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Item type:Publication, Earthquake surface ruptures on the altiplano and geomorphological evidence of normal faulting in the December 2016 (Mw 6.1) Parina earthquake, Peru(Elsevier, 2020-12-13)The 2016 Mw 6.1 Parina earthquake ruptured a shallow-crustal normal fault within the high Andes of south Peru. We use high-resolution DEMs and field mapping of the surface ruptures generated by the earthquake, in combination with co-seismic and post-seismic InSAR measurements, to investigate how different features of the geomorphology at Parina are generated by the earthquake cycle on the Parina Fault. We systematically mapped 12 km of NW-SE trending surface ruptures with up to ~27 cm vertical displacement and ~25 cm tensional opening along strike, separated by a gap with no observable surface ruptures. Co- and post-seismic InSAR measurements require slip below this gap in surface ruptures, implying that surface offsets observed in paleoseismic trenches may not necessarily be representative of slip at seismogenic depths, and will typically yield an underestimate of paleo-earthquake magnitudes. The surface ruptures developed along 10–20 m high cumulative scarps cutting through late Quaternary fluvio-glacial deposits and bedrock. The 2016 Parina earthquake did not rupture the full length of the late Quaternary scarps, implying that the Parina Fault does not slip in characteristic, repeat earthquakes. At Parina, and across most of the Peruvian Altiplano, normal faults are most-easily identified from recent scarps cutting late Quaternary moraine crests. In regions where there are no recently-deposited moraines, faults are difficult to identify and lack time constraints to quantify rates of fault slip. For this reason, current fault maps may underestimate the seismic hazard in the Altiplano. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Pliocene river capture and incision of the northern altiplano: Machu Picchu, Peru(Geological Society of London, 2020-01-01)The Abancay Deflection, forming the northern edge of the Altiplano in the Peruvian Andes, is a remarkable geomorphological feature marking the along-strike segmentation of the Andes. Little is known about the timing and spatial distribution of exhumation in this area. To constrain the exhumation history of the Abancay Deflection and its drivers, we present apatite (U–Th)/He and fission-track thermochronology data from samples collected along an elevation transect at Machu Picchu. Geomorphological analysis demonstrates recent and continuing drainage reorganization recorded by the spatial distribution of the normalized steepness index ( k sn ) and normalized integrated drainage area ( χ ) parameters. Thermochronologically derived cooling rates are converted into exhumation using regionally constrained geothermal gradients between 16 and 26°C km −1 . Time–temperature inversions imply steady and slow exhumation (<0.05 km Ma −1 ) between 20 and 4 Ma, followed by rapid exhumation (>0.9 km Ma −1 ) since 4 Ma. The timing of rapid exhumation, combined with the geomorphological analysis, suggests that fluvial capture of the previously endorheic Altiplano by the Urubamba River drove recent incision and exhumation. Depending on the value of the geothermal gradient used, total exhumation since 4 Ma can be explained by river incision alone or requires additional exhumation driven by tectonics, possibly associated with movement on the Apurimac fault. Supplementary material: Additional information is available at 10.6084/m9.figshare.c.5177343 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Locating active faults in the Cusco Valley using magnetotelluric and radon gas data(RELX Group (Netherlands), 2024-01-01)