Coseismic Uplift of Holocene Marine Terraces in the Pakarae River Area, Eastern North Island, New Zealand

Abstract

Holocene marine terraces along 15 km of the northeastern coast of North Island record episodic tectonic uplift. A maximum of seven terraces are arranged in staircase fashion and lie about 20 km above the subduction interface between the Pacific and Australian plates. The highest (T1) corresponds with the maximum of the Holocene marine transgression about 6700 ¹⁴C yr B.P. Younger terraces are marine abrasion platforms overlain by thin beach deposits. Radiocarbon ages of marine shells from beach deposits indicate that uplift above marine conditions occurred ca. 6700(T1), 5500(T2), 3900(T3), 2500(4), 1600(T5), 1000(T6), and slightly younger than 600(T7) yr B.P. Uplift probably occurred coseismically. The maximum late Holocene uplift rate in the study area is 8 mm/yr. Altitudinal distribution of terraces suggests deformation exists as a ca. 20-km elongate dome, broken at the southern end by the Pakarae fault, which trends across the dome. Rupture on this fault has accompanied the growth of the dome but is not responsible for it. Bathymetric profiling suggests that an active fault, parallel to and about 5 km offshore, is probably responsible for the episodic coastal uplift.