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Insitute of Physics, University of Urbino, Italy
62 results
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- PublicationOpen AccessApplication of the Post-Widder Laplace inversion algorithm to postseismic rebound models(2006-12-11)
; ; ; ; ;Cannelli, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Melini, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Piersanti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Spada, G.; Institute of Physics, University of Urbino, Italy; ; ; The computation of global postseismic rebound in a spherically symmetric, stratified, self-gravitating Earth with Maxwell viscoelastic rheology can be carried out semi-analytically with a normal-mode approach. The solution scheme usually involves the application of standard propagator techniques to the equivalent problem in the Laplace domain; to recover the temporal dependence a numerical Laplace anti-transform is required. This step involves the solution of the so-called “secular equation”, whose degree increases linearly with the detail of the stratification modeling, and whose coefficients become extremely ill-conditioned for high harmonic orders. As a result, the practically solvable models are limited to a few viscoelastic layers, and are anyway affected by severe numerical instabilities. To overcome these difficulties, alternative approaches have been explored by several authors, ranging from Runge-Kutta purely numerical integration to the evaluation of Laplace antitransform by a numerical discretization of the Bromwich integral. The Post-Widder algorithm allows the estimation of the Laplace antitransform by sampling numerically the transform on the positive real axis. This method, which has been recently applied to the computation of GIA viscoelastic Love numbers, allows to bypass completely the root-finding procedure while preserving at the same time the analytical normal-mode solution form. In this work, we apply the Post-Widder method to the computation of post-seismic rebound models. We perform a series of benchmarks to optimize the algorithm for speed while checking its stability against earlier results.180 381 - PublicationOpen AccessVertical ground displacement at Campi Flegrei (Italy) in the fifth century: Rapid subsidence driven by pore pressure drop(2014)
; ; ; ; ; ; ; ; ; ; ;Campi Flegrei (Italy) caldera has experienced episodes of ground deformation throughout its geological history, alternating between uplift and subsidence phases. Although uplift periods are typically more alarming, here we focus on subsidence, looking for its driving mechanisms and its role in the caldera evolution. Historical and archaeological records constrain ground deformation over the last two millennia. Here we revise such records and combine them with published radiometric dating and with the simulation of sea level change. The resulting analysis highlights for the first time a rapid subsidence during the fifth century. We show that rate and magnitude of this subsidence are consistent with the compaction of porous material caused by a pressure drop of ~ 1 MPa within the hydrothermal system. We interpret this event as the decompression of the hydrothermal system following an unrecognized episode of unrest, during Roman times. These findings redefine the pattern of ground deformation and bear important implications for volcanic hazard assessment380 169 - PublicationOpen AccessIntermittent Sea Level Acceleration(2013)
; ; ;Olivieri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Spada, G.; Dipartimento di Scienze di Base e Fondamenti, Urbino University “Carlo Bo”; Using instrumental observations from the Permanent Service for Mean Sea Level (PSMSL), we provide a new assessment of the global sea{level acceleration for the last 2 centuries (1820-2010). Our results, obtained by a stack of tide gauge time series, con firm the existence of a global sea level acceleration (GSLA) and, coherently with independent assessments so far, they point to a value close to 0:01 mm/yr2. However, di fferently from previous studies, we discuss how change points or abrupt inflections in individual sea level time series have contributed to the GSLA. Our analysis, based on methods borrowed from econometrics, suggests the existence of two distinct driving mechanisms for the GSLA, both involving a minority of tide gauges globally. The first effectively implies a gradual increase in the rate of sea level rise at individual tide gauges, while the second is manifest through a sequence of catastrophic variations of the sea level trend. These occurred intermittently since the end of the 19th century and became more frequent during the last four decades.452 258 - PublicationOpen AccessAnomalous secular sea-level acceleration in the Baltic Sea caused by isostatic adjustment(2014)
