Coastal evidence for Holocene subduction-zone earthquakes and tsunamis in central Chile

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

“…On the other hand, the five criteria neatly summarised, 1 -lateral extent of peat-mud couplets with sharp contacts; 2 -suddenness of submergence; 3 -amount of vertical motion; 4 -presence of tsunami deposited sediments directly above the peat horizon, and, 5 -synchroneity with other sites, provided a valuable means to frame the research in a number of later studies (e.g. Briggs et al, 2014;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;Nelson et al, 2009;Nelson et al, 2006;Shennan et al, 2009;Witter et al, 2003). In order to reflect developments in research over the past twenty years, for paleoseismological studies of tidal wetland sediment sequences an approach framed around such are criteria is better summarised as assessing the following:…”

“…Newly applied analytical methods include stable carbon isotope and geochemical proxies Dura et al, 2011;Engelhart et al, 2013;Hawkes et al, 2011;Witter et al, 2016). The last decade has also seen a lot written on identifying sediments deposited by tsunami (Alam et al, 2012;Chagué-Goff et al, 2011;Dura et al, 2015;Engel and Brückner, 2011;Garrett et al, 2013;Goff et al, 2011a;Goff et al, 2011b;Goto et al, 2011;Grand Pre et al, 2012;Kortekaas and Dawson, 2007;Morton et al, 2007;Nelson et al, 2015;Okal et al, 2011;Pilarczyk et al, 2014;Shanmugam, 2012;Witter et al, 2016).…”

“…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).…”

“…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. …”

Social Perception of Ecosystem Services in a Coastal Wetland Post-Earthquake: A Case Study in Chile

“…In general, it was observed that the regulating and cultural ecosystem services obtained a high valuation in terms of frequency of provision despite morphological, social, and environmental changes from the last earthquake. In fact, in the regulating services, the high recurrence of natural (tsunamis, floods) and anthropogenic disasters (fires) that affect the Chilean Mediterranean region [31,37,51] may have positively influenced the utilitarian valuation of the wetland by the population, as it forms part of the inhabitants' collective memory. This is not novel, and is consistent with Barbosa and Villagra [52] as wetlands are essential to mitigate the effects of such catastrophes, and are socially valued as spaces of recovery after earthquakes, especially if they provide biophysical attributes such as water [53].…”