2002 Summary: AG0011: Pacific Northwest Seismograph Network Operations

PACIFIC NORTHWEST SEISMOGRAPH NETWORK OPERATIONS
01HQAG0011
S.D. Malone, R.S. Crosson, and A.I. Qamar, P.I.s
Dept. of Earth and Space Sciences, University of Washington
Seattle, WA 98195-1310
Phone:(206)543-1190 FAX:(206)543-0489
e-mail: steve, bob, tony, or ruth@ess.washington.edu
URL: /SEIS/PNSN/
Key words: Seismology, Education-lay, Real-time earthquake information

Oct. 1, 2001 - Sept. 30, 2002

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, 2001 and Sept. 30, 2002 the PNSN analyzed 5,425 events. Of these, 4,531 were earthquakes or blasts within the network (1,859 of which were too small to locate). Within the network area, 2,030 tectonic earthquakes were located west of 120.5 degrees west longitude (including 623 in the general vicinity of Mount St. Helens, which has not had a magmatic eruption since 1986), and 204 east of 120.5 degrees west longitude. The remaining events were blasts within the network (487), regional earthquakes (292), teleseisms (602), low-frequency events (417 events, 12 locatable, probably icequakes, near the summit of Mt. Rainier), and surficial events (588 events, 4 locatable, mostly rockfalls near the summits of Mt. St. Helens and Mt Rainier).

Between Oct. 1, 2001 and Sept. 30, 2002, 24 earthquakes were reported felt in Washington west of the Cascades, ranging in magnitude from 1.6 to 4.1. Forty-four earthquakes (magnitudes -1.6 to 4.0; negative magnitudes are possible due to the logarithmic nature of the magnitude scale) were reported felt east of the Cascades. Most of these were part of a sporadic sequence of very shallow earthquakes (less than 2 km deep) located in downtown Spokane. Due to the shallow depth and the urban environment, many extremely small earthquakes were felt. The Spokane sequence began in May of 2001 and continued to be fairly vigorous through Dec. 2001. The largest event in the sequence, magnitude 4.0, occurred on Nov. 11, 2001. In 2002, only a half-dozen events were located in Spokane. Spokane is usually seismically quiet. No similar sequence is known.

In Oregon four earthqukes were reported felt, including the largest event during the reporting period, a magnitude 4.5 earthquake near Mt. Hood on June 29. Seismic activity near Mount Hood began to increase in May with several one- or two-day clusters of 10-15 events/day. Early June had a few smaller clusters with 5-7 events/day, and activity increased dramatically on June 29 following the magnitude 4.5 earthquake. Eighty-nine earthquakes were located in the Mt. Hood area on June 29 and 30, and activity continued into July, with the number of events/day diminishing as the month went on (91 located events in July), and continuing to diminish through August (44 located events). By September activity was at a background level (4 located events). The M 4.5 mainshock was located at about 6 km depth. About 76% of the aftershocks were in the 4-8 km depth range, and about 22% were shallower than 4 km.

Network Operations

The Pacific Northwest Seismograph Network (PNSN) operates 175 short-period, broad-band, or strong-motion seismic stations west of 120 degrees west longitude under this agreement, and 40 additional stations under other support. Some stations include up to 7 components. PNSN stations in southern and central Oregon are maintained by the University of Oregon under Cooperative Agreement 01HQAG0012. The PNSN exchanges real-time data with adjacent networks to improve our ability to locate earthquakes on the edge of our network. The PNSN records and assists with the maintenance of several short-period stations operated by the USGS, and receives real-time data from four US National Network (USNSN) stations in Washington and Oregon.

Figure 1a. Seismograph stations operated by or recorded at the PNSN at the end of September, 2002. Black crosses indicate the locations of short-period seismometers, Red triangles represent the locations of three-component broad-band seismometer installations, and white squares show the locations of strong-motion stations.

Figure 1b. Detail of Fig. 1a. Puget Sound Seismograph stations operated by or recorded at the PNSN at the end of September, 2002. Symbols as in Fig. 1a.

