Seismic site response of unstable steep slope using noise measurements: the case study of Xemxija Bay area, Malta

Panzera, Francesco; D’Amico, Sebastiano; Lotteri, Alessandra; Galea, Pauline; Lombardo, Giuseppe

doi:10.5194/nhess-12-3421-2012

Cited by 75 publications

(41 citation statements)

References 30 publications

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“…The first important observation is the presence of a ubiquitous resonance peak at between 1.0 and 2.0 Hz. This is not surprising because previous ambient noise studies have repeatedly confirmed that all areas of the Maltese islands where UCL outcrops and is underlain by a layer of Blue Clay exhibits a peak in the H/V of this consistent frequency (Panzera et al 2012Vella et al 2013). The clay layer in the Maltese archipelago reaches thicknesses of more than 50 m in the west, and thins as a layer towards the east.…”

Section: E T H O D O L O G Y a N D A N A Ly S I Smentioning

confidence: 61%

“…Lately, slope and coastal instabilities have also been investigated by recording ambient noise, Active coastal spreading and ambient noise 1167 and the use of techniques such as H/V (horizontal-to-vertical spectral ratio) analysis, f-k analysis, site spectral ratios, polarization analysis, etc. (Del Gaudio et al 2008;Burjánek et al 2010Burjánek et al , 2012Coccia et al 2010;Panzera et al 2012). In particular, single station methods prove to be a very cost effective and rapid way of surveying an area, bypassing the problem of bringing bulky instrumentation into mostly inaccessible areas.…”

Section: Introductionmentioning

confidence: 99%

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Dynamic characteristics of an active coastal spreading area using ambient noise measurements—Anchor Bay, Malta

Galea

D’Amico

Farrugia

2014

Geophysical Journal International

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S U M M A R YAnchor Bay and surrounding regions are located on the northwest coast of the island of Malta, Central Mediterranean. The area is characterized by a coastal cliff environment having an outcropping layer of hard coralline limestone (UCL) resting on a thick (up to 50 m) layer of clays and marls (Blue Clay, BC). This configuration gives rise to coastal instability effects, in particular lateral spreading phenomena and rock falls. Previous and ongoing studies have identified both lateral spreading rates and vertical motions of several millimetres per year. The area is an interesting natural laboratory as coastal detachment processes in a number of different stages can be identified and are easily accessible. We investigate the site dynamic characteristics of this study area by recording ambient noise time-series at more than 30 points, over an area of 0.07 km 2 , using a portable three-component seismograph. The timeseries are processed to give both horizontal-to-vertical spectral ratio graphs (H/V) as well as frequency-dependent polarisation analysis. The H/V graphs illustrate and quantify aspects of site resonance effects due both to underlying geology as well as to mechanical resonance of partly or wholly detached blocks. The polarization diagrams indicate the degree of linearity and predominant directions of vibrational effects. H/V curves closer to the cliff edge show complex responses at higher frequencies, characteristic of the dynamic behaviour of individual detached blocks. Particle motion associated with the higher frequencies shows strongly directional polarization and a high degree of linearity at well-defined frequencies, indicative of normalmode vibration. The stable plateau areas, on the other hand, show simple, single-peak H/V curves representative of the underlying stratification and no predominant polarization direction. These results, which will be compared with those from other experiments in the area, have important implications for the understanding of ongoing processes in geologically active and unstable coastal environments.

