Datensatz

Zusammenfassung

Preliminary locations for earthquakes recorded by the Central Andean southern PUNA seismic array, which operated between December 2007 and November 2009, show widespread low magnitude seismicity in the region of the well known teleseismic gap between 25°S and 28°S, which is here referred to as the Antofalla teleseismic gap. The southern PUNA experiment, which is a collaboration of Argentine, Chilean, German and U.S. scientists, consisted of 75 stations deployed over an area bounded by 25°S to 28°S and 70°W to 65°W. The US component of the network included 23 broad band and 22 short period seismometers; the German component included 9 broadband and 21 short period seismometers. Previous regional geophysical studies (e.g. Cahill and Isacks 1992) showed a relative lack of crustal earthquakes as well as few large events below 100 km in the Wadati-Benioff zone between 25°S and 28°S. The southern Puna Antofalla gap in teleseismicity is also evident in the current PDE global catalog. Nevertheless, new data from the PUNA network show substantial low magnitude seismic activity (generally <3.5), both within the crust and at depths 200~300 km appropriate for the subducting Nazca plate between 25°S and 28°S and 70°W to 65°W. Comparison of preliminary event locations from the PUNA array with positions of working mine blasts indicates a location accuracy of 5 km for these events. The high ratio of smaller to larger magnitude events in the Antofalla teleseismic gap is consistent with high temperatures in both the crust and upper mantle related to late Neogene steepening of the Wadati-Benioff zone and delamination of thickened crust and lithosphere. High crustal and mantle temperatures are reflected by post-Pliocene mafic lava flows and silicic ignimbrite eruptions including the giant Galán eruption.