bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of the volcanic plumbing systemof Alicudi (Aeolian Islands - Italy): evidence from fluid and melt inclusionsin quartz xenoliths
Authors: R. Bonelli  , M. L. Frezzotti  , V. Zanon  , A. Peccerillo
Published: June 2021

Quartz-rich xenoliths in lavas (basalts to andesites; 90-30 ka) from Alicudi contain abundant melt and fluid inclusions. Two generations of CO2-rich fluid inclusions are present in quartz-rich xenolith grains: early (Type I) inclusions related to partial melting of the host xenoliths, and late Type II inclusions related to the fluid trapping during xenolith ascent. Homogenisation temperatures of fluid inclusions correspond to two density intervals: 0.93-0.68 g/cm3 (Type I) and 0.47-0.26 g/cm3 (Type II). Early Type I fluid inclusions indicate trapping pressures around 6 kbar, which are representative for the levels of partial melting of crustal rocks and xenolith formation. Late Type II fluid inclusions show lower trapping pressures, between 1.7 kbar and 0.2 kbar, indicative for shallow magma rest and accumulation during ascent to the surface. Data suggest the presence of two magma reservoirs: the first is located at lower crustal depths (about 24 km), site of fractional crystallization, mixing with source derived magma, and various degrees of crustal assimilation. The second magma reservoir is located at shallow crustal depths (about 6 km), the site where magma rested for a short time before erupting.
An analysis of the first-arrival times picked on the DSS and wide-angle seismic section recorded in Italy since 1968
Authors: L. De Luca  , R. De Franco  , G. Biella  , A. Corsi  , R. Tondi
Published: June 2021

We performed an analysis of refraction data recorded in Italy since 1968 in the frame of the numerous deep seismic sounding and wide-angle reflection/refraction projects. The aims of this study are to construct a parametric database including the recording geometric information relative to each profile, the phase pickings and the results of some kinematic analyses performed on the data, and to define a reference 1D velocity model for the Italian territory from all the available refraction data. As concerns the first goal, for each seismic section we picked the P-wave first-arrival-times, evaluated the uncertainties of the arrival-times pickings and determined from each travel time-offset curve the 1D velocity model. The study was performed on 419 seismic sections. Picking was carried out manually by an algorithm which includes the computation of three picking functions and the picking- error estimation. For each of the travel time-offset curves a 1D velocity model has been calculated. Actually, the 1D velocity-depth functions were estimated in three different ways which assume: a constant velocitygradient model, a varying velocity-gradient model and a layered model. As regards the second objective of this work, a mean 1D velocity model for the Italian crust was defined and compared with those used for earthquake hypocentre locations and seismic tomographic studies by different institutions operating in the Italian area, to assess the significance of the model obtained. This model can be used in future works as input for a next joint tomographic inversion of active and passive seismic data.
Information on subsoil geological structure in the city of Catania (Eastern Sicily) from microtremor measurements
Authors: E. Giampiccolo  , S. Gresta  , M. Mucciarelli  , G. De Guidi  , M. R. Gallipoli
Published: June 2021

Nakamuras technique, or the H/V spectral ratio method, has been applied to microtremor measurements carried out in the urban area of Catania (Eastern Sicily) to obtain information on the geological structure of some sites,and to make a hypothesis on their seismic response. In general, sites located on soft soils or anthropic debris fillings have shown greater amplification at high frequencies (above 1 Hz). However, a strong lateral variation was observed in the frequency band, thus a denser grid of measurement points is necessary for a precise mapping of the resonant frequencies. In the low frequency range, between 0.1 and 1 Hz, a common peak around 0.2 Hz was observed. The fundamental resonant frequency inferred from the main peak in the H/V spectrum has been used to calculate the depth of the interface between the clays and the main reflector on the basis of the shear-wave velocity: it has been estimated as about 700 m.
Broadband waveforms and site effects at a borehole seismometer in the Po alluvial basin (Italy)
Authors: M. Cocco  , F. Ardizzoni  , R. M. Azzara  , L. Dall'Olio  , A. Delladio  , M. Di Bona  , L. Malagnini  , L. Margheriti  , A. Nardi
Published: June 2021

Broadband seismograms recorded at a borehole three-component (high dynamic range) seismic station in the Po Valley (Northern Italy) were analyzed to study the velocity structure of the shallow sedimentary layers as well as the local site effects in soft sediments. The broadband borehole seismometer was installed at a depth of 135 m just below the quaternary basement, while a second digital broadband seismometer was installed in the same site at the Earth surface. The velocity structure in the shallower layers was determined both by means of cross-hole and up-hole measurements and by inverting seismic data recorded during a seismic exploration experiment.Velocity discontinuities are quite well related to the stratigraphy of the site. We are interested to record local earthquakes as well as regional and teleseismic events. The analyzed data set includes local, regional and teleseismic events, most of which were recorded during the seismic sequence that started on October 15, 1996, near Reggio Emilia 80 km away from the borehole site. The orientation of the borehole sensor is determined using the recordings of a teleseismic event and of some local earthquakes. The noise reduction for the borehole sensor is 2 decades in power spectral density at frequencies larger than 1.0 Hz. We studied the site amplification of the shallow alluvial layers by applying the spectral ratio method. We analyzed the spectral ratios of noise recorded by the surface and borehole seismometers as well as those from local earthquakes. We compared these observations with a theoretical model for the site response computed by the Haskell-Thomson method.
Some preliminary results of a worldwide seismicity estimation: a case study of seismic hazard evaluation in South America
Authors: T. M. Tsapanos  , C. V. Christova
Published: June 2021

