Comparison of Source Scaling Relations of Eastern and Western North American Earthquakes

Source scaling relations have been obtained for earthquakes in eastern North America and other co'ntinental interiors, and compared with a relation obtained for earthquakes in western North America. The scaling relation for eastern North American earthquakes was constructed from measurements of seismic moment and source duration obtained by the waveform modeling of seismic body waves. The events used include nine events of mbLg magnitude 4. 7 to 5.8 that occurred after 1960, and four earlier events with magnitudes between 5.5 and 6.6. The scaling relation for events in other continental interiors was used for comparative purposes and to provide constraints for larger magnitudes. Detailed analysis of the uncertainties in the scaling relations has allowed the resolution of two important issues concerning the source scaling of earthquakes in eastern North America. First, the source characteristics of earthquakes in eastern North America and other continental interiors are consistent with constant stress drop scaling, and are inconsistent with nonconstant scaling models such as that of Nuttli (1983). Second, the stress drops of earthquakes in eastern North America and other continental interiors are not significantly different from those of earthquakes in western North America, and have median values of approximately 100 bars. The source parameters of earthquakes in eastern North America are consistent with a single constant stress drop scaling relation, whereas the source parameters of earthquakes in western North America are much more variable and show significant departures from an average scaling relation in which stress drop decreases slightly with seismic moment.