bluuebunny/crossref_metadata_2025 huggingface dataset:
Harnessing the Demographic Dividend in Africa Through Lessons From East Asia's Experience
Authors: Omoruyi Ehizuelen Michael Mitchell
Published: June 2021

Notably, East Asian Economies successfully capitalized on shifts in their age structures to gain a boost in economic productivity, a phenomenon known as the demographic dividend. Nowadays, despite the hitherto sluggish pace of Africa’s transition, experts remain optimistic that similar transformation in Africa may lead to faster development in coming decades. The paper attempts to answer the following three questions: (i) Can natural resource development help African economies harness its demographic dividend? (ii) as China forty years long, demographic dividend draws to an end, China is actively trying to capture fresh economic opportunities in higher-value-added productive activity. Can Africa seize this opportunity provided by its own emerging demographic dividend era? (iii) Can imitation game help African economies harness its demographic dividend? Arguably, for African economies to imitate the East Asian miracle and harness a maximum demographic dividend, they should adhere to these three mechanisms: labor supply, savings, and human capital.
Synthesis of Ni-B/Hydroxyapatite by Electrochemical Method and Its Application as Catalyst on NaBH4 Hydrolysis
Authors: Nur Adrian , Nazriati Nazriati , Fajaroh Fauziatul , Arthaningrum Ajeng , Nurcahyani Ika , Cipto Diajeng L.R.P. , Kurniawan Febri
Published: June 2021

The result of burning hydrogen which is environmentally friendly makes hydrogen as a very attractive fuel. Hydrogen storage is interesting research material. One alternative to hydrogen storage is a metal-hydride as NaBH4. In this paper, the catalyst for hydrogen production from storage, namely The result of burning hydrogen, which is environmentally friendly, makes hydrogen a desirable fuel. Hydrogen storage is exciting research material. One alternative to hydrogen storage is a metal-hydride as NaBH4. In this paper, the catalyst for hydrogen production from storage, namely NaBH4, was synthesized by electrochemical. Ni-B catalyst with hydroxyapatite as catalyst support was prepared by electrochemical. Ni-B/HA catalyst was synthesized at various current densities (namely 67, 133, and 200 mA/cm2) and various electrolysis times (namely 30, 60, and 90 minutes). The resulting catalysts were analyzed by XRD and used as the catalyst for hydrogen production from the hydrolysis reaction of NaBH4. The fastest hydrogen production was obtained using a catalyst generated at 133 mA/cm2 and an electrolysis time of 60 minutes. The reaction rate equation for the hydrolysis of NaBH4 has a first-order reaction to the concentration of NaBH4. The resulting reaction rate constant ranged from 233.33 mL/g/min to 861.11 mL/g/min. The relationship between reaction temperature and reaction rate constant can be expressed by the equation k = 2.2x106exp (5534/T).
Machine Learning Model for Predicting Postoperative Survival of Patients with Colorectal Cancer
Authors: Osman Mohamed Hosny , Mohamed Reham Hosny , Sarhan Hossam Mohamed , Park Eun Jung , Baik Seung Hyuk , Lee Kang Young , Kang Jeonghyun
Published: June 2021

Purpose Machine learning (ML) is a strong candidate for making accurate predictions, as we can use large amount of data with powerful computational algorithms. We developed a ML based model to predict survival of patients with colorectal cancer (CRC) using data from two independent datasets.Materials and Methods A total of 364,316 and 1,572 CRC patients were included from the Surveillance, Epidemiology, and End Results (SEER) and a Korean dataset, respectively. As SEER combines data from 18 cancer registries, internal validation was done using 18-Fold-Cross-Validation then external validation was performed by testing the trained model on the Korean dataset. Performance was evaluated using area under the receiver operating characteristic curve (AUROC), sensitivity and positive predictive values.Results Clinicopathological characteristics were significantly different between the two datasets and the SEER showed a significant lower 5-year survival rate compared to the Korean dataset (60.1% vs. 75.3%, p < 0.001). The ML-based model using the Light gradient boosting algorithm achieved a better performance in predicting 5-year-survival compared to American Joint Committee on Cancer stage (AUROC, 0.804 vs. 0.736; p < 0.001). The most important features which influenced model performance were age, number of examined lymph nodes, and tumor size. Sensitivity and positive predictive values of predicting 5-year-survival for classes including dead or alive were reported as 68.14%, 77.51% and 49.88%, 88.1% respectively in the validation set. Survival probability can be checked using the web-based survival predictor (http://colorectalcancer.pythonanywhere.com).Conclusion ML-based model achieved a much better performance compared to staging in individualized estimation of survival of patients with CRC.
The isometries of the space of Kähler metrics
Authors: Darvas Tamás
Published: June 2021

Given a compact Kähler manifold, we prove that all global isometries of the space of Kähler metrics are induced by biholomorphisms and anti-biholomorphisms of the manifold. In particular, there exist no global symmetries for Mabuchi’s metric. Moreover, we show that the Mabuchi completion does not even admit local symmetries. Closely related to these findings, we provide a large class of metric geodesic segments that cannot be extended at one end, exhibiting the first such examples in the literature.
The 3550 year BP-1944 A.D.magma-plumbing system of Somma-Vesuvius: constraints on its behaviour and present state through a review of Sr-Nd isotope data
Authors: L. Pappalardo  , M. Piochi  , G. Mastrolorenzo
Published: June 2021

