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Management of Historical Seismic Data Using GIS: The Island of Ischia (Southern Italy) 总被引：1，自引：0，他引：1
This paper presents the results of the use of Geographic Information Systems (GIS) inmanaging information on the effects of earthquakes in historical times on the island ofIschia. The unpublished sources on the Casamicciola earthquake of 28 July 1883 andthe extensive bibliography documenting the island's seismicity from 1228 showed theneed to proceed towards a type of data storage that would also allow management ofthe same data. Application of GIS techniques allowed us to insert, extract, handle,manage and analyse the data for the zoning of seismic damage on the island of Ischia.The end-product consists of information layers, such as maps of isoseismals, the damage, and hazard involved, as well as numerical tables associated to maps.The study was developed using GIS Arc-View 3.2 software (ESRI) and is structured inthematic vectorial levels and rasters. The overlapping themes constitute a cartographicdata base of the island. The damaged sites are located on a map at a scale of 1:10,000,with all the information on the 1883 earthquake (total number of houses, number ofcollapsed houses, collapsed or damaged rooms, photographs, plans of buildings, etc.)being associated to each site. The GIS is structured in such a way as to be able to beintegrated with further georeferenced data and with other databases. It is thus able toprovide support both for in-depth analyses of the dynamic processes on the island andextend the assessment to other natural risks (volcanic, landslides, flooding, etc.). 相似文献
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The catastrophic 1883 earthquake at the island of Ischia (southern Italy): macroseismic data and the role of geological conditions 总被引：1，自引：0，他引：1
This article presents the results of a detailed study of the effects of the 1883 earthquake, which occurred at the island
of Ischia (Gulf of Naples) and produced the total destruction of buildings in the epicentral area (Casamicciola town). Despite
the moderate magnitude, this event was characterised by very high intensities (I
max = XI degree MCS) mainly due to the shallow depth of the source. The study of the earthquake shows that the intensities, which
decreased rapidly with distance, were affected by source directivity, according to the causative fault geometry and tectonic
structures, while local amplification of damage was observed where soft soils outcrop. The attenuation of seismic intensity
with distance was evaluated using the well-known relation of intensity versus epicentral distance (Blake’s method). The diverse
gradients of attenuation, observed in different directions, were ascribed to the various geological features of the shallow
crust of the island. In order to evaluate the role of geology in the damage level, we computed different attenuation models
for stiff and soft soils outcropping on the island. A systematic local amplification of about 1 MCS degree associated to the
presence of reworked tuffs was obtained. This study also shows the influence of geological conditions on the evaluation of
macroseismic data and supplies useful elements to derive a predictive map of potential site effects. 相似文献
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A 45-km-long regional dike was emplaced over a period of 2 weeks in August 2014 at the boundary between the East and North Volcanic Zones in Iceland. This is the first regional dike emplacement in Iceland monitored with modern geophysical networks, the importance of which relates to regional dikes feeding most of the large fissure (e.g., Eldgja 934 and Laki 1783) and lava shield (e.g. early Holocene Skjaldbreidur and Trölladyngja) eruptions. During this time, the dike generated some 17,000 earthquakes, more than produced in Iceland as a whole over a normal year. The dike initiated close to the Bardarbunga Volcano but gradually extended to the northeast until it crossed the boundary between the East Volcanic Zone (EVZ) and the North Volcanic Zone (NVZ). We infer that the strike of the dike changes abruptly at a point, from about N45°E (coinciding with the trend of the EVZ) to N15°E (coinciding with the trend of the NVZ). This change in strike occurs at latitude 64.7°, exactly the same latitude at which about 10 Ma dikes in East Iceland change strike in a similar way. This suggests that the change in the regional stress field from the southern to the northern part of Iceland has been maintained at this latitude for 10 million years. Analytical and numerical models indicate that the dike-induced stress field results in stress concentration around faults and particularly shallow magma chambers and calderas in its vicinity, such as Tungnafellsjökull, Kverkfjöll, and Askja. In particular, the dike has induced high compressive, shear, and tensile stresses at the location of the Bardarbunga shallow chamber and (caldera) ring-fault where numerous earthquakes occurred during the dike emplacement, many of which have exceeded M5 (the largest M5.7). The first segment of the dike induced high tensile stresses in the nearby part of the Bardarbunga magma chamber/ring-fault resulting in radially outward injection of a dike from the chamber at a high angle to the strike of the regional dike. The location of maximum stress at Bardarbunga fluctuates along the chamber/ring-fault boundary in harmony with dike size and/or pressure changes and encourages ring-dike formation and associated magma flow within the chamber. Caldera collapse and/or eruption in some of these volcanoes is possible, most likely in Bardarbunga, but depends largely on the future development of the regional dike. 相似文献
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5.
