bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of macroseismic field in Central Greece
Authors: V. Kouskouna  , S. Chailas  , K. C. Makropoulos  , D. Michalopoulou  , J. Drakopoulos
Published: June 2021

The distribution of seismic intensity is generally influenced by major geological and tectonic features and, on a smaller scale, by local geological conditions, such as the type of surface soil, the surface-to-bedrock soil structure in sedimentary basins and the depth of the saturated zone, The present paper attempted to determine the distribution of macroseismic intensities based on published attenuation laws in the area of Central Greece, using the epicentral intensity, magnitude, length and direction of fault and a considerable number of observation sites, for which the above mentioned information is available, The expected intensity values were then compared to those observed in the same sites, from four earthquakes in Volos, Central Greece, for which the fault plane solutions are also known. The deviations of the observed values from the theoretical model were then related to the local geological conditions and the corresponding correction factor determined for each site.
The reliability of reported depths of some earthquake sequences in Northwestern Greece (Epirus and Corfu Island) and the geodynamic situation of the area
Authors: B. Muço
Published: June 2021

The study of the earthquakes of the rectangle with coordinates 39°-40°N 19°-21°E is very important for a better understanding of the geodynamics of this area. In and near this zone, the subduction of the Aegean arc stops, and northward, going to the Albanian coast, the confrontation between the Adria microplate and the Albanian orogen is probably of collisional type. In this approach based on records of Greek seismological stations situated in this area as well as southern stations of the Albanian Seismological Network (ASN), the depth of the earthquakes of some sequences that occurred recently in this zone is carefully investigated. Some records of Southern Albanian seismological stations resulting from earthquakes with the same epicentral zone but reported with different depth are compared. The importance of detailed studies of this zone is stressed to shed light on the geodynamics of a key segment of the northwestern end of the Aegean arc.
Mitigation of seismic hazard of a megacity: the case of Naples
Authors: C. Nunziata  , D. Fah  , G. F. Panza
Published: June 2021

The seismic ground motion of a test area in the eastern district of Naples was computed with a hybrid technique based on the rnode surnrnation and the finite difference methods. This technique allowed the realistic modelling of source and propagation effects, including local soil conditions. In the modelling, as seismic source we considered the 1980 Irpinia earthquake, a good example of strong shaking for the area of Naples, located about 90 km from the source. Along a profile through Naples, trencling N86°W, the subsoil is mainly formed by alluvial (ash, stratified sand and peat) and pyroclastic materials overlying a pyroclastic rock (yellow Neapolitan tuff) representing the Neapolitan bedrock. The detailed information available on the subsoil mechanical properties and its geometry warrants the application of the sophisticated hybrid technique. For SH waves, a comparison was made between a realistic 2-D seismic response and a standard I-D response, based on the vertical propagation of waves in a plane layered structure. As expected the sedimentary cover caused an increase in the signal's amplitudes and duration. If a thin uniform peat layer is present, the amplification effects are reduced, and the peak ground accelerations are similar to those observed for the bedrock model. This can be explained by the backscattering of wave energy at such a laqer. The discrepancies evidenced between the l -D and the 2-D seismic response suggest that serious caution must be taken in the formulation of seismic regulations. This is particularly true in the presence of the thin peat laqer where the misinatch between the l -D and the 2-D amplification functions is particularly evident in correspondence of the dominant peak and of the second significant peak.
Local administrative sources on population movements after the Messina earthquake of 1908
Authors: G. Restifo
Published: June 2021

Contrary to what one might expect, we have only a rough idea of the movements of the population of Messina after the 1908 earthquake. The exact figures regarding the number of dead are lacking; the fugitives were registered in difficult conditions; the numbers of immigrants can only be estimated. The two censuses of 1901 and 1911 are the only general source of comparison. To date nobody has examined the forms filled in by the families, from which it is possible to deduce the origins of the inhabitants of Messina. The analysis of local sources such as marriage registers and church records can provide information to fill this gap. An overall survey of the available documentation allows us to reconstruct the vertiginous movement of population caused by the earthquake.
An unknown destructive earthquake in 18th century Sicily
Authors: D. Mariotti
Published: June 2021

