Thread: IRIS WEBINAR - Seismic study of the structure and tectonics of northeast Tibet - 5/21 1 PM Eastern

Started: 2014-05-16 07:30:08
Last activity: 2014-05-16 07:30:08
Topics: Early Careers
*"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:

You will be emailed a confirmation containing a link for watching the
live broadcast. Afterwards, IRIS will post the webinar here: Access to older webinars and
related materials and information are found at the webinar page
(, 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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