29th March 2022
Speaker: Dr Antonia Hardwick, Director and Chief Geoscientist, Hardwick Geophysical Ltd
Topic: Insights into the deeper crustal structure of the England, Wales and Irish Sea areas from local earthquake tomography and associated seismological studies. What drives UK seismicity and associated geological hazards?
For the past three decades, deep crustal studies of the British Isles have been restricted to the interpretation of 2-D seismic reflection and refraction profiles, mostly acquired offshore. The British Geological Survey (BGS) seismic monitoring network has grown substantially over the past twenty years to a density and quality unprecedented for a region of low seismicity. The BGS network records approximately 40 locally occurring earthquakes in the crust beneath the British Isles in an average year with local magnitudes of over 2.0. Statistical tests show the pattern of modern and historical earthquakes is not random, yet the tectonic processes responsible are poorly understood. A factor is the sparseness of deep crustal models onshore where the majority of earthquakes are concentrated. Local earthquake tomography is an increasingly common method applied to produce high resolution 3-D images of seismic P- and S-wave velocity in seismically active areas.
Seismic events recorded on the BGS network from the past 25 years are used in this study to produce similar images of the crust and uppermost mantle beneath England, Wales and the Irish Sea. Events from a relatively long time period are required to account for the low level of seismicity. A subset of over 1,000 well located events and 18,000 seismic arrival times are used to derive 3-D models of P-velocity and the P- to S-wave velocity ratio.
The models highlight short and long wavelength anomalies that can be related to the observed pattern of seismicity. A strong link is demonstrated between Palaeocene magmatism in the East Irish Sea area and earlier phases of Caledonian magmatism that affected England and Wales more widely. The influence of the present day configuration of crustal blocks is also considered in relation to regional intraplate stresses and the lithostatic stress from overburden pressure.
Dr Antonia Hardwick, Director and Chief Geoscientist, Hardwick Geophysical Ltd
Antonia joined Bedford Interactive Processing Services (BiPS) in October 1998, after completing a Masters degree in Exploration Geophysics at the University of Leeds as a Processing Geophysicist working on 2D land seismic data. BiPS was soon acquired by TGS and Antonia moved onto processing multi-client 2D and 3D marine seismic and as Senior Geophysicist was a project leader.
Antonia returned to full time study later in 2004 to undertake a PhD in Geophysics at the University of Leicester with the British Geological Survey (BGS). For her thesis she developed high resolution models of the seismic velocity in the crust and upper mantle beneath the British Isles using local earthquake tomography by inverting seismic arrival times recorded by the BGS monitoring network over a 25-year period. As well as assisting the teaching of geology and geophysics to undergraduate students she was involved in fieldwork to image the Chicxulub Impact Crater in Mexico and the state of isostatic equilibrium in Fenno-Scandinavia.
In April 2008 Antonia returned to industry joining ARKeX as an Interpretation Geophysicist integrating gravity gradiometry and seismic data, with models from forward modelling and inversion incorporated into pre-stack depth migration workflows. Antonia rejoined TGS in February 2009 as an Advising Geophysicist and was promoted to Senior Advising Geophysicist in 2012. During this time, she implemented and developed many new processing techniques and established R&D in the Bedford office. Working with R&D she played a key role in developing TGS’ proprietary deghosting techniques and new demultiple algorithms. In collaboration with the University of Leeds she worked on improving the derivation of the seismic quality factor (Q) and has supervised numerous Master projects with both the University of Leeds and Imperial College London.
In 2013 Antonia took on the role of Technology Manager supervising the growing team of Geophysical Advisors and implementing new technologies before becoming Principal Geophysicist in 2015. She worked on Ocean Bottom Node (OBN) datasets at TGS, representing the company and clients on the world’s largest OBN dataset by trace count acquired over the Utsira High offshore Norway. She also oversaw the project management and development of state-of-the-art OBN processing capabilities within research and development at TGS. Antonia has authored or co-authored over thirty-five abstracts and publications in wide ranging areas of geophysics, presenting at international conferences. Antonia currently shares her time as an independent Geophysical consultant offering a range of services to the upstream oil and gas exploration industry alongside a Senior Geoscientist position at ARK CLS Limited who specialise in geoscience software development. Antonia is also a teaching fellow at the University of Leicester teaching reflection seismology to the third-year undergraduates.