Global data have been widely used for seismicity and seismic hazard assessment by seismologists. In the present study we evaluate worldwide seismicity in terms of maps of maximum observed magnitude (Mmax), seismic moment (M 0 ) and seismic moment rate (M 0S). The data set used consists of a complete and homogeneous global catalogue of shallow (h £ 60 km) earthquakes of magnitude MS ³ 5.5 for the time period 1894-1992. In order to construct maps of seismicity and seismic hazard the parameters a and b derived from the magnitude-frequency relationship were estimated by both: a) the least squares, and b) the maximum likelihood, methods. The values of a and b were determined considering circles centered at each grid point 1° (of a mesh 1° ´1°) and of varying radius, which starts from 30 km and moves with a step of 10 km. Only a and b values which fulfill some predefined conditions were considered in the further procedure for evaluating the seismic hazard maps. The obtained worldwide M max distribution in general delineates the contours of the plate boundaries. The highest values of M max observed are along the circum-Pacific belt and in the Himalayan area. The subduction plate boundaries are characterized by the largest amount of M 0 , while areas of continental collision are next. The highest values of seismic moment rate (per 1 year and per equal area of 10 000 km 2) are found in the Southern Himalayas. The western coasts of U.S.A., Northwestern Canada and Alaska, the Indian Ocean and the eastern rift of Africa are characterized by high values of M 0 , while most of the Pacific subduction zones have lower values of seismic moment rate. Finally we analyzed the seismic hazard in South America comparing the predicted by the NUVEL1 model convergence slip rate between Nazca and South America plates with the average slip rate due to earthquakes. This consideration allows for distinguishing between zones of high and low coupling along the studied convergence plate boundary.
Satellite magnetic anomalies of the Antarctic crust
Authors: R. R. B. von Frese  , H.R. Kim  , L. Tan  , J. W. Kim  , P. T. Taylor  , M. E. Purucker  , D. E. Alsdorf  , C. A. Raymond
Published: June 2021

Spatially and temporally static crustal magnetic anomalies are contaminated by static core field effects above spherical harmonic degree 12 and dynamic, large-amplitude external fields. To extract crustal magnetic anomalies from the measurements of NASA's Magsat mission, we separate crustal signals from both core and external field effects. In particular, we define Magsat anomalies relative to the degree 11 field and use spectral correlation theory to reduce them for external field effects. We obtain a model of Antarctic crustal thickness by comparing the region's terrain gravity effects to free-air gravity anomalies derived from the Earth Gravity Model 1996 (EGM96). To separate core and crustal magnetic effects, we obtain the pseudo-magnetic effect of the crustal thickness variations from their gravity effect via Poisson's theorem for correlative potentials. We compare the pseudo-magnetic effect of the crustal thickness variations to field differences between degrees 11 and 13 by spectral correlation analysis. We thus identify and remove possible residual core field effects in the Magsat anomalies relative to the degree 11 core field. The resultant anomalies reflect possible Antarctic contrasts due both to crustal thickness and intracrustal variations of magnetization. In addition, they provide important constraints on the geologic interpretation of aeromagnetic survey data, such as are available for the Weddell Province. These crustal anomalies also may be used to correct for long wavelength errors in regional compilations of near-surface magnetic survey data. However, the validity of these applications is limited by the poor quality of the Antarctic Magsat data that were obtained during austral Summer and Fall when south polar external field activity was maximum. Hence an important test and supplement for the Antarctic crustal Magsat anomaly map will be provided by the data from the recently launched Ørsted mission, which will yield coverage over austral Winter and Spring periods when external field activity is minimal.
The tectonic source of the 1755 Lisbon earthquake and tsunami
Authors: N. Zitellini  , F. Chierici  , R. Sartori  , L. Torelli
Published: June 2021

The SW continental margin of Iberia is affected by several tectonic structures of Cenozoic to Recent age, gen-erated by the dynamics of the Iberia-Africa plate margin. This activity is testified by diffuse seismicity along the eastern portion of the Azores-Gibraltar line. The most important active structure, detected during a reflection seismic survey in 1992, is a thrust-fault, some 50 km long and with dip-slip throw of more than 1 km, located offshore Cabo de S. Vincente. A relocation of historical earthquakes in the area shows that this structure lies very close to the epicentre of the catastrophic 1755 Lisbon earthquake and that it should be the generator of the event. This submarine structure can now be studied for modelization of tsunamis and consequent risk mitigation.
First GPS measurements across the Central-Western Mediterranean area
Authors: M. Anzidei  , P. Baldi  , G. Casula  , A. Galvani  , S. Kahlouche  , A. Pesci  , F. Riguzzi  , N. Saadi  , S. Touman  , A. Zanutta
Published: June 2021

