Paleoearthquakes at the junction of the Tokomaru and Northern Ōhāriu faults, implications for fault interactions in the southern North Island, New Zealand

Abstract

ABSTRACT The Tokomaru Fault extends along the west side of the southern North Island of New Zealand. Given the fault’s proximity to major and expanding population centres, new work was undertaken to understand its contribution to seismic hazard in the Wellington-Levin corridor. Two paleoseismic trenches excavated across the southern end of the Tokomaru Fault, close to its junction with the Northern Ōhāriu Fault, show that it and the Northern Ōhāriu Fault are more active than previously thought. Ages of the two youngest events on the Tokomaru Fault are 93–220 and 1179–1254 cal yr BP, and result in a recurrence interval of 470–2300 years. These ages agree with the two youngest events on the Ōhāriu Fault and the timing of some events on the Wellington Fault. This suggests that the Tokomaru, Northern Ōhāriu, Ōhāriu, and Wellington faults may have ruptured together in the past, have triggered earthquakes on each other, or host slip that is triggered by larger nearby earthquakes. The results of this work illustrate the importance of fault interactions in the southern North Island and show that even if faults here do not rupture together, they likely play a key role in influencing the earthquake behaviour of each other.