Figure 1c. Detail of Fig. 1a. Willamette Valley Seismograph stations operated by or recorded at the PNSN at the end of September, 2002. Symbols as in Fig. 1a.

A PNSN seismologist is always available on-call, 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 calls from Washington or Oregon emergency management agencies or 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, e-mail, and the national QDDS earthquake message system. Simultaneously, an automatic Web-site is created for the event (see /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 emergency weather notification system.

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 King County and City of Seattle Emergency Operations Centers and an independent direct phone link to the Washington State Dept. of Emergency Services.

The PNSN provides "Recent Earthquakes" web pages using the national "Quake Data Delivery System", "ShakeMap" pages (showing instrumental intensity, PGA, and PGV), and links to the USGS CIIM (Community Internet Intensity Maps) site, which collects, compiles, and interprets web-based felt reports from the public.

The PNSN Strong Motion Program: Since 1996, the PNSN has installed digital strong-motion instruments, mostly in the Puget Sound urban area. In summer 2002, 10 new instruments (including 3 sites in Oregon instrumented with equipment purchased by the Oregon Dept. of Geology and Mineral Industries, and one former USGS National Strong Motion Program (NSMP) site) were installed. One PNSN site was reconfigured to participate in the NSMP. There are now 51 ANSS instruments in the Pacific Northwest, and a total of 81 strong-motion real-time stations in our network. 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 the installation of three other new CREST stations bringing the total number of CREST stations to 16.

Data Availability: Continuous telemetry data streams from most broadband stations and a few selected short-period stations are recorded at the UW, and all broad-band and short-period data are provided to IRIS in near real-time on the IRIS BUD system. Complete unedited trace-data are saved for all network triggers. Edited event trace-data are archived at the UW on large disks, 2.1 GByte exabyte tape, and on high-speed, high-capacity (20 GByte) digital linear tape (DLT) cartridges. Edited event trace-data are also backed-up 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. Current seismic activity, and other information is available via Internet on the World-Wide-Web (WWW): /SEIS/PNSN

The installation of strong-motion instruments has encouraged the formation of research relationships with organizations who are interested in the data collected and the potential for useful data products. These organizations, in turn, provide the PNSN with station sites and/or telemetry. Cooperative efforts will contribute to more robust and diversified network telemetry, additional non-federally funded strong motion seismograph stations, and increased support for critical staff.

Special Events:

Feb. 28 was the first anniversary of the damaging Nisqually Earthquake, and PNSN staff provided background and contact information for in-depth TV and newspaper coverage. The U.W.'s Burke Museum chose the Nisqually anniversary date to open a long-planned earthquake exhibit The Big One, Earthquakes in the Pacific Northwest. PNSN staff contributed content, equipment, and expertise.
The PNSN website was remodeled following the USGS Earthquake Program website design. The new navigation system makes it easier to locate information, and also makes clearer the scope and depth of our offerings. New pages were added to improve usability.
Many presentations were given: to policy makers such as the Washington State Seismic Safety Committee, the Oregon Seismic Safety Policy Advisory Commission, and the Idaho Bureau of Disaster Services; to professional groups such as the Boeing Disaster Preparedness Conference, American Institute of Architects, Partners in Preparedness Conference; and to general audiences including at the Burke Museum (several lectures), the Forest Service Research Center (Olympia, WA), the Cascade Volcano Observatory (Vancouver, WA), at the Geological Survey of Canada (several presentations), the Northwest Geological Society (Seattle), Seattle Public Utilities, Cougar Rock Campground (Mt. Rainier), and to many, many other groups.
Ruth Ludwin provided presentations on the effects of Cascadia Subduction Zone earthquakes and their representation in Native American oral tradition to general audiences, including the Burke Museum (3 presentations), the Makah and Quileute Tribal councils, a FEMA-Sponsored Tribal Emergency Management Workshop (attended by representatives from 42 Washington and Oregon Tribes), and the national meeting of the Society for the Advancement of Chicanos and Native Americans in Science (Anaheim, CA). The Washington State/Local Tsunami Working Group is developing a K-6 video based on Native earthquake/tsunami traditions.
PNSN Staff participated in numerous meetings, workshops, and media events including a Army Corps of Engineers Cascadia Regional Response workshop, a TV broadcast on the Nisqually earthquake, a National Public Radio interview on the Spokane earthquake sequence, City of Seattle's Disaster Saturday, the "Business of Earthquakes" CREW conference, several USGS-Seattle Press Conferences, a video production for the Travel Channel, a workshop for BP/Olympic Pipeline, a visit from a hazards mitigation specialist form the Government of India, CVO meeting on Three-Sisters volcano, and presentations at the SSA and Cordilleran GSA meetings.
The PNSN hosted several meetings of the ANSS Pacific Northwest Region Advisory Committee (see www.ess.washington.edu/SEIS/ANSS/), as well as several meetings of Cascadia Regional Earthquake Workgroup (CREW) subcommittees. Tony Qamar, Washington State Seismologist and Chair of the Information and Technology Subcommittee of the Seismic Safety Committee of the Washington State Emergency Management Council convened several meetings of the subcommittee.

