Determination of parameters for historicaI British earthquakes

Abstract

Examination of 20th century data from the U.K. shows a good correlation between felt area and instrumental magnitude, producing good magnitude values for historical earthquakes where felt area is known; this is a more reliable method than using I0. The equations: ML = 1.03 log A3:; -0.19; ML = 0.92 log A4 + 0.71 give magnitude from areas within isoseismals 3 and 4 MSK. Dcpths for historical earthquakes have also been obtained using a modification of the well-known Sponheuer method, using the program MACDEP; the regional value for (á is 0.003 and depths for events with magnitude above 4 ML range from 3 to 25 km.