Three‐dimensional density model of the Nazca plate and the Andean continental margin

Abstract

[1] We forward modeled the Bouguer anomaly in a region encompassing the Pacific Ocean (85°W) and the Andean margin (60°W) between northern Peru (5°S) and Patagonia (45°S). The three-dimensional density model that reproduces the gravity field is a continental-scale representation of density structure to 410 km depth that characterizes the mantle and crust of the oceanic Nazca plate, subducted slab and continental margin with a minimum number of bodies. We predefined the density of each body after studying the dependency of density on composition of crustal and mantle materials and pressuretemperature conditions appropriate for the Andean setting. A database of independent geophysical information constrains the geometry of the top of the subducted slab, locally the Moho of the oceanic and continental crusts and, indirectly, the lithosphereasthenosphere boundary underneath the continental plate. Other boundaries, notably the intracrustal density discontinuity separating upper from lower crust below the continent, were not constrained and their geometry is the result of fitting the observed and calculated Bouguer anomaly during forward modeling. This contribution presents the model to the Andean geoscientific community and contains some tools, like a sensitivity analysis, that helps potential users of the model to interpret its results. We describe and discuss some of these results in order to illustrate the application of the model to the study of a wide range of phenomena (e.g., modification of oceanic plate structure by hot spots, shape of the subducted slab, thermal structure of the continental lithosphere, compensation mechanism and formation of orogenic relieve, causes of Andean segmentation).Citation: Tassara, A., H.-J. Götze, S. Schmidt, and R. Hackney (2006), Three-dimensional density model of the Nazca plate and the Andean continental margin,

Comparison of postseismic afterslip models with aftershock seismicity for three subduction-zone earthquakes: Nias 2005, Maule 2010 and Tohoku 2011

“…We assume a constant shear modulus μ = ρ * v 2 s = 35 GPa calculated from v s = 3385 m s −1 and ρ = 3050 km m −3 derived from tomography and gravity studies (Tassara et al 2006;Haberland et al 2009;Hicks et al 2012). Together with the scaling relations this results in a unique mapping between magnitude, slip and area (Fig.…”

Impact of megathrust geometry on inversion of coseismic slip from geodetic data: Application to the 1960 Chile earthquake

“…[4] In recent years, the crustal structure of the southcentral Chile margin has been derived from local seismological networks [Bohm et al, 2002;Haberland et al, 2006;Lange et al, 2007], deep seismic reflection and refraction profiles [Lüth et al, 2003;Groß et al, 2007], and forward modeling of the gravity field [Tassara et al, 2006;Tašárová, 2007]. The precise geometry of the slab obtained from combining these geophysical data sets differs notably from Barrientos and Ward's assumption of a planar slab; in the present image the dip angle has significant changes along the strike of the margin ( Figure S1 of the auxiliary material).…”

Assessing the tsunami building vulnerability PTVA-3 and PTVA-4 models after the 16S 2015 event in the cities of Coquimbo – La Serena (Chile)

“…it is smaller than in other regions of Chile, where the most typical distances range between 120 and 140 km (Fuentes 25 et al, 2016). According to Tassara et al (2006) and Pardo et al (2002) in this zone the subduction angle of the Nazca plate is almost horizontal at depths close to 100 km. This almost horizontal geometry of the plate gives rise to a strongly coupled inter-plate contact, a highly compressed continental crust with back-arc seismicity and shortening of the crust, together with the absence of active quaternary volcanoes in the Andes Cordillera (Jordan et al, 1983).…”