Crustal motion and deformation in Ecuador from cGNSS time series

Abstract

In this paper, we present the first velocity field from cGNSS (continuous GNSS) stations in the Continuous Monitoring GNSS Network (REGME) in Ecuador. We have analyzed data from 33 cGNSS REGME stations for the 2008–2014 period in order to characterize horizontal crustal motion and deformation in Ecuador. Prior to this, we analyzed the time series for the 33 REGME stations in order to determine their seasonality and the type of spectral noise. For most stations, we found a predominance of uncorrelated white noise with annual and semi-annual variations as the predominant first and second periods. Velocity was estimated by introducing the trend, seasonality and noise in each series in the general model, thus allowing us to improve accuracy as well as magnitude. The velocity and strain distribution correspond to the transpressive right-lateral slip of the westward-dipping faults of the Major Dextral System and the NNE movement of the North Andean Block (NAB) relative to the South American plate. The distributions of our deformation rate and velocity field indicate a differentiated tectonic behavior between northern, central and southern Ecuador. In northern Ecuador, there is an estimated right-lateral motion of 7.6 ± 0.5 mm/yr, consistent with the NNE movement of the NAB relative to the South American plate. In central Ecuador, the right-lateral motion decreases to 5.3 ± 0.4 mm/yr. In the southern region of Ecuador (from the Guayaquil Gulf to Peru) there is no strain accumulation, GNSS velocities decrease and turn to south. This zone belongs to the so-called Inca or Peru sliver.

These results are consistent with the distinct behavior of subduction in Ecuador, with no coupling in southern Ecuador, and increased coupling towards the north, in the zone where megathrust earthquakes have occurred over the last century. The southern part of the Carnegie Ridge marks the limit between the two zones.

We suggest that the main driving force responsible for the ongoing crustal deformation in Ecuador is the convergence between the Nazca and South American plates with the variable coupling pattern and the collision of the Carnegie Ridge. This results in different velocity patterns for the northern and the southern parts of Ecuador.