Earth
and Space Sciences Faculty |
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Robert
S. Crosson |
Areas of Interest:
Seismology, earth structure, tectonics, and earthquake hazards
Research Group:
Seismology
and Tectonics
Education:
Ph.D., Geophysics, Stanford University,
1966
Current Research:
Recently my research has
focused on efforts to improve our understanding of structure, tectonics, and
earthquake hazards in the Pacific Northwest using observations made with the
Pacific Northwest Seismograph Network.
Cascadia Subduction Zone
The increasing recognition of the possibility of large subduction earthquakes
on the Cascadia Subduction Zone (CSZ) of the Pacific Northwest has brought a
sense of urgency to efforts to understand the hazards of this very accessible
but still poorly understood subduction zone. Our early efforts in earthquake
hypocenter analysis resulted in the first identification of the Wadati-Benioff
zone for the CSZ. More recently we have utilized three-component broadband measurements
in combination with regional network observations to define an arch-like structure
in the subducted Juan de Fuca plate in the vicinity of Puget Sound. This discovery
has already stimulated further work on the origin of the Olympic Mountains and
the origins of the observed plate geometry.
The higher quality and quantity of data from local and regional earthquakes that is now available has allowed my students and me to develop and apply tomographic imaging methods using earthquakes as sources of "illumination." From these efforts, we have determined a first-order regional three-dimensional structure image of the crust in the Puget Sound and Mt. St. Helens regions of western Washington. In another study, we used recordings of earthquakes at distant locations to construct an image of the portion of the CSZ to several hundred kilometers depth. We recently successfully constructed a profile of structure across the Cascade Range of Washington State using local earthquakes as sources of energy in place of the more conventional explosion methods.
Regional Tectonics
My students and I have analyzed focal mechanisms of regional earthquakes to
demonstrate that the continental crust (North American plate) in the Pacific
Northwest is generally in a state of N-S compression. Our work on the analysis
of focal mechanisms and regional stress in continuning with research on the
aftershocks of the Scotts Mills earthquake which occurred in northwest Oregon
in 1993.
Recently, geologists have proposed new a new tectonic model for western Washington. We are currently undertaking a careful restudy of earthquake hypocenter locations west of the Cascade Range in light of this model. In this work, we are using an advanced method of earthquake location that allows us to include the three-dimensional structure of the earth's crust.
We have observed earthquake generated waves from regional earthquakes that arise due to a guided wave effect that appears to be unique to subduction zones. These observations may permit more accurate determination of subduction zone structure. Such waves have been observed previously in Japan.
Pacific Northwest Seismograph Network (PNSN)
A number of technical as well as analytical advances have occurred in the past
10 years that have made possible some significant advances in our knowledge.
My early efforts were devoted to the establishment of a regional seismological
network in Washington. With the effort of many, this network has now grown to
over 120 telemetered seismograph stations. During the last 15 years, digital
data recording for large regional networks has provided substantial opportunities
for increasing our analysis capability through both higher quality and quantity
of seismic data. Much of my research in the last several years has been devoted
to both developing methodologies to take advantage of the new higher quality
data, and applying these methodologies to achieve a better understanding of
the earth.
To efficiently perform initial analysis of the large quantities of digital data generated by the regional network, I have worked with students and colleagues to developed an advance automated processing system to carry out the initial steps of analysis. This system will be particularly important when a major earthquake strikes our region since it will allow rapid access to preliminary analysis by the seismologist and will allow us to stay on top of the enormous volume of data likely to be generated when a large local or regional earthquake strikes our region. Experience with the 1989 Loma Prieta earthquake, and more recently with the 1994 Northridge earthquake, both in California, has demonstrated the importance of having this capability.
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Earth and Space Sciences (Geology, Geophysics, Geological Sciences) University of Washington Johnson Hall 070 • Box 351310 4000 15th Avenue NE • Seattle, WA 98195-1310 Phone 206-543-1190 • Fax 206-543-0489 • Site Info: webmaster@ess.washington.edu • ESS Advising: advising@ess.washington.edu |