Structure of the Middle America trench in Oaxaca, Mexico
1988; Elsevier BV; Volume: 154; Issue: 3-4 Linguagem: Inglês
10.1016/0040-1951(88)90106-0
ISSN1879-3266
AutoresF. A. Nava, F. J. Núñez-Cornũ, Diego Córdoba, M. Mena, Jörg Ansorge, José A. González, M. Rodríguez, E. Banda, St. Mueller, Agustín Udías, Maritza Roxana García-García, G. Calderón,
Tópico(s)Geological and Tectonic Studies in Latin America
ResumoDeep seismic profiling was carried out in south and central Oaxaca as a multinational (Mexico, Spain and Switzerland) project. Sixteen sea-bottom explosions, ranging from 20 to 1000 kg were recorded by thirty portable instruments along three profiles, two along the coast and one going inland in an approximate N-S direction. Gravity surveys were carried out over the seismic profile lines, and the resulting Bouguer anomalies are interpreted together with the seismic data. Preliminary results indicate changes in the crustal thickness along the coast, near the town of Pinotepa Nacional, from 23.5 km in the northwest to 19 km in the southeast, reaching a minimum of some 15 km near the middle of the profile, about 140 km northwest of Puerto Angel. The coastal structure section consists roughly of two layers, an upper one with P-wave velocities that range from 5.1–5.4 to 5.8–6.0 km/s and a lower one where the P velocity range is from 6.0–6.2 to 6.3–6.4 km/s, overlying material with P-wave velocities of 7.45 km/s. Along the coast from Puerto Angel to Salina Cruz, the dip of the Cocos plate appears to be much less than it is to the northwest. A low-velocity zone, which corresponds to the top of the subducted oceanic crust, with P-wave velocities of 6.5–6.9 km/s, is found beneath the 2–3 km thick 7.45 km/s layer. The possible presence of an intrusive body is suggested by anomalous seismic arrivals and by a large gravimetric anomaly near Puerto Angel, close to the southern tip of Mexico.
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