Seismicity

Between Oct. 1, 2001 and Sept. 30, 2002, 24 earthquakes were reported felt in Washington west of the Cascades, ranging in magnitude from 1.6 to 4.1. Forty-four earthquakes (magnitudes -1.6 to 4.0) were reported felt east of the Cascades, and four earthquakes ranging in magnitude from 3.2 to 4.5 were reported felt in Oregon.

Figure 2. Earthquakes magnitude 2.0 or larger between Oct. 1, 2001 and Sept. 30, 2002. 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.

		TABLE 2-- FELT EARTHQUAKES 10/1/01-9/30/02

		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
01/10/05 02:26:41    48.82N 122.11W  12.1   3.0  BB     7.6 km   E of Deming, WA
01/10/06 10:52:09    48.83N 122.10W  13.2   3.0  CB     8.2 km   E of Deming, WA
01/10/15 04:57:01    48.15N 123.06W  44.4   2.9  BA    28.6 km   E of Port Angeles, WA
01/11/10 18:30:59    48.93N 123.04W  15.4   3.4  CD    21.7 km   S of Vancouver,BC
01/11/11 16:00:29    47.68N 117.40W   4.7   4.0  BC     2.0 km NNE of Spokane, WA (Mission & N Division)
01/11/11 17:21:33    47.68N 117.40W   0.6   3.1  BC     1.3 km NNE of Spokane, WA (Mission & N Division)
01/11/12 03:03:02    47.68N 117.40W   0.6   3.3  BC     2.0 km   N of Spokane, WA (Mission & N Division)
01/11/12 03:07:40    47.68N 117.41W   0.6   1.9  CC     1.7 km   N of Spokane, WA (Mission & N Division)
01/11/12 03:11:15    47.68N 117.41W   0.6   2.4  BB     1.9 km NNW of Spokane, WA (Mission & N Division)
01/11/12 11:44:18    47.68N 117.39W   0.6   1.7  BD     2.4 km  NE of Spokane, WA (Mission & N Division)
01/11/12 13:25:59    47.68N 117.40W   0.5   1.9  CD     2.0 km NNE of Spokane, WA (Mission & N Division)
01/11/13 05:41:45    47.69N 117.40W   0.6   2.3  BC     2.4 km   N of Spokane, WA (Mission & N Division)
01/11/13 07:39:05    47.68N 117.42W   0.6   2.1  CD     1.4 km  NW of Spokane, WA (Mission & N Division)
01/11/13 10:14:01    48.86N 122.46W  22.0   2.5  BC    11.7 km   N of Bellingham, WA
01/11/13 20:26:26    47.69N 117.40W   0.6   3.0  BC     2.2 km NNE of Spokane, WA (Mission & N Division)
01/11/14 01:50:51    47.69N 117.38W   0.6   1.2  BD     3.6 km  NE of Spokane, WA (Mission & N Division)
01/11/14 16:41:20    47.69N 117.32W   0.6   1.6  CD     7.3 km ENE of Spokane, WA (Mission & N Division)
01/11/15 00:11:46    47.69N 117.39W   0.0   2.1  CC     2.7 km NNE of Spokane, WA (Mission & N Division)
01/11/16 01:42:29    47.68N 117.39W   0.5   1.8  BD     2.2 km  NE of Spokane, WA (Mission & N Division)
01/11/17 16:18:49    47.68N 117.42W   0.4   1.4  CB     1.9 km NNW of Spokane, WA (Mission & N Division)
