Matthew Agius

University of Malta

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

Sergei Lebedev

University of Cambridge

Nicholas Harmon

Woods Hole Oceanographic Institution

C. Rychert

University of Southampton

Sebastiano D’Amico

University of Malta

Pauline Galea

University of Malta

J. M. Kendall

University of Oxford

Saikiran Tharimena

Jet Propulsion Laboratory

A. J. Schaeffer

Geological Survey of Canada

Fabrizio Magrini

Australian National University

David Schlaphorst

University of Lisbon

Cooperative Institutions

Dublin Institute For Advanced Studies

University of Malta

Centre National de la Recherche Scientifique

Monterey Bay Aquarium Research Institute

Istituto Nazionale di Geofisica e Vulcanologia

ETH Zurich

Roma Tre University

University of Southampton

University of Catania

Planetary Science Institute

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

Insights to the Damaging Effects of August 7, 2020 (Mw 5.0) Mila Earthquake and Seismic Hazard Analysis of Northeast Algeria

Research Square (Research Square) (2024)

Mouloud Hamidatou Nassim Hallal Saad Lebdioui Matthew Agius Rashad Sawires

Abstract Here, we present a seismic hazard evaluation for the August 7, 2020 (Mw 5.0) Mila earthquake that occurred in northeast Algeria. The study addresses the environmental factors that could contribute significantly to the highly damaging impact of this event. The following aspects were included in an interdisciplinary methodology that was adopted: the earthquake catalog, the coseismic geologic impacts with respect to the Environmental Seismic Intensity (ESI) scale standards, and estimations of peak ground acceleration values based on both probabilistic and deterministic seismic hazard approach. A comprehensive study of main and secondary impacts was performed for three districts (El-Kherba, Grareme-Gouga, and Azzeba), to obtain a good seismic intensity assessment. A PSHA- and DSHA based hazard analysis for the region concluded that the unique intensity values were related to the Modified Mercalli Intensity (MMI) and PGA distributions. Our work shows that the considered hazard estimation processes can result in very diverse values of the PGA distributions. Furthermore, PGA values frequently deviate significantly from macroseismic intensity levels derived using the ESI scale. As a result, the combination of the environmental factors attached to the hazard assessments seems to be necessary to obtain an additional accurate seismic assessment. In the final phase, seismic hazard assessment methods were applied to obtain the estimated damage distributions at the risky locations for 50 years of exposure time. The results show the importance of taking precautions to reduce earthquake casualties in vulnerable old urban centers. This work proposes a probable methodology for conducting site-specific hazard and vulnerability estimations to mitigate earthquake hazards and support risk reduction measures.

10.21203/rs.3.rs-3950022/v1

Cite

Citations (0)

Electromagnetic, seismic and petro-physical investigations of the lithosphere-asthenosphere boundary in central Tibet

AGU Fall Meeting Abstracts (2011)

J. Vozár Javier Fullea Alan G. Jones Matthew Agius Sergei Lebedev

Asthenosphere

Magnetotellurics

Source

Cite

Citations (0)

A thin mantle transition zone beneath the equatorial Mid-Atlantic Ridge

Nature (2021)

Matthew Agius C. Rychert Nicholas Harmon Saikiran Tharimena J. M. Kendall

Seafloor Spreading

Hotspot (geology)

Mid-Atlantic Ridge

Classification of discontinuities

Ocean surface topography

Low-velocity zone

10.1038/s41586-020-03139-x

Cite

Citations (32)

Exploring the Signature of the Apollo Medicane in the Central Mediterranean Sea Through Multi-source Data Analysis: Satellites, Radar HF, Marine Buoys, and Seismic Data in October 2021

Lecture notes in computer science (2023)

Luca Piroddi Adam Gauci Rami Kalfouni Matthew Agius Davide Melfi

Buoy

10.1007/978-3-031-37126-4_39

Cite

Citations (0)

A monitoring system for earthquake-generated tsunamis on the Maltese islands (Central Mediterranean)

EGU General Assembly Conference Abstracts (2019)

Matthew Agius Sebastiano D’Amico Pauline Galea George Bozionelos Aldo Drago

Maltese

Source

Cite

Citations (1)

Lithospheric structure in the Baikal–central Mongolia region from integrated geophysical‐petrological inversion of surface‐wave data and topographic elevation

