An Approach to Seismic Zoning in Southern New England

Abstract

An approach to seismic zoning was developed for an area bounded by latitudes 41°N and 44°N and longitudes 70°W and 75°W. The definition of seismic zones requires a thorough study of the earthquake record. The record for the study area was found to be deficient in comparison with modern capabilities of earthquake reporting. However, statistical procedures (Stepp, 1973) help improve the estimates of earthquake frequency necessary to the zoning procedure. Possible criteria for determining zone boundaries include the frequency and geographic distribution of earthquakes, relative susceptibility of geographic areas to earthquake damage, and the locations of the high intensity earthquake epicenters. These criteria are quantitatively defined for southern New England as far as the existing record allows. The distribution of earthquakes is strongly related to geography. It was found that coastal and lowland areas have a high level of earthquake activity, and mountainous areas, with the exception of the Adironacks, have a low level. The distribution of earthquakes may be related to crustal movement and heat flow anomalies in relationships unresolved at this time. This approach to seismic zoning requires that: (1) the size of the study area should include as many epicenters as possible without obscuring geographic and geologic details; (2) the criteria for defining zones be based on the local earthquake record; (3) information from areas with a different seismic character should not strongly influence the zoning procedure.