Tectonic geomorphology and Holocene paleoseismicity of the Molesworth section of the Awatere Fault, South Island, New Zealand

Abstract

The Molesworth section comprises a 55 km long, N72°E‐striking reach of the 175 km long dextral‐reverse(?) Awatere Fault, which has an overall trend of N55–60°E. Well‐preserved fault scarps display normal‐oblique slip, with vertical offsets up to 30 m and horizontal offsets up to 72 m on latest glacial terraces (age c. 10 000 yr B.P.), equating to a mean slip rate of c. 8 mm/yr. The two latest paleo‐carthquakes on the main fault trace are bracketed by ¹⁴C and weathering‐rind age estimates of 522–597 cal. yr B.P. and c. 2500–4500 years ago, respectively, and display single‐event horizontal offsets of 6–8 and 4–8 m. The two latest paleoearthquakes on the 9.5 km long upper Wairau splay fault yield sufficiently different ages (751–873 cal. yr B.P. and 1296–2923 cal. yr B.P.) that they are inferred to be different from the events on the main trace. The large displacements per event imply ruptures much longer than the 55 km length of the Molesworth section. This disparity suggests that this geometrically defined section is not bounded by persistent segment boundaries, and probably ruptures along with longer segments to the east and west, in earthquakes of M _w= 7.5–7.8.

Keywords:

• Awatere Fault
• Molesworth Station
• tectonic geomorphology
• paleoseismicity
• neotectonics
• slip rates
• recurrence interval
• radiocarbon dates
• NZMS sheets N30C, N30D