New evidences of rupture of crust and mantle in the subducted Nazca plate at intermediate-depth

摘要

Between 33 degrees-36 degrees S, the Nazca plate subducts below South American plate with an angle of similar to 30 degrees, and it is seismically active until similar to 200-280 km depth. At 33.5 degrees S, the seismicity decreases drastically at 120 km depth, just below the volcanic arc. In this paper, we studied a pair of associated earthquakes located in the area where the frequency of seismicity changes. The hypocenters of the M-w = 6.4, June 16th, 2000 and M-w = 5.7 January 7th, 2003 earthquakes were found nearby, adjacent to the oceanic Moho, closely associated with each other. The slip on the plane of the 2000 event produced Coulomb stress changes on the fault plane of 2003, both westward dipping, with a variation from similar to 1 bar near the hypocenter of the latter to similar to 0.1 bars in the deepest part of the plane. The two earthquakes combined process describes a normal focal mechanism, which cuts through the crust and breaks the mantle, reaching depths of similar to 40 km below the Moho.