134 research outputs found
InSAR Time Series Analysis of Natural and Anthropogenic Coastal Plain Subsidence: The Case of Sibari (Southern Italy)
We applied the Small Baseline Subset multi-temporal InSAR technique (SBAS) to two SAR datasets acquired from 2003 up to 2013 by Envisat (ESA, European Space Agency) and COSMO-SkyMed (ASI, Italian Space Agency) satellites to investigate spatial and temporal patterns of land subsidence in the Sibari Plain (Southern Italy). Subsidence processes (up to ~20 mm/yr) were investigated comparing geological, hydrogeological, and land use information with interferometric results. We suppose a correlation between subsidence and thickness of the Plio-Quaternary succession suggesting an active role of the isostatic compensation. Furthermore, the active back thrusting in the Corigliano Gulf could trigger a flexural subsidence mechanism even if fault activity and earthquakes do not seem play a role in the present subsidence. In this context, the compaction of Holocene deposits contributes to ground deformation. Despite the rapid urbanization of the area in the last 50 years, we do not consider the intensive groundwater pumping and related water table drop as the main triggering cause of subsidence phenomena, in disagreement with some previous publications. Our interpretation for the deformation fields related to natural and anthropogenic factors would be a comprehensive and exhaustive justification to the complexity of subsidence processes in the Sibari Plain
CF-GNNExplainer: Counterfactual Explanations for Graph Neural Networks
Given the increasing promise of graph neural networks (GNNs) in real-world
applications, several methods have been developed for explaining their
predictions. Existing methods for interpreting predictions from GNNs have
primarily focused on generating subgraphs that are especially relevant for a
particular prediction. However, such methods are not counterfactual (CF) in
nature: given a prediction, we want to understand how the prediction can be
changed in order to achieve an alternative outcome. In this work, we propose a
method for generating CF explanations for GNNs: the minimal perturbation to the
input (graph) data such that the prediction changes. Using only edge deletions,
we find that our method, CF-GNNExplainer, can generate CF explanations for the
majority of instances across three widely used datasets for GNN explanations,
while removing less than 3 edges on average, with at least 94\% accuracy. This
indicates that CF-GNNExplainer primarily removes edges that are crucial for the
original predictions, resulting in minimal CF explanations.Comment: Accepted to AISTATS 202
The VELISAR initiative for the measurement of ground velocity in italian seismogenic areas
VELISAR (Ground VELocity in Italian Seismogenic Areas) is a scientific research
initiative aimed at producing a map of the ground deformation over most of the seismogenic
areas of Italy, using the space-based technique of multitemporal Synthetic
Aperture Radar Interferometry (InSAR). The ground velocities derived from InSAR
data will be validated by means of ground based data obtained from GPS, optical leveling,
seismological and neotectonic studies. The scope of the project is to produce
a high-resolution ground deformation dataset useful to model the seismic cycle of
strain accumulation and release at the scale of the single faults. The main objective of
VELISAR is to produce maps of ground velocity with the following characteristics:
- A ground resolution better than 100 m. - Average uncertainty of LoS velocity measurements
smaller than 2 mm/yr . - Temporal coverage of at least 7 years. - Retrieval
of East and Up components from ascending and descending LoS.
VELISAR will exploit the potential of the long time series (1992-2000) of ERS InSAR
data maintained in the ESA archives; over 4000 ERS images will have to be processed
to accomplish its objectives. Presently, two InSAR techniques for the measurement
of slow ground deformation are used in VELISAR: the Permanent Scatterers (PS)
technique developed by the Politecnico of Milano (POLIMI), and the Small Baseline
Subset (SBAS) technique, developed by the Institute for Remote Sensing of Environment
(IREA-CNR), in Napoli. The PS technique is applied by TRE preferably over
areas characterised by diffuse temporal decorrelation due to, for instance, erodible
lithologies, agricultural land use and strong vegetation cover. In these areas we expect
to obtain good temporal coherence mainly on sparse point scatterers. The SBAS
technique is applied by IREA and INGV mostly over areas where limited temporal
decorrelation is expected: urban areas, scarcely vegetated areas. The ground resolution
at which these data are originally processed is 80 m. An important goal of the
VELISAR initiative is to disseminate the information on the InSAR-derived ground
velocity measurements, to the scientific community and to the public in general. Such
goal is accomplished through a dedicated web site, where the velocity maps of the
italian seismogenic areas will be progressively published. We will present the initiative,
its scope and objectives, the technical details and the data processing strategies,
and some examples of ground velocity maps.PublishedVienna, Austriaope
Coseismic deformation and source modeling of the May 2012 Emilia (Northern Italy) earthquakes
On May 20th, 2012, an ML 5.9 earthquake (Table 1) occurred near the town of Finale Emilia, in the Central Po Plain, Northern Italy (Figure 1). The mainshock caused 7 casualties and the collapse of several historical buildings and industrial sheds. The earthquake sequence continued with diminishing aftershock magnitudes until May 29th, when an ML 5.8 earthquake occurred near the town of Mirandola, ~12 km WSW of the mainshock (Scognamiglio et al., 2012). This second mainshock started a new aftershock sequence in this area, and increased structural damage and collapses, causing 19 more casualties and increasing to 15.000 the number of evacuees.
