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The Chyulu Hills volcanic field (Kenya): lineament traces and volcanic vents
No full textThe Chyulu Hills volcanic field (Kenya): lineament traces and volcanic vents
Francesco Mazzarini, Ilaria Isola
Istituto Nazionale di Geofisica e Vulcanologia, Pisa, Italy
Via Cesare Battisti, 53, 56125, Pisa
[email protected]; [email protected]
The Chyulu Hills, located in the eastern branch of the East African Rift System (EARS), is a northwest-southeast-aligned, elongated volcanic field almost 150 km long and up to about 30 km wide covering an area of around 2840 km^2. The volcanic field consists of numerous volcanic edifices and cinder cones and their erupted products (lava flows). These edifices form a prominent ridge of hundreds of individual and coalesced volcanoes and cinder cones that rise from the surrounding plains (<900 m above sea level) to a maximum elevation of 2175 m above sea level.
This data set consists of the data collected in the CHVF by inspection of satellite imagery and digital elevation models. Data are point-like features (vent) and linear features (lineament, vent alignment and elongation). These features have been derived by i) the analysis of shaded relief images derived from the SRTM digital elevation model with a cell size of 90 m and a vertical exaggeration (3x) was used; ii) the analysis of panchromatic SPOT satellite images using Google Earth software with pixel resolution ranging from 2.5 to 20 m.
The data set consists of three text files (txt file tab-delimited). All the map coordinates are in UTM zone 37S WGS84 (EPSG:32737 - WGS 84 / UTM zone 37S). For lines and elongations, the azimuth is in degree
1- Vents data set (file CHVF-vents.txt)
The data sets consist of the locations (easting and northing of vent barycentre) with a clear volcanic morphology. No vents with a diameter smaller than a few pixels (i.e., less than 60 m) or disrupted vents with unclear morphology are in the data set.
2- Vent elongation and alignment data set (file CHVF-vent-elongation.txt)
Vent elongation has been mapped as a line of constant length passing through the centre of the vent. Alignments of vents have been mapped only when they had a strong spatial correlation and low azimuth dispersion.
3- Lineament data set (file CHVF-lines.txt)
We assumed that lineaments are the intersection of the fracture network with the Earth’s surface; we thus consider lineaments as traces of fractures and will hereafter refer to lineaments as fractures. Fracture traces have been derived by the analysis of shaded relief images derived from the digital elevation model and satellite images. Surfing in Google Earth allows complete rotation of images and the continuous variation of points of view thus providing a very useful tool for fracture mapping
The Chyulu Hills volcanic field (Kenya): lineament traces and volcanic vents
No full textThe Chyulu Hills volcanic field (Kenya): lineament traces and volcanic vents
Francesco Mazzarini, Ilaria Isola
Istituto Nazionale di Geofisica e Vulcanologia, Pisa, Italy
Via Cesare Battisti, 53, 56125, Pisa
[email protected]; [email protected]
The Chyulu Hills, located in the eastern branch of the East African Rift System (EARS), is a northwest-southeast-aligned, elongated volcanic field almost 150 km long and up to about 30 km wide covering an area of around 2840 km2. The volcanic field consists of numerous volcanic edifices and cinder cones and their erupted products (lava flows). These edifices form a prominent ridge of hundreds of individual and coalesced volcanoes and cinder cones that rise from the surrounding plains (<900 m above sea level) to a maximum elevation of 2175 m above sea level.
This data set consists of the data collected in the CHVF by inspection of satellite imagery and digital elevation models. Data are point-like features (vent) and linear features (lineament, vent alignment and elongation). These features have been derived by i) the analysis of shaded relief images derived from the SRTM digital elevation model with a cell size of 90 m and a vertical exaggeration (3x) was used; ii) the analysis of panchromatic SPOT satellite images using Google Earth software with pixel resolution ranging from 2.5 to 20 m.
The data set consists of three text files (txt file tab-delimited). All the map coordinates are in UTM zone 37S WGS84 (EPSG:32737 - WGS 84 / UTM zone 37S). For lines and elongations, the azimuth is in degree
1- Vents data set (file CHVF-vents.txt)
The data sets consist of the locations (easting and northing of vent barycentre) with a clear volcanic morphology. No vents with a diameter smaller than a few pixels (i.e., less than 60 m) or disrupted vents with unclear morphology are in the data set.
2- Vent elongation and alignment data set (file CHVF-vent-elongation.txt)
Vent elongation has been mapped as a line of constant length passing through the centre of the vent. Alignments of vents have been mapped only when they had a strong spatial correlation and low azimuth dispersion.
