Earthquake hazard assessment in Southeastern Brazil

Abstract

Southeastern Brazil is subject to the low level of seisihi.c activity typical of intra-plate regions. One large-magnitude eartltquake (mb=6.3) and three more with mb magnitude above 5.0 have occurred in this region during the last 200 years. Just over a dozen earthquakes with ffib magnitude between 4.0 and 5.0 ~e known. Instrumental data are available since the 1970's when the South American Array Station was installed in Brasilia. Several other short period vertical stations have now been installed within the region. The frequency/magnitude relation from mb>3.0 is given by Log•(N)=3.09 (±0.12)-1.06(±0.10)mb. The b value with the maximum likelihood method is 1.10(±0.33), in close agreement with the value presented above. Using the extreme value method, it is possible to determine other recurrence curves and to estimate the seismic risk in the region. Recurrence intervals agree with observed values of magnitude m~5.0. For larger magnitude events, the catalog is too small to make valid comparisons. The recurrence intervals for mb magnitude 5.1, 5.5 and 6.3 events are 200, 600 and 4,000 years respectively.