Beach ridges as paleoseismic indicators of abrupt coastal subsidence during subduction zone earthquakes, and implications for Alaska-Aleutian subduction zone paleoseismology, southeast coast of the Kenai Peninsula, Alaska

Tsunami recurrence in the eastern Alaska-Aleutian arc: A Holocene stratigraphic record from Chirikof Island, Alaska

“…Elsewhere in the eastern Alaska-Aleutian arc, information on the recurrence of high tsunamis or the great earthquakes likely to have accompanied them over the past 3500 yr is limited (Carver and Plafker, 2008;Shennan et al, 2014aShennan et al, , 2014bKelsey et al, 2015). Carver and Plafker (2008) compiled radio carbon ages from studies of Kodiak Island coastal stratigraphy by Carver and Gilpin (1992), Gilpin et al (1994), and Gilpin (1995) to infer the times of four mega thrust earthquakes prior to the 1964 earthquake, at least three of which were accompanied by tsunamis (Fig.…”

“…12). From stratigraphic and landform evidence on the Kenai Peninsula, 500 km northeast of Chirikof Island, Kelsey et al (2015) inferred that the ca. A.D. 1020-1150 earthquake probably ruptured the Kenai Peninsula part of the megathrust, as suggested by Shennan et al (2014a), and that a younger Kenai megathrust earthquake may have coincided with either the A.D. 1440-1620 or 1788 earthquakes.…”

Detection limits of tidal-wetland sequences to identify variable rupture modes of megathrust earthquakes

“…While these criteria were proposed with respect to tidal marsh sequences adjacent to the Cascadia subduction zone, they have proved valuable for numerous studies since (e.g. Clark et al, 2015;Dura et al, 2015;Dura et al, 2016;Dura et al, 2011;Engelhart et al, 2013;Garrett et al, 2015b;Grand Pre et al, 2012;Hamilton and Shennan, 2005a;Hayward et al, 2015;Kelsey et al, 2015;Leonard et al, 2004;McCalpin and Carver, 2009;Nelson et al, 2009;Nelson et al, 2006;Shennan et al, 2009;Witter et al, 2003).…”

“…Atwater and Hemphill-Haley, 1997;Hayward et al, 2006;Kelsey, 2015;Nelson, 2015;Nelson et al, 1996;Witter, 2015) debate moved on to questions critical for hazard assessment, emergency planning and international building code design (Mueller et al, 2015;Wesson et al, 2007). Key questions include the extent of past great earthquake ruptures (a proxy for magnitude), the identification of the boundaries between rupture segments, the persistence of these boundaries over multiple earthquake cycles, recurrence intervals of great earthquakes in each segment, the role of aseismic slip, and whether segments of plate boundaries that are currently creeping can generate great earthquakes Goldfinger et al, 2012;Hayward et al, 2015;Kelsey et al, 2015;Mueller et al, 2015;Scholz, 2014;Witter et al, 2014).In order to address these questions, coastal paleoseismology continues to seek evidence to discriminate between alternative hypotheses. This inevitably results in returning to the field evidence and the quantifiable resolution of the age, the extent, and the pattern of vertical surface displacement of each rupture.…”

“…While these criteria were proposed with respect to tidal marsh sequences adjacent to the Cascadia subduction zone, they have proved valuable for numerous studies since (e.g. Clark et al, 2015;Dura et al, 2015;Dura et al, 2016;Dura et al, 2011;Engelhart et al, 2013;Garrett et al, 2015b;Grand Pre et al, 2012;Hamilton and Shennan, 2005a;Hayward et al, 2015;Kelsey et al, 2015;Leonard et al, 2004;McCalpin and Carver, 2009;Nelson et al, 2009;Nelson et al, 2006;Shennan et al, 2009;Witter et al, 2003).In this review, we first introduce general principles regarding indicators of relative sea-level change in tidal wetlands and the conditions in which paleoseismic indicators must be distinct from those resulting from non-seismic processes.Section 2 summarises the tectonic setting and Holocene chronology of great earthquakes in the region of the 1964 Alaska M w 9.2 earthquake since we use evidence from this region to revisit the criteria recommended by Nelson et al (1996) for identifying coseismic subsidence and use the evidence to test working hypothesis of variable rupture modes during the late Holocene.In section 3, we consider developments over the past 20 years in popular methods of reconstructing relative sea-level change and their application to paleoseismic records from tidal wetlands.Section 4 presents evidence from sites across southcentral Alaska to illustrate different detection limits and how these constrain alternative interpretations for marsh submergence and emergence.In section 5, we evaluate the predicted surface displacement of different rupture modes against the reconstructions of marsh submergence and emergence based on field data.In the final sections, we consider the broader implications of detection limits of tidal wetland sequences at subduction zones around the world and suggest an expansion of the Nelson et al(1996) criteria. …”