Multimillennial Incremental Slip Rate Variability of the Clarence Fault at the Tophouse Road Site, Marlborough Fault System, New Zealand

Abstract

Incremental slip rates of the Clarence fault, a dextral fault in the Marlborough fault system of South Island, New Zealand, varied by a factor of 4–5 during Holocene–latest Pleistocene time, as revealed by geomorphic mapping and luminescence dating of faulted fluvial landforms at the Tophouse Road site. We used high‐resolution lidar microtopographic data and field surveys to map the fine‐scale geomorphology and precisely restore the offset features. We dated the offsets using a stratigraphically informed protocol for infrared stimulated luminescence dating. These data show that incremental slip rates varied from ~2.0 to 9.6 mm/year, averaged over multiple earthquakes and millennial timescales. Comparison to incremental slip rates of the nearby Awatere fault suggests that these faults may behave in coordinated (and anticorrelated) fashion. This study adds to a growing body of evidence suggesting that incremental slip rate variation spanning multiple earthquake cycles may be more common than previously recognized.

Seismic Hazard Analyses From Geologic and Geomorphic Data: Current and Future Challenges

“…Amos et al (2010). (a) Interpreted lidar topography from Zinke et al (2019) showing right-laterally offset fluvial channel and terrace sequence across the Clarence Fault in New Zealand. Green dots denote location of IRSL samples.…”

“…Offsets are commonly reconstructed by backslipping the current topography along a fault, until the offset piercing point is restored to its original, undeformed geometry (e.g., Frankel et al, 2007). For example, Zinke et al (2019) computed four increments of late Pleistocene to Holocene right‐lateral offset (averaging multiple meters) along the Clarence Fault in New Zealand by restoration of a sequence of offset terraces, channel systems, and other markers to their original positions (Figure 2a).…”

Time‐Invariant Late Quaternary Slip Rates Along the Agua Blanca Fault, Northern Baja California, Mexico

“…Prolonged periods of zero slip lasting multiple average earthquake cycles have been proposed for the Garlock Fault in southern California (Dolan et al, 2016), and apparent accelerations and decelerations exceeding a factor of 10 have been measured along the Warm Springs Valley Fault in western Nevada (R. D. Gold et al, 2013) and the Awatere Fault in New Zealand (Zinke et al, 2017), although analysis of an earlier slip rate dataset from the Awatere Fault found a more moderate (factor of ~2–3) change in slip rate (R. D. Gold & Cowgill, 2011). Less extreme but still resolvable slip rate variations (factor of 3–8) have been measured on sections of the Clarence (Zinke et al, 2019) and Wellington (Ninis et al, 2013) Faults in New Zealand, as well as on a section of the Dead Sea Transform in Israel (Wechsler et al, 2018) and the Mojave section of the San Andreas Fault (Weldon et al, 2004). Most of these examples document multimillennial deviations from a long‐term average—the longest slip rate record is 760 kyr, but most are less than 100 kyr, with a median of 17 kyr—but short pulses of accelerated slip lasting just several hundred years have been identified in dense datasets from the Altyn Tagh Fault in China (R. D. Gold et al, 2017) and the San Andreas Fault (Weldon et al, 2004) (Table 4).…”

“…Generally, faults with constant rates are more structurally isolated than those with variable rates (Table 4). Constant rates (and near‐regular earthquake recurrence—see Berryman et al, 2012) on the linear and structurally isolated Alpine Fault give way to variable slip rates as it splays into the Marlborough fault system, a 150‐km‐wide zone of four primary faults that includes the variable slip rate Awatere and Clarence Faults (Sutherland et al, 2006; Zinke et al, 2017, 2019). The variable slip rate Garlock Fault has high‐angle intersections with both the San Andreas Fault and the many faults of the Eastern California Shear Zone‐Walker Lane (Dolan et al, 2016).…”

“…Although regularity in earthquake occurrence and the assumption that post‐rupture reset should significantly lower the probability of another earthquake are known oversimplifications of elastic rebound theory, the classic characteristic, slip‐predictable, and time‐predictable models for earthquake recurrence incorporate this assumption by restricting variability such that fault slip rates over two to three earthquake cycles approximate the long‐term average (Shimazaki & Nakata, 1980). However, a growing number of paleoseismic and paleoslip (slip rate) studies have measured slip rate variations of several orders of magnitude lasting multiple millennia (Dolan et al, 2016; R. D. Gold 2011; R. D. Gold et al, 2017; Goldfinger et al, 2013; Ninis et al, 2013; Onderdonk et al, 2015; Wechsler et al, 2018; Weldon et al, 2004; Zinke et al, 2017, 2019). Identifying the factors that cause strain to be released periodically or in punctuated bursts is critical for understanding fault mechanics and requires reconstructing slip histories from the geologic record for a variety of faults.…”