The two seismic transects of the TANGO Project will be the first deployment to utilize nodal instruments at a large spatial and temporal scale in the Andes.
The northern transect, at latitude ~23 °S, will be 600 km long with broadband seismic stations 2-3 km spaced (Figure below). The southern transect, at latitude ~36 °S, will be 400 km long with broadband seismic stations 30 km spaced, and 40 stations outside of the transects will improve earthquake locations and surface wave tomography (Figure below).
These data will provide a 3D view of the Andes at depth, allowing us to see lithospheric features such as the Moho discontinuity and the top of the subducting slab (Figures below). Seismic high resolution tomography is one of the most important ways to understand the structure of the Earth deeper than the surface, and it is crucial to study most of the Tectonic and Natural Hazard problems in science.
Map showing proposed broadly spaced broadband seismic stations (red stars), existing permanent stations (blue triangles), and previously temporary deployed seismic stations (black circles). Insets show an enlarged map of the two dense transects of 3-component nodal seismic stations (black bars with broadband station every ~30 km) and active volcanoes (magenta triangles). Stations CORD, ZOND and TRQA are permanent. Small black circles are previous seismic deployments with small apertures and only recorded during a limited time.
Planned Seismic Methods
Examples of types of seismic analysis proposed. (A) Example of finite frequency teleseismic P-wave tomography using 3D ray tracing from Portner et al., (2020) to image the deep portion of the slab especially at latitudes south of 34°S. (B) Reprocessed CCP receiver functions along the dense REFUCA seismic line with 10 km station spacing (Wölbern et al., 2009) at ~21.5°S (Isaacs, U. Arizona M.S. Thesis, 2016). This image was migrated with variable bin sizes based on a minimum number of crossing rays in each bin. The continental Moho (CM) has a high amplitude conversion under the western Altiplano (AP) and the eastern part of the Eastern Cordillera (EC) and Subandean zone (SAZ) but is gradational beneath the eastern Altiplano. The gradational Moho may indicate ongoing lithospheric removal. We interpret the west dipping detachment (WDD) as the Main Andean Thrust based on the Elger et al. (2006) geologic cross-section. We expect to be able to produce much better images along the two proposed dense seismic lines. (C) Example of a joint receiver function surface wave (Ambient Noise) inversion at 25.2°S across the arc in the southern Puna from Delph et al. (2017) using seismic data with ~20-30 km station spacing. (D) Example of local tomography from the Cascades in Oregon. a) Earthquake source gather from a M2.5 earthquake that occurred at the east end of a 130 km east-west line of 174 3C nodal seismometers in central Oregon. Prominent seismic phases are labeled. b) Final Vp model. c) Final Vp/Vs model. Large gray circles are earthquakes used in the local earthquake tomography study and small gray circles are earthquakes from the PNSN catalog for the past 10 years. White dashed line outlines the change from low Vp to high Vp in the lower crust. (E) Progressive joint inversion of local travel times and Rayleigh wave dispersion in the Chile forearc near ~31°S from Comte et al. (2019). Grey circles are earthquakes.
Department of Geosciences, University of Arizona, 1040 E 4th St., Tucson, AZ 85721
Contact slbeck@arizona.edu, veledamuller@arizona.edu, and cadenhowlett@arizona.edu for more information.