ORCID Profile
0000-0003-0004-5009
Current Organisations
Princeton University
,
University of Cambridge
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Publisher: Wiley
Date: 25-07-2018
DOI: 10.1111/BRE.12308
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-4477
Abstract: & & The maximum achievable resolution of a tomographic model varies spatially and depends on the data s ling and errors in the data. The significant and continual measurement-error decreases in seismology and data-redundancy increases have reduced the impact of random errors on tomographic models. Systematic errors, however, are resistant to data redundancy and their effect on the model is difficult to predict often this results in models dominated by noise if the target resolution is too high. Here, we develop a method for finding the optimal resolving length at every point, implementing it for surface-wave tomography. As in the Backus-Gilbert method, every solution at a point results from an entire-system inversion, and the model error is reduced by increasing the model-parameter averaging. The key advantage of our method consists in its direct, empirical evaluation of the posterior model error at a point.& & & & We first measure interstation phase velocities at simultaneously recording station pairs and compute phase-velocity maps at densely, logarithmically spaced periods. Numerous versions of the maps with varying smoothness are then computed, ranging from very rough to very smooth. Phase-velocity curves extracted from the maps at every point can be inverted for shear-velocity (V& sub& S& /sub& ) profiles. As we show, errors in these phase-velocity curves increase nearly monotonically with the map roughness. We evaluate the error by isolating the roughness of the phase-velocity curve that cannot be explained by any Earth structure and determine the optimal resolving length at a point such that the error of the local phase-velocity curve is below a threshold.& & & & A 3-D V& sub& S& /sub& model is then computed by the inversion of the composite phase-velocity maps with an optimal resolution at every point. Importantly, the optimal resolving length does not scale with the density of the data coverage: some of the best-s led locations display relatively low lateral resolution, due to systematic errors in the data.& & & & We apply this method to image the lithosphere and underlying mantle beneath Ireland and Britain. Our very large data produces a total of 11238 inter-station dispersion curves, spanning a very broad total period range (4& #8211 s), yielding unprecedented data coverage of the area and providing state-of-the-art regional resolution from the crust to the deep asthenosphere. Our tomography reveals pronounced, previously unknown variations in the lithospheric thickness beneath Ireland and Britain, with implications for their Caledonian assembly and for the mechanisms of the British Tertiary Igneous Province magmatism.& &
Publisher: American Geophysical Union (AGU)
Date: 08-2012
DOI: 10.1029/2012GC004138
Publisher: Elsevier BV
Date: 11-2019
Publisher: Oxford University Press (OUP)
Date: 08-05-2023
DOI: 10.1093/GJI/GGAD194
Abstract: Ireland and neighbouring Britain share much of their tectonic history and are both far from active plate boundaries at present. Their seismicity shows surprising lateral variations, with very few earthquakes in Ireland but many low-to-moderate ones in the adjacent western Britain. Understanding the cause of these variations is important for our understanding of the basic mechanisms of the intraplate seismicity distributions and for regional hazard assessment. The distribution of microseismicity within Ireland and its underlying causes have been uncertain due to the sparsity of the data s ling of the island, until recently. Here, we use the data from numerous recently deployed seismic stations in Ireland and map its seismicity in greater detail than previously. The majority of detectable seismic events are quarry and mine blasts. These can be discriminated from tectonic events using a combination of the waveform data, event origin times, and the epicentres’ proximity to quarries and mines, catalogued or identified from the satellite imagery. Our new map of natural seismicity shows many more events than known previously but confirms that the earthquakes are concentrated primarily in the northernmost part of the island, with fewer events along its southern coast and very few deeper inland. Comparing the seismicity with the recently published surface wave tomography of Ireland and Britain, we observe a strong correspondence between seismicity and the phase velocities at periods s ling the lithospheric thickness. Ireland has relatively thick, cold and, by inference, mechanically strong lithosphere and has very few earthquakes. Most Irish earthquakes are in the north of the island, the one place where its lithosphere is thinner, warmer and, thus, weaker. Western Britain also has relatively thin lithosphere and numerous earthquakes. By contrast, southeastern England and, probably, eastern Scotland have thicker lithosphere and, also, few earthquakes. The distribution of earthquakes in Ireland and Britain is, thus, controlled primarily by the thickness and mechanical strength of the lithosphere. The thicker, colder, stronger lithosphere undergoes less deformation and features fewer earthquakes than thinner, weaker lithosphere that deforms more easily. Ireland and Britain are tectonically stable and the variations in the lithospheric thickness variations across them are estimated to be in a 75–110 km range. Our results thus indicate that moderate variations in the lithospheric thickness within stable continental interiors can exert substantial control on the distributions of seismicity and seismic hazard—in Ireland, Britain and elsewhere around the world.
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-10503
Abstract: & & Stable continental areas& #8212 those largely unaffected by currently active plate-boundary processes& #8212 undergo little deformation and feature low seismicity rates. Notable exceptions, such as the well-known large earthquakes in the central United States or the Fennoscandian Craton, are rare but highlight the importance of understanding the seismicity in low-strain regions. One long-standing question, debated for over a century, relates to the seismicity of Ireland. Why is it much lower than that in the neighbouring Britain, even though they were assembled in the same Caledonian orogeny, share many of the ancient tectonic boundaries, and are subjected to similar tectonic stresses? Our new catalogue of Ireland& #8217 s seismicity, produced using the greatly improved seismic station coverage of the island over the last decade, shows many more micro-earthquakes than known previously but confirms the much lower seismicity rates in Ireland compared to Britain.& & & & Comparing the distribution of seismicity with high-resolution, surface-wave tomography (performed using the abundant new data) we observe that areas with thicker, colder lithosphere feature lower seismicity than those with thinner lithosphere. This must be because the thicker and colder lithosphere is mechanically stronger and less likely to deform, compared to the thinner and weaker lithosphere under the same tectonic stress. According to the new tomography, Ireland has thicker lithosphere than most of Britain, which can explain its lower seismicity rates. The thinnest lithosphere in Ireland is found in the north of the island, in Co Donegal, and this is where most of Ireland& #8217 s micro-seismicity occurs. A similar relationship between the lithospheric thickness and seismicity rates is observed in Britain, with the London Platform in the southeast of the island showing thick lithosphere and low seismicity.& & & & Together, lithospheric tomography and seismicity maps thus offer a solution to a seismo-tectonic puzzle first formulated in the 19-th century. Evidence of the lithospheric mantle controls on earthquake occurrence can be seen elsewhere around the world as well. The improving accuracy of the tomographic imaging of the lithosphere presents a useful new line of evidence on the mechanisms that control the regional distributions of intraplate earthquakes.& &
Publisher: American Geophysical Union (AGU)
Date: 10-03-2011
DOI: 10.1029/2010GL046358
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Sergei Lebedev.