Seismic Activity in Palhano, CE, October, 1988, Preliminary Results

Abstract

A swarm of activity in Palhano, Cearâ, was studied with five portable
seismographs during a period of ten days following the fîrst large event of
magnitude 4.2 ry occurred on october 19, 1988. The events are confined to a depth range between about 2.5 and 5 km. The spatial distribution of the
hypocenters showed that rupture occurred on a wN"w-ESE oriented fault with a steep dip to NNE. A composite focal mechanism indicates a predominantly strike-slip (dextral) motion with a small component of normal faulting. These characteristics are very similar to other earthquake swaÍns near the border of the Potiguar Sedimentary Basin (Pacajus, CE, 1980, and João Câmara, RN, 1986/39). However, the NW-SE orientation of the P axis in Palhano is somewhat different from the roughly E-W orientation for the other two swarms. This difference may suggest that the regional stress field, with average wN'tw-ESE orientation for o1, could be locally modified by the Potþuar Sedimentary Basin.