This report includes epicenters for seismic events that occurred from March through April 1983 as published in the PDE (Preliminary Determination of Epicenters), U.S. Geological Survey, National Earthquake Information Service. It is limited to three types of events: earthquakes occurring anywhere with a magnitude of 6 or more, those causing substantial damage regardless of the magnitude, and domestic or foreign events judged to be of special interest.

Time is given in Coordinated Universal Time (UTC), unless otherwise specified. Latitude and longitude are given to hundredths of a degree for all locations except for better resolution at the Nevada Test Site. Depths constrained to “normal” (33 km) are indicated by “constrained.” Those made to agree with depth phases are marked “depth phases.” Reports followed by (GS) are taken from the PDE. All intensities are reported using the Modified Mercalli Intensity Scale, unless they are indicated as RF (Rossi-Forel), JMA (Japan Meteorological Agency), or MSK (USSR). Sources of the magnitudes are (BRK) University of California, Seismograph Station, Berkeley; (GS) U.S. Geological Survey, National Earthquake Information Service; (HVO) U.S. Geological Survey, Hawaiian Volcano Observatory; and (PAS) California Institute of Technology, Seismological Laboratory, Pasadena, Magnitude (SLM) indicates an mb value calculated from Pn or Lg phases by Saint Louis University. Magnitudes followed by (GS) are mb values as defined by Gutenberg and Richter computed from the P phase only; they are average values determined from data forwarded by cooperating standard stations and other observatories. Magnitude MS is the average of surface-wave magnitudes determined from amplitude data from standard long-period vertical seismometers. Magnitude ML is the original local magnitude scale based on the maximum recorded amplitudes at local and regional distances.

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