Vesuvius, dominating the densely-populated Neapolitan area, is one of the most dangerous volcanoes in the World. Its destructive power derives from energetic subplinian and plinian eruptions, such as the one which occurred in 79 A.D. Generally such large-scale events follow a long period of quiescence; a behaviour interpreted as the gradual build-up of magma volumes between periods of major activity. After the 1631 subplinian eruption until the last 1944 A.D. eruption, it experienced an almost continuous and less energetic explosive/effusive activity. The erupted magmas are characterized by undersaturated potassic to ultrapotassic nature, and compositional and Sr-isotopic variability. Furthermore geobarometric studies indicate two different crystallization depths located at 4 and >11 km, respectively. According to most of the recent literature, the eruptions were triggered by the injection in a shallower magma chamber, of isotopically distinct magma batches derived from heterogeneous mantle source(s) and/or contamination processes occurred within the deep reservoir. In our review of petrochemical data, we consider the period between the 3550 years BP plinian eruption and the 472 A.D. sub-plinian eruption, which includes 79 A.D. event, and the most recent period of activity which started in 1631 A.D. and lasted up to the 1944 A.D. eruption, characterized by a near continuous effusive/explosive activity. For both periods we identify a correlation between Sr-isotopical features of magmas and their crystallization depth. In particular, we show that pyroxenes have Sr-isotopic ratios lower than 0.7074 and an equilibrium crystallization depth of 22-11 km. Moreover feldspars have higher 87Sr/86Sr values (0.7075-7) and an equilibrium crystallization depth of about 4 km. Therefore the most radiogenic magmas did not derive from a deeper reservoir but their higher Sr-isotopic ratios have been acquired at a shallower depth likely by crustal contamination during magma evolution. In contrast, the lower Sr-isotope compositions characterise the less contaminated magmas coming from deeper crustal levels. On the basis of this evidence, the temporal Sr-isotopical variation of magma which erupted in the 1631-1944 A.D. period probably derives from the progressive withdrawal of the shallow magma chamber, which was completely empty before the 1805-1944 A.D. period of volcanism. Therefore the effusive and explosive events of the most recent 1805-1944 A.D. period were fed directly by the deep reservoir located at a depth exceding 11 km.
Bayesian analysisof a probability distribution for local intensity attenuation
Authors: R. Rotondi  , G. Zonno
Published: June 2021

Intensity attenuation and its variation as a function of the distance and earthquake size is still a critical issue in evaluating seismic hazard. We present a method that allows us to incorporate additional information from the historical earthquake felt reports in the probability estimation of local intensity attenuation. The approach is based on two ideas: a) standard intensity versus epicentral distance relationships constitute an unnecessary filter between observations and estimates; and b) the intensity decay process is affected by many, scarcely known elements (the physical parameters of the source, propagation path effects, building vulnerability, the semi-qualitative character of macroseismic scales, etc.). Hence intensity decay should be treated as a random variable as is the macroseismic intensity. We assume here that decay, defined on the set {0,1, ..., I0}, follows a binomial distribution with parameters (I0, p); p depends on the distance from the epicenter and is related to the probability of null decay at that distance. According to the Bayesian approach this p parameter is, in turn, a Beta random variable. The observations related to earthquakes with their epicenter outside the area concerned, but belonging to homogeneous zones, are used as prior knowledge of the phenomenon, while the data points of events inside the area are used to update the estimates through the posterior means of the quantities involved. Our methodology is described in detail in an application to the Umbria-Marche area in Central Italy. The data sets examined are the macroseismic intensity database DOM4.1 and the zonation ZS.4, both compiled by the Italian Group for Defence against Earthquakes (GNDT). The method is validated by comparing the observed and the estimated intensity data points of the Camerino (28/07/1799) and of the Colfiorito (26/09/1997) earthquakes.
Morphology of bottom surfaces of glacier ice tongues in the East Antarctic region
Authors: C. Bianchi  , M. Chiappini  , I. E. Tabacco  , A. Passerini  , A. Zirizzotti  , E. Zuccheretti
Published: June 2021

During three Antarctic summer campaigns (1995/97/99) Radio Echo Sounding (RES) system data from some glacier ice tongues in the East Antarctic regions between Victoria Land and George V Land were collected. The morphology and structure of the bottom surfaces deduced from the electromagnetic interpretation of echo signal were observed. The bottom surfaces at the ice/water interface show either irregular or flat contours or both. Some ice tongues are nearly perfectly flat, others show clear signs of irregularities while three of them have good regular spaced rippled bottom surfaces. The latter structures are well-evident in the longitudinal traverse of the tongues, whereas the transversal paths do not show the same features. This particular shape of the bottom surfaces related to the ablation process and detachment mechanism could be interesting especially to determine some physical characteristics and the possible fracture points of the ice tongues.
Computer animation as a tool to visualize effects of seismic wave propagation inside heterogeneous media
Authors: A. Caserta  , P. Lanucara
Published: June 2021

