Deriving a long paleoseismic record from a shallow-water Holocene basin next to the Alpine fault, New Zealand

Abstract

A sedimentary sequence that was highly sensitive to fault rupture-driven changes in water level and sediment supply has been used to extract a continuous record of 22 large earthquakes on the Alpine fault, the fastest-slipping fault in New Zealand. At Hokuri Creek, in South Westland, an 18 m thickness of Holocene sediments accumulated against the Alpine fault scarp from ca. A.D. 800 to 6000 B.C. We used geomorphological mapping, sedimentology, and paleoenvironmental reconstruction to investigate the relationship between these sediments and Alpine fault rupture. We found that repeated fault rupture is the most convincing mechanism for explaining all the features of the alternating peat and silt sedimentary sequence. Climate has contributed to sedimentation but is unlikely to be the driver of these cyclical changes in sediment type and paleoenvironment. Other nontectonic causes for the sedimentary alternations do not produce the incremental increase in basin accommodation space necessary to maintain the shallow-water environment for 6800 yr. Our detailed documentation of this near-fault sedimentary basin sequence highlights the advantages of extracting paleoearthquake records from such sites-the continuity of sedimentation, abundance of dateable material, and pristine preservation of older events.

Late Holocene rupture behavior and earthquake chronology on the Hope fault, New Zealand

“…7) of the peat unit 4; (2) changes in the depositional environment (change from a quiet unit 4 peat to a more energetic alluvial environment unit 5 sand); and (3) the unconformity between units 4 and 5 to the north of T-2. Our interpretation, which relies on the changes in depositional environment as earthquake proxies, is consistent with the work of other researchers (e.g., Cowan and McGlone, 1991;Berryman et al, 2012;Clark et al, 2013).…”

A 2000 Yr Paleoearthquake Record along the Conway Segment of the Hope Fault: Implications for Patterns of Earthquake Occurrence in Northern South Island and Southern North Island, New Zealand

“…Whereas a >2,000-year-long paleoearthquake record has been documented for the Alpine fault [Berryman et al, 2012b;Howarth et al, 2012Howarth et al, , 2014Howarth et al, , 2016Clark et al, 2013;Cochran et al, 2017;see Howarth et al, 2018 for review], the paleoearthquake record of the Conway segment of the Hope fault is not well documented beyond an approximate age of the most recent event [Langridge et al, 2003]. In this study, we document and provide age constraints for at least the five most recent events along the Conway segment.…”

“…To complete plate boundary system earthquake behavior analysis, we study the fastestslipping strike-slip faults of the Australian-Pacific plate boundary of the northern South Island and southern North Island of New Zealand, where previous studies have documented patterns of earthquake recurrence on many of these major faults [e.g., Cooper and Norris, 1990;Wells et al, 1999;Langridge et al, 2003Langridge et al, , 2013Mason et al, 2006;Sutherland et al, 2007;Little et al, 2009;Van Dissen and Nicol, 2009;Berryman et al, 2012aBerryman et al, , 2012bDe Pascale and Langridge, 2012;Howarth et al, 2012Howarth et al, , 2014Howarth et al, , 2016Clark et al, 2013Clark et al, , 2015Nicol et al, 2016;Khajavi et al, 2016;Cochran et al, 2017;Nicol and Dissen, 2018]. The Hope fault, the subject of this manuscript, is the central link between high slip-rate faults to the southwest (Alpine fault) and northeast (Jordan-Kekerengu-Needles fault and the Wairarapa fault in southern North Island).…”

Geophysical imaging of disrupted coastal dune stratigraphy and possible mechanisms, Haast, South Westland, New Zealand

“…The Alpine Fault generates coseismic landslides that provide pulses of sediments to the local catchments (e.g. Howarth et al 2012;Clark et al 2013). These sediments are then transported to the Tasman Sea (Figs.…”

“…A number of studies have concluded that large Alpine Fault events result in large pulses of sediment (e.g. Berryman et al 2012;Clark et al 2013;Howarth et al 2012), which are efficiently delivered to the catchments during large rainfall events (Fitzsimons et al 2013). Coastal areas of these catchments record the large rainfall, landslide, and faulting events as pulses of sediments that are redistributed by long-shore transport and then by wave and wind action to form coastal dunes, which are subsequently populated by trees and shrubs within decades of an event Goff 2006, 2007).…”