The knowledge about the distribution of active faults is crucial for hazard assessment (Costa et al., 2020; Santibáñez et al., 2019; Wesnousky, 1986) but also provides insights into tectonic control on hydrological processes (Binnie et al., 2020; Jeffery et al., 2013; Pan et al., 2013) or georesource distribution (Goldsworthy & Jackson, 2000; Viguier et al., 2018). Furthermore, tectonically driven topographic uplift and its impact on climate (Armijo et al., 2015; Houston & Hartley, 2003; Rech et al., 2019; Zhisheng et al., 2001) can be better understood if a systematically mapped fault database exists.
Here we present an active fault database, as well as the distribution of drainages, for an area between 18.50°S and 19.45°S in Northern Chile forearc, which were systematically mapped in the framework of the project “Cluster C05-Tectonic Geomorphology: Adaptation of drainage to tectonic forcing” of the CRC1211- Earth Evolution at the Dry Limit.
The Central Andes forearc at this latitude is located at a highly tectonically active convergent margin and hosts major earthquakes not only on the plate boundary itself (e.g., Métois et al., 2016), but also in the overriding crust (e.g., Comte et al., 1999). It comprises, from west to east, the Coastal Cordillera, Longitudinal Valley and the Western Flank of the Altiplano, showing an impressive amount of topographic variability of ca. 4000 m. Nevertheless, Neogene crustal tectonic structures and surface deformation are poorly documented. The overall landscape appears as a gentle west-sloping pediplain dissected by deep transversal canyons (quebradas), which reach the current Pacific Ocean (Mortimer, 1980). The Longitudinal Valley is a sedimentary basin filled with 432 to 2000 m of Tertiary to Quaternary deposits derived from the Altiplano in the east as well as the Coastal Cordillera in the west (García et al., 2017). Its surface is composed by a multiphase planation surface called the Pacific Paleosurface (PPS), which distribution is suggested to be controlled by crustal tectonics (Evenstar et al., 2017). Depending on the low ratio of tectonic displacement rate to sedimentation rate, many active faults are hidden and only a specialized approach of high-resolution fault mapping, together with a morphometric analysis of the drainage pattern provides systematic information about the distribution of active faults, folds and related structures.
The present fault database is the result of creating a comprehensive catalogue of faults classified by the age of last proven/probable tectonic activity. This is accompanied by a compilation of existing age data and a map of drainage pattern. These datasets were compiled in QGIS 3.16.5 (https://www.qgis.org) and are available as. gpkg for GIS applications and as .kml formats to be visualized in Google Earth.
We present a new seismic tomography model for the crust and upper-mantle beneath the Central Andes based on multi-scale full seismic waveform inversion, proceeding from long periods (40–80 s) over several steps down to 12–60 s. The spatial resolution and trade- offs among inversion parameters are estimated through the multi-parameter point-spread functions. P and S wave velocity structures with a spatial resolution of 30–40 km for the upper mantle and 20 km for the crust could be resolved in the central study region. In our study, the subducting Nazca slab is clearly imaged in the upper mantle, with dip-angle variations from the north to the south. Bands of low velocities in the crust and mantle wedge indicate intense crustal partial melting and hydration of the mantle wedge beneath the frontal volcanic arc, respectively and they are linked to the vigorous dehydration from the subducting Nazca plate and intermediate depth seismicity within the slab. These low velocity bands are interrupted at 19.8-21° S, both in the crust and uppermost mantle, hinting at the lower extent of crustal partial melting and hydration of the mantle wedge. The variation of lithospheric high velocity anomalies below the backarc from North to South allows insight into the evolutionary foundering stages of the Central Andean margin. A high velocity layer beneath the southern Altiplano suggests underthrusting of the leading edge of the Brazilian Shield. In contrast, a steeply westward dipping high velocity block and low velocity lithospheric uppermost mantle beneath the southern Puna plateau hint at the ongoing lithospheric delamination.