Regional Seismology in Argentina
Final technical rept. 1 May 1979-30 Sep 1980
UNIVERSIDAD NACIONAL DE TUCUMAN (ARGENTINA) FACULTAD DE CIENCIAS EXACTAS Y TECHNOLOGIA
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An orientation study on regional seismology in Argentina reveals extensive actual and projected seismometry. Data digitization is being initiated at some stations, and modern computing systems are being acquired. Most of the regional seismicity is explained in terms of the subduction of the Nazca plate under the South American continent, but also intraplate earthquakes have occurred. Part of the subduction, initially with a dip angle of 30 deg, is horizontal. Seismicity gaps exist in the Province of Tucuman, and in depth between 350 and 500 km. Source parameters for the Salta, 1973 and Caucete, 1977 earthquakes are reported. Refraction profiles suggest complex velocity structures in the earths upper 6 km. Short-period noise levels vary more than 30 dB with local geologies. Micro-seismic storm long-period energy is mainly between 5 and 10 seconds periods. Negative first motion on Argentinian P-waves from Nevada Test Site presumed underground nuclear explosions may indicate tectonic strain release associated with these events. Primary Eurasian event signals are PKP-waves, in correspondence with standard travel time vs. distance curves. Signal arrivals between P- and S-waves seem to be P- to S-wave and S- to P-wave conversions on the lithosphere-asthenosphere boundary, according to the literature, suggesting that this boundary may be at a depth of 400 km.