Disentangling coseismic complexity in the earthquake cycle, using seismology and geodesy

Overview

Hazardous earthquakes rarely occur in isolation; they are often closely associated with other earthquakes (“foreshocks” and “aftershocks”), and are commonly followed by slow and silent aseismic slip. Aseismic slip has even been observed before major earthquakes in a handful of cases. Isolating and separating out these different processes is critical for understanding the basic mechanics of faulting and earthquakes, and for characterising the evolution of earthquake hazard through time: the various processes interact with one another, and have the potential to significantly modify hazard.

However, disentangling these different processes is challenging. Observational datasets have limited sensitivity and spatio-temporal resolution, and past studies have relied on inversion methods that necessitate major simplifying assumptions. This project aims to address these issues by developing a variety of new cutting-edge methods to jointly exploit and analyse both geodetic (satellite radar and GNSS time-series) and seismological datasets, and investigate this entire extended coseismic interval (pre-, co- and post-seismic deformation) within a common and self-consistent framework.

These methods will be used to systematically measure and model pre-, co- and post-seismic ground deformation associated with global continental earthquakes of Mw 5.5-7, to investigate the relationship between patterns of pre-, co- and post-seismic slip, and to investigate how earthquake hazard is typically modified through time by pre- and post-seismic processes.

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Image Captions

Figure 1: Temporal evolution of afterslip following the 2014 S. Napa earthquake in California (blue, green and red boxes and time-series), and comparison to the region of seismic slip (pink polygon), as estimated by satellite radar. Adapted from Floyd et al. (2016).

Methodology

For several tens of Mw > 5.5 earthquakes since 2014, interferometric SAR (InSAR), GNSS time-series and body-wave seismology will be used to systematically analyse deformation signals over the epicentral region before, during and after the event.

The student will have the opportunity to employ, further develop and combine advanced analysis and inversion methods developed by the supervisory team. These including machine-learning-based methods for enhancing data quality (Shakeel et al., in prep) and for inference (e.g. Kufl et al., 2016), time-series inversion methods for distinguishing coseismic from pre- and post-seismic slip in InSAR datasets (e.g. Fig 1, Floyd et al., 2016, Walters et al. 2018), and novel inversion methods that can enable joint analysis of seismological and geodetic datasets (e.g. O’Toole et al., 2013; Valentine & Sambridge, 2020). These methods will be used to disentangle and model slip throughout the extended coseismic interval in a self-consistent framework for a global catalogue of earthquakes.

Project Timeline

Year 1

Training will be provided in space geodetic and seismological techniques, in particular the processing, analysis and modelling of satellite radar and teleseismic data. Work on development and combination of seismological and geodetic analysis and inversion methods. Processing and analysis of radar, GNSS and seismological data for selected example earthquakes.

Year 2

Completion of method development and application to select examples. Publication of this work in one or two papers. Start systematic global application of methods to radar and seismological datasets.

Year 3

Completion of systematic investigation of global continental earthquakes. Analysis of completed catalogue of pre-/co-/post-seismic deformation. This work should lead to an additional publication.

Year 3.5

Focus on combining the published outputs and associated material into a PhD thesis.

Training
& Skills

The student will receive training in space geodesy and seismological measurement and modelling techniques, in particular the handling and processing of satellite radar, GNSS and teleseismic data, and in the modelling co- pre- and postseismic deformation from these datasets. They will also become familiar with a range of approaches to inversion and inference, including Bayesian and machine-learning-based techniques. Training in a wide range of essential skills (e.g. presentation skills, paper/thesis writing, and computational skills) important both for life as a PhD student and afterwards is provided by the Department of Earth Sciences and Durham University, and the student will also benefit from cross-disciplinary training provided as part of IAPETUS2.
The student will become a member of the UK’s Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET), benefitting from the shared expertise of Geosciences staff in several universities, and attending regular meetings where the research of these various groups is discussed. The student will have opportunities to work with other partners in the UK and internationally and they are encouraged to travel to national and international scientific meetings to present results. We aim to see all students publish at least two papers in leading scientific journals during their PhD. Upon completion, the student will be well equipped for a career in academia or in a range of industries.

References & further reading

Floyd, M.A., Walters, R.J., Elliott, J.R., Funning, G.J., et al., 2016. Spatial variations in fault friction related to lithology from rupture and afterslip of the 2014 South Napa, California, earthquake. GRL, 43(13)
Kufl, P., Valentine, A.P. and Trampert, J., 2016. Probabilistic point source inversion of strong-motion data in 3D media using pattern recognition: A case study for the 2008 Mw5.8 Chino Hills earthquake. Geophysical Research Letters, 43, 2016GL069887.
Valentine, A.P. and Sambridge, M., 2020. Gaussian Process Models I. A framework for probabilistic continuous inverse theory. Geophysical Journal International, 214, pp.486-507.
Walters, R.J., Gregory, L.C., Wedmore, L.N., Craig, T.J., et al., 2018. Dual control of fault intersections on stop-start rupture in the 2016 Central Italy seismic sequence. Earth and Planetary Science Letters, 500
O’Toole, T.B., Valentine, A.P. and Woodhouse, J.H., 2013. Earthquake source parameters from GPS-measured static displacements with potential for real-time application. GRL, 40(1)

Further Information

Dr Richard Walters
richard.walters@durham.ac.uk
+44(0) 1913 341727

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