NSFGEO-NERC: Latest Pleistocene-Holocene incremental slip record of the Kekerengu-Jordan fault system, northern South Island, New Zealand

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The standard model for rupture of large earthquakes along strike-slip faults is that the slip that generates the earthquake occurs on a single surface. The November 14, 2016 Kaikoura, New Zealand, magnitude 7.8 earthquake shook up this thinking about fault slip behavior. In what initially seemed to be an event resulting from slip along a single fault, turned out to be more complex with slip jumping from one fault to another within a network of faults called the Marlborough fault system. In this project, a research team from the University of Southern California, United Kingdom, and New Zealand will use a variety of cutting-edge methods to reconstruct the slip and paleo-earthquake history of one of the Marlborough fault system faults, the Kekerengu-Jordan fault system, which experienced about 12 meters of slip in the 2016 event. Data collected in this project would be used in conjunction with data from other faults in system to better understand earthquake recurrence rates and, more importantly, the temporal and spatial linkage between these faults, something that was clearly not well understood before the Kaikoura earthquake. Understanding the threat from major earthquakes to an increasingly urbanized American population is of critical importance for facilitating proactive and efficient measures to reduce future loss of life and property. Yet understanding of what to expect in terms of the occurrence of large earthquakes in time and space remains severely limited by the current lack of information about how entire systems of inter-connected earthquake faults store and release seismic energy in large, potentially damaging earthquakes. Comprehensive data sets, such as those that will result from this project will reveal how the major faults in a fault system interact with one another to generate potentially damaging earthquakes. These kinds of observations will, in turn, allow for better forecasting of what to expect from similar fault networks in the United States, particularly in earthquake-prone California, but more generally for all of the major faults that underlie large parts of the country. The project has potential to benefit society or advance desired societal outcomes through full participation of women in STEM, increased public scientific literacy with STEM through outreach activities, improved well-being of individuals in society by better understanding of fundamental processes underlying earthquakes that would improve the capability to model earthquake hazards, development of a diverse, globally competitive STEM workforce through graduate student training, and increased partnerships through international collaboration.The primary aim is to advance understanding of the collective behavior of regional fault networks, particularly the importance of emergent phenomena such as earthquake clusters and strain transients that may not be expected in the current understanding of earthquake physics and that are not accounted for in current seismic hazard assessment strategies. Mounting evidence suggests that the occurrence of large earthquakes on both single faults and fault systems is not a random process, with increasing observations of temporal and spatial earthquake clustering, changes in incremental fault slip rates, variations in fault loading rates, and potentially coordinated waxing and waning of slip on mechanically complementary faults in regional fault systems. Although a thorough understanding of both the causes and generality of such phenomena is of basic importance for fault mechanics, earthquake physics, and more accurate assessment of seismic hazard, evaluation of the importance of these behaviors has been severely data limited. In particular, there are too few comprehensive paleo-earthquake and incremental fault slip rate data sets to fully assess the collective behavior of major plate-boundary fault systems in time and space. This study focuses on the Pacific-Australia plate boundary in northern South Island New Zealand in order to document a complete latest-Pleistocene-Holocene (15 ka-present) record of incremental plate boundary slip encompassing all major structures in the system. The research team will build on previous work by developing robust records for the Kekerengu-Jordan fault system, an 85-km-long, oblique reverse-dextral fault system, which is the fastest-slipping fault in the onshore part of the plate boundary at 25-30 mm/year. Slip on the Kekerengu-Jordan fault system generated most of the moment release in the 2016 Mw=7.8 Kaikoura earthquake. The new post-IR IRSL225 luminescence dating protocol will be used at key sites on the Kekerengu-Jordan fault system, and at additional sites located with the new post-earthquake high-resolution lidar data collected by the New Zealand government. This new luminescence dating technique provides precise and reproducible dating of carbon-poor sediments typical of those in the study area with precision roughly equal to that of radiocarbon dating. Combining incremental fault offsets and trench observations with post-IR IRSL225 dating, and carbon-14 analysis will yield detailed fault slip rates and earthquake ages along the fault system spanning individual ruptures back though several dozen earthquakes. In conjunction with existing data sets from both the onshore and offshore faults, including the subduction megathrust that underlies the Kekerengu-Jordan fault system, the research will facilitate a comprehensive, system-level analysis of plate-boundary strain release through time and space during latest Pleistocene-Holocene time.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.