The local magnitude scale and seismicity of the central United States

A local magnitude scale is developed for the central U.S. The distance correction function can be expressed as - log Ao = 0.939*log(r/100)--0.000276*(r--100) + 3.0, with amplitude Ao in mm and hypocentral distance r in km, showing a weak attenuation with distance. Estimations for b values and magnitudes of earthquakes with a return period of 500 years in the central U.S. are performed, based on the original New Madrid catalog (MD or m bLg) and the newly created ML catalog. Results show that the b value is smaller for the ML catalog (0.790), yielding one M 7.5 event every 500 years, a result that converges with the paleoearthquake estimate for the region. On average, the relation between ML and MD or mbLg (for 1.5 ≤ MD ≤ 5.0) can be expressed as ML=1.008*MD +0.0714.; We develop local magnitude scales for the Mississippi embayment of the central U.S. and the Kachchh basin of western India to understand the distance attenuation in these two regions. Results show that Kachchh basin distance attenuation is closer to southern California than to the central U.S., suggesting fundamental differences in local wave propagation between these two intraplate regions.; The spatial distribution of earthquake energy release for the New Madrid seismic zone (NMSZ) is mapped using the standard empirical magnitude-energy relation. The depth distribution of earthquake energy release may be a better proxy for modeling crustal strength than seismicity histograms in the NMSZ. We also map global earthquake energy release based on parameters of 445,373 events of the NEIC earthquake catalog with magnitudes equal to or greater than 1.0 over the time period from 1973 to 2006. The pattern of earthquake energy release in North America shows evidence of a seismic belt that encircles the cratonic interior. The global average relationship between earthquake energy release and strain rate is estimated to be log10 E = 1og10 3&d2; + 25 (with energy release in ergs and time in years). Using this relationship, the strain rate for the central U.S. is estimated to be between 7.9x10 -19 s-1 and 5.5x10-15 s-1.