This paper concerns the displacement field of the central-western part of the Mediterranean basin estimated by the analysis of three repeated GPS surveys (1995, 1996 and 1997) consisting of 8 sites of a network. This network includes for the first time the stations of Algiers and Arzew, located in Northern Algeria, an area not yet investigated by regional GPS surveys. Lampedusa station is located in the Sicily Straits rifting area while the other five stations of Cagliari, Wettzell, Madrid, Matera and Noto belong to the IGS permanent tracking network. The statistical analysis of 1995, 1996 and 1997 data show significant displacements at five stations. The displacement vectors of the African sites show a convergence between the African and the Eurasian plates at a rate of 0.8 ± 0.4 cm within a two year time span. A comparison between the displacements estimated in the present work and the ITRF96 determinations for the five permanent stations allow us to evaluate the motion of Lampedusa, Algiers and Arzew in the IERS Terrestrial Reference System.
The external magnetic sources over the polar caps - Feasible modelling unrealistic expectations
Authors: G. P. Gregori
Published: June 2021

No average status can be defined for the sources of the external magnetic field over the polar caps, no index can provide with any such model, the observation of no single quantity or parameter can give the ultimate solution. Rather, every case history has to be considered independently. It is possible, however, to approach the problem from an interdisciplinary viewpoint, and to attempt to make an instant modelling of the electric currents that flow in the ionosphere and magnetosphere above the area of aeromagnetic prospecting. A few relevant previous such examples are discussed (such as Akasofu's inference on magnetospheric substorms derived by means of polar auroras, or the presently unfashionable Svalgaard vortex by means of the observed geomagnetic field and dealing with the pattern of the electric field within the magnetosphere, or the Sun-aligned auroral arcs inside the oval that are monitored by satellite, or, perhaps, the luminosity curve of polar auroras). It appears likely that some substantial achievement will be attained altogether with the progress in the understanding of the general pattern of a few typical recurrent configurations over the polar caps, in terms of a multidisciplinary input from different observations, either by ground-based observatories, or by space platforms.
Mapping and interpretation of satellite magnetic anomalies from POGO data over the Antarctic region
Authors: M. E. Purucker  , R. R. B. von Frese  , P. T. Taylor
Published: June 2021

A satellite magnetic anomaly map made using the POGO magnetic field data is compared to three maps made using Magsat data. A total of 14 anomalies with magnitudes greater than 3 nT can be identified in all four of the maps poleward of 60°S latitude. Forward models of the Antarctic continental and oceanic lithosphere are produced which use magnetic crustal thickness based on seismic and heat flow data, and which also use the distribution of the Cretaceous Quiet Zone from marine geophysics. These simple models can explain significant parts of eight of the 14 identified anomalies. The remaining anomalies may be caused by lateral variations of magnetization, inadequate models of the magnetic crustal thickness, or remanent magnetizations in directions other than the present field. In addition, contamination of the magnetic anomaly maps by fields of time-varying external origin (and their corresponding internal parts) is still a significant problem in the Antarctic region.
Tornillo seismic events at Galeras volcano, Colombia: a summary and new information from broadband three-component measurements
Authors: D. M. Gómez M.  , R. A. Torres C.  , D. Seidl  , M. Hellweg  , H. Rademacher
Published: June 2021

Long-duration events have been recorded at several active, andesitic volcanoes. Their main characteristics are a single, sharp frequency peak, and an exceptionally long coda. Because their seismograms resemble a screw, these signals are called "tornillos" in Colombia. These events have been recorded during different stages of volcanic activity at various volcanoes worldwide. Tornillos have occurred for example, as a short-term precursor to eruptions at Galeras volcano, Colombia (1992-1993); and at Asama volcano, Japan, (1983). At Tokachi volcano, Japan, they were recorded after an eruption (1989). The Tornillo's dominant frequency appears to be related to the time of occurrence during an eruption cycle. It is independent of epicentral distance, azimuth, travel time, and lapse time, indicating that it is a source characteristic. Damping coefficients for the tornillo's coda range between 0.002 and 0.02. In contrast, damping coefficients for normal long-period events lies between 0.010 and 0.025 and for volcano-tectonic events between 0.010 and 0.040. In March 1996, the Galeras seismic network, which consists of short period, single-component seismometers, was augmented with a broadband, three-component station. This station, installed 1.5 km south of Galeras active cone, recorded a series of six tornillos. Narrowband and broadband tornillo records have similar characteristics in the time and frequency domains.
Maximum entropy estimation of values at Mt. Etna: comparison with conventional least squares and maximum likelihood results and correlation with volcanic activity
Authors: C. Centamore  , G. Patanè  , T. Tuvè
Published: June 2021

