Coseismic strike slip at a point during the last four earthquakes on the Wellington fault near Wellington, New Zealand

Abstract

[1] We analyze progressively displaced late Quaternary (<12 ka) fluvial terraces along the Wellington fault, near Wellington, New Zealand. Optically stimulated luminescence dating indicates that degradational terraces were produced at a rate of about one terrace per 1000 years, similar to the rate of earthquake surface rupturing. Along the Hutt River near Te Marua, we measured the strike slip of 15 terrace risers and paleochannels on the lowest 8 of these terraces, of Holocene age. The river, after earthquakes, was generally capable of smoothing its faulted riverbanks. The dextral offsets appear to fall into several groupings that record slip accumulation during the last four earthquakes. We calculate a mean single-event slip of 5.0 ± 0.24 m (95% confidence) with an RMS scatter (1s) of slips about the mean of ±1.5 m. The coefficient of variation (CV) of single-event slip is thus 0.30. This CV is slightly less than a recently compiled global average for point measurements on strike-slip faults, suggesting that the southernmost Wellington fault has behaved in a more nearly characteristic way. We speculate that recent large earthquake ruptures have been bounded on their southern end by the Wellington fault's offshore fault termination and perhaps on their northern end by a ∼2 km wide releasing step over. Such persistent sources of rupture arrest might have led to a relative uniformity of rupture dimensions and slip amounts. We infer a late Holocene dextral slip rate of ≥4.5 ± 0.4 mm/yr (1s) and <8.2 mm/yr, and a mean earthquake recurrence interval of ∼610-1100 years.

Variability of recurrence interval and single-event slip for surface-rupturing earthquakes in New Zealand

“…The coefficient of variation is a normalised measure of dispersion of a probability distribution that has been widely used in the paleoearthquake literature (e.g. Marco et al 1996; McCalpin & Nishenko 1996; Dawson et al 2008;Mouslopoulou et al 2009a;Robinson et al 2009a;Little et al 2010;Berryman et al 2012;Hecker et al 2013). We follow many of these publications in assuming that RI and SES populations on individual faults are normally distributed and that C v = standard deviation/arithmetic mean.…”

“…The faults in Table 1 range in SES from 0.5 to 16.9 m, with the lower bound defined by the detection limit of geological investigations of normal faults. In New Zealand, SES on individual faults may be approximately uniform (Van Dissen & Nicol 2009;Little et al 2010;Townsend et al 2010) or vary by up to a factor of five (Nicol et al , 2011bTownsend et al 2010; Figure 2). Whether most faults adhere to the quasi-uniform or variable SES models, and under what geological conditions each of these models applies, are important questions (e.g.…”

“…Figure 2); and (3) changes in slip distributions along fault traces occur between earthquakes (e.g. Hemphill-Haley & Weldon 1999;Biasi & Weldon 2006;Wesnousky 2008;Little et al 2010;Nicol et al 2010;Hecker et al 2013). Point-sample measurement of earthquake parameters will most often depart from mean or maximum values on long faults and/or approaching fault tips.…”

“…One advantage of using C v to quantify earthquake variability is that it is relatively simple to calculate and has been widely adopted in the literature for geological data and simulations in New Zealand (e.g. Robinson et al 2009aRobinson et al , 2011Little et al 2010;Berryman et al 2012;Biasi et al 2015; this study) and globally (e.g. Sieh et al 1989;McCalpin & Nishenko 1996;Weldon et al 2004;Dawson et al 2008;Hecker et al 2013).…”

Optical Dating of Sediments in Khari River Basin and Slip Rate Along Katrol Hill Fault (KHF), Kachchh, India

“…Besides these instances optically stimulated luminescence dating has been suitably applied to estimate the slip-rates of a number of other faults in different regions of the world e.g. the HarUs-Nuur fault (Mongolian Altai) , Wellington fault near Wellington, New Zealand (Little et al, 2010), Duzce fault of the North Anatolian fault zone, Turkey (Pucci et al, 2008) and Dheshir fault, Central Iran (Fattahi et al, 2010 and references there in). The present study therefore aimed towards Optical dating of sediment offsets in a segment of the KHF near Bharasar in the Khari River basin to estimate slip-rate in the study area.…”