Issues Regarding Earthquake Source Characterization and Seismic Hazard Analysis within Passive Margins and Stable Continental Interiors

Abstract

We summarize several important issues related to the characterization of earthquake sources within stable continental interiors and we present some effective methods for incorporating uncertainties in source characteristics into seismic hazard analyses. The focus of the conclusions drawn is the central and eastern United States (CEUS), but they may be applicable to other analogous regions as shown in an example. Three important aspects of hazard analysis considered here are earthquake source location, maximum earthquake size, and earthquake recurrence. Historically, estimates of the location of future earthquake sources has relied heavily on seismicity data and on the pattern of past earthquake occurrence. Because the historical record may be too short to include all earthquake sources, tectonic data are being considered. The stress regime in the CEUS appears to be regionally compressive and to have a generally uniform NE to ENE orientation, suggesting far-field tectonic stress mechanisms. Within this regime, some tectonic features appear to be reactivated, although local stress concentration may also be important. A variety of approaches toward estimating maximum earthquakes have been proposed, most relying to some extent on the historical record or extrapolation thereof. These methods are described and an ongoing study that uses worldwide observations of large earthquakes is also summarized. Detailed studies of earthquake recurrence at active seismic zones in the CEUS strongly suggest that earthquakes are temporally and spatially clustered. Preliminary work at these locations suggests that a temporal cluster has a lifetime of at least several thousand years and that the locations of the most recent prehistoric earthquakes has been generally at the locations of observed events. We describe the use of logic trees to document and incorporate the uncertainties in seismic source characteristics into seismic hazard analysis, and we present an example of their application in the Norwegian North Sea.