The variations of the b coefficient in the frequency-magnitude relationship for earthquakes which occurred at Mt. Etna from 01/01/90 to 31/12/92 are analyzed; the completeness threshold for our earthquakes catalogue is M = 2.30. The b values calculated using the Maximum Entropy Principle (MEP) are compared to those obtained by conventional methods of Least Squares (LS) and Maximum Likelihood (ML). All the differences among the b values computed using these methods, and the reasons for these differences, are discussed and examined. In particular, our results show that the b values obtained by MEP are lower than the others calculated using LS and ML; this implies that, on the average, LS and ML underestimate the seismic hazard at Mt. Etna. Moreover, temporal variations of bMEP are more evident than the corresponding ones of bLS and bML; indeed, in some cases the trend of bMEP variation is opposite those of bLS and bML. A significant correlation between temporal variations of the volcanic activity and the b values is evident only if the MEP is used; this means that, if b temporal variations are analyzed in order to detect changes in the volcano dynamics and predict the eruptions, the maximum entropy approach should be preferred. Finally, the observed pattern of bMEP temporal variations with regard to the changes in the volcanic activity is consistent with the hypothesis of a compressive stress field acting on Mt. Etna.
The scientific life of Luigi Palmieri 100th Anniversary commemoration(21/04/1807-09/09/1896)
Authors: L. Casertano
Published: June 2021

I present here a commemoration of the scientific life of Luigi Palmieri, II Director of the Osservatorio Vesuviano. His research on both volcanic and tectonic phenomena was supported by his development of the first electromagnetic seismograph, which he also built in a "portable" version. He had the intuition to relate seismic activity to eruptive episodes, and, in this sense, he was the first scientist to imagine the eruption forecast in a modern way.
In search of evidence of deep fluid discharges and pore pressure evolution in the crust to explain the seismicity style of the Umbria-Marche 1997-1998 seismic sequence (Central Italy)
Authors: F. Quattrocchi
Published: June 2021

Starting soon after the first main-shocks of the long seismic sequence which has occurred along the Umbria-Marche boundary since September 1997, fluid geochemistry surveying was accomplished (around 200 samples) over the epicentre area as a whole, collecting information on hydrological variations too. The collected experimental data allowed to discuss the spatial and temporal evolution of the circulating fluids, either in the chemistry or in the dynamic paths, during the different stages of the seismic sequence. All the geo-structural, seismological and fluid geochemistry information gathered in this sector of the Central Apennines are discussed together in an attempt to speculate about the possible role and evolution of pore-pressure at depth up to surface within the seismogenic process recalling the "Fault Valve Activity Model", the "Coseismic Strain Model", the "frictional heating-frictional stress coupling model" and the "Dilatancy Model". This overview may also explain the geochemical and hydrological experimentally observed anomalies, in occurrence of the seismic sequence. The seismic style of the long sequence is revised in terms of pore-pressure regime down to seismogenic depth (2-10 km), within the poly-phase Evaporite Triassic Basement (ETB) and the Paleozoic Crystalline Basement (PCB), corresponding to the horizons of transient dehydration reactions: process triggered and enhanced during the seismogenic process, involving further fluid overpressure, and consequently further seismicity (chain effect). All the recalled processes and models may explain fluid remobilization and over-pressuring in the upper crust starting soon after the main-shocks, along relict low angle planes (close Apennine and anti-Apennine fault segments), rendering the Umbria-Marche boundary a "transiently weakened frictional instability zone", for a period spanning more than one year.
Temporal characteristics of some aftershock sequences in Bulgaria
Authors: S. Simeonova  , D. Solakov
Published: June 2021

We apply statistical analysis to study the temporal distribution of aftershocks in aftershock sequences of five earthquakes which occurred in Bulgaria. We use the maximum likelihood method to estimate the parameters of the modified Omori formula for aftershock sequences which is directly based on a time series. We find that: the maximum likelihood estimates of the parameter p show a regional variation, with lower values of the decay rate in North Bulgaria; the modified Omori formula provides an appropriate representation of temporal variation of the aftershock activity in North Bulgaria; the aftershock sequences in South Bulgaria are best modeled by the combination of an ordinary aftershock sequence with secondary aftershock activity. A plot of the cumulative number of events versus the frequency-linearized time t clearly demonstrates a transition from aftershock to foreshock activity prior to the second 1986 Strazhitsa (North Bulgaria) earthquake.
Seismic hazard map of the western hemisphere
Authors: K. M. Shedlock  , J. G. Tanner
Published: June 2021

