GAGE/SAGE Plenary Webinar, Behavior at and coupling across key Earth interfaces, 9/24 at 2 PM Eastern

Danielle Sumy danielle.sumy at iris.edu
Thu Sep 17 16:05:35 UTC 2020


Please join us for a virtual GAGE/SAGE Plenary Webinar on *September 24,
2020* at *2 PM Eastern*. The plenary session is *Behavior at and coupling
across key Earth interfaces*. The in-person GAGE/SAGE Science Workshop was
postponed from August 2020 to August 2021. In the meantime, several of the
planned speakers are presenting in this webinar series so we learn more
about these subjects before next year.

Please click the link below to join the webinar:
https://zoom.us/j/92513984587?pwd=amEyTUhWYTA0MkhwSC9ZdkQ0ZEZqZz09
Passcode: 997363
Or iPhone one-tap :
    US: +13017158592,,92513984587#  or +19292056099,,92513984587#
Or Telephone:
    Dial:
        US: +1 301 715 8592
Webinar ID: 925 1398 4587
    International numbers available: https://zoom.us/u/abUDH2KsN0

*Presented by:* Drs. Heather Ford, UC-Riverside, and Diego Melgar,
University of Oregon

Dr. Ford will present on *The Seismic Signature of Past and Present
Tectonic and Dynamic Processes on the Lithosphere-Asthenosphere Boundary. *

Dr. Melgar will present on *Geodetic coupling at subduction megathrusts and
tsunami hazards: An example from Cascadia*

*Plenary Abstract: **This session is aimed at understanding the structure
and processes associated with interfaces and boundaries within the Earth
system. Examples include the boundary between the solid Earth and its fluid
envelopes, the boundary between the solid mantle and the liquid outer core,
the land/ocean interface at continental margins, and Earth's permeable
near-surface boundary layer known as the critical zone. It will include
contributions that highlight new data sets and observation strategies that
target these interfaces, those that reveal new understanding of the
processes operating at them, and studies that explore the ways that
different regions of the Earth interact and how different components of the
Earth system are coupled across interfaces.*

*Dr. Ford's Abstract:* The lithosphere-asthenosphere boundary is a
rheological boundary that connects the Earth’s rigid lithosphere to the
underlying convecting mantle asthenosphere. Better understanding the range
of physical and rheological properties of the lithosphere-asthenosphere
boundary has important implications for plate tectonics and mantle
dynamics, yet considerable uncertainty in our understanding of this
boundary remains. The boundary is commonly defined as the depth at which
heat transfer changes from conductive (lithosphere) to convective
(asthenosphere). However, other factors including chemical composition,
water content, grain size and melt are thought to play a role. One
important characteristic of the lithosphere-asthenosphere boundary (among
others) is the well-established correlation between lithospheric age and
boundary depth, with older lithosphere typically corresponding to a deeper
lithosphere-asthenosphere boundary. Where well-resolved deviations from
this correlation exist, tectonic and/or dynamic processes may be invoked in
order to explain these differences.

In this webinar we will begin by providing a framework for imaging and
analyzing the characteristics of the lithosphere-asthenosphere boundary. We
provide this framework by first presenting a Sp receiver function case
study in which pronounced lateral variations in seismic properties at the
lithosphere-asthenosphere boundary are observed to be coincident with the
surface expression of the Pacific-North American plate boundary in
California. We then report new evidence of a well-resolved step in
lithospheric thickness coincident with the surface expression of the
Taconic/Gander boundary in eastern North America. Here, our work suggests
that the present-day lithosphere-asthenosphere boundary is inherited from
the collision of the Laurentia and Appalachian terranes, and that
subsequent tectonism and/or thermal evolution have not overprinted this
structure. Such a conclusion runs counter to our current understanding of
the thermal evolution of the lithosphere-asthenosphere system, as described
in the first paragraph of this abstract, and future discussion and research
is needed.

*Dr. Melgar's Abstract: *It is widely accepted that the degree to which a
fault is coupled, or locked, should influence how hazardous it is perceived
to be. As a result, over the last decades, observations from space geodesy,
and in particular from Global Navigation Satellite Systems (GNSS) have been
used to measure interseismic velocities and infer locking on faults. For
subduction megathrusts, where large portions of the fault are offshore,
there can be significant ambiguity in whether this portion of the fault is
locked or not. This is due to the resolution of onshore measurements
decaying rapidly with distance. Seafloor geodesy through the GPS-A
technique continues to gain traction and GPS-A sites are being deployed at
many subduction zones worldwide. As the networks slowly grow this promises
to increase resolution and sharpen the picture of where and to what degree
megathrusts are locked offshore. However, once the locking is known, how
should we use the information in a quantitative sense to inform hazards
assessments? In this talk we will show a new approach which uses locking
models as pre-conditions to efficiently generate thousands of stochastic
rupture scenarios which can in turn be utilized to simulate tsunamis or
strong shaking at locations of interest. As a demonstration of the
methodology we will focus on the Cascadia subduction zone and show how
assuming different locking models leads to very different probabilistic
tsunami hazard assessments. We will also show the comparison to when no
locking model is used to precondition the simulated ruptures and conclude
that knowledge of coupling at the fault is a first order control in tsunami
hazard assessment.

*PLEASE NOTE: T*he webinar is limited to 500 participants. Please hop on
the webinar early for your best chances to see the webinar live. Remember
that all webinars are archived for later viewing at
https://www.youtube.com/playlist?list=PLD4D607C2FA317E6D

Any questions? Contact us at webinar at iris.edu
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