Catalog of earthquakes in south-central Alaska, April - June 1972

Abstract

The National Center for Earthquake Research of the U.S. Geological Survey (USGS) installed a network of eleven seismograph stations in south-central Alaska in the summer of 1971 to collect seismological data for investigating seismic and tectonic processes in the Cook Inlet region, for evaluating the seismic hazard in the Cook Inlet region and in the Chugach Mountains along the southern end of the route of the proposed trans-Alaska oil pipeline, and for studying the structure of the crust and upper mantle in south-central Alaska. The first recordings from the network were obtained in late September 1971. The first earthquakes to be located with data from the network occurred in October 1971. This earthquake catalog, which is the first to be compiled for the USGS Alaska network, presents origin times, focal coordinates and magnitudes for 210 shocks occurring in the second quarter of 1972 (except from June 15 to 23) in south-central Alaska, primarily in the Cook Inlet region. Readings from a total of 18 stations were used to locate the shocks. To supplement the readings from the 10 USGS stations that were operative during this quarter, arrival times were obtained from 6 stations operated by the Palmer Seismological Observatory of the National Oceanic and Atmospheric Administration (NOAA) and 2 stations operated by the Geophysical Institute of the University of Alaska (U of A). The data in this catalog are the most detailed and precise earthquake data compiled to date for earthquakes within the Cook Inlet region. Earthquakes in south-central Alaska as small as magnitude 3.0 have been routinely located by the National Earthquake Information Center of NOAA (currently the National Earthquake Information Service of USGS) since the great Alaska earthquake of 1964 and published in the reports "Preliminary Determination of Epicenters" (PDE). In contrast the shocks included in this catalog are as small as magnitude 1.0 and most are smaller than magnitude 3.0. Data for the larger historic earthquakes in south-central Alaska have been tabulated by Davis and Echols (1962) and U.S. Coast and Geodetic Survey (1966). The locations of the eleven stations of the NCER seismograph network are plotted in Figure 1 and listed in Table 1 along with the additional stations from which readings were obtained. The USGS stations have single, vertical-component seismometers except for NKA and SKL, which also have two horizontal seismometers. The station ERN was installed in the summer of 1971, however the telemetry circuit was not available until September 1972.