998 Rapid Earthquake Data Distribution System via the Internet, EOS, V. 79, N. 45, p. F570.

Johnson, J.B., J.M. Lees, M.R. Romero, Plugs and Chugs - Strombolian activity at Sangay, Ecuador, and Karymsky, Russia, 1998, EOS Transactions, V.79, N. 45.

Johnson, J.B., and J.M. Lees, 1999, Integration of seismic and infrasonic data: essential to the understanding of explosion source dynamics at volcanoes, Seismological Research Letters, V. 70, N. 2., p. 223.

Lees, J.M. and J.B. Johnson, 1999, Two Chugging Giants: Karymsky and Sangay, Seismological Research Letters, V. 70, N. 2., p. 223.

Malone, Steve, The Future of Regional Seismic Networks and the Council of the National Seismic System, 1998, IRIS Annual Workshop 1998 Program (extended abstract).

Musumeci, C, S.D. Malone, B. Giampiccolo, and S. Gresta, 1999, Evidence for an intermittent supply of magma at Mount St. Helens, Washington, Seismological Research Letters, V. 70, N. 2., p. 223.

Norris, R.D., C.S. Weaver, K.L. Meagher,A. Qamar, and R.J. Blakely, 1999, Earthquake swarms at Mount Hood: Relation to geologic structure, Seismological Research Letters, V. 70, N. 2., p. 218.

Symons, N.P, S.C. Morean, R.S. Crosson, K.C. Creager, and M.A. Fisher, 1999, Seismic tomography in the Pacific Northwest and its interpretation; relationship between crustal structure and the distribution of crustal seismicity, Seismological Research Letters, V. 70, N. 2., p. 210.

Weaver, C.S., Meagher, K.L., Qamar, A., Blakely, R.J., and Wells, R.E., 1999, The June 23, 1997 Bainbridge Island, Washington, Earthquake: evidence that the seattle fault is seismically active, Seismological Research Letters, V. 70, N. 2., p. 219.

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