Quaternary rupture of a crustal fault beneath Victoria, British Columbia, Canada

The seismic potential of crustal faults within the forearc of the northern Cascadia subduction zone in British Columbia has remained elusive, despite the recognition of recent seismic activity on nearby fault systems within the Juan de Fuca Strait. In this paper, we present the first evidence for earthquake surface ruptures along the Leech River fault, a prominent crustal fault near Victoria, British Columbia. We use LiDAR and field data to identify >60 steeply dipping, semi-continuous linear scarps, sags, and swales that cut across both bedrock and Quaternary deposits along the Leech River fault. These features are part of an ~1-km-wide and up to >60-km-long steeply dipping fault zone that accommodates active forearc transpression together with structures in the Juan de Fuca Strait and the U.S. mainland. Reconstruction of fault slip across a deformed <15 ka colluvial surface near the center of the fault zone indicates ~6 m of vertical separation across the surface and ~4 m of vertical separation of channels incising the surface. These displacement data indicate that the Leech River fault has experienced at least two surface-rupturing earthquakes since the deglaciation following the last glacial maximum ca. 15 ka, and should therefore be incorporated as a distinct shallow seismic source in seismic hazard assessments for the region.This research was supported by an NSERC Discovery grant to KM and NSF EAR IRFP Grant #1349586 to CR

EON-ROSE and the Canadian Cordillera Array – Building Bridges to Span Earth System Science in Canada

EON-ROSE (Earth-System Observing Network - Réseau d’Observation du Système terrestrE) is a new initiative for a pan-Canadian research collaboration to holistically examine Earth systems from the ionosphere into the core. The Canadian Cordillera Array (CC Array) is the pilot phase, and will extend across the Cordillera from the Beaufort Sea to the U.S. border. The vision for EON-ROSE is to install a network of telemetered observatories to monitor solid Earth, environmental and atmospheric processes. EON-ROSE is an inclusive, combined effort of Canadian universities, federal, provincial and territorial government agencies, industry, and international collaborators. Brainstorming sessions and several workshops have been held since May 2016. The first station will be installed at Kluane Lake Research Station in southwestern Yukon during the summer of 2018. The purpose of this report is to provide a framework for continued discussion and development.RÉSUMÉEON-ROSE (Earth-System Observing Network - Réseau d’Observation du Système terrestrE) est une nouvelle initiative de collaboration de recherche pancanadienne visant à étudier de manière holistique les systèmes terrestres, depuis l’ionosphère jusqu’au noyau. Le Réseau canadien de la cordillère (CC Array) en est la phase pilote, laquelle couvrira toute la Cordillère, de la mer de Beaufort jusqu’à la frontière étasunienne. L’objectif d’EON-ROSE est d’installer un réseau d’observatoires télémétriques pour suivre en continu les processusterrestres, environnementaux et atmosphériques. EON-ROSE est un effort combiné et inclusif des universités canadiennes, des organismes gouvernementaux fédéraux, provinciaux et territoriaux, de l’industrie et de collaborateurs internationaux. Des séances de remue-méninges et plusieurs ateliers ont été tenus depuis mai 2016. La première station sera installée à la station de recherche du lac Kluane, dans le sud-ouest du Yukon, au cours de l’été 2018. Le but du présent rapport est de fournir un cadre de discussion et de développement continu

Current strain accumulation in the hinterland of the northwest Himalaya constrained by landscape analyses, basin-wide denudation rates, and low temperature thermochronology

