Advanced seismic instruments for challenging environments: road testing UK technology to unravel earthquake hazard and tectonics in North Borneo

Subduction describes the process in which one tectonic plate descends into the mantle beneath an adjoining tectonic plate as a result of convergence. Currently active subduction zones can be found in many parts of the world, including western South America, the NW Pacific and southeast Asia. Subduction may have been operating on Earth for over three billion years, and plays a fundamental role in the creation and evolution of the continents, the generation of new oceanic crust and the exchange of water between the Earth, oceans and atmosphere. Subduction zones are also the principal source of volcanic and seismic hazard around the globe, with the devastating 2011 Tohoku earthquake and tsunami in Japan being one of many examples of the destructive power they hold.
Subduction zones, therefore, are one of the primary keys to understanding how our Earth works, and as a result, they have been the subject of intensive study by Earth Scientists from around the world. However, one aspect of the subduction cycle that has received little attention is the termination phase, where, for potentially a variety of reasons, the descent of the downgoing slab ceases. Given that all subduction zones have a finite lifetime, this process is likely to have profoundly influenced the way in which our continents have evolved, but to date no credible model has been developed for what might happen to the crust and upper mantle in such circumstances. This knowledge gap means that there is a unique and timely opportunity to provide new insight into this fundamental Earth process.

I aim to make a step-change in our understanding of how post-subduction continental margins evolve and how the crust and upper mantle interact by combining seismic imaging, earthquake source mechanism studies and geological observations in North Borneo (east Malaysia), which last experienced active subduction 5-6 million years ago. Evidence of recent structures and processes which may be connected to subduction termination make it an ideal setting to examine links between the near surface geology and underlying mantle. To achieve this, I will provide the first detailed picture of an active post-subduction continental margin, and will properly resolve a previously identified upper mantle high velocity anomaly beneath North Borneo. Together with analysis of earthquake source mechanisms, my new imaging results will help build a model of how the continental lithosphere responds to subduction termination.

To enhance the scientific outcomes of the project, and contribute to the improvement of UK export technology, we have teamed up with one of only a few global manufacturers of seismic sensors, Guralp Systems Limited (GSL), which is the only one based in the UK. The central objective of the proposal is to deploy a dense array of seismometers both onshore and offshore North Borneo to record local and regional earthquakes, active shooting of airgun shots off-shore and ambient seismic noise (the Earths "hum" caused by atmospheric disturbances and oceanic microseisms), in order to image the underlying crust and mantle at high resolution. The off-shore OBS deployment and active shooting will be carried out by our collaborators the Chinese Academy of Sciences and State Ocean Administration of China. At the same time, we will be able to test existing new generation GSL instruments, improve their design and performance, help in the development of new technologies and potentially open new markets, thus strengthening GSL's international reputation and visibility as a world-leading firm of seismic instrument manufacturers.