Orogenic plateaus can exist in a delicate balance in which the buoyancy forces due to gravity acting on the high topography and thick crust of the plateau interior are balanced by the compressional forces acting across their forelands. Any shortening or extension within a plateau can indicate a perturbation to this force balance. In this study we present new observations of the kinematics, morphology and slip rates of active normal faults in the South Peruvian Altiplano obtained from field studies, high resolution DEMs, Quaternary dating and remote sensing. We then investigate the implications of this faulting for the forces acting on the Andes. We find that the mountains are extending ~NNE-SSW to ~NE-SW along a normal fault system that cuts obliquely across the Altiplano plateau, which in many places reactivates Miocene age reverse faults. Radiocarbon dating of o set late Quaternary mor...

[EN] 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...

We present the results of a paleoseismic survey of the Incapuquio Fault System, a prominent transpressional fault system cutting the forearc of South Perú. High-resolution Digital Elevation Models, optical satellite imagery, radiocarbon dating, and paleoseismic trenching indicate that at least 2–3 m of net slip occurred on the Incapuquio Fault generating a complex, ∼100-km long set of segmented fault scarps in the early 15th century (∼1400–1440 CE). We interpret the consistent along-strike pattern of fault scarp heights, geometries and kinematics to reflect a surface rupture generated by a single Mw 7.4–7.7 earthquake, suggesting that brittle failure of the forearc poses a significant, yet mostly overlooked, seismic hazard to the communities in coastal areas of Perú. The timing of this earthquake coincides with the collapse of the Chiribaya civilization in ∼1360–1400 CE, ...

Trabajo presentado en el “6th Colloquium on historical earthquakes & paleoseismology studies : Their contribution to the knowledge of the long-term seismic activity and to seismic hazard assessment”, 24-26 October 2018, Han-sur-Lesse, Bélgica.

A system of active normal faults around the city of Cusco have severely damaged the city in major earthquakes in pre-hispanic times, 1650 and 1950 CE. Detailed studies of these faults adjacent to Cusco are therefore needed to build an understanding of seismic hazard in the region. We present new geomorphological and paleoseismological evidence for multiple Holocene earthquakes on the Tambomachay Fault, a 20 km-long normal fault that runs along the northern margin of the Cusco Basin. The western segment of the fault preserves fault scarps that cut moraine crests with a mean throw of 4.3 ± 0.4 m. We determine a 13.8 ± 0.6 ka depositional age of these moraines using 10Be cosmogenic surface-exposure dating of boulders embedded in the moraines, implying a Holocene-average fault slip rate of 0.3 ± 0.1 mm/yr. We also excavated a trench across the moraine crests. By reconstructing the trench ...