Shortly after the first mainshock, the Department of Civil Protection (DPC) activated the Italian Space Agency (ASI), which provided post-seismic SAR Interferometry data coverage with all 4 COSMO-SkyMed SAR satellites. Within the next two weeks, several SAR Interferometry (InSAR) image pairs were processed by the INGV-SIGRIS system (Salvi et al., 2012), to generate displacement maps and preliminary source models for the emergency management. These results included continuous GPS site displacement data, from private and public sources, located in and around the epicentral area.
In this paper we present the results of the geodetic data modeling, identifying two main fault planes for the Emilia seismic sequence and computing the corresponding slip distributions. We discuss the implication of this seismic sequence on the activity of the frontal part of the Northern Apennine accretionary wedge by comparing the co-seismic data with the long term (geological) and present day (GPS) velocity fields.Published645-6551.1. TTC - Monitoraggio sismico del territorio nazionale1.9. Rete GPS nazionale1.10. TTC - Telerilevamento3.2. Tettonica attivaJCR Journalrestricte
Activation of the SIGRIS monitoring system for ground deformation mapping during the Emilia 2012 seismic sequence, using COSMO-SkyMed InSAR data
On May 20, 2012, at 02:03 UTC, a moderate earthquake
of local magnitude, ML 5.9 started a seismic sequence in the
central Po Plain of northern Italy (Figure 1) [Scognamiglio
et al. 2012, this volume]. The mainshock occurred in an area
where seismicity of comparable magnitude has neither been
recorded nor reported in the historical record over the last
1,000 years [Rovida et al. 2011].
The aftershock sequence evolved rapidly near the epicenter,
with diminishing magnitudes until May 29, 2012,
when at 07:00 UTC a large earthquake of ML 5.8 occurred
12 km WSW of the mainshock, starting a new seismic sequence
in the western area (Figure 1); a total of seven earthquakes
with ML >5 occurred in the area between May 20 and
June 3, 2012 (Figure 1). The details of the seismic sequence
can be found in the report by Scognamiglio et al. [2012].
Immediately after the mainshock, the Italian Department
of Civil Protection (Dipartimento di Protezione
Civile; DPC) requested the Italian Space Agency (Agenzia
Spaziale Italiana; ASI) to activate the Constellation of Small
Satellites for Mediterranean Basin Observation (COSMOSkyMed)
to provide Interferometric Synthetic Aperture
Radar (InSAR) coverage of the area. COSMO-SkyMed consists
of four satellites in a 16-day repeat-pass cycle, with
each carrying the same SAR payload [Italian Space Agency
2007]. In the current orbital configuration, within each 16-
day cycle, image pairs with temporal baselines of 1, 3, 4 and
8 days can be formed from the images acquired by the four
different sensors. Combined with the availability of a wide
range of electronically steered antenna beams with incidence
angles ranging from about 16° to 50° at near-range
[E-geos 2012], this capability allows trade-offs between temporal
and spatial coverage to be exploited during acquisition
planning.
A joint team involving the Istituto Nazionale di Geofisica
e Vulcanologia (INGV; National Institute of Geophysics
and Volcanology) and the Istituto per il Rilevamento
Elettromagnetico dell'Ambiente (IREA-CNR; Institute for
the Electromagnetic Sensing of the Environment) was activated
to generate InSAR-based scientific products to support
the emergency management. In this framework, the
ASI and DPC requested that INGV activated the Spacebased
Monitoring System for Seismic Risk Management
(SIGRIS) [Salvi et al. 2010]. SIGRIS consists of a hardware/
software infrastructure that is designed to provide the
DPC with value-added information products in the different
phases of the seismic cycle. During earthquake emergencies,
its goal is to rapidly provide decision-support
products, such as validated ground-displacement maps and
seismic source models.
This study reports the details of the activation of the
SIGRIS system in the case of the Emilia sequence. It provides
a description of the COSMO-SkyMed datasets and processing
procedures, as well as selected interferometric results for
the coseismic and post-seismic ground deformation. Fault
modeling results for the seismic sources of the largest earthquakes,
and a more detailed discussion of the observed
ground deformations are reported in Pezzo et al. [2012]
The SAVEMEDCOASTS-2 webGIS: The Online Platform for Relative Sea Level Rise and Storm Surge Scenarios up to 2100 for the Mediterranean Coasts
Here we show the SAVEMEDCOASTS-2 web-based geographic information system (webGIS) that supports land planners and decision makers in considering the ongoing impacts of Relative Sea Level Rise (RSLR) when formulating and prioritizing climate-resilient adaptive pathways for the Mediterranean coasts. The webGIS was developed within the framework of the SAVEMEDCOASTS and SAVEMEDCOASTS-2 projects, funded by the European Union, which respond to the need to protect people and assets from natural disasters along the Mediterranean coasts that are vulnerable to the combined effects of Sea Level Rise (SLR) and Vertical Land Movements (VLM). The geospatial data include available or new high-resolution Digital Terrain Models (DTM), bathymetric data, rates of VLM, and multi-temporal coastal flooding scenarios for 2030, 2050, and 2100 with respect to 2021, as a consequence of RSLR. The scenarios are derived from the 5th Assessment Report (AR5) provided by the Intergovernmental Panel on Climate Change (IPCC) and encompass different Representative Concentration Pathways (RCP2.6 and RCP8.5) for climate projections. The webGIS reports RSLR scenarios that incorporate the temporary contribution of both the highest astronomical tides (HAT) and storm surges (SS), which intensify risks to the coastal infrastructure, local community, and environment
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