Rupture associated with the 25 April 2015 Mw 7.8 Gorkha (Nepal) earthquake highlighted our incomplete understanding of the structural architecture and seismic cycle processes that lead to Himalayan mountain building in Central Nepal. In this paper we investigate the style and kinematics of active mountain building in the Himalayan hinterland of Northwest India, approximately 400 km to the west of the hypocenter of the Nepal earthquake, via a combination of landscape metrics and long- (Ma) and short-term (ka) erosion rate estimates (from low temperature thermochronometry and basin-wide denudation rate estimates from 10Be concentrations). We focus our analysis on the area straddling the PT2, the physiographic transition between the Lesser and High Himalaya that has yielded important insights into the nature of hinterland deformation across much of the Himalaya. Our results from Northwest India reveal a distinctive PT2 that separates a Lesser Himalaya region with moderate relief (∼1000 m) and relatively slow erosion ( \u3c 1 mm/yr) from a High Himalaya with extreme relief (∼2500 m), steep channels, and erosion rates that approach or exceed 1 mm/yr. The close spatial similarity in relative rates of long- and short-term erosion suggests that the gradient in rock uplift rates inferred from the landscape metrics across the PT2 has persisted in the same relative position since at least the past 1.5 Ma. We interpret these observations to suggest that strain accumulation in this hinterland region throughout at least the past 1.5 Ma has been accomplished both by crustal thickening via duplexing and overthrusting along transient emergent faults. Despite the \u3e 400 km distance between them, similar spatiotemporal patterns of erosion and deformation observed in Northwest India and Central Nepal suggest both regions experience similar styles of active strain accumulation and both are susceptible to large seismic events

Geomorphology reveals active decollement geometry in the central Himalayan seismic gap

The similar to 700-km-long ``central seismic gap'' is the most prominent segment of the Himalayan front not to have ruptured in a major earthquake during the last 200-500 yr. This prolonged seismic quiescence has led to the proposition that this region, with a population >10 million, is overdue for a great earthquake. Despite the region's recognized seismic risk, the geometry of faults likely to host large earthquakes remains poorly understood. Here, we place new constraints on the spatial distribution of rock uplift within the western similar to 400 km of the central seismic gap using topographic and river profile analyses together with basinwide erosion rate estimates from cosmogenic Be-10. The data sets show a distinctive physiographic transition at the base of the high Himalaya in the state of Uttarakhand, India, characterized by abrupt strike-normal increases in channel steepness and a tenfold increase in erosion rates. When combined with previously published geophysical imaging and seismicity data sets, we interpret the observed spatial distribution of erosion rates and channel steepness to reflect the landscape response to spatially variable rock uplift due to a structurally coherent ramp-flat system of the Main Himalayan Thrust. Although it remains unresolved whether the kinematics of the Main Himalayan Thrust ramp involve an emergent fault or duplex, the landscape and erosion rate patterns suggest that the decollement beneath the state of Uttarakhand provides a sufficiently large and coherent fault segment capable of hosting a great earthquake

Magnitude and timing of transient incision resulting from large-scale drainage capture, Sutlej River, Northwest Himalaya

Few studies have constrained the magnitudes and timescales associated with large-scale drainage captures (areas \u3e103 km2), even though these constraints are crucial to reconstruct sediment budgets, assess the potential for drainage reorganization to be preserved in the rock record, and determine the extent to which environmental signals (i.e., structures, composition and fossil assemblages within sedimentary rocks that are influenced by sediment supply and transport) are representative of conditions during deposition. In this work, we characterize the Pleistocene capture of the Zhada Basin, an ~23 000 km2 extensional basin in southern Tibet, by the Sutlej River, a prominent tributary to the Indus River. We quantify the magnitudes and timescales of capture-driven erosion using knickpoint celerity modelling, paleotopographic reconstructions, 10Be-derived denudation rates, and topographic analyses of drainage divides. We find that capture has removed 2010 ± 400 km3 of sediment from the Zhada Basin, increasing sediment supply to the Sutlej network by 17%–29% since 735 ± 269 ka. This work represents a crucial step towards reconstructing the Pleistocene sediment budget of the Indus sedimentary system and identifying potential impacts from sediment redistribution. We also identify several plausible tectonic or autogenic mechanisms that may have facilitated capture of the Zhada Basin, including: (1) preferential erosion of weak lithologies along active faults, (2) headward erosion in response to prior capture of the Spiti River and (3) headward erosion generated by breaching of a structural culmination downstream (the Kullu-Rampur Window). This provides a framework to assess the mechanistic links between arc-parallel extension, large-scale drainage capture, landscape evolution and orogenic wedge deformation