A technique to make computer animations representing the propagation of antiplane shear waves in heterogeneous dissipative media is presented. The aim is to develop a useful tool to better investigate the physics of site effectsin the 2D approximation. We apply this technique to real case studies that were the subject of previous papers. For each case study a movie has been made to illustrate the wavefield time evolution and its interaction with the geological structure. All the movies can be seen and downloaded at the web site http://sigfrido.ingrm.it/movies.html. The paper shows the most representative frames of movies, providing an overview of the role played by the topographic irregularities and the geometry of internal discontinuities in trapping and focusing energy. The details of the dynamics are well visualized through movies. Particular attention is devoted to the representation of simulated ground motion in sediment-filled basins under resonance conditions. Problems related to color scales and frame normalization are analysed and discussed.
The October 9, 1996 earthquake in Cyprus: seismological, macroseismic and strong motion data
Authors: I. Kalogeras  , G. Stavrakakis  , K. Solomi
Published: June 2021

On October 9, 1996, an earthquake of magnitude 6.8 occurred in the sea area SW of Cyprus, Eastern Mediterranean. This earthquake, which caused damage mostly in the area of Paphos and Limassol, triggered an accelerograph installed at Yermasoyia dam, north of Limassol. The Geodynamic Institute of the National Observatory of Athens in cooperation with the Geological Survey of Cyprus deployed five digital accelerographs in order to record large aftershocks. Although the aftershock activity lasted over four months and included a large number of earthquakes with magnitudes 4.5 and greater, only the largest aftershock of January 13, 1997, having a magnitude of 5.9, triggered two of these five accelerographs. Moreover another digital accelerograph, operated by the Water Development Department of Cyprus, was triggered and this record was also taken into account in this study. The first Cyprean strong motion records obtained to date, gave us the opportunity to compare the results from their analysis to the already proposed attenuation relationships from other areas of the world with a similar seismotectonic regime. Although a general fitting to the attenuation curves for subduction events and strike-slip/reverse fault events was found, the calculated peak ground accelerations were found to be lower than others. Unfortunately, due to the lack of data from previous Cyprean earthquakes, it was not possible to conclude to precise attenuation
Development of a new generation gravity map of Antarctica: ADGRAV Antarctic Digital Gravity Synthesis
Authors: R. E. Bell  , C. Small  , R. A. Arko
Published: June 2021

The U.S. National Science Foundation (NSF) has agreed to support the development of a new generation gravity map of Antarctica (ADGRAV - Antarctic Digital Gravity Synthesis), funding the development of a web based access tool. The goal of this project is the creation of an on-line Antarctic gravity database which will facilitate access to improved high resolution satellite gravity models, in conjunction with shipboard, airborne, and land based gravity measurements for the continental regions. This database will complement parallel projects underway to develop new continental bedrock (BEDMAP) and magnetic (ADMAP) maps of Antarctica.
Volcanic tremor associated with eruptive activity at Bromo volcano
Authors: E. Gottschämmer
Published: June 2021

Three broadband stations were deployed on Bromo volcano, Indonesia, from September to December 1995. The analysis of the seismograms shows that the signals produced by the volcanic sources cover the frequency range from at least 25 Hz down to periods of several minutes and underlines, therefore, the importance of broadband recordings. Frequency analysis reveals that the signal can be divided into four domains. In the traditional frequency range of volcanic tremor (1-10 Hz) sharp transitions between two distinct values of the tremor amplitude can be observed. Additional tremor signal including frequencies from 10 to 20 Hz could be found during late November and early December. Throughout the whole experiment signals with periods of some hundred seconds were observed which are interpreted as ground tilts. For these long-period signals a particle motion analysis was performed in order to estimate the source location. Depth and radius can be estimated when the source is modeled as a sudden pressure change in a sphere. The fourth frequency range lies between 0.1 and 1 Hz and is dominated by two spectral peaks which are due to marine microseism. The phase velocity and the direction of wave propagation of these signals could be determined using the tripartite-method.
Laboratory studies on electrical effects during volcanic eruptions
Authors: H. Röder  , B. Zimanowski  , R. Büttner
Published: June 2021

This laboratory study reports on electrical phenomena during the explosive eruption of a basaltoid silicate melt. Contact electricity is produced in the phase of thermo-hydraulic fracturing of magma during the explosive interaction with water. The electrical charge produced is directly proportional to the force of the explosion, as the force of explosion is linearly proportional to the surface generated by the thermo-hydraulic fracturing. Simulation of the ejection history using inerted gas as a driving medium under otherwise constant conditions did not result in significant electric charging. The results have the potential to explain in nature observed lightening in eruption clouds of explosive volcanic events.
A method for f0F2 monitoring over Spain using the El Arenosillo digisonde current observations
Authors: A. V. Mikhailov  , B. A. de la Morena  , G. Miro  , D. Marin
Published: June 2021

