Bina, C. R., and R. M. Russo, Stress triggering of aftershocks to the 09 July 1997 Cariaco, Venezuela, earthquake, Eos, Transactions of the American Geophysical Union, 80, Spring Supplement, S42A-08, 1999.
We calculate surface displacements, strains, and tilts due to motion on a buried rectangular fault modeled to represent the magnitude Mw = 6.9 Cariaco, Venezuela, earthquake of 09 July 1997. We examine the resulting model strain field for correlations with the observed spatial distribution of aftershocks, as recorded by portable seismic networks deployed locally (by ourselves and others) immediately following the main shock. The main shock, which ruptured the ground surface from near San Antonio del Golfo in the west to near Casanay in the east, exhibited dextral slip on an E-W striking segment of the El Pilar Fault. The preliminary centroid moment tensor focal mechanism (determined by Harvard University) and the observed distribution of 180 aftershocks indicate largely dextral E-W strike-slip on a steeply N-dipping fault plane. Our results indicate that the main shock should have generated a lobe of large tensional strains extending to the SE of the epicenter. This zone of calculated tension corresponds to the region of aftershock seismicity observed up to ~60 km SE of the rupture zone, suggesting that the spatial distribution of aftershocks far from the source may reflect changes in the static stress field triggered by the main shock. If so, then the aftershocks should exhibit mechanisms consistent with optimal orientations for the Coulomb failure criterion.Copyright © 1999 American Geophysical Union