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Section: E T H O D O L O G Y a N D A N A Ly S I Smentioning

confidence: 61%

Section: Introductionmentioning

confidence: 99%

Dynamic characteristics of an active coastal spreading area using ambient noise measurements—Anchor Bay, Malta

Galea

D’Amico

Farrugia

2014

Geophysical Journal International

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“…They showed that block slides occurring along the NW coast of Malta are active and move with different trends and rates (Mantovani et al, 2016). Slow-moving landslides are not very common in the eastern part of Malta, although they affect some coastal areas of Xemxija Bay (Panzera, D'Amico, Lotteri, Galea, & Lombardo, 2012), Ras Il-Grieb and Mellieha Bay. Limited block slides and rock fall deposits can also be found along the eastern coast of Comino.…”

Section: Gravity-induced Landformsmentioning

confidence: 99%

Geomorphological mapping of terrestrial and marine areas, northern Malta and Comino (central Mediterranean Sea)

et al. 2017

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This paper presents an integrated geomorphological map of terrestrial and marine areas of northern Malta and Comino (central Mediterranean Sea) at 1:25,000 scale. The map is the result of terrestrial and marine analyses of different types of data such as aerial photos, digital terrain model of the seafloor and its acoustic backscatter image. The research is intended to emphasise the relationships and continuity of geomorphological features of both the land-and sea-scape, and outline their evolution. The map highlights the occurrence of fluvial, karst and gravity-induced landforms both on land and on the seafloor, such as palaeo-fluvial channels, sinkholes and landslides, which were shaped during sea level lowstands of the last glacial cycle.

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“…These slow-moving landslides detach and move hundreds of limestone blocks from the karst plateaus towards the sea, forming peculiar coastal landforms named "rdum" by locals. Conversely, slow-moving landslides and related slope-failure accumulations are not common on the NE coast, although rock spreads and block slides have been recognised and investigated on the northern side of Xemxija Bay by Panzera et al (2012).…”

Section: The Study Areamentioning

confidence: 99%

Boulder accumulations related to extreme wave events on the eastern coast of Malta

Biolchi

Furlani

Antonioli

et al. 2016

Nat. Hazards Earth Syst. Sci.

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Abstract. The accumulation of large boulders related to waves generated by either tsunamis or extreme storm events have been observed in different areas of the Mediterranean Sea. Along the eastern low-lying rocky coasts of Malta, five sites with large boulder deposits have been investigated, measured and mapped. These boulders have been detached and moved from the nearshore and the lowest parts of the coast by sea wave action. In the Sicily-Malta channel, heavy storms are common and originate from the NE and NW winds. Conversely, few tsunamis have been recorded in historical documents to have reached the Maltese archipelago.We present a multi-disciplinary study, which aims to define the characteristics of these boulder accumulations, in order to assess the coastal geo-hazard implications triggered by the sheer ability of extreme waves to detach and move large rocky blocks inland.The wave heights required to transport 77 coastal boulders were calculated using various hydrodynamic equations. Particular attention was given to the quantification of the input parameters required in the workings of these equations, such as size, density and distance from the coast. In addition, accelerator mass spectrometry (AMS) 14 C ages were determined from selected samples of marine organisms encrusted on some of the coastal boulders. The combination of the results obtained both by the hydrodynamic equations, which provided values comparable with those observed and measured during the storms, and radiocarbon dating suggests that the majority of the boulders have been detached and moved by intense storm waves. These boulders testify to the existence of a real hazard for the coasts of Malta, i.e. that of very high storm waves, which, during exceptional storms, are able to detach large blocks of volumes exceeding 10 m 3 from the coastal edge and the nearshore bottom, and also to transport them inland. Nevertheless, the occurrence of one or more tsunami events cannot be ruled out, since radiocarbon dating of some marine organisms did reveal ages which may be related to historically known tsunamis in the Mediterranean region, such as the ones in AD 963, 1329, 1693 and 1743.

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Seismic site response of unstable steep slope using noise measurements: the case study of Xemxija Bay area, Malta

Cited by 75 publications

References 30 publications

Dynamic characteristics of an active coastal spreading area using ambient noise measurements—Anchor Bay, Malta

Dynamic characteristics of an active coastal spreading area using ambient noise measurements—Anchor Bay, Malta

Geomorphological mapping of terrestrial and marine areas, northern Malta and Comino (central Mediterranean Sea)

Boulder accumulations related to extreme wave events on the eastern coast of Malta

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