Five things about the cold forearc mantle wedge
About the Event:
The forearc mantle wedge plays a critical role in the geodynamics of subduction zones. From five perspectives, I will highlight its thermal, petrologic, and mechanical states and how it affects megathrust slip behaviour. (1) Heat flow data and seismic imaging indicate that the forearc mantle wedge is cold, referred to as the “cold nose”, in sharp contrast with the hot arc-backarc region. With fluids supplied by the dehydrating slab, hydrous minerals form in the ultramafic cold nose. (2) Maintaining the cold and stable thermo-petrologic state requires the forearc wedge to be fully decoupled from the subducting slab and does not participate in mantle wedge flow. This is supported by the lack of seismic anisotropy in the cold nose as inferred from local-earthquake shear wave splitting analysis in the Japan Trench subduction zone. (3) The cold state gives rise to high stiffness, affecting postseismic deformation following megathrust earthquakes. The mechanical contrast of the cold nose with the rest of the mantle wedge is clearly reflected in geodetically observed postseismic uplift between the cold nose and the volcanic arc. (4) In warm-slab subduction zones, a very high degree of serpentinization of the tip area of the mantle wedge is expected to diminish permeability. The hydrological consequence is inferred to foster a geological condition for episodic tremor and slip (ETS) downdip of, but separated from, the megathrust seismognic zone. (5) In colder-slab subduction zones, serpentinite derived from the base of the forearc mantle wedge affects the mechanics of the megathrust fault zone, resulting in complex seismogenic behaviour downdip of the Moho-megathrust intersection. I will use the 2010 M=8.8 Maule, Chile, earthquake as an example to show how this process may affect coseismic slip, stress drop, and aftershock distribution under the specific P/T condition in this area.
About the Speaker:
Kelin Wang is a senior Research Scientist with the Geological Survey of Canada. Most of his current research is on geodynamics of subduction zones and related earthquake and tsunami hazards, but he has also worked on a range of other topics regarding the thermal, mechanical, and hydrogeological processes of Earth’s lithosphere. He is particularly interested in exploring how different components of the subduction zone affect one another, addressing questions like how mantle flow and slab metamorphism affect earthquake generation and arc volcanism, how stresses and stress changes along subduction faults affect intraplate stress and deformation, how mantle rheology controls deformation cycles of subduction earthquakes, and how sediment accretion at the trench is related to great earthquakes, etc. He is an Adjunct Professor at the University of Victoria and an Honorary or Guest Professor for several other scientific institutions. He is Editor-in-Chief for scientific journal Tectonophysics and was or still is on the Editorial Boards of a number of other journals such as Journal of Geophysical Research, Geology, Journal of Geodynamics, Science in China (Earth Science), and Earthquake Science. He was formerly the Secretary of the Canadian Geophysical Union and Chair of the International Professionals for the Advancement of Chinese Earth Sciences. In 2015, he was awarded the J. Tuzo Wilson Medal by the Canadian Geophysical Union and elected the Birch Lecturer by the American Geophysical Union.
You may also view Dr Wang's profile here.