TECTONIC AND KINEMATIC REGIME ALONG THE NORTHERN CARIBBEAN PLATE BOUNDARY - NEW INSIGHTS FROM BROAD-BAND MODELING OF THE MAY 25, 1992, M-S=6.9 CABO-CRUZ, CUBA, EARTHQUAKE

On May 25th, 1992, an M-s = 6.9 earthquake occurred off the southweste rn tip of Cuba, alone the boundary between the Caribbean and North Ame rican plates. This earthquake was the largest to strike southern Cuba since 1917 and the largest ever recorded in that region by global seis mic networks. It is therefore a key element for our understanding of t he tectonic and kinematic regime along the northern Caribbean plate bo undary. In order to test the previously proposed source parameters of the Cabo Cruz earthquake and to better constrain its focal mechanism, we derived a new set of source parameters from unfiltered broad-band t eleseismic records. We used a hybrid ray tracing method that allows us to take into account propagation effects of seismic waves in a realis tic crustal model around the source. Our solution is consistent with t he long-period focal mechanism solution of Virieux er al. (1992). Our solution also models the higher frequency crustal and water layer phas es. The primarily strike-slip focal mechanism has a small thrust compo nent. Its shows an east-west trending nodal plane dipping 55 degrees t o the north that we interpret as the rupture plane since it correspond s to the geometry of the major active fault in that area. The displace ment on this plane is a left-lateral strike-slip combined with a small amount of southward thrust. The result is in good agreement with the active tectonic structures observed along the Oriente fault south of C uba. The small thrust component demonstrates that, contrary to prior b elief, the transpressive regime extends along this whole segment of th e Caribbean/North American plate boundary. Together with historical se ismicity, it, suggests that most of the stress accumulated by the Cari bbean/North American plate motion is released seismically along the so uthern Cuban margin during relatively few but large earthquakes.