The application of intertidal foraminifera to reconstruct coastal subsidence during the giant Cascadia earthquake of AD 1700 in Oregon, USA

Coastal subsidence in Oregon, USA, during the giant Cascadia earthquake of AD 1700

“…We analyzed a vibracore taken on the south side of the river across from the contemporary training set of Hawkes et al (2010). Grant (1994) and Minor and Grant (1996) found widespread stratigraphic and plant macrofossil evidence of subsidence during the AD 1700 earthquake exposed in bank sections over much of the lower estuary that traces landward for hundreds of meters.…”

“…However, these and other early microfossil studies were also semi-quantitative and relied on differences between intertidal elevational zones with broad ranges to estimate RSL changes (e.g., Nelson and Kashima, 1993;Darienzo et al, 1994Darienzo et al, , 1995Hemphill-Haley, 1995, Nelson et al, 1996aAtwater and Hemphil-Haley, 1997;Shennan et al, 1998;Williams and Hutchinson, 2000;Scott et al, 2001;Hawkes et al, 2005). In the late 1990s, application of transfer function analysis, widely used on microfossils from deep marine cores to reconstruct climate change, revitalized studies of Holocene sealevel change on many coasts (e.g., Horton et al, 1999;Gehrels et al 2001;Horton and Edwards, 2006;Kemp et al, 2009) including Cascadia (e.g., Guilbault et al, 1995Guilbault et al, , 1996Hughes et al, 2002;Sabean, 2004;Nelson et al, 2008;Hawkes et al, 2010).…”

“…Calibration is then used to reconstruct past elevation from microfossil assemblages in cores or outcrops. When combined with lithostratigraphic data, the RSL reconstructions have precisions of ±0.1-0.3 m (e.g., Gehrels et al, 2008;Horton and Edwards, 2006;Kemp et al, 2009;Hawkes et al, 2010). With sufficient sample density, the transfer function provides a continuous record of RSL change during interseismic parts of the earthquake cycle; essential information for understanding the mechanics of plate-boundary ruptures in subduction zones.…”

“…With sufficient sample density, the transfer function provides a continuous record of RSL change during interseismic parts of the earthquake cycle; essential information for understanding the mechanics of plate-boundary ruptures in subduction zones. Hawkes et al (2010) developed a regional transfer function using an intertidal foraminiferal dataset from five Oregon estuaries. In this paper we apply the Hawkes et al (2010) transfer function to fossil foraminiferal assemblages in samples from cores and sections that encompass the AD 1700 earthquake at Nehalem River, Nestucca River, Salmon River, Suislaw River and South Slough (Figure 1, 2).…”

“…Hawkes et al (2010) developed a regional transfer function using an intertidal foraminiferal dataset from five Oregon estuaries. In this paper we apply the Hawkes et al (2010) transfer function to fossil foraminiferal assemblages in samples from cores and sections that encompass the AD 1700 earthquake at Nehalem River, Nestucca River, Salmon River, Suislaw River and South Slough (Figure 1, 2). From transfer function derived paleomarsh elevations, we quantify the amount of sudden RSL rise across the contact between the pre-and post-seismic sediment, and thus infer the amount of coseismic subsidence along 400 km of the Oregon coast.…”