Association of Mw = 6.4, 2000/06/16 and Mw = 5.7, 2003/01/07 intermediate-depth earthquakes, in subducted Nazca plate

SPAGNOTTO, S. L; TRIEP, E.G.; LAURA GIAMBIAGI; NACIF, S. V.

Bogotá

Congreso; III Congreso Latinoamericano de Sismología; 2014

IASPEI Regional Assembly. Latin-American and Caribbean Seismological Commission. LACSC

The Nazca plate is subducted beneath the South American plate characterized by along-strike variations in slab dip angle. The angle of subduction is ~ 27° in the studied earthquakes area. The intermediate earthquakes in a subduction environment have been related to pull slab forces and dehydration processes of the slab. The Mw=6.4, 16/6/2000 and Mw=5.7 7/1/2003 intermediate depth (~ 120 km) earthquakes were analyzed. These earthquakes are closely related to each other, with the first one, which breaks the oceanic subducted crust, increasing the Coulomb static stress around ~ 1 bar in the area where the rupture of the second one began (Figure 2). The rupture of the second event was developed in the mantle and penetrated into it to about 40 km in depth. The mechanisms were obtained by waveform inversion (Kikuchi and Kanamori, 1982, 1991, Kikuchi et al. 1993) and slip distribution using direct modeling with the same software. Coulomb static stress changes were calculated using Coulomb 3.2 software (Toda et al, 2005, Lin and Stein, 2004). For the 2003 earthquake, the fault plane is defined by aftershocks which were determined by Marot et al (2012); while for the 2000 earthquake, we define the fault plane by association with the 2003 earthquake. We propose that both earthquakes are related, indicating the subducted crust rupture of 2000 earthquake which promotes the rupture of 2003 earthquake on the mantle around 18 months later. The 2000 and 2003 rupture planes strike parallel to the outer rise, suggest that the crustal fault is originated in this tectonic environment.