01/11/18 19:51:12    47.68N 117.42W   0.8   1.6  BB     1.5 km  NW of Spokane, WA (Mission & N Division)
01/11/19 04:47:06    47.68N 117.41W   2.2   1.2  BB     1.5 km NNW of Spokane, WA (Mission & N Division)
01/11/19 04:47:52    47.69N 117.41W   1.2   0.5  AD     2.9 km NNW of Spokane, WA (Mission & N Division)
01/11/20 06:03:56    47.67N 117.44W   2.6   1.0  AD     2.3 km WNW of Spokane, WA (Mission & N Division)
01/11/20 12:14:42    47.67N 117.44W   0.0   1.4  AD     2.5 km   W of Spokane, WA (Mission & N Division)
01/11/22 04:43:01    47.68N 117.42W   2.5   1.4  CB     1.2 km  NW of Spokane, WA (Mission & N Division)
01/11/24 00:32:10    47.67N 117.43W   2.1-  0.5  AD     1.6 km WNW of Spokane, WA (Mission & N Division)
01/11/26 04:13:15    47.68N 117.42W   2.2   0.9  CB     1.6 km NNW of Spokane, WA (Mission & N Division)
01/11/26 09:41:37    47.69N 117.40W   0.0-  0.8  AD     3.0 km NNE of Spokane, WA (Mission & N Division)
01/11/26 09:41:53    47.68N 117.43W   2.1   0.0  AC     1.8 km  NW of Spokane, WA (Mission & N Division)
01/11/26 09:59:53    47.68N 117.38W   4.7-  1.6  BD     2.3 km  NE of Spokane, WA (Mission & N Division)
01/11/26 10:12:11    47.68N 117.40W   2.3-  1.6  AD     1.6 km   N of Spokane, WA (Mission & N Division)
01/11/26 11:56:07    47.68N 117.41W   2.2   0.7  CC     1.8 km   N of Spokane, WA (Mission & N Division)
01/11/27 08:26:58    47.65N 117.44W   0.5-  0.9  AD     3.4 km  SW of Spokane, WA (Mission & N Division)
01/12/06 23:24:08    46.89N 122.36W  20.4   2.4  BA     8.1 km WNW of Eatonville, WA
01/12/19 06:39:26    47.69N 117.38W   0.0-  0.8  AD     3.1 km NNE of Spokane, WA (Mission & N Division)
01/12/19 21:32:17    47.67N 117.44W   2.0-  0.8  BD     2.2 km WNW of Spokane, WA (Mission & N Division)
01/12/20 03:03:20    47.67N 117.44W   2.0-  0.5  AD     2.3 km   W of Spokane, WA (Mission & N Division)
01/12/20 08:30:43    47.67N 117.43W   1.8-  0.1  AD     2.1 km   W of Spokane, WA (Mission & N Division)
01/12/25 03:58:53    47.68N 117.42W   0.2-  0.7  AC     1.7 km  NW of Spokane, WA (Mission & N Division)
01/12/27 22:11:20    47.66N 117.43W   0.0-  0.5  AD     2.0 km   W of Spokane, WA (Mission & N Division)
01/12/29 11:57:27    47.67N 117.43W   0.0-  0.8  AD     2.0 km   W of Spokane, WA (Mission & N Division)
02/01/04 07:16:12    47.67N 117.41W   0.6-  0.7  AD     0.7 km WNW of Spokane, WA (Mission & N Division)
02/01/09 03:26:54    48.11N 123.12W  21.8   2.9  BB    23.4 km   E of Port Angeles, WA
02/01/26 14:01:46    47.13N 122.13W   8.5   2.4  BB    13.7 km  SW of Enumclaw, WA
02/02/12 19:16:41    48.41N 122.28W  18.6   3.0  CA     4.0 km   E of Mount Vernon, WA
