Evidence for Past Subduction Earthquakes at a Plate Boundary with Widespread Upper Plate Faulting: Southern Hikurangi Margin, New Zealand

Abstract

At the southern Hikurangi margin, New Zealand, we use salt marsh stratigraphy, sedimentology, micropaleontology, and radiocarbon dating to document evidence of two earthquakes producing coseismic subsidence and (in one case) a tsunami over the past 1000 yrs. The earthquake at 520-470 yrs before present (B.P.) produced 0:25 0:1 m of subsidence at Big Lagoon. The earthquake at 880-800 yrs B.P. produced 0:45 0:1 m of subsidence at Big Lagoon and was accompanied by a tsunami that inundated ≥ 360 m inland with a probable height of ≥ 3:3 m. Distinguishing the effects of upper plate faulting from plate interface earthquakes is a significant challenge at this margin. We use correlation with regional upper plate paleoearthquake chronologies and elastic dislocation modeling to determine that the most likely cause of the subsidence and tsunami events is subduction interface rupture, although the older event may have been a synchronous subduction interface and upper plate fault rupture. The southern Hikurangi margin has had no significant (M > 6:5) documented subduction interface earthquakes in historic times, and previous assumptions that this margin segment is prone to rupture in large to great earthquakes were based on seismic and geodetic evidence of strong contemporary plate coupling. This is the first geologic evidence to confirm that the southern Hikurangi margin ruptures in large earthquakes. The relatively short-time interval between the two subduction earthquakes (∼350 yrs) is shorter than in current seismic-hazard models.

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

“…While the careful consideration of what constraint each sample age places on an inferred earthquake, such as a minimum limiting age above a contact or a maximum limiting age from below a contact, remains unaltered, Bayesian age modelling provides a range of options by which to assess age correlation and intervals between inferred earthquakes (Berryman et al, 2012;Bronk Ramsey, 2008Clark et al, 2015;DuRoss et al, 2011;Kelsey et al, 2015;Lienkaemper and Bronk Ramsey, 2009;Nelson et al, 2015;Shennan et al, 2014a;Shennan et al, 2014c;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. …”

Liquefaction Features Produced by the 2010–2011 Canterbury Earthquake Sequence in Southwest Christchurch, New Zealand, and Preliminary Assessment of Paleoliquefaction Features

“…Timing of major historic earthquakes, prehistoric fault ruptures, and large landslides in the wider region. Timing information from subduction zone, Clark et al (2015); Alpine fault, Berryman et al (1992), Berryman, Cochran, et al (2012), Berryman, Cooper, et al (2012), and Howarth et al (2012Howarth et al ( , 2014; Hope fault, Conway segment, Langridge et al (2003); Hope fault, Hope River segment, Cowan and McGlone (1991); Hope fault, Hurunui segment, Langridge et al (2013) and Khajavi et al (see Data and Resources); Poulter fault, Berryman and Villamor (2004); Acheron rock avalanche, Smith et al (2006); Porters Pass fault, Howard et al (2005); Ashley fault, Sisson et al (2001); Moncks Cave, Jacomb (2008Jacomb ( , 2009. Location information for all faults from Litchfield et al (2014) and references therein.…”

“…13). The Porters Pass fault (most recent event), the Alpine fault (either of the last two events), the subduction zone (earthquake 1 of Clark et al, 2015, which could be a multiple segment rupture), or any of the faults with no earthquake record (Hororata, Springbank, Ashley, and Rakaia) are potential candidates. The Porters Pass fault is a strong candidate because the timing of its most recent event may coincide with dates for the sealing of Moncks Cave in Sumner, Christchurch, by a rock avalanche (Jacomb, 2008;.…”