On Saturday evening, January the 28th, 1995, at 7:11:23 pm Pacific Standard Time, a fault ruptured inside the earth beneath Point Robinson on Maury Island in Puget Sound, generating an earthquake. About 5 seconds later, a seismometer buried beneath the forest floor in Seward Park on the south end of Lake Washington, operated by the UW Geophysics Program, was jolted off scale as the first earthquake waves arrived at that site. The signal from the seismometer was sent via a dedicated phone line and recorded almost instantly at the UW Seismology Lab.
These first shock waves, called primary or P waves, continued to propagate all across the UW seismograph network, exciting station after station. Within a few seconds, enough stations had recorded the earthquake to cause a computer to be triggered to record the event on the entire network of more than 130 stations throughout the states of Washington and Oregon. Both telemetry and communication lines are used to transmit data back to the lab. Fifty seconds after the trigger, a pager alert sounded on the beeper of the seismologist on call that night, giving the latitude, longitude, and approximate magnitude of the event. Meanwhile, seventy-five seconds after the fault ruptured, the first seismic waves were streaming into Klamath Falls in southern Oregon.
Back at the UW Seismology Lab, a computer system automatically analyzed data coming in from all the stations, and generated a preliminary magnitude of about 5 for the quake. Seven minutes after the earthquake hit, computer electronic mail alerts were being sent out to a list of key individuals. At this point, the system was programmed to send information by an automated fax to the emergency management agencies in the area.
That episode, which occurred in January 1995, gives a brief snapshot of some of the capabilities of the Pacific Northwest Seismograph Network, operated by the Seismology Lab in the UW Geophysics Program. Over the years, research conducted through the Seismology Lab has provided new and vitally important information about the geology of the Pacific Northwest.
Since the facility was founded in late 1969, the seismic data gathered and analyzed at the Lab have provided geologists with a picture of the geologic faults in the earth's crust in the Northwest, many of which were previously unknown or uncharacterized. At the same time, those discoveries have provided new insights about the nature and severity of earthquake hazards in the region.
Furthermore, the Lab took the lead in monitoring earthquake activity associated with the historic eruption of Mount St. Helens in 1980 and subsequent events there.
Principal Investigators of the Lab are Stephen D. Malone, Robert S. Crosson, and Anthony I. Qamar of the UW Geophysics Program. The Network has been supported by funding from the U. S. Geological Survey and Westinghouse Hanford Company.
In addition to conducting research, the UW Seismology Lab serves as an information clearinghouse in several respects. The most widely recognized is the service the Lab provides to the news media when earthquakes occur. But less well-known is the fact that, as part of the IRIS Consortium (Incorporated Research Institutions for Seismology, Arlington, Virginia), the University of Washington is the world's designated hub for collecting and maintaining seismic information from sites all over the globe, and for disseminating that information to scientists for further study.
Within the Pacific Northwest region, the Seismology Lab serves as a catalyst for bringing community, business, and government leaders together, not just to foster awareness of seismic hazards, but to promote critical planning for emergency situations that may require cooperation between these sectors. The Lab provides outreach to schools, participating in curriculum development efforts for elementary and secondary school students.
The Geophysics Program maintains a public computer bulletin board and a telephone audio library about regional and global earthquakes. And through the Internet, residents anywhere can now tap into a rich information resource on the Lab's World Wide Web page, originally developed by Malone, at http://geophys.washington.edu. As many as 31,000 "hits," or inquiries, per month to the page have been logged, says Bill Steele, Seismology Lab Coordinator in the UW Geophysics Program. The facility at that rate will be serving hundreds of thousands of users annually, he notes. The Lab is also making use of the Internet to collect information from residents about what they observed when an earthquake occurred. In analogy to "weather watchers" who transmit local weather observations, "quake watchers" send in their observations either by electronic mail or by conventional mail. It is the first time that the Internet has been used to obtain information from people in this way about earthquakes, says Qamar, who is State Seismologist in addition to being a UW geophysics faculty member.
Qamar explains that before about the 1970s, scientists believed that most of the largest earthquakes in the Pacific Northwest were deep quakes, similar to those that occurred in the Puget Sound area in 1949 and 1965. Now, as a result of information that the Lab has helped to obtain, and with a greater understanding of the plate tectonics of the region (see box), scientists know that there are three basic types of earthquakes in this region: deep, shallow, and subduction zone quakes (see Ancient Quakes).
Shallow quakes originate on faults close to the surface. An example is the Point Robinson quake described above. Another recently identified fault zone runs along a north-south line just to the west of Mount Rainier. Yet another, called the Seattle fault, underlies Puget Sound; it was responsible for a major earthquake 1,100 years ago. "Recording data from earthquakes at the Lab is helping us map out these faults," says Qamar. "We have an incomplete picture because the seismic network has only operated since 1969. We have to work in a very long time-frame."
"Like many of the large recent earthquakes in the Pacific Northwest, the Point Robinson quake took us by surprisewe didn't realize the fault was active, nor had we ever determined its direction and characteristics. The data we recorded gave us brand new information," says Qamar. By analyzing the data from the main shock and aftershocks of a quake from all of the different stations, it is possible to determine the orientation of the fault and other characteristics of the fault plane, such as the direction and type of movement of the earth that occurs when the fault ruptures. "The magnitude 6 earthquake that occurred in 1993 in the Klamath Falls area of southern Oregon also gave us information that previously was unknown. We knew there were lots of faults there, but earthquakes had never been recorded from most of them. As a result of that recent event, we now have mapped out several new faults."
Recent research by Crosson, Kenneth Creager, and graduate students in the geophysics program is aimed at taking a sort of "CAT" scan of the interior of the earth. The researchers are obtaining three-dimensional images of the structures within the earth by analyzing seismic information called "teleseismic body waves," the first such images ever obtained for this region.
Seismic studies of events at Mount St. Helens have given researchers a basis for interpreting new events, such as the increase in recent earthquake activity observed in September, 1995. During the explosive and dome-building eruption of the mountain between 1980 and 1986, volcanic activity was preceded and accompanied by intense shallow earthquake activity, located less than 2 miles beneath the crater. In contrast, the September 1995 quakes were smaller and originated at depths between about 1 and 6 miles; consequently, they do not suggest that an upward rise of magma was taking place. However, a similar increase in earthquake activity in 1989-90 was accompanied by several hazardous steam and ash eruptions.
The lessons that have been learned from the Mount St. Helens eruption "have been applied to eruptive activity elsewhere, including in Alaska and at Mount Pinatubo in the Philippines," says Ruth Ludwin, Research Scientist at the Lab. Seismic research also is featured in new studies by UW volcanologist Steve Malone and colleagues to reassess Mount Rainier's potential for volcanic activity.
Recently, the Lab has initiated an effort to monitor long-term movements of the earth's tectonic plates in the Northwest. As illustrated in the box, this region is the place where the North American plate and the Juan de Fuca plate are colliding and the ocean floor is being pushed beneath the North American continent along the Cascadia Subduction Zone. Previously, measuring movements of the crust relied on costly survey work to determine how far benchmarks in the ground had moved from each other over time periods of 10 to 100 years. Now, with the aid of Global Positioning Satellites, it becomes possible to continuously monitor the position of permanently-sited GPS receivers with respect to each other. "Our first permanent GPS receiver was installed at Neah Bay this summer ," says Qamar. "And within a year, we'll have four to ten more installed in cooperation with Central Washington University." Qamar says the system is sensitive enough to see millimeter changes in the distance between Seattle and Neah Bay, for example. Monitoring the build-up of strain along the plate boundary will be important to understanding earthquake activity over the long term.