Active Tectonics & Fault Geomorphology around Major Cities of the Northern Tien ShanProf. Richard Walker (University of Oxford)Contact email: J.Elliott@leeds.ac.uk
Mountains are created when continents collide, causing tectonic faults to move. Most faults are locked in the upper crust, slipping suddenly and catastrophically in earthquakes, and are part of the cycle of mountain growth (e.g. 2015 Gorkha earthquake, Nepal - Elliott et al. ). An open question in the deformation of the continents is how strain (and therefore earthquake hazard) is distributed through the crust. Earthquakes are a natural hazard that are killing an increasing number of people, in part because populations are growing and densifying into urban centres (Crowley & Elliott, 2012). The recurrence time between earthquakes may be hundreds of years; many cities that are large today were small towns or did not yet exist when the last big earthquake struck (Campbell et al. 2015). Population centres are often clustered along mountain ranges, with cities lying next to faults that cause significant damage when they rupture due to the proximity of vulnerable buildings (Elliott et al. 2012). Over 50 capital cities of the Least Developed Countries in the world lie on top of faults in regions that are building up significant stresses within the crust (Figure 1). Furthermore, urban development in the intervening years has often hidden the expressions of the active earthquake faults beneath and around a city, making them harder to identify today (Mackenzie et al. 2016). By targeting cities along the Northern Tien Shan, this project will better characterise the active faulting and seismic hazard in this collision zone, and develop approaches that will be applicable to interpreting faulting geomorphology globally. This particular collision zone has had major earthquakes in the past, but is less well studied than many orogens.
Figure 1: The capital city of Kyrgyzstan (Bishkek, population 0.9 million), lies in the shadow of the Tien Shan mountains. It and similarly large cities along the Northern Tien Shan are exposed to the hazard posed by large earthquakes. (image width 20 km, looking south, note mountains are vertically exaggerated 3x, rising over 4000 m above Bishkek). Image from GoogleEarth.
A recent explosion in the number of optical and radar satellite based platforms over the past decade, and their systematic acquisition strategies has provided a wealth of high resolution data with near-global coverage (Elliott et al., 2016b), which is available for tackling problems concerning active tectonics, continental deformation, faulting and earthquake hazard (Wright et al. 2012). The launches of the Sentinel-1A and 1B radar satellites by the European Space Agency in 2014 and 2016, with an open access data policy, has provided the opportunity for earthquake monitoring and measurements of crustal deformation over wide areas (Elliott et al, 2015). Commercially operated optical imagery satellites can be tasked to acquire stereo images over fault zones from which we can generate high resolution topographic images at the metre scale for geomorphic analysis of fault scarps and quantitative derivation of fault offsets (Zhou et al. 2015), something not possible with the current openly available 30 metre resolution topography in many parts of the world. This project will make use of these latest satellite technologies to better characterise the faulting and strain accumulation along the northern Tien Shan.
Figure 2: Hillshaded Digital Elevation Model (1 metre) of the 2013 Balochistan (Mw 7.8 Pakistan) earthquake rupture (the rupture is unannotated on the left and marked by red lines on the right) derived from Pleiades stereo satellite imagery (Zhou et al. 2015). Using these observations it is possible to derive quantitative measurements of the fault offsets and remotely interpret the rupture geomorphology and fault trace.
In this project, the student will work with leading scientists at Leeds (John Elliott & Tim Wright) and the University of Oxford (Richard Walker) to apply the latest techniques in measuring active tectonics, faulting and landscape evolution to the northern extent of the Tien Shan orogen of central Asia. In particular, according to your particular research interests, the studentship could be initiated with analysis of:
- Remote Sensing (DEMs and High Resolution Imagery) of the active tectonics of the northern Tien Shan: You will derive digital elevation models (DEMs) of parts of the faults around cities in the northern Tien Shan and produce orthorectified imagery using modern photogrammetry techniques applied to the latest high resolution optical satellite imagery (Zhou et al. 2015). From these data the student will identify potentially active faults in the landscape geomorphology both around and within cities. To aid this identification and additionally provide the workflow to potentially automate this with future global topographic datasets, you will implement strategies for the systematic estimation of landscape indices of fault activity based upon topographic slope and surface roughness. You will augment your findings with existing seismicity datasets and past earthquakes.
- Strain Accumulation (InSAR Velocity Mapping) of faults around the large cities: regional scale velocity fields for the continental regions will be produced as part of the Looking inside the Continents from Space (LiCS) project with the Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET http://comet.nerc.ac.uk/). This project will provide the opportunity to build upon these preliminary velocity fields by undertaking a more detailed study of strain accumulation in the immediate vicinity of cities along the Northern Tien Shan. This will make use of the Sentinel-1 data acquired since 2014 and throughout the timescale of the project to build up a long time series of deformation. This will enable estimation of current fault slip rates, and will involve analysis of Sentinel-1 InSAR data, mitigation of atmospheric noise (Walters et al., 2013) and potentially anthropogenic sources as well. The velocity fields will be augmented by the relatively sparse GPS for this region.
- Fieldwork (Corroborate remotely-derived observations): There is the potential to undertake short periods of fieldwork to the northern Tien Shan, in order to verify the remotely derived observations of fault scarps on the ground, make higher resolution measurements with GPS and Structure from Motion (SfM) techniques (Mackenzie et al. 2016) and sample fault offsets for chronological dating (Campbell et al., 2015). This will enable comparison of long-term slip rates with those derived geodetically, as well as establish whether fault structures are active.
