Micro-seismic measurements of cliff motion under wave impact and implications for the development of near-horizontal shore platforms

Dickson, Mark E.; Pentney, Rachael

doi:10.1016/j.geomorph.2012.01.006

Cited by 31 publications

(51 citation statements)

References 42 publications

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“…N0.3 Hz (Young et al, 2011), 7-20 Hz (Dickson andPentney, 2012), 1.1-50 Hz (Norman et al, 2013;Vann Jones et al, 2015), 20-45 Hz (Young et al, 2016)). Young et al (2013) observed a range of bands between 2 and 40 Hz across a variety of soft and hard rock cliffs globally.…”

Section: Cliff Ground Motions As Proxies Of Cliff Toe Wave Energymentioning

confidence: 99%

“…Key to this is the elevation relative to the tidal range, and thus where waves break relative to the cliff toe. For example, at a mesotidal site of high foreshore elevation relative to the high tide level, Dickson and Pentney (2012) observed the wave-cliff impact signal to be generated during low tides as waves broke at the steep seaward edge of the foreshore and shallow depths across the platform dissipated wave energy before reaching the cliff toe.…”

Section: Cliff Ground Motions As Proxies Of Cliff Toe Wave Energymentioning

confidence: 99%

“…Adams et al, 2005;Young et al, 2011Young et al, , 2012Young et al, , 2013Young et al, , 2016Dickson and Pentney, 2012;Norman et al, 2013;Earlie et al, 2015;Vann Jones et al, 2015), which typically include long-period ground motions (b0.05 Hz/N20 s) generated by infragravity waves on the foreshore/ beach (e.g. Young et al, 2011Young et al, , 2012; double frequency microseisms (0.1-0.2 Hz/5-10 s) generated by the superposition of waves either in deep water, or following reflection from the coast which have a period half of that of the ocean waves (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Norman et al, 2013;Young et al, 2013); high frequency cliff shaking (N1 Hz) is generated by wave impacts at the cliff toe (e.g. Vann Jones et al, 2015;Young et al, 2016) or foreshore edge (Dickson and Pentney, 2012) when tide heights allow. High frequency cliff shaking generated by wave-cliff impacts, have been found to provide a valuable proxy measurement of wave energy transfer directly to the cliff (Norman et al, 2013;Young et al, 2016), with statistically-significant relationships observed with monitored cliff erosion (Vann Jones et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

“…High frequency cliff shaking generated by wave-cliff impacts, have been found to provide a valuable proxy measurement of wave energy transfer directly to the cliff (Norman et al, 2013;Young et al, 2016), with statistically-significant relationships observed with monitored cliff erosion (Vann Jones et al, 2015). To date, cliff-top ground motion studies have largely focussed on single seismometers or on shore-normal transects of multiple seismometers (Dickson and Pentney, 2012;Young et al, 2012Young et al, , 2013), yet given the sensitivity of data to nearshore wave conditions and cliff toe impacts, it is reasonable to assume that alongshore variations in wave impacts and loading will be reflected in commensurate variations in microseismic response.…”

Section: Introductionmentioning

confidence: 99%

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Alongshore variability in wave energy transfer to coastal cliffs

2018

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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. The alongshore distribution of wave energy is believed to be an important control on the spatial variability of coastal erosion. There is, however, a lack of field data quantifying the alongshore variability in wave energy on rock coasts, whereby the relative control of coastline geometry versus foreshore characteristics on wave energy delivery remains unclear. A number of studies have identified high-frequency cliff-top ground shaking to be generated by wave impacts at the cliff toe during high tides (HT). To capture the variability of wave-cliff impact energy along-coast, we installed an array of cliff-top seismometers along a 1 km stretch of coastline in North Yorkshire, UK. Our aim is to constrain how wave energy transfer to the cliff toe varies, and to examine the relative energy transfer around typical coastline features, including a bay and headlands. Whilst the greatest HT ground motion energy is recorded at a headland and the lowest at the centre of the bay (5% of that observed at the headland), we identify no systematic alongshore variation in the HT ground motion energy that can be related to coastline morphology. We also note considerable variation between features of similar form: the total HT ground motion energy at one headland is only 49% of the next headland 1 km alongshore. Between neighbouring sites within the bay, separated by only 100 m, we observe up to an order of magnitude difference in ground motion energy transfer. Our results demonstrate the importance of the foreshore in driving the variations in energy delivery that we observe. Local alterations in water depth and foreshore topography control the alongshore distribution of wave energy available to generate cliff HT ground motions. Importantly, this apparently local effect overrides the influence of macroscale coastal planform morphology, which has previously been assumed to be the dominant control. The results show that foreshore characteristics that hold influence over wave energy transfer vary significantly over short (~100 m) distances, and so we expect erosion controlled by wave impacts to vary over similar scales.