02/03/11 00:43:51    47.50N 122.73W  22.7   1.7  AA    10.6 km  SW of Bremerton, WA
02/04/13 07:18:55    47.67N 117.43W   1.3-  0.2  AD     1.6 km WNW of Spokane, WA (Mission & N Division)
02/04/14 15:20:46    47.69N 117.39W   2.5-  0.9  AB     3.1 km NNE of Spokane, WA (Mission & N Division)
02/04/21 06:21:18    47.68N 117.42W   0.3-  0.4  AC     1.8 km  NW of Spokane, WA (Mission & N Division)
02/04/22 10:38:51    47.29N 122.29W  20.6   2.2  BA    12.1 km ENE of Tacoma, WA
02/05/01 09:09:45    48.45N 119.54W   3.7   2.9  DD    10.6 km NNE of Okanogan, WA
02/05/15 17:54:48    42.23N 121.90W   8.1   4.3  BB    10.0 km   W of Klamath Falls, OR
02/05/30 01:40:16    48.87N 122.20W  13.8   1.6  CB     5.9 km NNE of Deming, WA
02/06/06 14:42:46    47.72N 120.28W   7.2   3.4  CB     8.1 km  NW of Entiat, WA
02/06/16 17:11:10    47.47N 122.82W  16.1   3.7  CA    18.2 km  SW of Bremerton, WA
02/06/17 16:55:18    41.68N 124.07W  10.0   5.1  DD    13.0 km  SE of Crescent City, CA
02/06/22 08:56:21    40.53N 123.85W  10.0   0.0  CD    36.9 km  SE of Eureka, CA
02/06/29 14:36:04    45.33N 121.68W   6.2   4.5  BB     4.5 km   S of Mt Hood, OR
02/06/29 14:41:21    45.32N 121.68W   2.7   3.2  AD     5.4 km SSE of Mt Hood, OR
02/06/29 18:49:58    45.34N 121.67W   6.1   3.8  BB     3.9 km SSE of Mt Hood, OR
02/07/03 12:22:45    48.93N 123.04W  14.5   3.0  CD    21.9 km   S of Vancouver,BC
02/07/22 07:27:34    47.40N 121.78W  28.0   3.1  BA     9.8 km   S of North Bend, WA
02/07/30 21:20:47    48.03N 122.73W  58.6   2.6  BA    33.6 km NNW of Poulsbo, WA
02/07/31 09:01:58    47.40N 122.17W  49.3   2.9  CA    10.3 km   W of Maple Valley, WA
02/08/10 20:23:04    47.68N 117.41W   0.0-  0.2  AC     1.6 km NNW of Spokane, WA (Mission & N Division)
02/08/17 16:06:24    50.08N 120.13W  10.0   4.5  CD    66.2 km   S of Kamloops, BC
02/08/24 03:36:16    47.65N 120.29W   4.3   2.7  BB     5.1 km   W of Entiat, WA
02/09/18 04:37:28    47.57N 121.77W  11.2   2.0  BB     8.5 km   E of Fall City, WA
02/09/21 00:55:20    48.48N 123.12W  23.4   4.1  CA    10.6 km WSW of Friday Harbor, WA
02/09/21 08:07:14    48.52N 122.05W   0.0   2.5  BC    13.4 km ENE of Sedro Woolley, WA
02/09/25 05:30:54    48.60N 121.96W   0.0   2.4  CC    17.7 km WNW of Concrete, WA
02/09/25 05:35:49    48.61N 121.95W   0.0   2.6  CC    17.2 km WNW of Concrete, WA
02/09/25 07:30:55    47.79N 121.82W   7.2   2.4  CA    13.3 km ENE of Duvall, WA
02/09/26 07:00:04    48.48N 123.13W  23.1   2.9  CA    11.2 km WSW of Friday Harbor, WA
____________________________________________________________________________________________

