Harold Tobin
2020-11-19 09:46:01
SZ4D is hosting an International Webinar tomorrow, Friday Nov 20, by Dr.
Kelin Wang of the Pacific Geoscience Center, Geological Survey of Canada.
Dr. Wang is a global leader in research on the geodynamics of subduction
zones with a focus on the links between very large-scale processes and the
megathrust earthquake cycle. All welcome for what promises to be a
stimulating presentation!
*Five things about the cold forearc mantle wedge*
*Kelin Wang*
Pacific Geoscience Centre, Geological Survey of Canada
*November 20th, 2020 at 11 AM PDT*
Pre-register here for this Zoom Webinar:
https://washington.zoom.us/meeting/register/tJUtc-iqqj8qGNPijltff-j-2-JMzf7ZteiM
*Abstract*
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
seismogenic 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.
*SZ4D presents International Webinars, a series where the working groups
invite international scientists to present on different topics relevant to
their research and region. SZ4D values international voices and invites you
to learn from these research leaders.*
Kelin Wang of the Pacific Geoscience Center, Geological Survey of Canada.
Dr. Wang is a global leader in research on the geodynamics of subduction
zones with a focus on the links between very large-scale processes and the
megathrust earthquake cycle. All welcome for what promises to be a
stimulating presentation!
*Five things about the cold forearc mantle wedge*
*Kelin Wang*
Pacific Geoscience Centre, Geological Survey of Canada
*November 20th, 2020 at 11 AM PDT*
Pre-register here for this Zoom Webinar:
https://washington.zoom.us/meeting/register/tJUtc-iqqj8qGNPijltff-j-2-JMzf7ZteiM
*Abstract*
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
seismogenic 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.
*SZ4D presents International Webinars, a series where the working groups
invite international scientists to present on different topics relevant to
their research and region. SZ4D values international voices and invites you
to learn from these research leaders.*
