The 29th November, 2020 Earthquake in the Eastern Cordillera (NW Argentina): new results on InSAR and coherence time-series analyses

On November 29, 2020 an ~6 Mw earthquake occurred at a depth of almost 10 km (United States Geological Survey) in the Eastern Cordillera in northwestern Argentina. The epicenter was located near the towns of Caspalá and Santa Ana (Salta province) in the Quebrada de Humahuaca, and the maximum surface deformation was measured over the Hornocal syncline. The earthquake was the first recorded in this area in the last three decades. As a consequence, several mass movements were triggered from the nearby slopes composed of mechanically weakened rocks. Fortunately, only damage to buildings and infrastructure were reported.

This research presents the vertical deformation associated with this event relying on Sentinel 1A/1B C-band and ALOS2 L-band data. We generate interferometric time series from the Sentinel data, spanning 2 years prior to the event, on ascending and descending passes and invert to displacement time series. We use ALOS2 (Scansar mode) data on ascending and descending passes, and create interferograms by pairing images acquired before and after the earthquake. We determine the three-dimensional motion components by combining the four view angles. Using the Sentinel-1 data, we analyzed the coherence time series to identify mass movements triggered by the earthquake, thus we present a mass-movement detection approach for SAR coherence data using varying time scales and durations of coherence calculations.

Based on the interferometric time series from the Sentinel data on ascending and descending passes, we measured a maximum cumulative line-of-sight (LOS) displacement of about 10 cm over the Hornocal syncline. We measured similar LOS displacement in interferograms based on ALOS data. We determine that the Hornocal fold subsided and the maximum deformation area was constrained between 65.25° and 65.10° W longitude with 23.31° S as central latitude. Moreover, results based on the coherence time series showed that the maximum concentration of mass movements occurred within the closest 10 km of the epicentre, mainly on the slopes of the Hornocal syncline. Additional mass movement signals were recorded several kilometres from the source. The mass movements triggered by the earthquake exceed the number of mass movements associated with rainfall during the South American Monsoon.