Vulnerability to natural disasters increases with urbanization and development of associated support systems (reservoirs, power plants, etc.). Catastrophic earthquakes account for 60% of worldwide casualties associated with natural disasters. Economic damage from earthquakes is increasing, even in technologically advanced countries with some level of seismic zonation, as shown by the 1989 Loma Prieta, CA ($ 6 billion), 1994 Northridge, CA ($ 25 billion), and 1995 Kobe, Japan (> $ 100 billion) earthquakes. The growth of megacities in seismically active regions around the world often includes the construction of seismically unsafe buildings and infrastructures, due to an insufficient knowledge of existing seismic hazard. Minimization of the loss of life, property damage, and social and economic disruption due to earthquakes depends on reliable estimates of seismic hazard. National, state, and local governments, decision makers, engineers, planners, emergency response organizations, builders, universities, and the general public require seismic hazard estimates for land use planning, improved building design and construction (including adoption of building construction codes), emergency response preparedness plans, economic forecasts, housing and employment decisions, and many more types of risk mitigation. The seismic hazard map of the Americas is the concatenation of various national and regional maps, involving a suite of approaches. The combined maps and documentation provide a useful global seismic hazard framework and serve as a resource for any national or regional agency for further detailed studies applicable to their needs. This seismic hazard map depicts Peak Ground Acceleration (PGA) with a 10% chance of exceedance in 50 years for the western hemisphere. PGA, a short-period ground motion parameter that is proportional to force, is the most commonly mapped ground motion parameter because current building codes that include seismic provisions specify the horizontal force a building should be able to withstand during an earthquake. This seismic hazard map of the Americas depicts the likely level of short-period ground motion from earthquakes in a fifty-year window. Short-period ground motions effect short-period structures (e.g., one-to-two story buildings). The largest seismic hazard values in the western hemisphere generally occur in areas that have been, or are likely to be, the sites of the largest plate boundary earthquakes. Although the largest earthquakes ever recorded are the 1960 Chile and 1964 Alaska subduction zone earthquakes, the largest seismic hazard (PGA) value in the Americas is in Southern California (U.S.), along the San Andreas fault.
Intensity assignments from historical earthquake data: issues of certainty and quality
Authors: R. M. W. Musson
Published: June 2021

The use of macroseismic data in assessing parameters for historical earthquakes for use in seismic hazard assessment has thrown more attention on the way in which these data are treated. The processes involved in selecting which macroseismic data from a historical earthquake survive to the present day can be modelled as a series of filters, most of which are outside the control of the seismologist/historian, and which cause distortion in the resulting picture of the earthquake. The ways in which the data become distorted should be taken into account when interpreting the data as intensity values. One can usefully discriminate between the certainty of an intensity assignment (how well the data fits the scale) and the quality of an intensity assignment (how well one can trust that the value is a true reflection of what really happened). The expression of uncertainty is usually in the form of ranged intensity values; the expression of quality requires an extra symbol or rating of some sort. A system is presented for three types of quality problems: reliability of intensity assessment, locational certainty or uncertainty, and veracity of the original data. Each of these is treated as a binary variable, giving a final quality code ranging from 0 (best) to 7 (worst). This single integer quality code preserves three types of information which can then be expanded as required by computer programs designed to handle macroseismic data.
A time domain finite-difference technique for oblique incidence of antiplane waves in heterogeneous dissipative media
Authors: A. Caserta
Published: June 2021

This paper deals with the antiplane wave propagation in a 2D heterogeneous dissipative medium with complex layer interfaces and irregular topography. The initial boundary value problem which represents the viscoelastic dynamics driving 2D antiplane wave propagation is formulated. The discretization scheme is based on the finite-difference technique. Our approach presents some innovative features. First, the introduction of the forcing term into the equation of motion offers the advantage of an easier handling of different inputs such as general functions of spatial coordinates and time. Second, in the case of a straight-line source, the symmetry of the incident plane wave allows us to solve the problem of oblique incidence simply by rotating the 2D model. This artifice reduces the oblique incidence to the vertical one. Third, the conventional rheological model of the generalized Maxwell body has been extended to include the stress-free boundary condition. For this reason we solve explicitly the stress-free boundary condition, not following the most popular technique called vacuum formalism. Finally, our numerical code has been constructed to model the seismic response of complex geological structures: real geological interfaces are automatically digitized and easily introduced in the input model. Three numerical applications are discussed. To validate our numerical model, the first test compares the results of our code with others shown in the literature. The second application rotates the input model to simulate the oblique incidence. The third one deals with a real high-complexity 2D geological structure.
My first fifty years in ionospheric research
Authors: P. Dominici
Published: June 2021

The author, as an active witness, recalls what he has seen of the development of ionospheric physics during the last 50 years.
The dependence of ionospheric characteristics on the state of the solar-cycle
Authors: S. S. Kouris
Published: June 2021

A review on the solar-cycle dependence of the monthly median critical frequencies of the different ionospheric layers is attempted. Some of the existing questions are emphasized and the differing viewpoints are reported. Moreover, the correlations between daily values of the critical frequencies and solar activity indices are briefly considered and compared to those for monthly median values.
Ionospheric electron content: the European perspective
Authors: R. Leitinger
Published: June 2021

