CLOSE IN SCS AND SSCS REVERBERATIONS FROM THE 9 JUNE 1994 BOLIVIAN EARTHQUAKE

Recordings of the Bolivian Earthquake of 9 June, 1994 from two portable experiments were analyzed for ScS and sScS reverberations. These stations span the distance range 6 degrees - 22 degrees, sampling the mantle beneath South America along an EW line from the central Andes to the Brasilian Craton. We used the CORE method to obtain path-averaged locations of the Moho and 400 and 660 km discontinuities. The average depth for D-400 is 410km for the BANJO stations and 395km beneath Brazil, and the value for D-660 is 700km for BANJO and 675km for BLSP, while the difference D-660-D-400 = Delta D is 290km and 280km respectively. These values are much larger than the global average (around 245km) and suggest 200 degrees - 300 degrees colder temperatures in the region sampled. This is most plausibly explained by the reduced temperatures in the slab and surrounding region. We also detect a significant discontinuity at 210 km depth, with a shear wave impedance increase of at least 5%. Finally, we observe systematic variations in duration between P, ScS and sScS that can only be attributed to source finiteness. These observations constrain the inclination of an equivalent unilateral rupture velocity vector to be -17 degrees (positive up from horizontal). Our rupture model is consistent with models derived from subevent analysis of the P wave arrivals, and implies a source extent of 72 km.