Architecture of the Subduction to Strike-Slip Transition in New Zealand

点击翻译按钮获取中文摘要

In recent years, seismologists have come to recognize that many large earthquakes that occur involve slip on multiple faults. This phenomenon means that estimates of earthquake hazard based on the assumption that faults fail individually can underestimate the size of the largest possible earthquake in a region, and in turn the level of seismic hazard. The November 14, 2016 magnitude 7.8 Kaikoura earthquake in the northern South Island, New Zealand, stands out as one of the most complex earthquakes known, with rupture of the ground surface observed on more than 20 faults. The earthquake was followed by tens of thousands of aftershocks, and it also triggered a number of what are called "slow slip events" - fault slip occurring over days to months instead of seconds to minutes like most earthquakes. The Kaikoura earthquake is the latest in a series of damaging earthquakes in the northern part of the South Island in New Zealand that have struck in this decade. This project will examine several key questions related to the complicated geologic evolution of this region. This project will take advantage of data and results from a broad range of studies that have been carried out over the past two decades. It will also utilize seismic data from temporary arrays that were deployed to record aftershock and were operated, in part, with support of RAPID funding from NSF. The tasks of this project are to image the three-dimensional seismic velocity and attenuation structure, to relocate earthquakes that occurred in the region with high-precision, and to determine the fault slip geometry using the aftershock locations. This work will contribute to our understanding of how multiple-fault failure occurs in large earthquakes, thereby contributing to improving seismic hazard estimation. The work will be carried out in close collaboration with New Zealand scientists from GNS Science and Victoria University of Wellington. In addition, as part of the broader impacts, this project will mentor a female postdoctoral scholar.The November 14, 2016 Mw 7.8 Kaikoura earthquake in the northern South Island, New Zealand, stands out as one of the most complex seismic events known. Surface rupture has been mapped on at least 21 faults. Post-seismic slow slip events were triggered over a broad area, including substantial slip on the South Island megathrust underlying the activated crustal faults. The Kaikoura earthquake is the latest in a series of damaging earthquakes in the Canterbury and Marlborough regions of the South Island that have struck in this decade, starting with the Darfield and Christchurch earthquakes of 2010 and 2011, continuing with the Seddon and Lake Grassmere earthquakes of 2013, and culminating in the 2016 Kaikoura earthquake. We note that the Mw 7.1 Darfield earthquake was also a complex, multi-fault rupture.This project will examine several hypotheses related to the complex tectonics of this region of transition from subduction to strike-slip. The proposed study will take advantage of data and results from a broad range of studies that have been carried out in this region over the past two decades, and utilize data from temporary aftershock arrays supported in part by NSF through RAPID awards. The main analysis tools are seismic velocity and attenuation tomography that incorporate recent and planned methodological developments, high-precision earthquake relocation, and focal mechanism analysis. The work will be carried out in close collaboration with New Zealand scientists from GNS Science and Victoria University of Wellington and will engage a female postdoctoral scholar in the data analysis and interpretation.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.