Seismic investigation of the continental margin off- and onshore Valparaiso, Chile

Crustal structure across the coseismic rupture zone of the 1944 Tonankai earthquake, the central Nankai Trough seismogenic zone

“…The coseismic rupture zones of the 1985 event estimated from aftershock distribution [Choy and Dewey, 1988], tsunami modeling [Nakamura, 1992], and dislocation modeling of coseismic deformation [Barrientos, 1995] are all consistent with each other. The updip limit of this rupture zone is not shallower than the area of high-velocity rock (<5.5 km/s) in the upper plate that is interpreted as part of the continental framework [Fleuh et al, 1998]. Although Oleskevich et al [1999] proposed that thermal constraint to the downdip limit is provided by the intersection of the subducting oceanic plate with the continental forearc Moho at $40 km depth determined from hypocenter distribution, we believe that the crustal model of Fleuh et al [1998] directly deduced from wide-angle seismic survey across the entire presumed rupture zone [e.g., Barrientos, 1995] shows more precise information about the depth on the slab beneath the downdip limit.…”

“…Second, there are differences between crustal models of outside and inside of the coseismic rupture zone, e.g., the different subduction angle and the existence of the low-velocity zone in the sedimentary wedge. Fleuh et al [1998] interpreted these differences to be responsible for the ridge subduction which is recognized between these two profiles. The coseismic rupture zones of the 1985 event estimated from aftershock distribution [Choy and Dewey, 1988], tsunami modeling [Nakamura, 1992], and dislocation modeling of coseismic deformation [Barrientos, 1995] are all consistent with each other.…”

“…However, assuming a constant subduction angle, the landward extension of top of the subducting oceanic crust can be estimated to reach $25 km depth at the downdip limit, which is almost consistent with the uniform downdip limit depth of the Nankai Trough obtained from our study. Two crustal models deduced by wide-angle seismic profiles off Valparaiso, Chile, are presented by Fleuh et al [1998]; one is selected to cross the coseismic rupture zone of the 1985 earthquake (M w = 8.0) [Comte et al, 1986], and another is located just north of the rupture zone. These crustal models show the subducting Nazca plate beneath South America.…”

Structure and tectonics of the central Chilean margin (31°–33°S): implications for subduction erosion and shallow crustal seismicity

“…The shoots were triggered in time intervals of 60 s on full minutes UTC. At a speed of 5 knots that results in a shot point distance of 154 m. A constant hydrophone spacing of 25 m (108 channels) was chosen for the seismic processing, resulting in a common mid-point distance of Flueh et al (1998) and Zelt (1999), P1; and this work, P2. Pink triangles correspond to the OBH/S analysed in this study, while the yellow triangles indicate the two stations shown in Fig.…”

“…Basal erosion enhanced by the JFR subduction has most likely thinned the continental crust at large depths and increased the subsidence rate of the margin to form the Valparaíso Forearc Basin (VFB; Laursen et al 2002). South of the ridge-trench collision zone, the continental margin is characterized by a broad continental shelf (upper and middle slope), and a relatively large 20-40 km wide accretionary prism that constitutes the lower part of the upper plate (Flueh et al 1998;Zelt 1999;Contreras-Reyes et al 2013). In contrast, in the pre-and current collision zone, the upper slope descends steeply from a narrow (5-10 km wide) uplifted shelf, and the toe of the margin is truncated by subduction erosion processes (von Huene et al 1997;1999;Laursen et al 2002;Ranero et al 2006).…”