The electron content of the ionosphere is an important quantity which indicates overall ionization. It is measured by means of propagation effects on radio signals which penetrate the ionosphere. In Europe relevant investigations started after the launch of the first artificial satellites. Soon the necessity arose to organize international cooperation: the regional as well as the global geographical distribution of ionization parameters is important knowledge for any meaningful geophysical interpretation of ionization parameters. Despite the fact that international scientific Unions and Committees existed and had proven their usefulness and potential, private initiatives were taken to organize cooperation in the field of research based on transionospheric propagation effects. Only in 1971 three international groups joined together to form the "Beacon Satellite Group"as a "Working Party" of COSPAR. The "Beacon Satellite Group" still exists but is now a Working Group of URSI, the International Union for Radio Science. This contribution tries to summarize the European perspective with special emphasis on the long standing cooperation between the Istituto di Ricerca sulle Onde Elettromagnetiche (IROE) at Firenze and the Institut für Meteorologie und Geophysik of the University of Graz. Examples are given of important results.
Seismogeochemical algorithms for earthquake prediction: an overview
Authors: G. Etiope  , M. Calcara  , F. Quattrocchi
Published: June 2021

While the literature abounds with case histories related to geochemical precursory phenomena, only a few studies on definite seismogeochemical algorithms have been published so far. Currently, available theoretical algorithms are based on obsolete views of fluid migration processes that do not take into account the possibility of rapid and long-distance gas migration from the focal zone. Empirical algorithms are often based on a limited number of data and need validation for several geostructural environments. The algorithms of Sardarov (1981) and Rikitake (1987), for Rn and other geochemical elements, suggest that a definite relationship exists between geochemical parameters and seismic events. Their validation must be based on the verification of independence (maintained by the former author) or dependence (maintained by the latter) of the precursor time on the seismic data.
Paleomagnetic and Anisotropy of Magnetic Susceptibility (AMS) analyses of the Plio-Pleistocene extensional Todi basin, Central Italy
Authors: L. Alfonsi
Published: June 2021

In the last few years paleomagnetic investigations within the Apennine chain have revealed that the area is characterized by a complex pattern of deformation, not linkable to a simple and homogeneous process. In order to estimate the amount, sense and timing of vertical axis rotations within the Central Apennines, Neogene continental basins have been investigated for paleomagnetic studies. The paleomagnetic results obtained in the Plio-Pleistocene Todi basin showed that the Upper Pliocene-Lower Pleistocene evolution, associated with major dip-slip tectonics, has not involved vertical axis rotation since that time. The Anisotropy of Magnetic Susceptibility analysis (AMS), carried out on the same samples treated for paleomagnetic determination, revealed the presence of two groups of specimens characterized by different magnetic lineation directions. One direction trends NE-SW and is parallel to the orientation of the regional extension stress typical of the area. This direction is observed throughout the northern basin. The other, restricted to the southern basin, trends N-S and shows no links with the tectonic, hydrological-sedimentary conditions of the area. The results of the AMS analysis will be presented and discussed in the light of the rock magnetic results and the tectonic framework of the area.
Crustal and deep seismicity in Italy (30 years after)
Authors: A. Amato  , C. Chiarabba  , G. Selvaggi
Published: June 2021

The first modern studies of seismicity in Italy date back to the late 60's and early 70's. Although with a sparse seismic network available and only a few telemetered short-period stations, significant studies were carried out that outlined the main features of Italian seismicity (see, e.g., Boschi et al., 1969). Among these studies, one of the most important achievements was the reconnaissance of a Wadati-Benioff zone in Southern Tyrrhenian, described for the first time in detail in the papers of Caputo et al.(1970, 1973). Today, after three decades of more and more detailed seismological monitoring of the Italian region and tens of thousands earthquakes located since then, the knowledge of the earthquake generation processes in our country is much improved, although some of the conclusions reached in these early papers still hold. These improvements were made possible by the efforts of many institutions and seismologists who have been working hard to bring seismological research in Italy to standards of absolute quality, under the pivoting role of the Istituto Nazionale di Geofisica (ING). From the relocation of about 30000 crustal earthquakes and detailed studies on intermediate and deep shocks carried out in the last few years, we show that seismic release in peninsular Italy is only weakly related to the Africa-Eurasia convergence, but rather is best explained by the existence of two separate subduction/collision arcs (Northern Apennines and Southern Apennines-Calabria-Sicily). The width of the deforming belt running along peninsular Italy is 30 to 60 km, it is broader in the north than in the south, and the two arcs are separated by a region of more distributed deformation and stress rotations in the Central Apennines. Along the belt, the reconnaissance of regions of continuous and weak release of seismic energy, adjacent to fault areas which are currently «locked» (and therefore are the best candidates for future earthquakes) is another recent important achievement of the prolonged detailed seismic monitoring of our territory, which will provide in the future more and more precise indications of where earthquakes will strike. In addition, the accurate location of hundreds of intermediate and deep earthquakes beneath the two arcs has recently provided (together with seismic tomography results) new hints on the tectonic setting of Italy and its evolution over time, on the relations between deep processes and crustal stress, and ultimately on the mechanisms of earthquake generation in our country.
Seismic pulse propagation with constant Q and stable probability distributions
Authors: F. Mainardi  , M. Tomirotti
Published: June 2021