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Section: Cliff Ground Motions As Proxies Of Cliff Toe Wave Energymentioning

confidence: 99%

Section: Cliff Ground Motions As Proxies Of Cliff Toe Wave Energymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Alongshore variability in wave energy transfer to coastal cliffs

2018

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Ground motions on rocky, cliffed, and sandy shorelines generated by ocean waves

et al. 2013

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[1] We compare ground motions observed within about 100 m of the waterline on eight sites located on shorelines with different morphologies (rock slope, cliff, and sand beaches). At all sites, local ocean waves generated ground motions in the frequency band 0.01-40 Hz. Between about 0.01 and 0.1 Hz, foreshore loading and gravitational attraction from ocean swell and infragravity waves drive coherent, in-phase ground flexing motions mostly oriented cross-shore that decay inland. At higher frequencies between 0.5 and 40 Hz, breaking ocean waves and wave-rock impacts cause ground shaking. Overall, seismic spectral shapes were generally consistent across shoreline sites and usually within a few orders of magnitude despite the diverse range of settings. However, specific site response varied and was influenced by a combination of tide level, incident wave energy, site morphology, ground composition, and signal decay. Flexing and shaking increased with incident wave energy and was often tidally modulated, consistent with a local generation source. Flexing magnitudes were usually larger than shaking, and flexing displacements of several mm were observed during relatively large incident wave conditions (Hs 4-5 m). Comparison with traffic noise and earthquakes illustrate the relative significance of local ocean-generated signals in coastal seismic data. Seismic observations are not a simple proxy for wave-cliff interaction.

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Coastal cliff‐top ground motions as proxies for environmental processes

et al. 2013

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[1] A two-year dataset of coastal cliff microseismic ground motions is used to explore energy transfer to a cliff. The long-term dataset enables us to characterise cliff motion responses to a wide range of environmental processes and examine whether short-term characteristics are representative of the long-term. We examine whether cliff-top motions are reliable proxies for environmental processes to inform future investigations into the drivers of erosion. The study is based at an actively eroding, macrotidal, hard rock cliffed coast where considerable intra-annual variability in wave, tide, and storm conditions permit the examination of a full range of environmental permutations. Three frequency bands of ground motion are identified that represent wind and wave processes that transfer energy to the cliff. Examining mean energy transfer by aggregating the frequency bands by sea water elevation reveals a notable departure from tidal inundation duration alone, of relevance to understanding the timing, duration and intensity of effective processes of erosion. Peak energy transfer to the cliff face occurs during the largest storms where water levels significantly exceed those of tidal inundation rather than at locations most frequently inundated by tides. We anticipate it is therefore these conditions that are likely to be most effective in eroding hard rock coasts, rather than periods which accrue energy transfer associated with still or calm waters, and hence tidally modulated inundation may not relate well to coastal erosion. Promisingly, despite signal overlap and noise, cliff-top motions can be used as proxies for the processes that transfer energy to the coast.

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Micro-seismic measurements of cliff motion under wave impact and implications for the development of near-horizontal shore platforms

Cited by 31 publications

References 42 publications

Alongshore variability in wave energy transfer to coastal cliffs

Alongshore variability in wave energy transfer to coastal cliffs

Ground motions on rocky, cliffed, and sandy shorelines generated by ocean waves

Coastal cliff‐top ground motions as proxies for environmental processes

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