Geochemistry Geophysics Geosystems (2012)

Javier Fullea Sergei Lebedev Matthew Agius Alan G. Jones Juan Carlos Afonso

Recent advances in computational petrological modeling provide accurate methods for computing seismic velocities and density within the lithospheric and sub‐lithospheric mantle, given the bulk composition, temperature, and pressure within them. Here, we test an integrated geophysical‐petrological inversion of Rayleigh‐ and Love‐wave phase‐velocity curves for fine‐scale lithospheric structure. The main parameters of the grid‐search inversion are the lithospheric and crustal thicknesses, mantle composition, and bulk density and seismic velocities within the crust. Conductive lithospheric geotherms are computed using P‐T‐dependent thermal conductivity. Radial anisotropy and seismic attenuation have a substantial effect on the results and are modeled explicitly. Surface topography provides information on the integrated density of the crust, poorly constrained by surface waves alone. Investigating parameter inter‐dependencies, we show that accurate surface‐wave data and topography can constrain robust lithospheric models. We apply the inversion to central Mongolia, south of the Baikal Rift Zone, a key area of deformation in Asia with debated lithosphere‐asthenosphere structure and rifting mechanism, and detect an 80–90 km thick lithosphere with a dense, mafic lower crust and a relatively fertile mantle composition (Mg# < 90.2). Published measurements on crustal and mantle Miocene and Pleistocene xenoliths are consistent with both the geotherms and the crustal and lithospheric mantle composition derived from our inversion. Topography can be fully accounted for by local isostasy, with no dynamic support required. The mantle structure constrained by the inversion indicates no major thermal anomalies in the shallow sub‐lithospheric mantle, consistent with passive rifting in the Baikal Rift Zone.

Asthenosphere

Isostasy

Low-velocity zone

10.1029/2012gc004138

Cite

Citations (72)

Geodynamics of the Central Mediterranean (GEOMED) inferred from ambient seismic noise

Matthew Agius Fabrizio Magrini Giovanni Diaferia Fabio Cammarano Claudio Faccenna

The Central Mediterranean, the area encompassing Italy, Sardinia, Tunisia and Libya, is characterised by multiple tectonic processes (plate convergence, subduction, and backarc extension). The evolution and interaction of the plate margins within this relatively small area are still being unravelled particularly at the adjacent region known as the Sicily Channel located between Sicily, Tunisia, Libya and Malta. This Channel is characterised by a seismically and volcanically active rift zone. Much of the observations we have today for the southern parts of the Calabrian arc are either limited to the surface and the upper crust, or are broader and deeper from regional seismic tomography, missing important details about the lithospheric structure and dynamics. The project GEOMED (https://geomed-msca.eu) addresses this issue by processing all the seismic data available in the region in order to understand better the geodynamics of the Central Mediterranean.We measure Rayleigh- and Love-wave phase velocities from ambient seismic noise recordings to infer the structures of the Central Mediterranean, from the Central Apennines to the African foreland, with a special focus on the Sicily Channel Rift Zone (SCRZ). The phase-velocity dispersion curves have periods ranging from 5 to 100 seconds and sample through the entire lithosphere. We invert the dispersion data for isotropic and polarised shear velocities with depth and infer crustal thickness and patterns of radial anisotropy. We find that continental blocks have thick crust (30-50 km), whereas beneath the SCRZ the crust is thin (<25 km), and thinner beneath the Tyrrhenian Sea. Beneath the SCRZ and the Tyrrhenian Sea, the crustal shear velocities are characterised by positive radial anisotropy (VSH>VSV) indicative of horizontal flow or extension, whereas the uppermost mantle is characterised by slow shear velocities indicative of warmer temperatures and strong negative radial anisotropy (VSH>VSV) indicative of vertical flow. We discuss the relevance of these findings together with other geophysical studies such as the regional seismicity and GPS velocity vectors to identify the rifting process type of the SCRZ.This project has received funding from the European Union&#8217;s Horizon 2020 research and innovation programme under the Marie Sk&#322;odowska-Curie grant agreement No 843696.

geodynamics

Seismic anisotropy

Seismic Tomography

10.5194/egusphere-egu21-6028

Cite

Citations (0)

Optimal resolution seismic tomography with error tracking: imaging the upper mantle beneath Ireland and Britain

