Constraining fault growth rates and fault evolution in New Zealand

Abstract

Understanding how faults propagate, grow and interact in fault systems is important because they are primarily responsible for the distribution of strain in the upper crust. They localise deformation and stress release, often producing surface displacements that control sedimentation and fluid flow either by acting as conduits or barriers. Identifying fault spatial distribution, quantifying activity, evaluating linkage mechanism, and estimating fault growth rates are key components in seismic risk evaluation. Scientists from the National Institute of Water and Atmospheric Research (NIWA), New Zealand, and the Southampton Oceanography Centre (UK) are working on a collaborative project which aims to improve understanding of the processes of faulting in the Earth’s crust. The program comprises two research cruises to survey the Whakatane Graben, New Zealand, which is a zone of intense seismicity, active extensional faulting, and rapid subsidence within the back-arc region of the Pacific-Australia plate boundary zone (Fig. 1). Few places in the world offer the same potential to study the mechanisms by which major crustal faults have grown from small to large scale structures capable of generating moderate to large magnitude earthquakes. The aim of the project it to provide new insights into fundamental questions such as: (i) how do faults interact and link together to form fault systems, and (ii) how do fault propagation and linkage change with time? One of the most exciting results from the work in the Whakatane Graben is the potential for improving understanding of how and at what rates faults grow. The first survey was funded by the New Zealand Foundation for Research Science and Technology (FRST), and took place in November 1999 during which conventional marine geophysical data were collected. The second cruise is funded by the British Natural Environment Research Council (NERC), and is scheduled for January 2001. It will focus on the acquisition of high frequency shallow seismic and sidescan sonar data . This study of the Whakatane Graben will represent the most detailed regional investigation of active marine faults undertaken anywhere in the New Zealand region. Arguably, it could also become a case study of extensional fault growth and continental rift development of global significance.

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ORCID for J.M. Bull: orcid.org/0000-0003-3373-5807

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