Ellipticity of Rayleigh waves in basin and hard-rock sites in Northern Italy

Berbellini, Andrea; Morelli, A.; Ferreira, Ana M. G.

doi:10.1093/gji/ggw159

Cited by 20 publications

(28 citation statements)

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“…This information includes the ellipticity of Rayleigh waves -the H/V ratio between its horizontal and vertical amplitude components (Ferreira et al 2010) -and the dispersion or group velocity of Rayleigh waves that shows a diagnostic minimum known as the Airy phase (Gualtieri et al 2015). Both of these measures are particularly sensitive to upper-crustal structures beneath individual (ellipticity) and in-between (dispersion) seismometer stations, so that their quantification promises to generate high-quality tomographical images of subglacial sedimentary basins and their broader crustal settings (Berbellini et al 2016). SAN techniques can either be applied to archived data from existing permanent or temporary seismometer stations, or to bespoke stations deployed in the study area.…”

Section: Hydrological and Mechanical Conditions At The Ice-sheet Bedmentioning

confidence: 99%

Antarctic subglacial groundwater: a concept paper on its measurement and potential influence on ice flow

Siegert

Kulessa

Bougamont

et al. 2017

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Is groundwater abundant in Antarctica and does it modulate ice flow? Answering this question matters because ice streams flow by gliding over a wet substrate of till. Water fed to icestream beds thus influences ice-sheet dynamics and, potentially, sea-level rise. It is recognized that both till and the sedimentary basins from which it originates are porous and could host a reservoir of mobile groundwater that interacts with the subglacial interfacial system. According to recent numerical modelling, up to half of all water available for basal lubrication, and time lags between hydrological forcing and ice-sheet response as long as millennia, may have been overlooked in models of ice flow. Here, we review evidence in support of Antarctic groundwater and propose how it can be measured to ascertain the extent to which it modulates ice flow. We present new seismoelectric soundings of subglacial till, and magnetotelluric and transient electromagnetic forward models of subglacial groundwater reservoirs. We demonstrate that multifaceted and integrated geophysical datasets can detect, delineate and quantify the groundwater contents of subglacial sedimentary basins and, potentially, monitor groundwater exchange rates between subglacial till layers. The paper thus describes a new area of glaciological investigation and how it should progress in future.Gold Open Access: This article is published under the terms of the CC-BY 3.0 license. Water beneath the ice sheetAntarctic ice-sheet flow is fundamentally affected by water at the bed, as it reduces basal friction to encourage sliding and weakens till to enable bed deformation. Subglacial hydrology -the flow of water beneath the ice -is therefore a key element of the ice-sheet system. Studies to date on subglacial hydrology, and its impact on ice flow, have concentrated on water at or very near to the bed of the ice sheet.Basal water modulation of ice flow can be achieved in a number of ways. Over an impermeable bed, water can flow through channels cut either downwards into the substrate or upwards into the ice. Enhanced basal water pressures may occur where the channels and their linkages are distributed, increasing overriding ice flow through a reduction in the substrate's effective pressure. Conversely, where a well-organized channel system is formed, water pressures are lower and the hydrological effect on ice flow is reduced. If the ice stream rests on permeable subglacial till, its strength can affect ice flow as controlled by porewater pressures. High pressures lead to a reduction in material strength by pushing till grains apart, reducing bed friction and thus

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Section: Hydrological and Mechanical Conditions At The Ice-sheet Bedmentioning

confidence: 99%

Antarctic subglacial groundwater: a concept paper on its measurement and potential influence on ice flow

Siegert

Kulessa

Bougamont

et al. 2017

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“…This notation is in accordance to the commonly used HV ratio, and also corresponds to the conventions used by Berbellini et al (2016). This is slightly different from the convention used by Tanimoto & Rivera (2008), where the inverse ratio is used to avoid values going to infinity.…”

Section: The Ellipticity Of the Rayleigh Wave Fundamental Modementioning

confidence: 99%

“…We have chosen to present all our results at a frequency of 0.05 Hz (20 s period, corresponding to 75 km wavelength) which is appropriate for crustal studies (Berbellini et al 2016), but these results can easily be scaled to other frequencies. The surface wave modes needed to calculate the kernels are computed in the continental version of the PREM model (Dziewonski & Anderson 1981) with a software package from Saito (1988).…”

Section: K E R N E L S I N βmentioning

confidence: 99%

“…We see that the maximum sensitivity is clearly concentrated close to the receiver but with a complex pattern. This pattern may explain why measurements of HV ratio on single recordings yield unstable measurements (Ferreira & Woodhouse 2007;Tanimoto & Rivera 2008), and that averaging over many azimuths is necessary to obtain reliable data (Tanimoto & Rivera 2008;Berbellini et al 2016).…”

Section: Kernel For Azimuthally Averaged Ratiomentioning

confidence: 99%

“…The usage of the Rayleigh wave ellipticity as a source of information in larger-scale seismology is however more recent. Measurements of the Rayleigh wave ellipticity on single recordings have proven unstable (Ferreira & Woodhouse 2007;Tanimoto & Rivera 2008;Yano et al 2009), but averaged values measured either on noise recordings (Lin et al 2012;Workman et al 2017) or using azimuthally well-distributed sources (Tanimoto & Rivera 2008;Yano et al 2009;Berbellini et al 2016) have shown that stable measurements can be obtained.…”

Section: Introductionmentioning

confidence: 99%

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3-D sensitivity kernels of the Rayleigh wave ellipticity

Maupin

2017

Geophysical Journal International

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S U M M A R YThe ellipticity of the Rayleigh wave at the surface depends on the seismic structure beneath and in the vicinity of the seismological station where it is measured. We derive here the expression and compute the 3-D kernels that describe this dependence with respect to S-wave velocity, P-wave velocity and density. Near-field terms as well as coupling to Love waves are included in the expressions. We show that the ellipticity kernels are the difference between the amplitude kernels of the radial and vertical components of motion. They show maximum values close to the station, but with a complex pattern, even when smoothing in a finite-frequency range is used to remove the oscillatory pattern present in mono-frequency kernels. In order to follow the usual data processing flow, we also compute and analyse the kernels of the ellipticity averaged over incoming wave backazimuth. The kernel with respect to P-wave velocity has the simplest lateral variation and is in good agreement with commonly used 1-D kernels. The kernels with respect to S-wave velocity and density are more complex and we have not been able to find a good correlation between the 3-D and 1-D kernels. Although it is clear that the ellipticity is mostly sensitive to the structure within half-a-wavelength of the station, the complexity of the kernels within this zone prevents simple approximations like a depth dependence times a lateral variation to be useful in the inversion of the ellipticity.

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Vibrational enhancement of evolutionary monochromatic neutron transport

Haidar

2024

Nuclear Engineering and Technology

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Ellipticity of Rayleigh waves in basin and hard-rock sites in Northern Italy

Cited by 20 publications

References 28 publications

Antarctic subglacial groundwater: a concept paper on its measurement and potential influence on ice flow

Antarctic subglacial groundwater: a concept paper on its measurement and potential influence on ice flow

3-D sensitivity kernels of the Rayleigh wave ellipticity

Vibrational enhancement of evolutionary monochromatic neutron transport

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