3- Lineament data set (file CHVF-lines.txt)
We assumed that lineaments are the intersection of the fracture network with the Earth’s surface; we thus consider lineaments as traces of fractures and will hereafter refer to lineaments as fractures. Fracture traces have been derived by the analysis of shaded relief images derived from the digital elevation model and satellite images. Surfing in Google Earth allows complete rotation of images and the continuous variation of points of view thus providing a very useful tool for fracture mapping
Mapping of major volcanic structures on Pavonis Mons in Tharsis, Mars
Full text linkPavonis Mons, with its 300 km of diameter and 14 km of height, is one of the largest volcanoes of Mars. It rests on a topographic high called Tharsis rise and it is located in the centre of a SW-NE trending row of volcanoes, including Arsia and Ascraeus Montes. In this study we mapped and analyzed the volcanic and tectonic structures of Pavonis Mons in order to understand its formation and the relationship between magmatic and tectonic activity. We use the mapping ArcGIS software and vast set of high resolution topographic and multi-spectral images including CTX (6 m/pixel) as well as HRSC (12.5 m/pixel) and HiRiSE (∼0.25 m/pixel) mosaic images. Furthemore, we used MOLA (∼463 m/pixel in the MOLA MEGDR gridded topographic data), THEMIS thermal inertia (IR-day, 100 m/pixel) and THEMIS (IR-night, 100 m/pixel) images global mosaic to map structures at the regional scale. We found a wide range of structures including ring dykes, wrinkle ridges, pit chains, lava flows, lava channels, fissures and depressions that we preliminary interpreted as coalescent lava tubes. Many sinuous rilles have eroded Pavonis’ slopes and culminate with lava aprons, similar to alluvial fans. South of Pavonis Mons we also identify a series of volcanic vents mainly aligned along a SW-NE trend. Displacements across recent crater rim and volcanic deposits (strike slip faults and wrinkle ridges) have been documented suggesting that, at least during the most recent volcanic phases, the regional tectonics has contributed in shaping the morphology of Pavonis. The kinematics of the mapped structures is consistent with a ENE-SSW direction of the maximum horizontal stress suggesting a possible interaction with nearby Valles Marineris. Our study provides new morphometric analysis of volcano-tectonic features that can be used to depict an evolutionary history for the Pavonis Volcano
FEM modelling and fractal analysis of concentric and radial structures on Ascraeus Mons (Mars)
No full textAscraeus Mons è l’edificio vulcanico situato più a nord nella provincia dei
Tharsis su Marte. In questo lavoro vogliamo verificare l’ipotesi che afferma
che l’ultima attività vulcano-tettonica su Ascraeus possa essere stata indotta
dalla sovrapressione di una camera magmatica di forma oblata.
Il prodotto è un campo di stress che ha causato l’apertura di fratture utili
all’iniezione di dicchi radiali e cone sheets, aventi una distribuzione simile a
quelli rinvenuti sul Cuillins Complex (isola di Skye, Scozia). In quest’ultimo
caso tramite un modello a elementi finiti (FEM) si è dimostrato che questa
particolare distribuzione di dicchi e fratture è compatibile solamente con la
presenza di una camera magmatica oblata a una data profondità. Basandoci su
un’accurata mappatura di lineamenti e strutture concentriche e radiali su
immagini HRSC (High Resolution Stereo Camera con risoluzione 12 m/pixel)
combinata con parametri fisici e reologici marziani, e soprattutto con la
posizione della zona di transizione concentrico-radiale nei sistemi di fratture
intorno al vulcano, abbiamo potuto costruire un modello FEM di Ascraeus
Mons. Si è così potuta testare la possibile presenza e profondità di una camera
magmatica oblata al momento dell’ultimo evento vulcano-tettonico (datato con
la tecnica del conteggio di crateri).
