[unav_all] REMINDER: IRIS WEBINAR - Seismology at the Roof of the World - THIS WEDNESDAY

Andy Frassetto andyf at iris.edu
Tue May 20 10:01:17 MDT 2014


*"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. *

Please registerif you intend to participate in the webinar live: 
https://www2.gotomeeting.com/register/874190338

You will be emailed a confirmation containing a link for watching the 
live broadcast. Afterwards, IRIS will post the webinar here: 
http://www.youtube.com/user/IRISEnO. Access to older webinars and 
related materials and information are found at the webinar page 
(http://www.iris.edu/hq/webinar/), which is soon to be updated.

Presenters: Dr. Marianne Karplus (Post-doc, University of Southhampton, 
United Kingdom)

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.

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.

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^(TM) phone or Android tablet
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