; ; ; ;Spada, G.; Dip.to di Scienze di Base e Fondamenti, Università di Urbino, Urbino, Italy ;Olivieri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Galassi, G.; Dip.to di Scienze di Base e Fondamenti, Università di Urbino, Urbino, Italy; ; Observations from the global array of tide gauges show that global sealevel has been rising at an average rate of 1.5-2 mm/yr during the last ~150 years [Douglas 1991, Spada and Galassi 2012]. Although a global sea-level acceleration was initially ruled out [Douglas 1992], subsequent studies [Douglas 1997, Church and White 2006, Jevrejeva et al. 2008, Church and White 2011] have coherently proposed values of ~1 mm/year/century [Olivieri and Spada 2013]. More complex non-linear trends and abrupt sea-level variations have now also been recognized. Globally, these could manifest a regime shift between the late Holocene and the current rhythms of sea-level rise [Gehrels and Woodworth 2013], while locally they result from ocean circulation anomalies, steric effects and wind stress [Bromirski et al. 2011, Merrifield 2011]. Although isostatic readjustment affects the local rates of secular sea-level change [Milne and Mitrovica 1998, Peltier 2004], a possible impact on regional acceleration has been so far discounted [Douglas 1992, Jevrejeva et al. 2008, Woodworth et al. 2009] since the process evolves on a millennium time scale [Turcotte and Schubert 2002]. Here we report a previously unnoticed anomaly in the long-term sea-level acceleration of the Baltic Sea tide gauge records, and we explain it by the classical post-glacial rebound theory and numerical modeling of glacial isostasy. Contrary to previous assumptions, our findings demonstrate that isostatic compensation plays a role in the regional secular sea-level acceleration.344 125 - PublicationOpen AccessSea level changes in the Mediterranean: tectonic implications(2008-09-07)
; ; ; ; ; ; ; ; ; ; ; ;Anzidei, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Lambeck, K. ;Antonioli, F. ;Pondrelli, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Serpelloni, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Baldi, P. ;Stocchi, P. ;Spada, G. ;Gasperini, P. ;Sivan, D. ;Soussi, M.; ; ;; ; ; ; ; ; ;The interpretation of sea level variations along the coasts of the Mediterranean region must be accompanied by the evaluation of vertical land movements associated with seismic and volcanic sources. This can be tentatively carried out through seismic strain analysis based on data pertaining the last 2 millennia as well as from the study of maritime archaeological structures.143 68 - PublicationRestrictedMazara del Vallo tide gauge observations (1906-1916): land subsidence or sea level rise?(2015)
; ; ; ; ;Olivieri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Spada, G.; Dipartimento di Scienze di Base e Fondamenti, Urbino University “Carlo Bo” ;Antonioli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Galassi, G.; Dipartimento di Scienze di Base e Fondamenti, Urbino University “Carlo Bo”; ; ; Tide gauge data constitute an invaluable tool for the interpretation of short and long-term sea level changes occurring in the Mediterranean Sea. The complex geophysical environment and the limited amount of sufficiently long records make the interpretation of local signals problematic, since these are often affected by interlacing processes. Starting from newly disclosed tide gauge records from the site of Mazara del Vallo (SW Sicily), we analyze simultaneously the time series available from other locations in Sicily across the beginning of the 20th century (Messina and Palermo). Despite the limited record length, we show that these observations provide new perspectives on the causes of the observed sea level variations in the central Mediterranean region, and in particular they challenge previous tenets regarding the extent of land movements caused by the 1908 Messina Straits earthquake.586 78 - PublicationOpen AccessHolocene relative sea-level changes along the Caribbean and Pacific coasts of northwestern South AmericaPredicting coastal change depends upon our knowledge of postglacial relative sea-level variability, partly controlled by glacio-isostatic responses to ice-sheet melting. Here, we reconstruct the postglacial relative sea-level changes along the Caribbean and Pacific coasts of northwestern South America by numerically solving the sea-level equation with two scenarios of mantle viscosity: global standard average and high viscosity. Our results with the standard model (applicable to the Pacific coast) agree with earlier studies by indicating a mid-Northgrippian high stand of ~2 m. The high-viscosity simulation (relevant to the Caribbean coast) shows that the transition from far- to intermediate-field influence of the Laurentide Ice Sheet occurs between Manzanillo del Mar and the Gulf of Morrosquillo. South of this location, the Colombian Caribbean coast has exhibited a still stand with a nearly constant Holocene relative sea level. By analyzing our simulations considering sea-level indicators, we argue that tectonics is more prominent than previously assumed, especially along the Caribbean coast. This influence prevents a simplified view of regional relative sea-level changes on the northwestern South American coast.
