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EARLY HISTORY OF SEISMIC NETWORKS AND INSTRUMENTATION During the first 60 years of this century, several groups of seismologists, essentially independently, established and operated sets of seismograph stations equipped with similar types of instruments. These sets of stations were the forerunners of the Worldwide Standardized Seismograph Network (WWSSN) and other more sophisticated networks of recent years. A notable early global effort was the seis- mological program of the Jesuit colleges and universities, beginning in l900 and including their creation of the Jesuit Seismological Association in l925. Some processed information was collected and analyzed in their center at Saint Louis University. This effort offered the first model of a coordinated observatory network providing broad geographic coverage. Many national networks, such as that of the Coast and Geodetic Survey in the United States, and some regional networks were operated by universities and other institutions. Rapid improvement in instrumentation followed Galitzin's application in l9l2 of the electromagnetic transducer and galvanometric recording to the seismograph. Galitzin in- struments, especially a version modified by Wilip to im- prove stability and provide linearity of response, became the primary equipment in many observatories (see Figure 2). Other important advances in instrumentation were the Wood- Anderson torsion seismograph (l925), the Benioff quartz- rod strain seismograph (l935), the variable-reluctance transducer adapted for seismograph applications by Benioff in l932, and the application by LaCoste in l935 of the zero-length spring to systems suitable for detecting long- period vertical motions. In spite of these early advances in instrumentation, a fundamental requirement of a good seismographic observa- tory, accurate and reliable timing, was not met until 8
FIGURE 2 Galitzin vertical-component seis- mograph as manufactured by the Cambridge Instrument Company and installed at Georgetown University after World War I. (Appears on p. l63 of When the Earth Quakes by James B. Macelwane, S.J., l947. Courtesy of Bruce Publishing Company.) after World War II, when crystal clocks became readily available. Moreover, at the end of World War II most of the world's seismological observatories still lacked properly calibrated instrument systems with uniform re- sponse characteristics. A few individual stations did have calibrated systems, however; and special, long-period seismographs were installed in l956-l957, in widely separated places, by the Lamont Geological Observatory of Columbia University for use in the International Geo- physical Year program. These stations provided valuable experience that was exploited later when Project VELA Uniform established the WWSSN. VELA Uniform was conceived in l958 by the Panel on Seismic Improvement, appointed by the Special Assistant to the President of the United States for Science and Technology at the request of the Department of State in connection with the nuclear test ban negotiations. VELA Uniform required that a capability be developed to identify underground nuclear explosions. Before VELA, seismology was still in a relatively primitive state, and basic up- grading was needed. It depended then primarily on a
l0 handful of dedicated workers, usually with minimal re- sources, and on the early instruments, which were adequate only for the study of travel times of seismic waves, of amplitudes of short-period phases, and, in some cases, of surface waves with periods as long as a few minutes.
