Deaggregation of probabilistic ground motions in the central and eastern United States

Probabilistic seismic hazard analysis (PSHA) is a. technique for estimating the annual rate of exceedance of a specified ground motion at a site due t o known and suspected earthquake sources. The relative contributions of the various sources to the total seismic hazard are determined as a function o f their occurrence rates and their ground-motion potential. The separation of the exceedance contributions into bins whose base dimensions are magnitu de and distance is called deaggregation. We have deaggregated the hazard an alyses for the new USGS national probabilistic ground-motion hazard maps (F rankel et al., 1996). For points on a 0.2 degrees grid in the central and e astern United States (CEUS), we show color maps of the geographical variati on of mean and modal magnitudes ((M) over bar, (M) over cap) and distances ((D) over bar, (D) over cap) for ground motions having a 2% chance of excee dance in 50 years. These maps are displayed for peak horizontal acceleratio n and for spectral response accelerations of 0.2, 0.3, and 1.0 sec. We tabu late (M) over bar, (D) over bar, (M) over cap, and (D) over cap for 49 CEUS cities for 0.2- and 1.0-sec response. Thus, these maps and tables ase PSHA -derived estimates of the potential earthquakes that dominate seismic hazar d at short and intermediate periods in the CEUS. The contribution to hazard of the New Madrid and Charleston sources dominat es over much of the CEUS; for 0.2-sec response, over 40% of the area; for 1 .0-sec response, over 80% of the area. For 0.2-sec response, (D) over bar r anges from 20 to 200 km, for 1.0 sec, 30 to 600 km. For sites influenced by New Madrid or Charleston, D is less than the distance to these sources, an d M is less than the characteristic magnitude of these sources, because ave raging takes into account the effect of smaller magnitude and closer source s. On the other hand, (D) over cap Is directly the distance to New Madrid o r Charleston and (M) over cap for 0.2- and 1.0-sec response corresponds to the dominating source over much of the CEUS. For some cities in the North A tlantic states, short-period seismic hazard is apt to be controlled by loca l seismicity, whereas intermediate period (1.0 sec) hazard is commonly cont rolled by regional seismicity, such as that of the Charlevoix seismic zone.