Ionosphere monitoring implies: observations, prediction and mapping of ionospheric parameters. A case with one available (El Arenosillo) ionosonde is considered. Some statistical methods for f0F2 short-term (1-24 h in advance) prediction are compared. The analysis of multi-dimensional regression for Df0F2 (relative deviation from running median) with Ap, F10.7 and previous Df0F2 observations has shown that inclusion of additional terms with Ap and F10.7 improves the prediction accuracy for lead time more than 15 h. For lead time 1-6 h a linear regression with earlier observed Df0F2 provides the f0F2 forecast with Relative Mean Deviation (RMD) 6-11%. This is acceptable from a practical point of view. A 24-h forecast can be done with RMD 10-11%. Multi-regressional methods provide better prediction accuracy than the usual 10-day running median or quasi-inertial method based on such median. Hourly f0F2 values may be used to calculate the effective index R12eff used as input to the ITU-R monthly median model. This allows the ITU-R model to "breathe" following hour-to-hour f0F2 variations. Then standard surfering methods may be applied for f0F2 mapping over the whole area. The f0F2 mapping accuracy based on the hourly R12eff index is shown to be 9-11% depending on solar activity level.
Significance test for seismicity rate changes before the 1987 Chiba-toho-oki earthquake (M 6.7) Japan
Authors: K. Maeda  , S. Wiemer
Published: June 2021

A precursory seismic quiescence lasting 1.5 ± 0.5 years was observed prior to the 1987 M 6.7 Chiba-toho-oki earthquake, Central Japan. This event was the largest mainshock to occur in the region in 60 years. A quantitative analysis of the seismicity rates, using two independent catalogs provided by the NIED and JMA networks, shows that the precursory seismic quiescence is centered in the shallower part of the rupture zone of the subsequent mainshock, at a depth of 20-40 km. At the hypocenter of the 1987 Chiba-toho-oki mainshock, a 50% increase in the seismicity rate was detected in the NIED data, coinciding in time with the onset of quiescence (1986.4 ± 0.5). The simultaneous appearance of both quiescence in the shallow part of the rupture zone observed in two catalogs, and a rate increase in the immediate hypocenter region, suggest that these phenomena are causally linked to the subsequent mainshock. However, a quantitative analysis of both catalogs reveals that the precursory quiescence and rate increase are not unique, since rate changes of this duration and significance often occur in the data. A rate change of this significance rating could probably not be detected as a precursor in a real time approach. For the aid of real time monitoring of seismicity rate changes, we introduce the method to calculate the 95-percentile of confidence level for the significant rate changes.
Seismic hazard assessment for Adria
Authors: D. Slejko  , R. Camassi  , I. Cecic  , D. Herak  , M. Herak  , S. Kociu  , V. Kouskouna  , J. Lapajne  , K. Makropoulos  , C. Meletti
Published: June 2021

The Adriatic region was chosen as one of the test areas in the GSHAP program and, consequently, its seismic hazard was computed. The standard hazard map chosen by GSHAP represents PGA with a 475-year return period. Some other parameters, as the spectral acceleration and the uniform hazard response spectra for the main Adriatic towns, have been computed for a better representation of the regional hazard. The most hazardous area remains identified in the Cephalonia zone, where strong earthquakes frequently occur. The Southern Apennines are characterised by a slightly lower hazard, while the Adriatic Sea itself, the Poplain and the Apulian peninsula are almost aseismic.
Seismic hazard of Northern Eurasia
Authors: V. I. Ulomov  , . The GSHAP Region Working Group
Published: June 2021

The GSHAP Regional Centre in Moscow, UIPE, has coordinated the seismic hazard mapping for the whole territory of the former U.S.S.R. and border regions. A five-year program was conducted to assemble for the whole area, subdivided in five overlapping blocks, the unified seismic catalogue with uniform magnitude, the strong motion databank and the seismic zones model (lineament-domain-source), which form the basis of a newly developed deterministic-probabilistic computation of seismic hazard assessment. The work was conducted in close cooperation with border regions and GSHAP regional centers. The hazard was originally computed in terms of expected MSK intensity and then transformed into expected peak ground acceleration with 10% exceedance probability in 50 years.
Rapid assessment of S-wave profiles from the inversion of multichannel
Authors: G. A. Tselentis  , G. Delis
Published: June 2021

The importance of detailed knowledge of the shear-wave velocity structure of the upper geological layers was recently stressed in strong motion studies. In this work we describe an algorithm which we have developed to infer the 1D shear wave velocity structure from the inversion of multichannel surface wave dispersion data (ground-roll). Phase velocities are derived from wavenumber-frequency stacks while the inversion process is speeded up by the use of Householder transformations. Using synthetic and experimental data, we examined the applicability of the technique in deducing S-wave profiles. The comparison of the obtained results with those derived from cross-hole measurements and synthesized wave fields proved the reliability of the technique for the rapid assessment of shear wave profiles during microzonation investigations.
Revision of the 1844 Palestrina earthquake following the recovery of an unpublished document
Authors: A. Tertulliani  , S. Del Mese  , R. Di Giovambattista  , M. Pirro
Published: June 2021