The current Italian seismic catalogues are generally considered complete, as regards the destructive seismic events which occurred from the 17th century onwards. In fact, research performed using target methodologies still reveal earthquakes of high intensity, not yet known to the seismological tradition. This is the case of an earthquake which occurred on 14 September 1780, which caused serious damage and victims in some towns of the Tyrrhenian coast of North-eastern Sicily (I0, = VIII MCS). The information reported in an anonymous printed account was verified in the administrative records; this allowed a reconstruction of a macroseismic outline of great interest, which may make more precise the seismic hazard assessment in an area at high environmental risk due to the presence in Milazzo of an important chemico-industrial complex.
The 1930 earthquake and the town of Senigallia (Central Italy): an approach to seismic risk evaluation
Authors: P. Favali  , F. Frugoni  , D. Monna  , M. L. Rainone  , P. Signanini  , G. Smriglio
Published: June 2021

The town of Senigallia is located on the Adriatic coast of the Marche and Romagna regions (Central Italy), an area affected by offshore seismicity. This city was almost completely destroyed by an earthquake of IX degree intensity on the Mercalli-Cancani-Sieberg scale (MCS) on October 30, 1930. This quake is the most recent and the best documented. In particular, this shock was characterized by strong differences in the damage levels at a scale of hundreds and tens of metres. The geographic position of Senigallia at the mouth of a river and its soil conditions, similar to many other coastal historical and tourist centres in the region, make this earthquake an important case history, useful for a better understanding of the seismic risk of the entire coastal area. This note reports the first results of a study on the possible causes of the different damage levels. The research started with the history and town-planning evolution of Senigallia, then. the regional or local geological characteristics were considered by geological, geotechnical and geophysical investigations.
A large unknown historical earthquake in the Abruzzi region (Central Italy): combination of geological and historical data
Authors: G. D'Addezio  , F. R. Cinti  , D. Pantosti
Published: June 2021

The combination of paleoseismological and historical investigation can be used to obtain a complete knowledge of past earthquakes. In Italy the 1000 year-long record of historical earthquakes provides an opportunity to compare data from the catalogue with results from paleoseismologic investigations. Trenching results along the Ovindoli-Pezza Fault (OPF). in the Abruzzi region. showed two surface faulting events. The most recent of these events occurred after 1019 A.D. and should be reported in the Catalogue of Italian Seismicity. Nevertheless, the earthquake appears to be missed or not well located in the Catalogue. In order to define in which century a large earthquake on the OPF should have clearly left a sign in the historical record, we carried out historical investigations back to the XI century. The studies were mainly focu5ed on disclosing possible <> e vidence for the occurrence of the most recent event along the OPF. No clear records related to this event were found but on the basis of the information we obtained the occurrence of this earthquake can be constrained between 1019 A.D. and the XV century. possibly between 1019 A.D. and XIII century.
The new <>
Authors: E. Boschi  , P. Gasperini  , G. Smriglio  , G. Valensise
Published: June 2021

We describe a new catalogue of strong ltalian earthquakes that the Istituto Nazionale di Geofisica in collaboration with SGA, has recently made available to the international scientific community and to the general public. The new catalogue differs from previous efforts in that for each event the usual seismic parameters are complemented by a list of intensity rated localities, a complete list of relevant references, a series of synoptic comments describing different aspects of the earthquake phenomenology. and in most cases even the text of the original written sources. The printed part of the catalogue has been published as a special monograph which contains also a computer version of the full database in the form of a CD-ROM. The software package includes a computer program for retrieving, selecting and displaying the catalogue data.
Ambiguous evidence: earthquakes and ancient building techniques in an alpine example (4th-7th centuries)
Authors: S. Santoro Bianchi
Published: June 2021

Building techniques from the Roman Age using earth, stone and wood are frequently found in North Italy in town centres and in high-class residential buildings, as in smaller centres or n~ravl illages. In Italy, a study of building techniques has begun only very recently and little is known about the response of these techniques to seismic events. This paper deals with a fortified alpine settlement, located in a highly seismic area, whose buildings were constructed with the Roman techniques and may in two subsequent stages have been destroyed by earthquakes. The archaeological evidence is, however, ambiguous: we have no knowledge of the state of repair of the buildings at the time of collapse, and the stratigraphy has been upset by subsequent reworking for the purpose of recovering the building materials.
The 1638 earthquakes, migratory phenomena and geolinguistic consequences in Calabria
Authors: G. Chiodo  , I. Guerra  , J. Trumper
Published: June 2021

