Magnitude and Epicenter Estimations of Mexican Earthquakes form Isoseismic Maps

Relationships between magnitude, M, and areas, A i , of modified intensity contours IV, V and VI of the form M = λi log Ai + µi are derived from Mexican earthquakes. Due to insufficient data, λi has been fixed to 1. Events have been grouped broadly as interplate and intraplate events. Within the range of their validity (7.0≤ M ≤8.2 for interplate; 6.4 ≤ M ≤ 7.1 for intraplate) the relations would give estimate of M to within ± 0.3 to ± 0.4 unit ( one standard deviation) of magnitude. The attenuation of intensity for interplate earthquakes is higher than that for intraplate earthquakes. The attenuation for interplate earthquakes is comparable to or greater than for Southern California earthquakes. Epicenters estimated at the center of maximum intensity contours differ from instrumental epicenter bye 48 ± 22 km.