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Chapter 5. Solid-Earth SciencesSeismic Source Physics: Earthquakes and ExplosionsThe research on seismic sources has been based on a combination of field and instrumental studies of earthquake generation, laboratory studies of fault formation in rock specimens using holographic techniques, and the theory of fault rupture and wave generation. Engdahl's experience in designing and operating a seismic network at Amchitka Island before he came to CIRES provided a good basis for creating the Central Aleutians Seismic Network in 1974, when the U.S.G.S. began to support predictionrelated research. This network, which operated from Adak Island until 1992 under the National Earthquake Hazards Reduction Program, was expanded and upgraded as time passed. It provided quality data from thousands of earthquakes in a part of the most prominent subduction zone in the territory of the United States. When Engdahl left CIRES to join the National Earthquake Information Center of the U.S.G.S., Kisslinger took over the direction of the network, with major operational management responsibilities going to Selena Billington. S. T. Morrissey, on the staff of St. Louis University, provided the technical expertise for instrumentation installation and upgrades, and the maintenance of the network under very difficult field conditions. Several research assistants, including Sharon Kubichek, Robin Wright, Cyndi McDonald, Susanne Bell, Tom Toth, and Bruce Kindel provided the key staff support for the data analysis and catalog preparation. The data were the basis for many research papers and dissertations on the fundamentals of subduction zone seismology (see "List of Publications"), as well as prediction research described below. The network was dismantled in 1992, when funding was ended. The research on earthquake sources has not been confined to the Aleutians by any means. Studies have spanned the globe, from east Asia, through central Asia and the eastern Mediterranean, to Hawaii, the midcontinent of the United States and, especially, California. A series of aftershock studies was originally motivated by the thousands of aftershocks of the magnitude 8 earthquake of May 7, 1986, within the Central Aleutians Seismic Network. In addition to the Aleutians, the spatial and temporal distributions of aftershock sequences in California, Japan, and the Vrancea zone of Romania have been studied. One goal of these studies has been the clarification of fault-zone properties on the basis of aftershock behavior. Kisslinger and Susanna Gross have worked on improved mathematical models of earthquake decay rate. Early laboratory investigations, under Spetzler and Ivan Getting, used laser holography to monitor the deformation of a rock mass as fault formation and failure proceeded. They were joined in this work by many co-workers over the years, including Randolph Martin, who became a CIRES fellow, and Carl Sondergeld. The scope of this effort broadened and became thoroughly international, as specialists from a number of countries, listed at the end of this text, joined as research associates and visiting scientists. Processes associated with the preparation of a rock mass for fault slip were demonstrated and some effects could be correlated with field observations. More recent work in this laboratory, discussed below, has been concentrated on rock properties at high pressures, including wave attenuation, subjects more related to the interpretation of data on deep-earth processes than source studies. Archambeau carried out theoretical work on the production and propagation of earthquake- and explosion-generated seismic signals as a contribution to the national program of research on monitoring clandestine nuclear tests. He succeeded in developing useful criteria for discriminating between natural earthquakes and buried explosions. His work stimulated and was joined with observational studies of central Asian events under the Joint Seismic Program, led by Danny Harvey and Michael Ritzwoller of the Department of Physics. The University was the site of the Joint Seismic Program Center for about six years, 1991-1997. Anatoli Levshin, former chief of the Laboratory of Wave Fields Interpretation, International Institute of Earthquake Prediction Theory and Mathematical Geophysics of the Russian Academy of Science, joined the group in 1992. Engdahl joined this group in the Department of Physics on his retirement from the U.S.G.S. A large part of the work on fundamental seismology has moved out of CIRES into the Gamow Geophysical Laboratory, Physics Department. Recent work within CIRES on seismic sources has been led by John Rundle. He has concentrated on the development of computational and analytical techniques to model, simulate, interpret, and, ultimately, to understand the physics of earthquakes. In particular, he has developed the application of the methods of statistical physics to the modeling and analysis of earthquake source mechanisms. Many of the techniques he has developed may also have applications to other kinds of non-equilibrium driven systems, including complex non-linear earth systems. Rundle has taken the lead in the formulation and development of the new General Earthquake Model (GEM) simulation program. This collaboration of many scientists is based at the Southern California Earthquake Center. The GEM project will provide a modeling and simulation framework allowing large data sets being acquired with contemporary systems observing a variety of geophysical parameters to be properly interpreted within a setting of fully interacting, evolving earthquake fault systems. Rundle left CU at the end of the summer 2002, to take up a position at the University of California, Davis. Next > Studies of Crustal Deformation
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