[unav_all] IRIS-USArray Webinar on Western U.S. Seismic Imaging 1/15, 2 PM Eastern

Andy Frassetto andyf at iris.edu
Mon Jan 6 16:12:44 MST 2014

"The Western U.S. Lithosphere Blues" will be presented at 2 pm EST (7 pm 
UTC) on Wednesday, 1/15.

Register to attend: https://www2.gotomeeting.com/register/620067122

You will be emailed a confirmation containing a link for accessing the 
webinar. The presentation and subsequent interactions between the 
speaker, host, and audience are recorded and made available within a few 
days. Access to the webinar archive, along with related materials and 
more information on the series is found here: 

Presenter: Dr. Rob Porritt, NSF Post-doctoral Fellow, University of 
Southern California

Abstract: The Western United States has long been studied as the 
typically atypical plate boundary zone. Recent deformation is observed 
from the Pacific-North America coast to the Rocky Mountains. Along the 
coast and south of the Mendocino Triple Junction in Northern California, 
the San Andreas Fault Zone accommodates translational motion between the 
Pacific and North American plates through a series of en echelon 
strike-slip faults. North of the triple junction, the Juan de Fuca-North 
America plate boundary zone is a prolifically aseismic subduction zone 
with paleoseismic records of megathrust events, but insufficient events 
in the modern age to map the subducting plate deeper than 100km depth. 
Moving inboard from the coast, extension through the Basin and Range 
Province is pushing apart the Sierra Nevada block and the Colorado 
Plateau. Major igneous features include the Tertiary Ignimbrite 
Flare-up, the 17Ma Yellowstone and Newberry hotspot tracks, and the 
active Cascades Arc.

Using teleseismic and ambient noise data from the Earthscope USArray, 
regional seismic networks, and the US backbone seismic network, we image 
a generally low seismic wave-speed upper mantle with discrete high 
wave-speed features throughout the region. We interpret these features 
to be primarily fragments of the Farallon Plate caught in the upper 
mantle. Alternatively, many of these features have been interpreted as 
lithospheric instabilities as an explanation for the anomalously thin 
lithosphere and regional mantle anisotropy inconsistent with simple 
plate motion. In this webinar, I present the argument that many, if not 
all, of the observed high wave-speed anomalies are pieces of the 
Farallon plate. This argument does not rule out the important role 
played by lithospheric instabilities in long-term continental growth, 
but rather forces the discussion toward the expanded role of oceanic 
plate subduction in continental evolution.

Please direct any related inquiries or amusing memes to Andy Frassetto 
(andyf at iris.edu).

System Requirements
PC-based attendees: Windows® 8, 7, Vista, XP or 2003 Server
Mac®-based attendees: Mac OS® X 10.6 or newer
Mobile attendees: iPhone®, iPad®, Android™ phone or Android tablet

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