| Titre | Paleoseismic investigations on the Leech River Fault Zone, southern Vancouver Island |
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| Auteur | Bednarski, J; Rogers, G |
| Source | CANQUA - CGRG Biennial Meeting, programme and abstracts volume; 2009 p. 37  Accès ouvert |
| Liens | Online - En ligne
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| Année | 2009 |
| Séries alt. | Secteur des sciences de la Terre, Contribution externe 20090161 |
| Réunion | CANQUA-CGRG Biennial Meeting; Burnaby; CA; mai 3-8, 2009 |
| Document | livre |
| Lang. | anglais |
| Media | papier; en ligne; numérique |
| Province | Colombie-Britannique |
| SNRC | 92B/05; 92B/06; 92B/11; 92B/12; 92C/09; 92C/10 |
| Région | Île de Vancouver; Victoria |
| Lat/Long OENS | -125.0000 -123.0000 48.7500 48.2500 |
| Sujets | caractéristiques structurales; interpretations structurelles; failles; Oligocène; Miocène; Eocene; secousses séismiques; risque de tremblement de terre; études séismiques; Zone de faille de Leech River ;
Faille de Devil's Mountain ; tectonique; géologie structurale; géophysique; Cénozoïque; Tertiaire |
| Programme | Réduction des risques dus aux aléas naturels |
| Diffusé | 2009 01 01 |
| Résumé | (disponible en anglais seulement)
Victoria, southern Vancouver Island, is the largest Canadian urban centre situated next to major geologic fault, the Leech River fault zone. Although the fault
appears to have been inactive in recent history, the impact of a slip could be devastating. This is a report on recent investigations to assess the prehistoric activity of the Leech River fault zone. The Leech River fault zone records Late Eocene
accretion of Leech River schist (Pacific Rim Terrane) and Eocene basalt (Crescent Terrane) against the continental edge of western North America. The fault forms a north-dipping thrust that places the Metchosin volcanic rocks under the Leech River
schist. Movement along the fault occured during the Eocene, but some disruption of sediments of the Late Oligocene Sooke Formation sediments suggest that significant movement may have also taken place as late as the Miocene. On the west coast of
Vancouver Island the Leech River fault zone is expressed as a steep narrow valley cutting through the Island Ranges. Trending southeast, it passes through the rapidly expanding communities of Colwood and Langford and then extends along the Victoria
waterfront connecting with the Devil's Mountain Fault in the Strait of Juan de Fuca. Two damaging-level paleo-earthquakes have been identified on a splay of the Devil's Mountain Fault about 40 km east of Victoria, which occurred between 100 to 500
and 1100 to 2200 calendar years ago. Moreover, recent marine multibeam surveys have shown displaced Holocene sediments over the Devil's Mountain Fault just off the Victoria waterfront and in a splay fault through the southern Gulf Islands. In the
immediate Victoria area, the Leech River Fault zone is buried beneath thick glaciofluvial sediments. These deposits are mostly cross-stratified gravels and sands deposited during deglaciation, about 13.6 ka BP, when the retreating glacier still
occupied the land to the north. An ice-contact delta formed as meltwater flowed into a high relative sea level of at least 75 m. Successively lower meltwater channels were cut into the delta as relative sea level fell and the ice margins retreated
northward. This resulted in a series of terraces and scarps on the delta surface. However some scarps could also have been produced by surface ruptures if the Leech River fault slipped during postglacial time. In 2007, a Lidar survey was flown along
the length of the fault zone to detect surface lineaments which could be possible surface ruptures. Several identified lineaments were further investigated by ground resistivity and ground penetrating radar surveys, but the results are inconclusive.
Human disturbance of the original landscape and heavy urban development in the area hinders more intensive investigations. Although no evidence of prehistoric earthquakes has yet been found and the current models of seismic hazard for the Victoria
area do not need revision, more needs to be done to determine if the Leech River fault zone has been active in geologically recent times. |
| GEOSCAN ID | 247804 |
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