Leveling data from the epicentral area of the March 27, 1975, earthquake in Pocatello Valley, Idaho

Abstract

The epicentral area of the March 27, 1975, magnitude-6,Q earthquake in Pocatello Valley, Idaho, is traversed by a line of benchmarks established by the U.S. Geological Survey (USGS) in 1966 and releveled in July 1975 (fig. 1). The elevations determined by those two surveys are presented in table 1 of this report; they define a widespread area of subsidence generally centered over the epicentral region (fig. 2). Maximum relative subsidence along the line is 13 cm. Because no tectonic ground ruptures were associated with the earthquake, the origin of the inflection in the trends of elevation changes in the vicinity of benchmark 3FMK in the southwest part of the valley is unclear at present. No inflection is evident where the line enters the Samaria Mountains in the vicinity of the fault-bounded, geomorphically youthful, eastern margin of Pocatello Valley, described by Platt (1975). Abstracts of papers describing the seismological and surface effects of the earthquake have been published by Arabasz and others (1975), Cook and Nye (1975), and Kaliser (1975); a brief report of the earthquake is given by Rogers, Langer, and Bucknam (1975).