42 2 - PublicationOpen AccessNew estimates of ongoing sea level change and land movements caused by Glacial Isostatic Adjustment in the Mediterranean regionGlacial Isostatic Adjustment (GIA) caused by the melting of past ice sheets is still a major cause of sea level variations and 3-D crustal deformation in the Mediterranean region. However, since the contribution of GIA cannot be separated from those of oceanic or tectonic origin, its role can be only assessed by numerical modelling, solving the gravitationally self-consistent sea level equation. Nonetheless, uncertainties about the melting history of the late-Pleistocene ice sheets and the rheological profile of the Earth’s mantle affect the GIA predictions by an unknown amount. Estimating the GIA modelling uncertainties would be particularly important in the Mediterranean region, due to the amount of high quality geodetic data from space-borne and ground-based observations currently available, whose interpretation demands a suitable isostatic correction. Here we first review previous results about the effects of GIA in the Mediterranean Sea, enlightening the variability of all the fields affected by the persistent condition of isostatic disequilibrium. Then, for the first time in this region, we adopt an ensemble modelling approach to better constrain the present-day GIA contributions to sea level rise and geodetic variations, and their uncertainty.
73 35 - PublicationRestrictedA heuristic evaluation of long-term global sea-level acceleration(2015)
; ; ; ;Spada, G.; Dip.to di Scienze di Base e Fondamenti, Università di Urbino, Urbino, Italy ;Olivieri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Galassi, G.; Dip.to di Scienze di Base e Fondamenti, Università di Urbino, Urbino, Italy; ; In view of the scientific and social implications, the global mean sea-level rise (GMSLR), its possible causes and future trend have been a challenge for long. For the 20th century, reconstructions generally indicate a rate of GMSLR in the range of 1.5 to 2.0 mm yr−1. However, the existence of non-linear trends is still debated, and current estimates of the secular acceleration are subject to ample uncertainties. Here we use various GMSLR estimates published on scholarly journals since the 40’s for a heuristic assessment of global sea-level acceleration. The approach, alternative to sea-level reconstructions, is based on simple statistical methods and exploits the principles of meta-analysis. Our results point to a global sea-level acceleration of 0.54±0.27 mm/year/century (1σ) between 1898 and 1975. This supports independent estimates and suggests that a sea-level acceleration since the early 1900’s is more likely thancurrently believed.413 167 - PublicationOpen AccessSea-level rise along the Emilia-Romagna coast (Northern Italy) in 2100: scenarios and impactsAs a consequence of climate change and land subsidence, coastal zones are directly impacted by sea-level rise. In some particular areas, the effects on the ecosystem and urbanisation are particularly enhanced. We focus on the Emilia-Romagna (E-R) coastal plain in Northern Italy, bounded by the Po river mouth to the north and by the Apennines to the south. The plain is ∼ 130 km long and is characterised by wide areas below mean sea level, in part made up of reclaimed wetlands. In this context, several morphodynamic factors make the shore and back shore unstable. During next decades, the combined effects of land subsidence and of the sea-level rise as a result of climate change are expected to enhance the shoreline instability, leading to further retreat. The consequent loss of beaches would impact the economy of the region, which is tightly connected with tourism infrastructures. Furthermore, the loss of wetlands and dunes would threaten the ecosystem, which is crucial for the preservation of life and the environment. These specific conditions show the importance of a precise definition of the possible local impacts of the ongoing and future climate variations. The aim of this work is the characterisation of vulnerability in different sectors of the coastal plain and the recognition of the areas in which human intervention is urgently required. The Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) sea-level scenarios are merged with new high-resolution terrain models, current data for local subsidence and predictions of the flooding model in_CoastFlood in order to develop different scenarios for the impact of sea-level rise projected to year 2100. First, the potential land loss due to the combined effect of subsidence and sea-level rise is extrapolated. Second, the increase in floodable areas as a result of storm surges is quantitatively determined. The results are expected to support the regional mitigation and adaptation strategies designed in response to climate change.
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