Two disastrous earthquakes occurred in Calabria (Southern Italy) in 1638: on March 27th the first one had a destructive damage area on the Tyrrheniail side of Mid-Calabria. the second one hit the east side of the same region on June 9th. In historical times they are the most intensive seismic events in their respective epicentral areas. so that the reconstruction of their effects is very important for the analysis and assessment of seismic risk. They strongly influenced, moreover, the development of the economy and socio-cultural status of many urban communities. A study of these shocks has been carried out and has implied a thorough re-evaluation of the historical sources of information already known and the exploitation of possible new sources. The two macroseismic fields have been reconstructed: in particular that of the second seismic event, the strongest one in its epicentral area. stimulates a thorough revision of the seismotectonics of the Middle-eastern Calabria. Moreover the reconstruction of the historical facts accompanying and following the earthquakes has furnished elements that help to explain observed anomalies in the spatial distribution of Calabrian dialect phenomena.
Earthquake, GIS and multimedia. The 1883 Casamicciola earthquake
Authors: F. Bramerini  , S. Castenetto  , E. Cubellis  , M. G. Martini  , M. Rebuffat  , P. Soddu
Published: June 2021

A series of multimedia monographs concerning the main seismic events that have affected the Italian territory are in the process of being produced for the Documental Integrated Multimedia Project (DIMP) started by the Italian National Seismic Survey (NSS). The purpose of the project is to reconstruct the historical record of earthquakes and promote an earthquake public education. Producing the monographs. developed in ARC INFO and working in UNIX. involved designing a special filing and management methodology to integrate heterogeneous information (images, papers, cartographies, etc.). This paper describes the possibilities of a GIS (Geographic Information System) in the filing and management of documental information. As an example we present the first monograph on the 1883 Casamicciola earthquake. on the island of Ischia (Campania, Italy). This earthquake is particularly interesting for the following reasons: I) historical-cultural context (first destructive seismic event after the unification of Italy); 2) its features (volcanic earthquake); 3) the socioeconomic consequences caused at such an important seaside resort.
Did earthquakes fell Aksum obelisks ?
Authors: V. Francaviglia  , G. Augusti  , V. Sepe
Published: June 2021

Most of the obelisks at Alisum (Tigray, Ethiopia) are lying in pieces on the ground, as the Aksumite obelisk now in Rome had been before its removal to Italy. Preliminary inspection of the alignment of the ~larious fallen members makes it possible to identify a prevailing orientation. The historical tradition is very vague as regards the toppling of the obelisks (or stelae). Reference is made to Yodit or Gudit, a Jewish queen of the South. who supposedly had the pngnn stelae knocked down in the 10th century A.D.: to Irnam Ah~nedib n Ibrahim a1 Ghazi a1 gi-in?. Amir of Harar. who supposedly ordered thein to be felled by cannon fire: and to earthquakes. Analysis carried out on a nuruber of highly significant cases makes it possible to assert that some of the great obelisks at Aksum collapsed as a result of earthquakes. At the same time, inadequate systems of anchorage and the mediocre mechanical qualities of the soil were certainly conducive to collapse through both natural causes (earthquakes and erosion of foundations) and deliberate demolition.
A revision of the stratigraphyfor the Middle Pleistocene continentaI deposits of Rome(CentraI Italy): palaeomagnetic data
Authors: F. Florindo  , F. Marra
Published: June 2021

All improved knowledge of the stratigraphy of the Rome area has been achieved trom the interpretation and correlation of a large number of stratigraphic logs from drillings, stored in a data bank by the Istituto Nazionale di Geofisica which allowed the authors to identify a succession of "unconformity-bounded strati- graphic units". The possibility of correlating these stratigraphic units with the oxygen jsotope time scale is suggested leading to a substantial revision of the Quaternary stratigraphy of the Rome area. This paper pre- sents the results of a magnetostratigraphic study on a repere layer in Rome, demonstrating that this layer can- not be correlated with the basaI members ofthe formation outcropping in the type-site (Helicella clays, "Ponte Galeria Formation" ), as recently proposed as a result of morpho-stratigraphical studies with important implica- tions concerning the interpretation of the recent sedimentary and tectonic evolution of this area.
An analytic method for separating local from regional effects on macroseismic intensity
Authors: P. Tosi  , V. De Rubeis  , C. Gasparini
Published: June 2021