Raffaele Bonadio Sergei Lebedev Thomas Meier P. Arroucau A. J. Schaeffer

Spatial resolution, as the ability to distinguish different features that are close together, is a fundamental concept in seismic tomography and other imaging fields. In contrast with microscopy or telescopy, seismic tomography&#8217;s images are computed, and their resolution has a complex, non-linear dependence on the data sampling and errors. Linear inverse theory provides a useful resolution-analysis approach, defining resolution in terms of the closeness of the resolution matrix to the identity matrix. This definition is similar to the universal, multi-disciplinary one in some contexts but diverges from it markedly in others. In this work, we adopt the universal definition of resolution (the minimum distance at which two spike anomalies can be resolved). The highest achievable resolution of a tomographic model then varies spatially and depends on the data sampling and errors in the data. We show that the propagation of systematic errors is resistant to data redundancy and results in models dominated by noise if the target resolution is too high. This forces one to look for smoother models and effectively limits the resolution. Here, we develop a surface-wave tomography method that finds optimal lateral resolution at every point by means of error tracking. We first measure interstation phase velocities at simultaneously recording station pairs and compute phase-velocity maps at densely, logarithmically spaced periods. Multiple versions of the maps with varying smoothness are computed, ranging from very rough to very smooth. Phase-velocity curves extracted from the maps at every point are then inverted for shear-velocity (VS) profiles. As we show, errors in these phase-velocity curves increase nearly monotonically with the map roughness. Very smooth VS models computed from very smooth phase-velocity maps will be the most accurate, but at a cost of a loss of most structural information. At the other extreme, models that are too rough will be dominated by noise. We define the optimal resolution at a point such that the error of the local phase-velocity curve is below an empirical threshold. The error is estimated by isolating the roughness of the phase-velocity curve that cannot be explained by any Earth structure. A 3D VS model is then computed by the inversion of the phase-velocity maps with the optimal resolution at every point. The estimated optimal resolution shows smooth lateral variations, confirming the robustness of the procedure. Importantly, optimal resolution does not scale with the density of the data coverage: some of the best-sampled locations require relatively low lateral resolution, probably due to systematic errors in the data. We apply the method to image the lithosphere and underlying mantle beneath Ireland and Britain, using 11238 newly measured, broadband, inter-station dispersion curves. The lateral resolution of the 3D model is computed explicitly and varies from 39 km in central Ireland to over 800 km at the region boundaries, where the data coverage declines. Our tomography reveals pronounced, previously unknown variations in the lithospheric thickness beneath the region, with implications for the Caledonian assembly of the islands&#8217; landmass and the mechanism of the magmatism of the British Tertiary Igneous Province.

10.5194/egusphere-egu21-11754

Cite

Citations (0)

A Seismic Monitoring Tool for Tidal-Forced Aquifer Level Changes in the Río de la Plata Coastal Plain, Argentina

Sustainability (2024)

Luciano Galone Francesco Panzera Emanuele Colica Enrique Fucks Eleonora Carol

Ambient seismic noise has gained extensive applications in seismology and plays a pivotal role in environmental seismic studies. This study focuses on the Río de la Plata Coastal Plain, employing the horizontal-to-vertical spectral ratio (HVSR) method on ambient seismic noise records to analyze subsurface dynamics. The region’s hydrogeology is complex, featuring partially interconnected coastal aquifers. The HVSR analysis reveals two peaks, with P0 associated with the sediment-basement interface and P1 linked to a shallower stratigraphic discontinuity. Temporal analysis of P1 highlights cyclical patterns correlated with estuarine levels, suggesting a relationship between variations in seismic velocities and tidal dynamics. Comparisons with aquifer data support the hypothesis that tidal variations influence subsurface mechanical properties, impacting the HVSR function. The study hints at the potential of ambient seismic noise analysis as a non-invasive and cost-effective method for studying coastal aquifers and understanding groundwater dynamics. Ongoing research aims to further explore these relationships for enhanced groundwater resource management.

Ambient noise level

10.3390/su16041432

Cite

Citations (3)

The Greater India beneath Tibet: A detailed new seismic mapping

EGUGA (2014)

Sergei Lebedev A. J. Schaeffer Matthew Agius

Source

Cite

Citations (0)