abstract

An empirical amplitude-distance curve is determined for earthquakes registered at regional distances in conterminous Brazil. This curve is the basis of a regional magnitude scale, mR, using the maximum amplitude in the whole P-wave train with periods in the range 0.1 to 1.0 sec. In the distance range 200 ≦ R ≦ 1500 km, we find

 
mR=log(A/T)+2.3logR1.48.

This scale gives much better agreement with the teleseismic mb magnitudes than the values calculated using the regional Q factors of Gutenberg and Richter (1956). It is shown that, despite using a wide range of periods, mR should be a good estimate of the 1-sec teleseismic mb in the range 2 ≦ mb < 5.

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