Publications

Quarterly bulletins from the PNSN (/SEIS/PNSN/REPTS/quarterly.html) provide operational details and descriptions of seismic activity in Washington and Oregon. These are available from 1984 through the third quarter of 2001. Final published catalogs are available from 1970, when the network began operation, though 1989.

Reports and Articles

Bakun W.H, R.A. Haugerud, M.G. Hopper, and R.S. Ludwin, 2002 (in press), The December 1872 Washington State Earthquake, BSSA.

Malone, Steve, Real-time data exchange (revisited), 2002, Seismological Research Letters, V73, No. 2, pp. 185-187.

Musumeci, Carla, Stefano Gresta, Stephen D. Malone, 2002 (in press), Magma System Recharge of Mount St. Helens from precise relative hypocenter location of microearthquakes. Jour Geophys. Res.

Van Wagoner, T., R.S. Crosson, N.P. Symons, G.F. Medema, K.C. Creager, and L.A. Preston 2001 (in review), High resolution seismic tomography and earthquake relocation n the Puget Lowland, Washington, JGR.

Abstracts

Blakely, R.J., Wells, R.E., Weaver, C.S., Meagher, K.L., and Ludwin, R.,2002, The bump and grind of Cascadia forearc blocks: evidence from gravity and magnetic anomalies, Geological Society of America, Cordilleran Section, Abstract with Programs, V. 34., No. 5, p. A-33

Creager, K.C., Preston, L.A., Xu, Q., and Crosson, R.S., 2002, The 2001 Mw 6.8 Nisqually intraslab earthquake: an along-strike elongated fault rupturing entirely within the subducted oceanic crust?, Seis. Res. Lett. V. 73, No. 2, p. 213.

Jones, J., Malone, S.D., 2002, Constraints on Mt. Hood earthquake swarms from cross-correlation and joint hypocenter determination, Seis. Res. Lett. V. 73, No. 2, p. 253.

Malone, Stephen D., 2002, The Pacific Northwest Seismograph Network - A Multi-Hazard Data and Information System, Geological Society of America, Cordilleran Section, Abstract with Programs, V. 34., No. 5, p. A-11.

Oppenheimer, D., A. Bittenbinder, B. Bogaert, R. Buland, L. Dietz, R.Hansen, Malone, S., McCreery, C., Sokolowski, T., Weaver, C., 2002, The CREST Project: Consolidated Reporting of EarthquakeS and Tsunamis, Geological Society of America, Cordilleran Section, Abstract with Programs, V. 34., No. 5, p. A-11.

Preston, L.A., Creager, K.C., Crosson, R.S., 2002, Simultaneous inversion for hypocentral locations, 3-D wavespeeds and reflector geometry, Seis. Res. Lett. V. 73, No. 2, p. 225.

Thomas, G.C. and Lindemuth, A.L., 2002, Seismographs in schools: collaborations in critical monitoring of earthquakes, Geological Society of America, Cordilleran Section, Abstract with Programs, V. 34., No. 5, p. A-13.

Tusa G., Giampiccolo, E., Gresta, S., Musumeci, C., Malone, S.D., 2002, Temporal changes in seismic attenuation at Mount St. Helens, Seis. Res. Lett. V. 73, No. 2, p. 253.

Wright, A.K., Qamar, A., Ludwin, R.S., and Medema, G., 2002, The 2001 Spokane, WA earthquakes: an urban sequence in an unmonitored region, Seis. Res. Lett. V. 73, No. 2, p. 240.

Xu, Q., Creager, K.C., Crosson, R.S., 2002, Rupture history of the 2001 Nisqually, Washington earthquake, Seis. Res. Lett. V. 73, No. 2, p. 213.