A new chronology for tsunami deposits prior to the 1700 CE Cascadia earthquake from Vancouver Island, Canada

Tanigawa, Koichiro; Sawai, Yuki; Bobrowsky, Peter T.; Huntley, David; Goff, James; Shinozaki, Tetsuya; Ito, Kazumi

doi:10.1038/s41598-022-16842-8

Cited by 4 publications

(1 citation statement)

References 65 publications

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“…The central Hikurangi margin is an end member in terms of the range and complexity of earthquake sources at a subduction zone. Yet, we recommend that the same level of detail is required for interpreting paleoseismic evidence at other plate boundaries where the possible contribution of UPFs is often not explicitly addressed (Nelson et al, 2021;Tanigawa et al, 2022). Normally, a plate interface rupture source is justified by (i) similarity between the paleo-evidence and historic examples of subduction earthquakes (Cisternas et al, 2005;Garrett et al, 2013;Sieh et al, 2015) and/or (ii) along-strike correlations of co-temporal evidence over large areas that could only be satisfied by rupture of the interface (Goldfinger et al, 2003;Ishizawa et al, 2022).…”

Section: Discussionmentioning

confidence: 99%

Integrating onshore and offshore paleoseismic evidence to reveal past large earthquakes on the weakly coupled central Hikurangi margin, New Zealand

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Determining the location and recurrence of seismic slip at subduction zones is essential for constraining the hazard posed by great earthquakes. Although modern geodetic observations have revealed interseismically locked regions of the plate interface, it is unclear to what degree this reflects the potential for future rupture given the broad spectrum of possible slip behaviour and short instrumental record. Developing paleoearthquake records over multiple seismic cycles is therefore a powerful method of understanding spatiotemporal patterns in seismic slip behaviour at subduction margins. Conditionally stable parts of the plate interface adjacent to locked patches are identified as particularly important places to constrain long-term behaviour due to their potential to host multiple styles of interface slip.This thesis explores temporal variation in slip behaviour at subduction zones by investigating the paleoseismic record on the weakly coupled central Hikurangi margin in New Zealand. Previously, interpretation of paleoearthquake evidence in this region has been hindered by poorly constrained chronology, sparse distribution of study sites and incomplete consideration of source faults. Generating new paleoearthquake records was therefore necessary to constrain the timing and extent of large earthquakes, and to decipher whether they could represent rupture of the plate interface. Where precisely-dated tephra isochrons are available, they can provide a useful tool for accurate chronostratigraphic correlation between paleoseismic sites and improved temporal constraints within age-depth models of Holocene paleoearthquake chronologies. The age of the Waimihia tephra isochron was refined to 3574–3478 cal yr BP using integrated age modelling of 42 radiocarbon dates from proximal, distal onshore, and distal offshore locations. Using the refined isochron age alongside 68 radiocarbon dates, a new 5000-year record of four precisely-dated paleoearthquakes was generated at the Pakuratahi Valley near Napier, as a key locality for examining onshore coseismic deformation on the central Hikurangi margin. The evidence of both coseismic subsidence and uplift could have been caused by earthquakes on upper plate faults and/or the plate interface. To better distinguish between these sources and expand the paleoseismic record in space and time, a 7000- year record of seismoturbidites was developed from a suite of submarine sediment cores spanning the central margin. Integrating the onshore and offshore datasets permitted better characterization of evidence for widespread synchronous deformation across the central margin. The new interpretation of paleoseismic correlations suggests rupture of upper plate faults could generate some of the observed patterns of surface deformation, but that seismic slip on the subduction interface is likely for most earthquakes.Temporal agreement between the central Hikurangi paleoearthquakes and subduction earthquakes recorded on the southern, locked section of the margin provides strong evidence that multi-section ruptures, spanning a distance of >300 km, may have occurred. Examining the pattern of coseismic deformation on the central margin alongside current understanding of geophysical properties highlights the weakly coupled region of the interface between slow slip zones as an important location for propagating rupture along-strike from the locked patch. Conditional stability of this region is implied as a mechanism for supporting coseismic slip on the currently creeping part of the central Hikurangi margin. These observations add to the growing literature that suggests weakly coupled parts of the plate interface adjacent to locked patches can host multiple modes of interface slip and should therefore be considered a region of significant seismic hazard, due to their ability to support great (>Mw 8) multi-section subduction earthquakes.

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Section: Discussionmentioning

confidence: 99%

Integrating onshore and offshore paleoseismic evidence to reveal past large earthquakes on the weakly coupled central Hikurangi margin, New Zealand

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In search of Holocene trans-Pacific palaeotsunamis

Goff

Borrero

Easton

2022

Earth-Science Reviews

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A 5000 yr record of coastal uplift and subsidence reveals multiple source faults for past earthquakes on the central Hikurangi margin, New Zealand

Pizer,

Clark,

Howarth

et al. 2023

Geological Society of America Bulletin

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Prehistoric records of subduction earthquakes are often distinguished by evidence of synchronous widespread coastal deformation, the extent of which negates the plausibility of alternative source faults. At the Hikurangi subduction margin in New Zealand, untangling the record of subduction interface ruptures is complicated. Large earthquake age uncertainties inhibit unique solutions of along-strike correlations, and complex patterns of coastal deformation caused by upper-plate faulting prevent reliable indication of source faults. In this work, we improved paleoearthquake reconstructions on the central Hikurangi margin with a new, well-constrained 5000 yr earthquake record from Pakuratahi Valley near Napier, North Island, New Zealand. Evidence of laterally extensive paleoenvironmental changes is consistent with coseismic subsidence and coseismic uplift in large earthquakes. Radiocarbon dates on fragile terrestrial macrofossils and tephra isochrons were used to construct robust age models that yielded earthquake ages of 4839−4601 calibrated (cal.) yr B.P., 3630−3564 cal. yr B.P., 2687−2439 cal. yr B.P., and 1228−823 cal. yr B.P. Integration of these ages with refined earthquake chronology from nearby Ahuriri Lagoon indicated that the next large earthquake impacting the Napier area is more likely to cause coastal subsidence than uplift. Drawing on correlations with cotemporal evidence elsewhere on the central margin, we infer that the overall patterns of coseismic deformation could be generated by either rupture of the subduction interface or upper-plate faults, or both. This inability to separate source faults for past earthquakes limits the efficiency of forecasting future earthquakes. Similar problems of intertwined paleoearthquake signatures likely apply to other plate boundaries, where we recommend cautious interpretation of coastal deformation to accurately address the hazard from both types of source faults.

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A new chronology for tsunami deposits prior to the 1700 CE Cascadia earthquake from Vancouver Island, Canada

Cited by 4 publications

References 65 publications

Integrating onshore and offshore paleoseismic evidence to reveal past large earthquakes on the weakly coupled central Hikurangi margin, New Zealand

Integrating onshore and offshore paleoseismic evidence to reveal past large earthquakes on the weakly coupled central Hikurangi margin, New Zealand

In search of Holocene trans-Pacific palaeotsunamis

A 5000 yr record of coastal uplift and subsidence reveals multiple source faults for past earthquakes on the central Hikurangi margin, New Zealand

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