Estimation of Depth and Attenuation of Earthquakes in Bolivia

摘要

It is well known that, without depth phases or phases from a few nearby seismograph stations, the depths of many events cannot be accurately determined and must be assigned. This is especially true in regions of subduction. Carefully drawn intensity maps of 11 felt earthquakes in Bolivia have been examined and the depths of these earthquakes have been determined from the K vesligethy formula I(o)-I(n)=a log (r(n)/h) + b(r(n)-h) where r(n) is the mean hypocentral distance to the closest points of intensity I(n), h is depth, a and b are constants and I(n) is less than I(o). With the depths of the earthquakes determined, the approximate horizontal acceleration caused by them has been found to be log a(h)=0.35 M(w)-0.54 log (r/h)-0.0036 (r-h), h less than 70 km, log a(h)=0.33 M(w)-1.38 log (r/h), 70 km less than= h less than 150 km, log a(h)=0.30 M(w)-1.50 log (r/h), 150 km less than=h less than 330 km, log a(h)=0.21 M(w)-1.85 log (r/h), 330 km less than = h, where r is hypocentral distance and M(w) is moment magnitude. The attenuation corresponding to these accelerations has been compared with that for P waves of Richter (1958) and of Veith and Clawson (1972), and with that for P(g) and L(g) waves for France of Campillo and Plantet (1991). With the seismic array around Cochabamba in central Bolivia operating, locations of seismic events and observations of attenuation in Bolivia have been much improved.