Cascadia Paleoearthquakes

This page describes the Cascadia subduction zone and how paleoarthquake data can help us understand earthquake and tsunami processes.

I discuss more about the geologic studies of Cascadia subduction zone seismicity on this report page, considering the 315th anniversary of the last earthquake (1700 A.D.).

The Cascadia subduction zone is an approximately 1,200-kilometer convergent plate boundary that extends from northern California to Vancouver Island, Canada (Figure 1). The Juan de Fuca and Gorda plates are subducting eastwardly below the North American plate. Seismicity, crustal deformation, and geodesy provide evidence that the Cascadia subduction zone is locked and is capable of producing a great (magnitude greater than or equal to 8.5) earthquake (Heaton and Kanamori, 1984; McPherson, 1989; Clarke and Carver, 1992; Hyndman and Wang, 1995; Flück and others, 1997).(Figure 1)

Globally, great earthquakes along subduction zones have caused damaging ground shaking, ground rupture by upper-plate crustal faults, liquefaction, turbidites, uplifted marine terraces, and tsunamis (Plafker, 1972; Adams, 1990; Clarke and Carver, 1992; Merritts, 1989; Clague and Bobrowsky, 1994; Satake and others, 1996). Based on buried soil stratigraphy correlated with radiocarbon age data using tree ring wiggle matching and with the inference of a single orphan tsunami in Japan being caused by a single great earthquake, the entire length of the Cascadia subduction zone from Canada to California ruptured in January, 1700 A.D. (Satake and others, 1996; Jacoby and others, 1997; Yamaguchi and others, 1997).

There has been no historic Cascadia subduction zone earthquake along its entire length, but paleoseismic evidence indicates multiple earthquake cycles have occurred along the Cascadia margin over the last 8,000 years (Atwater, 1987; Hemphill-Haley, 1995; Garrison-Laney, 1998; Abramson, 1998; Kelsey and others, 2002; Witter and others, 2003; Figure 1). Evidence for Cascadia subduction zone earthquakes also has been found in Humboldt Bay Holocene stratigraphy in the form of buried soils (Carver and Burke, 1988; Vick, 1988; Clarke and Carver, 1992; Manhart, 1992; Li, 1992; Valentine, 1992; Carver and others, 1998; Leroy, 1999; Witter and others, 2002).

Quaternary deformation around Humboldt Bay has been dominated by contractile deformation due to Gorda – North America plate convergence and from northward Mendocino triple junction migration transpression (Ogle, 1953; McPherson, 1989; Carver and others, 1992b; Smith and others, 1993, and Burger and others, 2002; Williams, 2003). The deformation front of the Cascadia subduction zone lies approximately 75 kilometers offshore of Humboldt Bay (Clarke and Carver, 1992). East of the offshore deformation front is an 85- to 100-kilometer wide fold-and-thrust belt in the accretionary prism, which comes onshore in the Humboldt Bay region (Carver and Burke 1988; Clarke and Carver, 1992; inset Figure 1). Splays of the onshore fold and thrust belt include the Little Salmon fault and the Mad River fault zones (Fig 2). Transpression from Mendocino triple junction migration extends northward to at least the Table Bluff anticline (Burger and others, 2002).

Evidence for Holocene onshore tectonic activity includes (1) earthquakes on upper-plate faults of the Little Salmon fault in Salmon Creek valley and the Mad River fault zone in McKinleyville and Blue Lake (Carver and Burke, 1988), (2) sudden uplift of sections of the coast at Clam Beach (Figure 2) and Cape Mendocino (Figure 1; Clarke and Carver, 1992; Merritts, 1989, Stein and others, 1993, Carver and McCalpin, 1996), and (3) sudden subsidence along margins of Humboldt Bay and Eel River valley (Vick, 1988; Clarke and Carver, 1992; Li, 1992; Manhart, 1992; Valentine, 1992).


Here are some posters that i have presented:

2012
GEOPRISMS Cascadia Workshop southern CSZ miss-match between modern and paleogeodesy. (14MB pdf)

2011
GEOPRISMS Alaska Workshop southern CSZ miss-match between modern and paleogeodesy. (11MB pdf)
AGU fall meeting southern CSZ miss-match between modern and paleogeodesy. (23MB pdf)
Humboldt’s Ready Emergency Preparedness Fair southern CSZ Relative Sea Level. (5MB pdf)
Humboldt’s Ready Emergency Preparedness Fair Earthquake and Tsunami Hazards northern California. (4MB pdf)

2010
SSA annual meeting southern CSZ miss-match between modern and paleogeodesy. (16MB pdf)
AGU fall meeting southern CSZ miss-match between modern and paleogeodesy. (50MB pdf)
Humboldt Bay Symposium southern CSZ Relative Sea Level. (62MB pdf)

2009
SSA annual meeting southern CSZ miss-match between terrestrial and submarine paleorecord. (16MB pdf)

2005
Humboldt Bay Symposium Paleotsunami and Paleoseismic Investigation, Little Salmon fault. (5MB pdf)

2001
SSA Meeting Paleotsunami and Paleoseismic Investigation, Little Salmon fault; Panel 1. (12MB pdf)
SSA Meeting Paleotsunami and Paleoseismic Investigation, Little Salmon fault; Panel 2. (29MB pdf)
SSA Meeting Paleotsunami and Paleoseismic Investigation, Little Salmon fault; Panel 3. (22MB pdf)
SSA Meeting Paleotsunami and Paleoseismic Investigation, Little Salmon fault; Panel 4. (8MB pdf)


Here are some powerpoints that i have presented:

2012
College of the Redwoods public talk on Earthquake and Tsunami Hazards of the Mendocino Coast. (102MB pdf) Videos for this talk:

Video of tsunami generation. (3MB mpg)
Video of submarine landslide generation due to earthquakes. (0.8MB mpg)
Animation of tsunamigenesis. (8MB mpg)
Animation of tsunami modeling from Haida Gwaii tsunami. (8MB wmv)
CBC coring video off Sumatra. (8MB wmv)

2011
Humboldt Bay Initiative public talk on earthquake related deformation as it relates to local sea level. (17MB pdf)

2010
Oregon State University geosciences dept. brownbag, the discordance between terrestrial and submarine records of paleoearthquakes in northern California. (29MB pdf)

2005
Humboldt State University public lecture on earthquake hazards in northern California (follow up to the Sumatra-Andaman Earthquake and Tsunami. (20MB pdf)

2004
Humboldt State University Master’s thesis defense. (44MB pdf)

 

REFERENCES

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