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

SILVANA SPAGNOTTO; TRIEP, ENRIQUE; LAURA GIAMBIAGI; SILVINA NACIF; ORLANDO ALVAREZ

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2015 vol. 58 p. 141 - 147

0895-9811

Between 33°-36°S, Nazca plate subducts below South American plate with an angle of ~30°, and it is seismically active until ~200-280 km depth. At 33.5°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 Mw=6.4, June 16th, 2000 and Mw=5.7 January 7th, 2003 earthquakes were found nearby, adjacent to the oceanic Moho, closely associated between 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 ~ 1 bar near the hypocenter of the latter 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 ~ 40 km below the Moho. The composed fault plane of the 2000 and 2003 events corresponds to a west-dipping normal fault with strike and dip consistent with those of the outer ridge faults. Thus, it can be a preexisting fault originated in that environment. The slip on the composed fault plane is consistent with the bending produced by the slab pull. Dehydration might add some contribution to the process.