The paper presented originates from the recovery of an unpublished document that reports estimated damage in the city of Palestrina (Central Italy) following the 1844 earthquake. This document is not quoted in the sources and repertoires concerning earthquakes in the Palestrina area, and it has probably never before been used in studies for seismic hazard evaluation. Analysis of the document has allowed us to state the distribution and severity of damage due to the seismic event, assessing an intensity of VII MCS for Palestrina. Comparison with other coeval documents evidenced a possible lack of information with respect to the dwellings of the less well-to-do population, granting the hypothesis of a more serious damage level. The distribution of effects within the town centre of Palestrina has been compared with the surficial geology, evidencing a strong dependence of the seismic response on the local geomorphology. Such results are also confirmed by a similar damage pattern following the 1876 earthquake, and allow us to outline a realistic view of Palestrina's seismic vulnerability.
Interfacing and off-line analysis for VOS-1A Barry ionosonde
Authors: E. Zuccheretti
Published: June 2021

Ionospheric studies have a great importance in radiopropagation and planetary atmospheric physics. The basic instrument for the investigation of ionospheric physics is the sweep frequency H-F radar called ionosonde. Ionospheric measurements, like other geophysical quantities, are useful only if there is a long and unbroken history, both for scientific and service purposes. Therefore a huge amount of data is produced and only a few ionospheric characteristics are scaled. In the Istituto Nazionale di Geofisica, the ionospheric hard copy data bank (paper and film) already requires a large storage space. The rough data on hard copy are not suitable for complete analysis and they should be completely digitized before processing. Usually only some characteristics are digitized and stored (scaled ionogram), but in this way it becomes more difficult to extract important physical quantities like the electron density profile. In order to overcome these problems, an Ionospheric Data Acquisition System (IDAS) based on commercial PCs has been developed. This ensures reliability for data acquisition and the availability of commercial software packages for analysis, compression and storage.
Advances in regional ionospheric mapping over europe
Authors: B. Zolesi  , L. R. Cander
Published: June 2021

Over the past several years significant advances have been made in all areas of ionospheric modelling and mapping studies. Ionospheric models and maps of varying complexity have been formulated from analytic and simple numerical models that are user friendly" calculations to complete general circulation models that require hours on todays supercomputers. All have their place and are used in different applications. This review describes progress in regional ionospheric mapping over Europe in the frame of the COST 238 and 251 projects.
Solar, ionospheric and geomagnetic indices
Authors: L. Perrone  , G. De Franceschi
Published: June 2021

The most common solar, ionospheric and geomagnetic indices are here presented with particular reference to their application for radiocommunication prediction purposes. Summary tables of practical use are also included concerning the method of derivation of the indices, their time interval, their drawbacks, their time-history and the INTERNET node addresses where they are available.
Rheology of the Indian and Tarim plates in the Karakoram continent-to-continent collision zone
Authors: A. Caporali
Published: June 2021

Bouguer gravity anomalies in the region of Western Himalayas, Karakoram and Tien Shan show large negative values, but classical isostatic models are insufficient to account for the detailed pattern of the observed anomalies. In the past years the gravimetric surveys in the Karakoram done by Marussi, Caputo and others in 1954 have been extended and intensified. The full body of available gravimetric data, including the pendulum observations by De Filippi and Hedin at the beginning of this century, have been re-analyzed. Terrain corrections have been computed systematically for all available data using a unique algorithm and Digital Terrain Model. The isostatic anomalies along a profile from the Indo-Gangetic foredeep, across the Karakoram range and terminating in the Tarim basin show the oscillating values already noted by Marussi. It is here proposed that this oscillatory pattern can be explained by a model in which the convergent boundaries of the Indian and Tarim plates deform by elastic flexure, besides isostasy. The gravity data constrain the numerical values of the model parameters, particularly the flexural rigidity of the plates. For the Indian plate the best fitting value of the flexural rigidity is D = 5 1024 N m, a value very similar to those reported in Central Himalaya. The flexural rigidity of the Tarim plate turns out to be considerably larger D = 7 1025 N m, which makes the Tarim more rigid than the neighboring Central Tibet. Both plates are loaded by an estimated shear stress of 7 1012 N m-1 located in a region corresponding to the Nanga Parbat Haramosh syntaxis. It is concluded that the Indo-Asian continental collision in the Western Himalaya and Karakoram resulted in the development of flexural basins on both sides, unlike the Central Himalaya where the collision produced a flexural basin, the Ganga basin, to the south and, to the north, the indentation of an isostatically supported Tibetan block with possible rheological layering and eastward lateral extrusion.
A porous flow model of flank eruptions on Mt. Etna: second-order perturbation theory
Authors: M. Bonafede  , N. Cenni
Published: June 2021

