Research: Imaging the processes of intracontinental deformation

Supervisors: Keith Priestley (University of Cambridge, UK) and Steven Roecker (RPI, USA)


My research, so far, has focused on imaging the crust and upper mantle beneath the Kyrgyz Tien Shan. The Tien Shan are the largest active intracontinental orogenic belt on the Earth. While the mountain belt is likely to have developed as a response to the India-Eurasia collision, we want to better understand why mountains have formed in this location, some 1000-3000km form the former margin of Eurasia. I have used passive seismic data from the MANAS broadband array, deployed between July 2005 and July 2007, as well as other permanent stations in the region, to determine variations in crustal thickness and wavespeed across the range.

I have computed both P and S receiver functions for the stations in the MANAS array, and obtained new surface-wave dispersion measurements using both earthquake and ambient noise data. By using surface-wave dispersion measurements obtained from ambient noise cross-correlations it is possible to make measurements at shorter periods and for paths that are not possible using surface-waves measured from an earthquake. Adding my new measurements to previous work done at Cambridge has improved the Rayleigh wave group velocity tomographic maps we have of this region. On their own both surface-wave dispersion observations and receiver functions have limitation. Fundamental-mode surface-wave observations are sensitive to absolute wavespeed averages, whereas receiver functions are primarily sensitive to vertically integrated travel times, rather than absolute wavespeeds. To overcome these ambiguities, I am using joint inversion methods, including a new method to use S receiver functions in the inversion, to determine the velocity structure in this region.

Future work: Following on from using the joint inversion method in the Tien Shan I will apply the same techniques to another data set from Tibet. This will both provide further validation for the joint inversion scheme, and provide new information about the region. I am also testing whether reflection images can be obtained from the autocorrelation of noise from the MANAS array. A particular problem of interest is how to deal with the zero-lag signal.

This project  is funded by a NERC studentship and a CASE award from Weston Geophysical.

Conference presentations

Gilligan, A., Priestley, K. F. and Roecker, S. W. Joint Inversion of Receiver Functions and Surface Wave Group Velocities from the MANAS data set to Determine Crustal Thickness Variations in the Tien Shan (abstract T51F-2674, poster) AGU Fall Meeting, San Francisco, USA, December 2012

Gilligan, A., Priestley, K. F. and Roecker, S. W. Imaging the structure of the Tien Shan using receiver functions and sesimic ambient noise (oral). 3rd QUEST meeting, Tatranska Lomnica, Slovakia, May 2012


Previous work

 

Joint inversion of mantle wave and continuous GPS data for the fault mechanism to the 14th February 2008 M6.9 Greek Earthquake (Master's project for MEarthSci, University of Oxford)

The availability of high rate (>1Hz) continuous GPS time series has opened up the potential to use such data for seismological applications, adding to the tools at our disposal for studying earthquakes and fault mechanisms. The work undertaken demonstrated that by using continuous GPS data it was possible to place greater constraints on the depth of a solution and that the ratio between the displacement due to the Rayleigh wave arrival and the static offset was sensitive to structure. We were able to develop a method to perform a CMT inversion of GPS data, which could then be used in a joint inversion with mantle wave data.

Conference presentations

O'Toole, T. B., Valentine, A. P., Gilligan, A., and J.H. Woodhouse, 2010. Integrating seismological and geodetic datasets: New insights into the seismic source (abstract G41A-0796, poster), AGU Fall Meeting, San Francisco, USA, December 2012 abstract G41A-0796. Click here for the poster.
 


Publications: 2006-Present

Last updated on 20-Dec-12 15:09