Tectonics and Structural Geology Group (Prof. Dr. Toy)
Mechanics of subduction thrust faults
Subduction zones present the largest source of seismic hazard worldwide due to their potential to generate very large moment magnitude (MW>9.0) earthquakes and damaging tsunamis. In this project we try to understand how the structural fabrics and porosity of subduction thrust faults develop and evolve, and the mechanical implications of these fabrics. We analyse samples from some of Earth’s most active and hazardous such zones (e.g. Hikurangi Subduction system, NZ; Japan Trench, JP), and compare these with exhumed ancient subduction zone analogues (e.g. Waipapa/Torlesse Terrane, NZ; Shimanto belt, JP). We also consider the relationship between the fault rock fabrics and the plate tectonic motions during their generation.
Team: Toy, Kirilova, Cappuccio, Amiri, Madison Frank (PhD, Tsukuba University, Japan)
Alpine Fault – Deep Fault Drilling Project (DFDP)
The Alpine Fault is a globally significant plate boundary structure with the potential to fail, generating a <M8 earthquake in our lifetimes. The Alpine Fault is also unique because rapid uplift and erosion has exhumed fault rocks from depth, and perturbation of the thermal structure due to uplift continues to restrict earthquake activity to depths that are shallower than normal. The DFDP project proposes to drill, sample, and monitor the Alpine Fault at depth, to take advantage of excellent surface exposures and the relatively shallow depths of geological transitions, and hence to better understand fundamental processes of rock deformation, seismogenesis, and earthquake deformation.
Prof. Toy manages this project with Profs. Rupert Sutherland and John Townend (Victoria University of Wellington)
Two phases of drilling have thus far been carried out: DFDP-1 drilled two boreholes to 100 and 144m at Gaunt Creek in 2011.DFDP-2 drilled two boreholes, the most significant to 893m in 2014-2015.
Check out our YouTube Videos!
We hope there will be future phases of drilling. Watch this space for announcements!
Years: 2011 - 2020
Electrical and seismic properties of fault zone rocks
In combination, electrical and elastic wave measurements of fault zone rocks offer rich insights into their mechanics, and hazard and resource potential.
In this project we aim to calibrate fault zone rocks’ electrical properties, and the way they transmit elastic waves, to their composition, structure, and the rate and mechanics of their deformation.
Team: Toy, Kirilova, Sauer
Years: 2009 – 2020
Conceptual models illustrating pathways for electrical charge migration through conductive grain boundary phases (blue materials and flow lines). Saline fluids in isolated grain boundary pores such as those illustrated in (b,c) may interlink during active shear on the grain boundaries, providing new pathways for charge transport (green flow line) and yielding high dynamic conductivities.
Amorphous and nanocrystalline materials in fault zones
Traditionally, classification of a fault rock as pseudotachylyte has required proof of a friction melt origin – and amorphous TEM diffraction patterns from glassy matrix material have been accepted as a ‘gold standard’ proof. However, amorphous or partially amorphous materials have been reported in a number of recent experiments where frictional heating on fault surfaces would have been insufficient to generate melt.
We are interested in how amorphous materials are generated, how they mechanically behave, and whether their presence on natural faults provides information about fault slip rate and/or fault strength evolution.
Examples of projects within this research theme include experimental studies where amorphous materials were generated; (1) during shear on a saw-cut surface in quartzites, developing a nanopowder with a crystallographic preferred orientation (CPO) and (2) associated with temperature-dependent development of striations and slickenlines, as well as ongoing exploration of natural and experimentally-generated pseudotachylytes.
Rheology of peridotites
It is increasingly recognised that the uppermost mantle plays a fundamental role in stress transfer and localisation processes in the lithosphere.
In this project we explore naturally deformed peridotites to investigate rheological relationships in ultramafic rocks, in the hope of providing insights into the significance of mantle deformation for the earth’s tectonic system.
Field work sites include in the Dun Mountain Ophiolite Belt (NZ). Horoman Peridotite (JP), and Balmuccia Peridotite (Italy).
We also investigate the structure of serpentinised shear zones, and seismic wave transport through peridotites.
Team: Toy, Ofman
Funding sources: Otago Research Grants, NSF (NSF-1050041).