Stratigraphic record of Holocene coseismic subsidence, Padang, West Sumatra

Abstract

[1] Stratigraphic evidence is found for two coseismic subsidence events that underlie a floodplain 20 km south of Padang, West Sumatra along the Mentawai segment (0.5°S-0.3°S) of the Sunda subduction zone. Each earthquake is marked by a sharp soil-mud contact that represents a sudden change from mangrove to tidal flat. The earthquakes occurred about 4000 and 3000 cal years B.P. based on radiocarbon ages of detrital plant fragments and seeds. The absence of younger paleoseismic evidence suggests that late Holocene relative sea level fall left the floodplain too high for an earthquake to lower it into the intertidal zone. Our results point to a brief, few thousand year window of preservation of subsidence events in tidal-wetland stratigraphic sequences, a result that is generally applicable to other emergent coastlines of West Sumatra.Citation: Dura, T

Geohazards and myths: ancient memories of rapid coastal change in the Asia-Pacific region and their value to future adaptation

“…As in other regions, abrupt subsidence during (or immediately after) earthquakes is something that is common in parts of the Asia-Pacific region yet which is not always easy to detect in pre-monitoring records [68,69]. And while intuitively we might not expect it to be so, abrupt subsidence at coastal locations is also something that is frequently ignored in myths, usually because observers of these events focus on the large waves that accompany them.…”

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

“…We add additional criteria that may be present at some sites: liquefaction sediments (Atwater et al, 2001;Malik et al, 2011;Martin and Bourgeois, 2012;Obermeier and Dickenson, 2000;Walsh et al, 1995) and tree ring analysis (Yamaguchi et al, 1997). 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. …”

Reconstructing paleoseismic deformation, 2: 1000 years of great earthquakes at Chucalén, south central Chile

“…Long`term"sea`level"rise"provides"accommodation"space"and"promotes"sediment" 505" accumulation"and"the"preservation"of"stratigraphic"evidence"for"earthquakes"in"intertidal" 506" environments" (Dura"et#al.,"2011;"Grand"Pre"et#al.,"2012). "In"this"section"we"assess"the" 507" evidence"for"long`term"relative"sea`level"change"at"Chucalén"and"discuss"the"implications"for" 508" the"length"of"the"paleoseismic"record"at"this"site.""…”