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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 similar to 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.

Plain Language summary Faults are commonly assumed to accommodate relative tectonic motions (slip) at constant rates when averaged over several large earthquakes. Testing this assumption requires documenting how far a fault has slipped at several different points in time over the past several millennia. In this study, we examine a rare instance in which four independent markers of fault slip over time are recorded in the landscape along the Clarence fault - a major fault in the Marlborough fault system of South Island, New Zealand. We use high-resolution digital topographic laser scans (lidar) to document the fine-scale topography of the site, and luminescence dating to determine the ages at which the sediments constituting the landforms were last exposed to sunlight. Together, these markers show that, far from being constant over time, the Clarence fault at Tophouse Road has sped up and slowed by by a factor of four or five over the past eleven thousand years or so. This type of study needs to be conducted on other faults to examine whether they have exhibited similar behavior. Such phenomena can provide insights into the processes controlling tectonic plate behavior over timescales of hundreds to thousands of years.