A porous flow model for magma migration from a deep source within a volcanic edifice is developed. The model is based on the assumption that an isotropic and homogeneous system of fractures allows magma migration from one localized feeding dyke up to the surface of the volcano. The maximum level that magma can reach within the volcano (i.e., the «free surface» of magma, where fluid pressure equals the atmospheric pressure) is reproduced through a second-order perturbation approach to the non-linear equations governing the migration of incompressible fluids through a porous medium. The perturbation parameter is found to depend on the ratio of the volumic discharge rate at the source (m3/s) divided by the product of the hydraulic conductivity of the medium (m1/s) times the square of the source depth. The second-order corrections for the free surface of Mt. Etna are found to be small but not negligible; from the comparison between first-order and second-order free surfaces it appears that the former is higher near the summit, slightly lower at intermediate altitudes and slightly higher far away from the axis of the volcano. Flank eruptions in the southern sector are found to be located in regions where the topography is actually lower than the theoretical free surface of magma. In this sector, modulations in the eruption site density correlate well with even minor differences between free surface and topography. In the northern and western sectors similar good fits are found, while the NE rift and the eastern sector seem to require mechanisms or structures respectively favouring and inhibiting magma migration.
Physical modelling of lava flows
Authors: M. Dragoni
Published: June 2021

Lava flows are not only a fascinating scientific problem, involving many branches of continuum mechanics and thermodynamics, but are natural events having a strong social impact. A reliable evaluation of volcanic hazard connected with lava flows depends on the availability of physical models allowing us to predict the evolution of these phenomena. In this regard, the rheological properties of lavas are of major importance in controlling the dynamics of lava flows. Lava is a multi-phase and chemically heterogeneous system. This entails a characteristic, non-Newtonian behaviour of lava flows, which is emphasized by the fact that the rheological parameters are strongly temperature dependent and are therefore affected by the progressive cooling of lava after effusion. Physical models of lava flows show us the complex relationships between the many quantities governing this process and in the near future they may allow us to predict the dynamics of lava flows and to take effective measures for the reduction of volcanic risk.
Space-frequency analysis and reduction of potential field ambiguity
Authors: M. Fedi  , A. Rapolla
Published: June 2021

Ambiguity of depth estimation of magnetic sources via spectral analysis can be reduced representing its field via a set of space-frequency atoms. This is obtained throughout a continuous wavelet transform using a Morlet analyzing wavelet. In the phase-plane representation even a weak contribution related to deep-seated sources is clearly distinguished with respect a more intense effect of a shallow source, also in the presence of a strong noise. Furthermore, a new concept of local power spectrum allows the depth to both the sources to be correctly interpreted. Neither result can be provided by standard Fourier analysis. Another method is proposed to reduce ambiguity by inversion of potential field data lying along the vertical axis. This method allows a depth resolution to gravity or the magnetic methods and below some conditions helps to reduce their inherent ambiguity. Unlike the case of monopoles, inversion of a vertical profile of gravity data above a cubic source gives correct results for the cube side and density.
Geothermics of the Apenninic subduction
Authors: P. Harabaglia  , F. Mongelli  , G. Zito
Published: June 2021

The subduction of the Adriatic microplate is analysed from a geothermal point of view. In particular four main geodynamic units are distinguished: foreland, foredeep and slab, accretionary prism, and back-arc basin. Each of them is examined from a geothermal point of view and the related open question are discussed. The most relevant results are the determination of the undisturbed geothermal gradient in the aquifer of the foreland; the discovery of a « hot » accretionary prism; and a new model of instantaneous extension of the back-arc basins. The main conclusion is that geothermal data are consistent with a westward dipping subduction that migrated eastward producing a sequence of several episodes at the surface.
The sand grain and the butterfly. Instability in geodesy and geophysics
Authors: H. Moritz
Published: June 2021

The problems of convergence of series in celestial mechanics and of certain series in geodesy (Molodensky's series and spherical harmonics) show similar features, involving a curious instability. This is imaginatively expressed as the « butterfly effect» in chaos theory and the «sand-grain effect» for spherical harmonics. Similarly, the geodetic boundary-value problem (M.S. Molodensky, L. Hormander) and the KAM problem in nonlinear dynamics have a common mathematical structure: a «hard» inverse function problem. Such interrelations are reviewed in the present paper.
Imaging the Mediterranean upper mantle by p- wave travel time tomography
Authors: C. Piromallo  , A. Morelli
Published: June 2021

Travel times of P-waves in the Euro-Mediterranean region show strong and consistent lateral variations, which can be associated to structural heterogeneity in the underlying crust and mantle. We analyze regional and tele- seismic data from the International Seismological Centre data base to construct a three-dimensional velocity model of the upper mantle. We parameterize the model by a 3D grid of nodes -with approximately 50 km spacing -with a linear interpolation law, which constitutes a three-dimensional continuous representation of P-wave velocity. We construct summary travel time residuals between pairs of cells of the Earth's surface, both inside our study area and -with a broader spacing -on the whole globe. We account for lower mantle heterogeneity outside the modeled region by using empirical corrections to teleseismic travel times. The tomo- graphic images show generai agreement with other seismological studies of this area, with apparently higher detail attained in some locations. The signature of past and present lithospheric subduction, connected to Euro- African convergence, is a prominent feature. Active subduction under the Tyrrhenian and Hellenic arcs is clearly imaged as high-velocity bodies spanning the whole upper mantle. A clear variation of the lithospheric structure beneath the Northem and Southern Apennines is observed, with the boundary running in correspon- dence of the Ortona-Roccamonfina tectonic lineament. The western section of the Alps appears to have better developed roots than the eastern, possibly reflecting à difference in past subduction of the Tethyan lithosphere and subsequent continental collision.
Rheology and deep tectonics
Authors: G. Ranalli
Published: June 2021

