Evidence for an earthquake and tsunami about 3100–3400 yr ago, and other catastrophic saltwater inundations recorded in a coastal lagoon, New Zealand

Abstract

Abstract Okupe Lagoon is 2.02 masl, brackish, and ponded behind two boulder banks at the northern end of Kapiti Island, New Zealand. The sediments of the lagoon provide a record of late Holocene environmental changes such as tectonic uplift, catastrophic saltwater inundation, and vegetation change. Five main events were identified over a 5300-yr record, with a sixth representing a re-evaluation of previous work. An uplift event of 1.5–3.0 m and an associated tsunami are recorded and are inferred to have been caused by a local fault rupture, possibly the northern extension of the Wairau Fault, about 3360±40 yr BP. Two additional tsunami, generated by ruptures of either the Ohariu or Wellington Faults (∼1290 and ∼1220 AD, respectively) and either the Wellington or Alpine Faults (∼1450 AD) have been tentatively proposed. Two catastrophic saltwater inundations (CSIs) have also been identified, one possibly a tsunami generated by either the Wairarapa Fault (∼500 AD) or Taupo eruption (∼190 AD), the other about 4780±150 yr BP may relate to a local fault rupture. However, further work is needed to determine whether these are tsunami or storm surge related and they are therefore designated CSIs. The sixth event is the 1855 tsunami, recorded from a raised shore platform to the west of Okupe Lagoon.