Inoltre le strutture concentriche cartografate essendo direttamente correlate
ai sistemi di fratture in profondità collegati alla sorgente magmatica e al campo
di stress, sono state analizzate secondo la loro distribuzione spaziale. Questa
distribuzione è stata descritta da una legge di potenza con esponente frattale,
che permette di ricavare la profondità della camera magmatica e confrontarla
con quella ottenuta dal modello FEM. L’incrocio e la reciproca verifica di
risultati simili ottenuti con metodi indipendenti forniscono un forte constrain sulla presenza e posizione della camera magmatica, oltre che sulla bontà dei
metodi stessi
Seismic Imaging of Fractured Reservoirs in the Scansano-Amiata area, Southern Tuscany
No full textFresh water availability has recently become a serious concern in the Italian Apennines as various activities rely on a predictable supply. In southern Tuscany along the Scansano-Amiata ridge the situation is further complicated because of the contamination of the nearby alluvial aquifers. Locally aquifers consist of thin fractured reservoirs, generally within low-permeability formations, and planning exploitation of resources, based on conventional techniques, could be complicated. An integrated investigation program, based on remote sensing, structural geology and geophysical exploration, was initiated in 2002 to associate tectonics and groundwater circulation and better define the hydrological model. After the regional identification of fault and fracture patterns a major structure has been investigated in detail to accurately map the spatial position, and understand the associated aquifer geometry and properties to assess exploitation potentials. The subsurface around the fault zone was clearly imaged with Ground Probing Radar, 2D and 3D resistivity tomography and more recently with 3D shallow seismic. The vertical and the horizontal contacts between the different geological units of the Ligurian and of the Tuscan Series were resolved with a high degree of spatial accuracy. 3D high-resolution geophysical imaging proved to be very effective in small-scale fractured reservoir characterisation
Hints at diapirism in Arabia Terra craters, Mars
No full textArabia Terra is a region of Mars located at the boundary between the southern highlands and the northern lowlands
and classically dominated by heavily cratered terrain. Unlike the rest of the topographic dichotomy on the planet,
in Arabia Terra the elevation transition is very gentle, falling of 4 km over a distance of 2500 km (average
slope = 0.0016). Most of the impact craters within the region display a central bulge, bearing a well preserved
stratification and a wide range of smaller morphologies like pitted cones, mounds and knobs (Franchi et al. 2013).
Images acquired by HiRISE and CTX cameras on board MRO provided a comprehensive dataset in which also
these small features can be easily recognized. These are tens of meters of diameter and tens of meters high, and
many of them show an apical orifice. They are interpreted to have worked as pathways for subsurface fluid flow
(e.g. Pondrelli et al., 2011; Rossi et al., 2008). Indeed an active underground fluid flow activity in Arabia Terra It
has been recently hypothesized (e.g. Andrews-Hanna et al, 2011) , being crater central bulges a place of sulfate
precipitation, due to local water table emergence (e.g. Franchi et al., 2013).
To date, there is no clear explanation for occurrence of central bulges surrounded by prominent depressions in
Arabia craters. In addition, in Firsoff and Crommelin craters it is possible to recognize folds and outward dipping
strata on the central bulges and their surroundings. Interestingly, a few craters with a prominent bulged floor
elsewhere in Arabia Terra do not display stratification and are not explainable as impact related structures as their
expected pristine central peak derived by hydrocode modelling is 2km lower and one third the diameter than
the actual topography (Pozzobon et al., 2013). All these evidences are not consistent with a typical lacustrine
stratigraphic environment, whether interested by sulfate precipitation or not, and suggest active deformation after
or during bulge sequences deposition.
One or – more likely - multiple layers of sulfates below the shallower levels of Arabia Terra surface need, in our
opinion, to be hypothesized in order to explain all these contrasting observations. Indeed impact cratering on
such an evaporate bearing layered target might have provided the ideal conditions of faulting, interconnectivity of
evaporatic beds and lithostatic load release to allow diapirs ascent, In turn diapirism could have been responsible
for central bulging as testified by outward dipping strata on stratified bulges, broad un-stratified bulges and folding
(see Jackson and Vendeville, 1994 for typical salt tectonics). The depth of the fluid source calculated with a fractal
method (Pozzobon et al., 2013) using the position of the small widespread mounds within Firsoff and Crommelin
craters can give a hint of the average depth of the evaportic horizons (4 km).
As further developments we plan to test and quantify our model to take into account geological evidences, possible
kinematics, rheology and stratigraphic constrains
Rio Albano structural dara
No full textFault, fracture and veins attitude along with kinematic and infilling are reported for the area of Ria Albano, Eastern Island of Elba (Italy).Data are stored in excel files, planes are recorded as dip-direction/dip and lines as trend/plunge. A brief description is associated with each record.This data set has been used in the Manuscript SG_2019_10 titled: Structural and lithological control on fluid circulation, dilation and ore mineralization (Rio Albano mine Island of Elba, Italy). The manuscript is submitted to the Journal of Structural Geology.Any further information may be requested to the author: [email protected]
Rio Albano structural data
No full textFault, fracture and veins attitude along with kinematic and infilling are reported for the area of Ria Albano, Eastern Island of Elba (Italy).Data are stored in excel files, planes are recorded as dip-direction/dip and lines as trend/plunge. A brief description is associated with each record.This data set has been used in the Manuscript SG_2019_10 titled: Structural and lithological control on fluid circulation, dilation and ore mineralization (Rio Albano mine Island of Elba, Italy). The manuscript is submitted to the Journal of Structural Geology.Any further information may be requested to the author: [email protected]
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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