The distribution of the rheological properties of the lithosphere in space, and their variations in time, have a profound effect on the resulting tectonic deformation. A classical way of estimating these properties makes use of rheological profiles (strength envelopes). Although rheological profiles are based on assumptions and approximations which limit their resolving power, they are an efficient first-order tool for the study of lithosphere rheology, and their application clarifies the dynamics of tectonic processes. Two examples of the interaction of rheology and tectonics are discussed, namely, the post-orogenic relaxation of Moho topography (which is an additional factor to be considered in tectonic inversion), and the strength control on the level of necking in extension (which may lead to apparent local isostasy at passive continental margins and in sedimentary basins).
Magnetic measurements at Naples in the XIX century
Authors: P. Gasparini  , D. Pierattini
Published: June 2021

Measurements of elements of the Earth's magnetic field started in Naples in 1837 by the Astronomical Observatory. Declination and inclination daily averages were regularly published from 1840. In 1839 Macedonio Melloni was called in Naples by the Bourbon Government and asked to found an observatory to carry out regular measurements of geomagnetic elements and meteorological parameters. The observatory was built on Mt. Vesuvius and completed in 1848, but it started to operate only in 1852. Magnetic measurements were carried out in the following years, rather discontinuously, by Luigi Palmieri.
High-resolution aeromagnetic survey of the Teide volcano (Canary Islands): a preliminary analysis
Authors: A. Garcìa  , I. Blanco  , J. M. Torta  , I. Socías
Published: June 2021

To contribute to our understanding of the structure of the Teide volcano, a detailed aeromagnetic survey was carried out covering the area of Las Cañadas caldera and the Teide-Pico Viejo complex. Taking into account the rugged relief of the area (altitude ranges from sea level to almost 4000 m), a terrain correction has been applied. As a first approximation, the topography has been characterized by a uniform magnetization of 5 Am-1 (based on field and laboratory rock magnetic data). Several enhancement techniques have been applied to the residual map (original map minus topographic effect), such as reduction to the pole, pseudogravity integration and upward continuation. In the reduced-to-the-pole map the large positive anomaly that appears centered to the north of Pico Viejo is noteworthy and could be caused by a basaltic intrusion responsible for the last eruptions in this area. Also, a small magnetic low appears over Teide peak, which should be related to slightly-magnetized shallow phonolitic materials. The main tectonic direction of Tenerife, SW-NE, is also clearly reflected on the magnetic anomaly map. The comparison between the pseudogravity and the Bouguer anomaly maps indicates a good correlation between magnetic and gravimetric sources.
Magnetic study of the Furnas caldera (Azores)
Authors: I. Blanco  , A. Garcìa  , J. M. Torta
Published: June 2021

A local ground magnetic study of the Furnas caldera (S. Miguel Island, Azores) has provided new insight into the magnetic structure of this volcano. Analysis of the data comprised removal of the IGRF, reduction to the pole, pseudogravity integration and upward continuation. Also, a spectral method was applied to estimate the depth to the magnetic sources, as well as a 2.5D forward modelling technique. Magnetic properties obtained at the laboratory for some representative sample rocks were considered in the modelling process. The most relevant features are the existence of an important negative anomaly inside the caldera and of an intense positive anomaly to the south of the coast. The former points out a decrease in the magnetization of the caldera filling materials with respect to the surrounding rocks, which could be explained as the result of post-eruption processes such as hydrothermal alteration. This is expected as Furnas has an active hydrothermal system probably related with a magmatic reservoir at high temperature. The positive anomaly suggests the existence of a strongly-magnetized body beneath the south coast.
Crustal structure of the Gulf of Corinth in Central Greece, determined from magnetotelluric soundings
Authors: G. Chouliaras  , V. N. Pham  , D. Boyer  , P. Bernard  , G. N. Stavrakakis
Published: June 2021

The magnetotelluric sounding method at 15 sites was employed to investigate the electrical properties of the crust and upper mantle near the epicentral region of the June 15 1995, Ms = 6.1, destructive earthquake in the Gulf of Corinth, Central Greece. The magnetotelluric results indicate the presence of a conductive zone in the mid-crust at a depth of 9 to 12 km near the seismogenetic region. The existence of this zone with a thickness of around 7 km can be explained by the presence of fluids in a zone of ductile shear. A second electrical discontinuity was also found at a depth of about 28 km and this may well correspond to the Moho below the Gulf of Corinth.
Parametric time series analysis of geoelectrical signals: an application to earthquake forecasting in Southern Italy
Authors: G. Di Bello  , V. Lapenna  , M. Macchiato  , C. Satriano  , C. Serio  , V. Tramutoli
Published: June 2021

