Extension and Dynamics of the Andes Inferred From the 2016 Parina (Huarichancara) Earthquake

Abstract

The Mw 6.1 2016 Parina earthquake led to extension of the south Peruvian Andes along a normal fault with evidence of Holocene slip. We use interferometric synthetic aperture radar, seismology, and field mapping to determine a source model for this event and show that extension at Parina is oriented NE‐SW, which is parallel to the shortening direction in the adjacent sub‐Andean lowlands. In addition, we use earthquake source models and GPS data to demonstrate that shortening within the sub‐Andes is parallel to topographic gradients. Both observations imply that forces resulting from spatial variations in gravitational potential energy are important in controlling the geometry of the deformation in the Andes. We calculate the horizontal forces per unit length acting between the Andes and South America due to these potential energy contrasts to be 4–8 ×1012 N/m along strike of the mountain range. Normal faulting at Parina implies that the Andes in south Peru have reached the maximum elevation that can be supported by the forces transmitted across the adjacent foreland, which requires that the foreland faults have an effective coefficient of friction ≲0.2. Additionally, the onset of extension in parts of the central Andes following orogen‐wide compression in the late Miocene suggests that there has been a change in the force balance within the mountains. We propose that shortening on weak detachment faults within the Andean foreland since ∼5–9 Ma reduced the shear tractions acting along the base of the upper crust in the eastern Andes, leading to extension in the highest parts of the range.

Coseismic and Postseismic Deformation of the 2016 MW 6.2 Lampa Earthquake, Southern Peru, Constrained by Interferometric Synthetic Aperture Radar

“…The postseismic interferograms clearly show surface strain occurring (Figure ). The shape of the displacement pattern shows an NW‐SE alignment, which is consistent with the surface projection of west dipping fault model determined in section and the surface rupture reported by Wimpenny et al (). The time series of ascending and descending track updip the coseismic rupture show displacement toward the same direction in LOS, which implies significant vertical movements.…”

“…Postseismic deformation over ~1 year after the 2016 Lampa earthquake shows surface subsidence near the surface projection of the optimal fault model. This characteristic is well explained by the kinematic model of afterslip updip of the earthquake rupture (Wimpenny et al, ). The maximum afterslip over the observation period is 7.7 cm.…”

“…The ascending and descending track are both dominated by large negative LOS motion (away from the satellite locations), −3.2 cm for ascending track and −2.7 cm for descending track. Noting that the region marked Q in Figure is an open cast quarry, the abnormal surface deformation measured near that region may be due to the open cast quarrying activity (Wimpenny et al, ). Therefore, we masked this affected area (Figure ) during the inversion, because it might have nothing to do with postseismic slip and be biasing the misfit estimates.…”

Volcano-tectonic interactions at Sabancaya volcano, Peru: eruptions, magmatic inflation, moderate earthquakes, and fault creep

“…To establish any connection between seismicity and magmatic activity at Sabancaya, we must first rule out that the timing and location of the seismicity is simply due to local tectonics alone. The earthquakes modeled in this study and that of Jay et al [2015] are consistent with regional fault trends, and the normal faulting observed in this study is expected in this region due to a rotation of the stress tensor in areas of high relief [Dalmayrac and Molnar, 1981;Wimpenny et al, 2018;Mering et al, 1996;Devlin et al, 2012]. ure S1).…”

Observations and dynamical implications of active normal faulting in South Peru

“…However, these faults are thought to reflect permanent deformation in response to the megathrust earthquake cycle [Saillard et al, 2017], not orogen-wide changes in the force balance persistent over millions of years. Second, the extending regions in the high mountains correlate along-strike with areas of low-angle detachment faulting in the fold-thrust belt that bounds the eastern edge of the Andes, known as the sub-Andes [Wimpenny et al, 2018]. Finally, the suggested timing for the onset of extension in the Andes correlates with a change in the location and rate of shortening in the sub-Andes at ∼5-9 Ma [e.g.…”