The one-dimensional propagation of seismic waves with constant Q is shown to be governed by an evolution equation of fractional order in time, which interpolates the heat equation and the wave equation. The fundamental solutions for the Cauchy and Signalling problems are expressed in terms of entire functions (of Wright type) in the similarity variable and their behaviours turn out to be intermediate between those for the limiting cases of a perfectly viscous fluid and a perfectly elastic solid. In view of the small dissipation exhibited by the seismic pulses, the nearly elastic limit is considered. Furthermore, the fundamental solutions for the Cauchy and Signalling problems are shown to be related to stable probability distributions with an index of stability determined by the order of the fractional time derivative in the evolution equation.
Isochronal maps at Mt. Etna volcano (Italy): a simple and reliable tool for investigating large-scale heterogeneities
Authors: G. Patanè  , C. Centamore  , S. La Delfa
Published: June 2021

This paper analyses twelve etnean earthquakes which occurred at various depths and recorded at least by eleven stations. The seismic stations span a wide part of the volcanic edifice; therefore each set of direct P-wave arrival times at these stations can be considered appropriate for tracing isochronal curves. Using this simple methodology and the results obtained by previous studies the authors make a reconstruction of the geometry of the bodies inside the crust beneath Mt. Etna. These bodies are interpreted as a set of cooled magmatic masses, delimited by low-velocity discontinuities which can be considered, at present, the major feeding systems of the volcano.
Seismic vulnerability assessment of masonry buildings in a region of moderate seismicity
Authors: M. Riuscetti  , R. Carniel  , C. Cecotti
Published: June 2021

To assess the seismic vulnerability of masonry buildings is largely matter of personal feeling and experience especially when dealing with old houses made of heterogeneous materials and without a plan. One way to predict their resistance to earthquake forces is the experience on models put on a shaking table. Costs and scaling problems, particularly severe for stone walls, are limiting factors in the extensive use of this technique. After the Friuli 1976 earthquake, the regional government arranged a detailed survey of damages suffered by buildings to be repaired. These data organised in the FRED (Friuli Earthquake Database) make it possible to compare, on a statistically significant basis, the a priori vulnerability with the effective damage. One further step towards the practical use of the results is given by characterising the relevant features of the buildings with the same parameters which can be found in the General Census periodically produced by the Italian Statistical Institute (ISTAT).
Minimum 1D velocity models in Central and Southern Italy: a contribution to better constrain hypocentral determinations
Authors: C. Chiarabba  , A. Frepoli
Published: June 2021

We computed one-dimensional ( I D) velocity models and station corrections for Centrai and Southern Italy, in- verting re-picked P-wave alTival times recorded by the Istituto Nazionale di Geofisica seismic network. The re-picked data yield resolved P-wave velocity results and proved to be more suited than bulletin data for de- tailed tomographic studies. Using the improved velocity models, we relocated the most significant earthquakes which occurt.ed in the Apennines in the past 7 years, achieving constrained hypocentral determinations for events within most of the Apenninic belt. The interpretation of the obtained lD velocity models allows us to infer interesting features on the deep structure of the Apennines. Smooth velocity gradients with depth and low P-wave velocities are ob,'ierved beneath the Apennines. We believe that our results are effective to constrain hypocentral locations in Italy and may represent a first step towards more detailed seismotectonic analyses.
Active tectonics of the Eastern Mediterranean region: deduced from GPS, neotectonic and seismicity data
Authors: A. Barka  , R. Reilinger
Published: June 2021

This paper reviews the main tectonic features of the Eastern Mediterranean region combining the recent information obtained from GPS measurements, seismicity and neotectonic studies. GPS measurements reveal that the Arabian plate moves northward with respect to Eurasia at a rate of 23 ± 1 mm/yr, 10 mm/yr of this rate is taken up by shortening in the Caucasus. The internal deformation in Eastern Anatolia by conjugate strike-slip faulting and E-W trending thrusts, including the Bitlis frontal thrust, accommodates approximately a 15 mm/yr slip rate. The Northeast Anatolian fault, which extends from the Erzincan basin to Caucasus accommodates about 8 ± 5 mm/yr of left-lateral motion. The neotectonic fault pattern in Eastern Anatolia suggests that the NE Anatolian block moves in an E-ENE direction towards the South Caspian Sea. According to the same data, the Anatolian-Aegean block is undergoing a counter-clockwise rotation. However, from the residuals it appears that this solution can only be taken as a preliminary approximation. The Eulerian rotation pole indicates that slip rate along the North Anatolian fault is about 26 ± 3 mm/yr. This value is 10 mm/yr higher than slip rates obtained from geological data and historical earthquake records and it includes westward drift of the Pontides of a few millimetres/year or more. GPS measurements reveal that the East Anatolian fault accommodates an 11 ± 1 mm/yr relative motion. GPS data suggest that Central Anatolia behaves as a rigid block, but from neotectonic studies, it clearly appears that it is sliced by a number of conjugate strike-slip faults. The Isparta Angle area might be considered a major obstacle for the westward motion of the Anatolian block (Central and Eastern Anatolia). The western flank of this geological structure, the Fethiye-Burdur fault zone appears to be a major boundary with a slip rate of 15-20 mm/yr. The Western Anatolian grabens take up a total of 15 mm/yr NE-SW extension. The fact that motions in Central Anatolia relative to Eurasia, are 15-20 mm/yr while in Western Anatolia and Aegean Sea they are 30-40 mm/yr could suggest that Western Anatolia decouples from Central Anatolia and the Isparta Angle by the Fethiye-Burdur fault zone and Eski?ehir fault. It is also hypothesized that the differentiation of tectonic styles and velocities in the Anatolian-Aegean block are related to differences between the slabs lying under the Cyprus and Hellenic arcs.
Plate convergence, crustal delamination, extrusion tectonics and minimization of shortening work as main controlling factors of the recent Mediterranean deformation pattern
Authors: E. Mantovani  , D. Albarello  , C. Tamburelli  , D. Babbucci  , M. Viti
Published: June 2021

