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<div align="justify"> <b>"Crustal Structure and Tectonics of
Northeast Tibet from INDEPTH IV Wide-Angle Refraction and
Receiver Functions" will be presented at 1 pm EDT (5 pm UTC) on
Wednesday, 5/21. </b><br>
<br>
Please register<b class="moz-txt-star"><span class="moz-txt-tag"></span></b>
if you intend to participate in the webinar live:
<a class="moz-txt-link-freetext" href="https://www2.gotomeeting.com/register/874190338">https://www2.gotomeeting.com/register/874190338</a><br>
<br>
You will be emailed a confirmation containing a link for watching
the live broadcast. Afterwards, IRIS will post the webinar here: <a
class="moz-txt-link-freetext"
href="http://www.youtube.com/user/IRISEnO">http://www.youtube.com/user/IRISEnO</a>.
Access to older webinars and related materials and information are
found at the webinar page (<a class="moz-txt-link-freetext"
href="http://www.iris.edu/hq/webinar/">http://www.iris.edu/hq/webinar/</a>),
which is soon to be updated.<br>
<br>
Presenters: Dr. Marianne Karplus (Post-doc, University of
Southhampton, United Kingdom)<br>
<br>
Abstract: The project INDEPTH (International Deep Profiling of
Tibet and the Himalaya), phase IV, seismology group collected an
abundance of active- and passive-source seismic data in north
Tibet from 2007-2009, and I will present results from those
investigations and implications for crustal structure and
tectonics. Specifically, we derived seismic structure and P-wave
velocities from the 270-km long, roughly north-south,
active-source, wide-angle reflection and refraction profile
crossing the Songpan-Ganzi terrane, Kunlun Mountains, and Qaidam
Basin using first arrivals tomography and ray tracing. Then we
calculated P-to-S receiver functions using linear and regional
arrays of passive seismic stations in the same areas to provide
independent constraints on crustal thickness, lithospheric
structure, and Vp/Vs ratios.<br>
<br>
The wide-angle reflection and refraction velocity model shows a
crustal thickness change from 70 km beneath the Kunlun Mountains
to 50 km beneath central Qaidam. Crustal P-wave velocities in the
thickened Songpan-Ganzi terrane and Kunlun Mountains exhibit lower
velocity crust also characteristic of southern Tibet, whereas
crustal velocities in the central Qaidam Basin resemble average
continental crust. In contrast to previous work, we relocate the
20-km crustal thickness change to ~40 km north of the Kunlun
Mountains topographic front, in a region of overlapping bright
Moho reflectors at ~70 km and ~50 km. P-receiver functions
calculated for passive seismic stations coincident with the
active-source profile show a very similar Moho structure.
P-receiver functions calculated for stations scattered
along-strike from 91.5° to 98°E near the Kunlun-Qaidam boundary
show that the width of the overlapping region ranges from ~10-40
km at different locations along the boundary, and near Golmud the
deeper reflector may dip northwards. The crustal thickness change
appears unrelated to the strike-slip North Kunlun Fault. At depths
shallower than 100 km, we also see no evidence of southward
subduction of Eurasian lithosphere. Crustal velocities and
impedance contrasts suggest that instead weak Tibetan lower crust
is injected northward beneath stronger Qaidam crust.<br>
<br>
</div>
System Requirements <br>
PC-based attendees: Windows® 8, 7, Vista, XP or 2003 Server <br>
Mac®-based attendees: Mac OS® X 10.6 or newer <br>
Mobile attendees: iPhone®, iPad®, Android™ phone or Android tablet
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