Potential for high impact outcome
Earthquake hazard is a pressing issue facing many developing nations. We are in a unique position at Leeds to bring together a range of observational approaches to answer important unresolved questions about the relative activity of faulting around cities distributed in major collisional orogens. The research topic has immediate relevance to improving estimations of seismic hazard in these less well studied regions, and we anticipate the project generating several papers. There will be ample opportunities to deliver the results of the project at international conferences in addition to UK meetings. Through in-country collaborators, there will be the opportunity to communicate the earthquake hazard to local authorities and civil protection planners.
The student will work under the supervision of Dr. John Elliott and Prof Tim Wright within the Tectonics group of the Institute of Geophysics & Tectonics in the School of Earth & Environment at Leeds. This project provides a high level of specialist scientific training in: (i) Satellite optical data, (ii) Data processing (iii) Landscape interpretation. Co-supervision will involve regular meetings with our Oxford partner through joint supervision by Prof Richard Walker, who has undertaken a number of field campaigns in this region (Abdrakhmatov et al. (2016), Campbell et al. (2015, 2013)), in addition to other active faulting zones. The successful PhD student will have access to a broad spectrum of training workshops put on by the Faculty that include an extensive range from scientific computing through to managing your degree, to preparing for your viva (http://www.emeskillstraining.leeds.ac.uk/). The student will also have the opportunity to engage with scientists within the Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET http://comet.nerc.ac.uk/) at a range of other UK institutions who have a broad interest in problems of active tectonics and earthquakes.
The student should have a strong interest in active tectonics problems, a strong background in a quantitative science (geophysics, earth sciences, physics), and a familiarity and willingness to develop their skills in scientific computing.
Abdrakhmatov, K. E., R. T. Walker, G. E. Campbell, A. S. Carr, A. Elliott, C. Hillemann, J. Hollingsworth et al. (2016)
Multisegment rupture in the 11 July 1889 Chilik earthquake (Mw 8.0–8.3), Kazakh Tien Shan, interpreted from remote sensing, field survey, and paleoseismic trenching, Journal of Geophysical Research, 121, 4615-4640, doi:10.1002/2015JB012763.
Campbell, G. E., R. T. Walker, K. Abdrakhmatov, J. L. Schwenninger, J. A. Jackson, J. R. Elliott & A. C. Copley (2013)
Quaternary slip-rate, seismogenic potential and the role of strike-slip faulting in the northern Tien Shan region, Journal Geophysical Research, 118, 5681-5698, doi:10.1002/jgrb.50367
Campbell, G. E., R. T. Walker, K. Abdrakhmatov, J. A. Jackson, J. R. Elliott, D. Mackenzie, T. Middleton & J. L. Schwenninger (2015)
Great earthquakes in low strain rate continental interiors: An example from SE Kazakhstan, Journal Geophysical Research, 120, 5507-5534, doi:10.1002/2015JB011925.
Crowley, K. & J. R. Elliott (2012)
Earthquake disasters and resilience in the global North: lessons from New Zealand and Japan, The Geographical Journal, 178, 208-215, doi:10.1111/j.1475-4959.2011.00453.x.
Elliott, J. R., R. Jolivet, P. Gonzalez, J.-P. Avouac, J. Hollingsworth, M. Searle & V. Stevens (2016)
Himalayan Megathrust Geometry and Relation to Topography Revealed by the Gorkha Earthquake, Nature Geoscience, 9, 174-180, doi:10.1038/NGEO2623.
Elliott, J. R., A. Copley, R. Holley, K. Scharer & B. Parsons (2013)
The 2011 Mw 7.1 Van (Eastern Turkey) Earthquake, Journal Geophysical Research, 118, 1619-1637,doi:10.1002/jgrb.50117.
Elliott, J. R., R. J. Walters & T. J. Wright (2016)
The role of space-based observation in understanding and responding to active tectonics and earthquakes, Nature Communications.
Mackenzie, D., J. R. Elliott, E. Altunel, R. T. Walker, Y. C. Kurban, J. L. Schwenninger & B. Parsons (2016)
Seismotectonics and rupture process of the Mw 7.1 2011 Van reverse faulting earthquake, Eastern Turkey, and implications for hazard in regions of distributed shortening, Geophysical Journal International, 206, 501-524, doi:10.1093/gji/ggw158
Walters, R. J., J. R. Elliott, Z. Li, & B. Parsons (2013)
Rapid strain accumulation on the Ashkabad fault (Turkmenistan): a robust slip rate estimate from MERIS-corrected InSAR data, Journal Geophysical Research, 118, 3674-3690, doi:10.1002/jgrb.50236.
Wright, T. J., J. R. Elliott, H. Wang & I. Ryder (2013)
Earthquake cycle deformation and the Moho: Implications for the rheology of continental lithosphere, Tectonophysics,609, 504-523, doi:10.1016/j.tecto.2013.07.029.
Zhou, Y., J. R. Elliott, R. T. Walker & B. Parsons (2015)
The 2013 Balochistan earthquake: an extraordinary or completely ordinary event?, Geophysical Research Letters, 42, 6236-6243, doi:10.1002/2015GL065096.
Related undergraduate subjects:
- Earth science