It is argued that the time-space distribution of major post middle Miocene deformation events in the Central-Eastern Mediterranean region, deduced from the relevant literature, can be coherently explained as a consequence of the convergence between the Africa/Arabia and Eurasia blocks. This plate convergence has mainly been accommodated by the consumption of the thinnest parts of the Northern African (Ionian and Levantine basins) and peri-Adriatic margins. During each evolutionary phase the space distribution of trench zones is controlled by the basic physical requirement of minimizing the work of horizontal forces, induced by plate convergence, against the resisting forces, i.e., the cohesion of the upper brittle crustal layer and the buoyancy forces at the consuming boundaries. The significant changes of tectonic styles which determined the transition from one phase to the next, like those which occurred around the Messinian and the late Pliocene-early Pleistocene, were determined by the suture of consuming boundaries. When such an event occurs, the system must activate alternative consuming processes to accommodate the convergence of the major confining blocks. The observed deformations in the study area suggest that this tectonic reorganization mostly developed by the lateral extrusion of crustal wedges away from the sutured borders. This mechanism allowed the translation of maximum horizontal stresses from the locked collisional fronts to the zones where consumable lithosphere was still present, in order to activate the next consuming processes. The extensional episodes which led to the formation of basins and troughs in the Tyrrhenian and Aegean zones are interpreted as secondary effects of the outward escape of crustal wedges, like those which occurred in response to longitudinal compressional regimes in the Apennines and Aegean regions.
Tectonic process monitoring by variations of the geomagnetic field absolute intensity
Authors: D. B. Avdeev  , A. V. Kuvshinov  , O. V. Pankratov
Published: June 2021

We propose a novel technique for tectonic process monitoring. The technique includes: measurements of absolute intensity variations, at network sites, synchronously with measurements of horizontal geomagnetic field variations at a reference site; spectral analysis of measured time series and construction non-conventional transfer functions and interpretation of the transfer functions constructed in order to detect or/and to forecast the tectonic processes. Using numerical modelling we show the sensitivity of transfer functions obtained with respect to the temporal changes in the Earth's resistivity associated with tectonic processes. We also demonstrate that the components of the geomagnetic field are reconstructed in terms of spatial distribution of absolute intensity variations.
Magnetotelluric and deep geomagnetic induction data in the Bohemian Massif
Authors: V. Cerv  , J. Pek  , O. Praus  , A. Zaja  , A. Manzella
Published: June 2021

Manifestations of the increased tectonic activity (seismic activity, remnants of Tertiary volcanism and riftogenesis) in the Bohemian Massif are bound to geologically extremely complicated regions with a system of discordant structures and a mosaic of fault zones. The presented results concern the deep geoelectrical features of the tectonic transition between the Saxothuringian and Moldanubian tectonoblocks on the territory of West Bohemia, in close vicinity to the German deep drilling experiment KTB (Kontinentale Tiefbohrung der BRD). Three first-order tectonic lines demarcate the region under study í the Litomerice deep fault to the north, the West Bohemian deep fault zone to the east, and the Central Bohemian fault to the south. As a whole, the region involved is characterized by a regionally increased seismic activity with the most active zone just beyond the northern end-point of the profile investigated. The contribution can be considered an example of possible interpretation of MT/MV/AMT data in geologically extremely complicated conditions with evidently discordant structures affecting the geoelectrical data.
Self-potential, geoelectric and magnetotelluric studies in Italian active volcanic areas
Authors: R. Di Mai  , P. Mauriello  , D. Patella  , Z. Petrillo  , S. Piscitelli  , A. Siniscalchi  , M. Veneruso
Published: June 2021

We present the results of self-potential, geoelectric and magnetotelluric studies in Italian active volcanic areas as essential contributions both to structural modeling and to hazard evaluation. On Mt. Etna and Mt. Somma-Vesuvius complexes structural modeling was emphasized due to a lack of global information involving the whole apparatuses, at least from the electrical point of view. Hazard investigation was, instead, investigated with high resolution techniques on the island of Vulcano, where intense unrest phenomena have long been recorded.