Holocene faulting in the Bellingham forearc basin: Upper‐plate deformation at the northern end of the Cascadia subduction zone

Abstract

The northern Cascadia forearc takes up most of the strain transmitted northward via the Oregon Coast block from the northward‐migrating Sierra Nevada block. The north‐south contractional strain in the forearc manifests in upper‐plate faults active during the Holocene, the northern‐most components of which are faults within the Bellingham Basin. The Bellingham Basin is the northern of four basins of the actively deforming northern Cascadia forearc. A set of Holocene faults, Drayton Harbor, Birch Bay, and Sandy Point faults, occur within the Bellingham Basin and can be traced from onshore to offshore using a combination of aeromagnetic lineaments, paleoseismic investigations and scarps identified using LiDAR imagery. With the recognition of such Holocene faults, the northernmost margin of the actively deforming Cascadia forearc extends 60 km north of the previously recognized limit of Holocene forearc deformation. Although to date no Holocene faults are recognized at the northern boundary of the Bellingham Basin, which is 15 km north of the international border, there is no compelling tectonic reason to expect that Holocene faults are limited to south of the international border.

Quaternary Rupture of a Crustal Fault beneath Victoria, British Columbia, Canada

“…Within a zone up to 1 km wide, we observe near vertical faults, variable scarp facing directions, laterally discontinuous surface scarps, and field evidence for strike-slip and reverse faulting. These characteristics are typical of strike slip systems and are similar to features observed along active oblique-reverse faults in the adjacent Pacific Northwest (e.g., Johnson et al, 2001;Sherrod et al, 2008Sherrod et al, , 2016Kelsey et al, 2012;Personius et al, 2014;Blakely et al, 2014).…”

“…JF-Juan de Fuca plate; PA-Pacific plate. (B) Population centers (Balk et al, 2006) relative to mapped active faults in black USGS, 2010;Kelsey et al, 2012;Personius et al, 2014;Barrie and Greene, 2015). The Leech River fault (LRF) is shown as dashed line.…”

The paraglacial geomorphology of the Fraser Lowland, southwest British Columbia and northwest Washington

“…Consequently, early Holocene shorelines are presumably submerged unless they have been uplifted by tectonic deformation (e.g., Kelsey et al, 2012).…”

Holocene earthquakes and right-lateral slip on the left-lateral Darrington–Devils Mountain fault zone, northern Puget Sound, Washington

“…1A; Wells et al, 1998Wells et al, , 2014Wells and Simpson, 2001;McCaffrey et al, 2007). From south to north, paleo seismic and geologic mapping studies have identifi ed surface deformation indicating Holocene activity on the Olympia and Tacoma faults in the Tacoma Basin (Bucknam et al, 1992;Sherrod, 2001;Sherrod et al, 2004aSherrod et al, , 2004bNelson et al, 2008;Barnett et al, 2010;Sherrod and Gomberg, 2014), the Seattle fault in the Seattle Basin (Bucknam et al, 1999;Johnson et al, 1999;Sherrod et al, 2000;Nelson et al, 2003aNelson et al, , 2003bNelson et al, , 2014Kelsey et al, 2008), the Southern Whidbey Island, Utsalady Point, and Darrington-Devils Mountain faults in the Everett Basin (Johnson et al, 1996(Johnson et al, , 2001(Johnson et al, , 2004Dragovich and DeOme, 2006;Sherrod et al, 2008), and the Boulder Creek, Birch Bay, Sandy Point, and Drayton Harbor faults in the Bellingham Basin (Kelsey et al, 2012;Sherrod et al, 2013;Sherrod and Gomberg, 2014). Other Holocene faults that lie outside of the margins of the Tertiary basins include the Lake Creek-Boundary Creek (Little River) fault and the Saddle Mountains fault zone, which form parts of the north and east fl anks, respectively, of the uplifted Olympic Mountains (Wilson et al, 1979;Nelson et al, 2007;Walsh and Logan, 2007;Witter et al, 2008;Blakely et al, 2009;Sherrod and Gomberg, 2014).…”