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Refined slip distribution and moment magnitude of the 1848 Marlborough earthquake, Awatere Fault, New Zealand

2006; Taylor & Francis; Volume: 49; Issue: 3 Linguagem: Inglês

10.1080/00288306.2006.9515174

1175-8791

Dougal P. M. Mason, Timothy A. Little,

Geological and Geochemical Analysis

Abstract The Awatere Fault is an important element of the obliquely convergent plate boundary zone in northeastern South Island, New Zealand, and is comprised of two geo‐morphically distinct sections that join across a complex fault junction in the upper Awatere Valley. The M w c. 7.5 Marlborough earthquake of 1848 ruptured a c. 110 km length of the eastern section of the Awatere Fault, from the South Island's east coast extending inland to at least Barefell Pass. This study attempts to document the coseismic slip distribution during the 1848 earthquake rupture. We examine a previously unmapped length of the fault trace in the upper Awatere Valley, along which we measured as many small (metre‐scale) geomorphic displacements as possible. Based on these new data, and previous observations of inferred 1848 slip on other parts of the Awatere Fault, we infer that the 1848 earthquake had a mean coseismic displacement of 5.3 ± 1.6 m, a surface rupture length of 100–110 km, and a moment magnitude of Mw = 7.4–7.7. This new moment magnitude estimate supports previous estimates based on regressions of geometrical rupture parameters inferred for the 1848 earthquake and attenuation models of felt intensities. The set of second‐smallest horizontal geomorphic displacements (c. 8–15 m) are approximately double those attributed to the 1848 earthquake, suggesting the penultimate event was of a similar magnitude to the 1848 earthquake. Keywords: 1848 earthquakeAwatere Faultearthquake magnitudeMarlboroughNew Zealandpaleoseismologystrike‐slip faultsSouth Island