Surface rupture of the Poulter Fault in the 1929 March 9 Arthur's Pass earthquake, and redefinition of the Kakapo Fault, New Zealand

Abstract

The 1929 March 9 Arthur's Pass earthquake of MS7.1 occurred on a newly mapped fault in the Arthur's Pass region, which we name the Poulter Fault. Surface rupture of at least 16 km and possibly as much as 36 km occurred with 4 m of dextral displacement at one site. The extent of fault rupture coincides very closely with a narrow, elongate zone of intense landsliding. A best estimate of the dip‐slip component of faulting is 1–2 m (north side up), making the 1929 rupture a dextral to oblique‐dextral fault displacement, in keeping with earthquake first motion studies. The Poulter Fault is mapped from the South Hurunui River in a WSW direction to Williams Saddle near the confluence of the Mingha and Edwards Rivers, a distance of nearly 50 km. The 1929 earthquake was not on the Kakapo Fault as previously proposed by Yang. No active fault has been found along the line proposed by Yang, and the Kakapo Fault is here redefined as the southern element of a rhomboid fault wedge formed with the Hope Fault between Kakapo Brook and MacKenzie Stream in the upper Hurunui valley.