STRONG-MOTION INSTRUMENTATION IN THE CENTRAL AND EASTERN UNITED STATES

ABSTRACT: The strong-motion instrumentation network operated by the U.S. Geological Survey (USGS) in cooperation with other agencies in the central and eastern United States consists of approx imately 140 triaxial accelerographs located at 68 stations in 25 states east of the Rocky Mountains. This network is largely the result of programs of the U. S. Army Corps of Engineers (COE) to monitor strong ground shaking and structure response at COE dams and the Veterans Administration (VA) to measure base motions of large hospital buildings. In addition, the National Science Foundation (NSF) is supporting the USGS in development of accelerograph networks to obtain ground motion measurements in seismically active areas. Other organizations, including the Lamon-Doherty Geo-logical Observatory (LDGO) and numerous power utilities with nuclear generating units, have established small strong-motion arrays in this region. More than a dozen accelerograms have been recovered from instrumentation in the central and eastern United States since LDGO obtained the first of several records from a series of northern New York earthquakes in July-August 1973. The maximum reported acceleration (0.076.g.) for this region was recorded during the New Madrid earthquake of June 13, 1975 (magnitude 4.3) at an epicentral distance of about 10 km. As a result of recent studies of the recurrence of strong ground motion, the USGS will install about 36 accelerographs in the New Madrid seismic zone; this instrumentation will comprise a grid network with station spacings ranging from 10 to 25 km. The primary objective of the network, which is supported by NSF, is to obtain data for use in the investigation of the spectral characteristics and attenuation of strong ground motion