NZ3D PhD student and Post-Doctoral Research Associate positions available funded by the Leverhulme Trust!
Subduction zones are located where one of the Earth's tectonic plates slides beneath another - the boundary between the tectonic plates is called the plate boundary fault. These plate boundary faults are capable of generating the largest earthquakes and tsunamis on Earth, such as the 2011 Tōhuku-oki, Japan and the 2004 Sumatra-Andaman earthquakes. In the last 15 years a completely new type of seismic phenomenon has been discovered at subduction zones: silent earthquakes or slow slip events. These are events that release as much energy as a magnitude 6 to 7 earthquake, but do so over several weeks or even months and there is no ground-shaking at all. Slow slip events may have the potential to trigger highly destructive earthquakes and tsunamis on nearby parts of the plate boundary fault, but whether this is possible and why slow slip events occur at all are two of the most important questions in earthquake seismology today.
The Earth's crust is divided into a number of tectonic plates. In some areas these plates collide and one gets thrust beneath another- this is called subduction. The boundary between the plates at subduction margins produces the largest fault planes on Earth, which are capable of producing the largest earthquakes. Image courtesy of Darren D'Cruz, GNS Science
The northern Hikurangi margin, New Zealand
Slow slip events were first discovered in 2002 and since then slow slip events beneath the town of Gisborne have happened regularly every 1-2 years. The slow slip events beneath Gisborne are particularly shallow, occurring at depths of 2 - 15 km beneath the seabed. This makes them suitable to study with man-made acoustic waves and with academic drilling.
The NZ3D FWI experiment
From December 2017 to March 2018 we will install over 200 seismometers in New Zealand to detect earthquakes and also to listen for sound waves produced by a ship 90 km away from the Gisborne coast. The sound waves will travel through the plate boundary fault and the time and strength of the sound waves detected by our seismometers will tell us about the rock properties beneath Gisborne and in the slow slip zone. We will be applying a cutting-edge method called "3D Full waveform Inversion" (FWI) to produce extremely high resolution models of rock properties to depths of 10 km.
In Dec 2017 and March 2018 the International Ocean Discovery program will also be drilling offshore and installing instruments that will examine how the Earth behaves in a slow slip event. You can read more about these experiments on the East Coast LAB tab and at GNS Science.