An autoregressive model was selected to describe geoelectrical time series. An objective technique was subsequently applied to analyze and discriminate values above (below) an a priorifixed threshold possibly related to seismic events. A complete check of the model and the main guidelines to estimate the occurrence probability of extreme events are reported. A first application of the proposed technique is discussed through the analysis of the experimental data recorded by an automatic station located in Tito, a small town on the Apennine chain in Southern Italy. This region was hit by the November 1980 Irpinia-Basilicata earthquake and it is one of most active areas of the Mediterranean region. After a preliminary filtering procedure to reduce the influence of external parameters (i.e. the meteo-climatic effects), it was demonstrated that the geoelectrical residual time series are well described by means of a second order autoregressive model. Our findings outline a statistical methodology to evaluate the efficiency of electrical seismic precursors.
Observations of rapid-fire event tremor at Lascar volcano, Chile
Authors: G. Asch  , K. Wylegalla  , M. Hellweg  , D. Seidl  , H. Rademacher
Published: June 2021

During the Proyecto de Investigaciòn Sismològica de la Cordillera Occidental (PISCO '94) in the Atacama desert of Northern Chile, a continuously recording broadband seismic station was installed to the NW of the currently active volcano, Lascar. For the month of April, 1994, an additional network of three, short period, three-component stations was deployed around the volcano to help discriminate its seismic signals from other local seismicity. During the deployment, the volcanic activity at Lascar appeared to be limited mainly to the emission of steam and SO2. Tremor from Lascar is a random, «rapid-fire» series of events with a wide range of amplitudes and a quasi-fractal structure. The tremor is generated by an ensemble of independent elementary sources clustered in the volcanic edifice. In the short-term, the excitation of the sources fluctuates strongly, while the long-term power spectrum is very stationary.
A note on two expressions for the spatial power spectrum of the geomagnetic field
Authors: A. De Santis  , D. R. Barraclough
Published: June 2021

The spatial power spectrum of the geomagnetic field is usually assumed to be exponential in the spherical harmonic degree (n). An equally valid assumption, however, is that the spectrum at the surface of the Earth's core has a power-law dependence on n. Some implications of these two assumptions are discussed, noting that, in the first case, a value for the core radius can be derived from the slope of the spectrum and, in the second, that the spectrum for radii greater than the radius of the core is a mixture of the exponential and power-law types.
Palaeoseismologic and geomorphic investigations along the middle portion of the Ovindoli-Pezza Fault (Central Italy)
Authors: G. D' Addezio  , D. Pantosti  , P. M. De Martini
Published: June 2021

his paper presents the results of a detailed investigation performed along the central part of the Ovindoli- Pezza Fault with the aim of improving our understanding of the seismic behaviour of this fault within Central Italy seismogenesis. Results of the trenching investigations we performed across the central part of the fault confirm and strengthen the results obtained at other sites located in the northern part. There is clear evidence that the two most recent surface faulting events occurred within the same interval of time at the different trench sites and thus, at least during these two events, the fault was activated for its entire length. The most recent surface faulting event occurred between 860 and 1300 A.D. Geomorphic and microtopographic investigations indicate that although the trace of the fault shows an important bend, the kinematics of the fault seem to be prevalently normal, consistent with the other seismogenic faults that accommodate the NE-SW extension in this part of the Apennines. The maximum horizontal movement derived using geomorphic methods along the central part of the Ovindoli-Pezza Fault did not exceed 30% of the vertical movement. Slip rate and average recurrence interval were obtained using data both from trenching and Late Pleistocene-Holocene geomorphology. Resulting slip rate ranges between 0.7 and 1.2 mm/year whereas the average recurrence time varies between 1000 and 3000 years.
A single-station prediction model as a source of additional screen-points for PRIME model
Authors: I. Stanislawska  , G. Juchnikowski
Published: June 2021

The aim of this paper is to present a possible improvement to the global map of the f0F2 parameter obtained using statistical or any other model, by adding to it the additional screen points. The proposed method is illustrated by combining the CCIR model and a set of single points data. The comparison of the pure global CCIR model and CCIR model modified by the additional screen-points with measurements for different seasons and different solar activity is presented. The results show significant improvement of the f0F2 map.
Influence of the interplanetary magnetic field on the variability of the mid-latitude F2-layer
Authors: J. Bremer  , J. Lastovicka  , Y. Tulunay
Published: June 2021

The structure of the Interplanetary Magnetic Field (IMF) is responsible for an essential part of the variability of the ionospheric plasma as demonstrated by investigations of the influence of IMF sector boundary crossings as well as of ?Bz-changes (defined from satellite observations) to the maximal electron density of the F2-layer at different stations in mid-latitudes. It could be shown that negative Bz-values cause distinct negative ionospheric effects. Maximal effects were detected at high geomagnetic latitudes (ionospheric response decreases with decreasing latitude), high solar/geomagnetic activity, equinoxes and night-time conditions.
Status of available N(h) model profiles
Authors: L. R. Cander  , B. Zolesi  , P. A. Bradley
Published: June 2021

This paper attempts to highlight progress in the ionospheric electron-density height profile modelling made during the last few years. It consists of a brief review of some major aspects associated with available theoretical, parameterised and empirical N(h) models. Emphasis is placed on pointing out the key issues in the areas that are relevant for the COST 238 PRIME project.