Liquefaction features on the Fraser delta: evidence for prehistoric earthquakes?

Abstract

Sand dykes and sills and vented sand boils on the Fraser River delta and adjacent Serpentine River floodplain in southwestern British Columbia record one or more major liquefaction events. The source of the dykes is a shallow subsurface saturated sand unit that was deposited in foreslope and distributary-channel environments during Holocene progradation of the Fraser delta. The dykes cut steeply through a crust of delta topset muds and locally flatten out as sills in overlying peaty sediments. At two sites, evidence was found for venting of sand onto a subaerial or intertidal surface. Liquefaction and upward movement of sand and water locally deformed the intruded sediments, causing some subsidence and uplift of the delta surface. All observed liquefaction features are younger than ca. 3500 BP, and at least some are younger than 2400 BP. It is not clear, however, whether they formed during one or several separate events. A review of possible causes suggests that the liquefaction features probably are seismically generated; they thus may provide the first direct evidence for moderate to large, prehistoric earthquakes in the Vancouver metropolitan area.

British Columbia Smart Infrastructure Monitoring System

“…Analysis of contemporary crustal deformation proves the same strain accumulation in the subduction boundary (Gragert et al 1994;Dragert et al 1994;Dragert and Hyndman 1995). Even though Vancouver has not yet experienced a large damaging earthquake, the paleo seismic evidence on the Fraser delta, south of Vancouver, confirms that large earthquakes have occurred in prehistoric time (Clague et al 1992). Ongoing occurrence of earthquakes, which are large enough to cause damage to structures, is a reminder of the fact that the southwest coast of BC is still a seismically active area.…”

“…This zone, called the Cascadia subduction zone, is capable of producing large, up to magnitude 9.0, earthquakes (Goldfinger et al 2012). The last megaquake in this region was approximately 300 years ago (Goldfinger et al 2012) and evidence suggests that strain has been accumulating in the subduction boundary, off the west coast of Vancouver Island (Clague et al 1992;Gragert et al 1994). Analysis of contemporary crustal deformation proves the same strain accumulation in the subduction boundary (Gragert et al 1994;Dragert et al 1994;Dragert and Hyndman 1995).…”

Geological and site specific factors influencing earthquake hazard assessment for New Brunswick, Canada

“…Deterministic studies include the examination of bedrock faults or overlying deformed sediments caused by underling or nearby fault-generated seismic activity (e.g., Reiter, 1990;Tuttle and Seeber, 1991;Clague et al 1992;Doughty et al 2010). Such studies can contribute valuable information and enable extrapolation of magnitude, timing and number of seismic occurrences beyond the historical record (e.g., Tuttle et al 1996;Rajendran 2000).…”

Enigma variations: the stratigraphy, provenance, palaeoseismicity and depositional history of the Lower Old Red Sandstone Cosheston Group, south Pembrokeshire, Wales

“…Sieh 1978). Ball-and-pillow SSD in lacustrine deposits (Sims 1975;Hempton and Dewey 1983), and 'sand blows' (volcanoes, pipes, dykes and sills) (Sieh 1978;Obermeier et al 1985;Saucier 1989;Clague et al 1992) have been used to detect palaeo-earthquakes. Most largescale Cosheston Group SSD structures are compatible with Sims's (1975) criteria for identifying earthquakeinduced SSD.…”

“…Leeder 1987;Clague et al 1992 and references therein) were summarized by Mayall (1983). Deformation is caused 'by liquefaction due to cyclic loading, and to undulatory ground motion resulting from the passage of surface Rayleigh waves' (Mayall 1983), the amount of sediment liquefaction being proportional to the magnitude and duration of a seismic event (Leeder 1987).…”