Stefano Carlino 《Bulletin of Volcanology》2012,74(5):947-961
This study provides an analysis of the evolution of resurgence from 55?ka for the active volcanic island of Ischia, southern Italy, using a laccolith model proposed in previous studies. This paper explores the uplift phases, eruptive behavior, and associated seismic activity of Ischia Island, which are important issues as the island has a high volcanic risk. Through an analysis of stress and strain over time for laccolith pressurization, it is shown that during resurgence, Ischia Island has undergone flexural uplift and progressive fracturing and faulting of the shallow crust (2?km thick), with an increase in the laccolith’s volume of at least 80?km3 and an average magma influx of 0.015?m3?s?1. Different elastic and viscoelastic mechanisms are used to evaluate the modes of stress relaxation due to this laccolith pressurization phase. Stress relaxation can occur through uplift and seismicity, without eruption, or with eruption. It is also shown that large eruptions should be expected only for long-term uplift of the central part of Ischia Island (the Mount Epomeo block). In contrast, the occurrence of small effusive and explosive eruptions should involve the peripheral areas of the resurgent block, and these are more likely to occur in the near future than are large events. 相似文献
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Loreto Rossi M. Letizia Costantini Pasquale Carlino Antonella di Lascio David Rossi 《Aquatic Sciences - Research Across Boundaries》2010,72(2):227-236
The high numbers of primary producers represent multiple sources of organic matter accumulating onto lake bottoms. The difficulty
of distinguishing the relative contribution to the mixture presents considerable challenges to the analysis of these organic
deposits. In this study, dual-stable isotope analysis and IsoSource model were used to identify allochthonous and autochthonous
components of detritus deposits (Particulate Organic Matter: POM) at two different bottom slope sites of a volcanic lake (lake
Bracciano). Experiments were carried out to calibrate IsoSource on constructed plant mixtures and assess changes in isotope
ratios during plant decomposition. IsoSource satisfactorily discriminated the constructed mixture sources with a few exceptions.
Changes in isotopic enrichment during decomposition were low, and thus did not represent a confounding variable in the isotopic
analysis. By contrast, chemical and geological differences of the study sites were associated with differences in plant δ13C and δ15N values (more than 2‰ within single plant species). At both sites, the isotopic signals of POM fell between polygons delineated
by source end members with an evident shift of δ13C toward allochthonous sources. POM amount and diversity were greater at the flatter bottom site, where allochthonous contributions
were larger than at the other site. In particular, IsoSource ranked species contributions as follows: A. glutinosa > P. australis > A. donax > S. alba > P. nigra > the benthic macroalga Chara sp. at the first site, and A. glutinosa > P. nigra > the aquatic macrophyte C. demersum at the latter. The composition of littoral POM was determined by allochthonous sources in proportion to their relative abundances
(as percent land cover) with differences between sites due to bottom slope. 相似文献
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Caldera eruptions are among the most hazardous of natural phenomena. Many calderas around the world are active and are characterised
by recurrent uplift and subsidence periods due to the dynamics of their magma reservoirs. These periods of unrest are, in
some cases, accompanied by eruptions. At Campi Flegrei caldera (CFc), which is an area characterised by very high volcanic
risk, the recurrence of this behaviour has stimulated the study of the rock rheology around the magma chamber, in order to
estimate the likelihood of an eruption. This study considers different scenarios of shallow crustal behaviour, taking into
account the earlier models of CFc ground deformation and caldera eruptions, and including recent geophysical investigations
of the area. A semi-quantitative evaluation of the different factors that lead to magma storage or to its eruption (such as
magma chamber size, wall-rock viscosity, temperature, and regional tectonic strain rate) is reported here for elastic and
viscoelastic conditions. Considering the large magmatic sources of the CFc ignimbrite eruptions (400–2,000 km3) and a wall-rock viscosity between 1018 and 1020 Pa s, the conditions for eruptive failure are difficult to attain. Smaller source dimensions (a few cubic kilometres) promote
the condition for fracture (eruption) rather than for the flow of wall rock. We also analyse the influence of the regional
extensional stress regime on magma storage and eruptions, and the thermal stress as a possible source of caldera uplift. The
present study also emphasises the difficulty of distinguishing eruption and non-eruption scenarios at CFc, since an unambiguous
model that accounts for the rock rheology, magma-source dimensions and locations and regional stress field influences is still
lacking. 相似文献
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