nterpretation of macroseismic data is hazardous, due to its qualitative nature. This, linked with errors in eval- uation,) and the variations of local intensity, makes it difficult to draw valid conclusions. This study presents a statistical method as the basis for distinguishing the diverse components that constitute a macroseismic field. The method is based on the polar transformation of the coordinate system and on the analysis of the fractal di- mension of the intensity values, exposed to the gradually increasing action of a two-dimensional filter. The fractal dimension is shown to be an ideaI parameter with which to measure out the filtering process in order to separate the local components from the regional trend. This method has been applied to two Italian events and to an earthquake which took pIace in the Former Yugoslavian Republic of Macedonia (FYROM).
Estimation of strong ground motion in broad-frequency band based on a seismic source scaling model and an empirical Green's function technique
Authors: K. Irikura  , K. Kamae
Published: June 2021

We introduce a generalized method for simulating strong ground motion from large earthquakes by summing subevent records to follow the ?2 law. The original idea of the method is based on a constant stress parameter between the target event and the subevent. It is applicable to a case where both events have a different stress drop after some manipulation. However, the simulation for a very large earthquake from a small event with this method has inevitably some deficiencies of spectral amplitudes in the intermediate frequency range deviating f`rom the ?2 model, although the high and low frequency motions match the scaling. We improve the simulation algorithm so as not to make spectral sags, introducing self-similar distribution of subfaults with different sizes in the fault plane, so-called fractal composite faulting model. We show successful simulations for intermediate-sized earthquakes (MJMA = 5.0, 6.0 and 6.1), the large aftershocks of the 1983 Akita-Oki earthquake. using the records of smaller aftershocks (MJMA = 3.9 and 5.0) as an empirical Green's function. Further, we attempted to estimate strong ground motion for the 1946 Nankai earthquake with Mw 8.2, using the records of a MJMA 5.1 earthquake occurring near the source region of the mainshock. We found that strong ground motions simulated for the fractal composite faulting model with two asperities radiating significantly high frequency motions matched well the observed data such as the near-field displacement record, the source spectrum estimated from the teleseismic record, and the seismic intensity distribution during the 1946 Nankai earthquake.
Seismic source dynamics, heterogeneity and friction
Authors: R. Madariaga  , A. Cochard
Published: June 2021

It has recently been proposed by several authors that stress distribution around active faults may become critical spontaneously. Other authors believe that heterogeneity is a permanent feature of fault planes. We test these ideas on a simple but realistic fault model in the presence of non-linear rate-dependent friction. We find that if friction increases with decreasing slip rate, slip becomes unstable at low slip rates generating supersonic healing phases that lock slip prematurely. Locking of slip in turn produces stress heterogeneity. For a fault model containing a single localized asperity, Das and Okubo found that rupture starts at the asperity and propagates until it either encounters a strong barrier or the stress intensity reduces below a minimum level. Rupture in these models is completely controlled by the physics of the rupture front. Rate dependent friction changes the behavior of the fault in a fundamental way: friction can lock the fault prematurely generating supersonic healing phases. Unlike stopping phases produced by barriers, a healing phase is not a wave phenomenon; it is a direct consequence of the non-linearity of friction. In this case rise time for slip on the fault is no longer controlled by the overall size of the fault as in conventional constant-friction crack models. We find that in our asperity models it is rise time or the healing mechanism that controls the final size of the fault. Studying models involving several isolated asperities we find that stress heterogeneity is preserved provided that friction is strongly rate dependent. Depending on the details of the rupture process, the final state of stress on the fault can be quite complex. This behavior is not universal, it depends on the degree of rate-dependence of friction.
The effect of lateral variations of friction on crustal faulting
Authors: J. Boatwright  , M. Cocco
Published: June 2021

We propose that lateral variations in fault friction control the heterogeneity of slip observed in large earthquakes, We model these variations using a rate and state-dependent friction law, where we differentiate velocity-weakening into strong and weak-seismic fields, and velocity-strengthening into compliant and viscous fields. The strong-seismic field comprises the seismic slip concentrations, or asperities. The two «intermediate» frictional fields, weak-seismic and compliant, modulate both the tectonic loading and the dynamic rupture process. During the interseismic period, the compliant and viscous regions slip aseismically while the strong-seismic regions remain locked, evolving into stress concentrations that fail only in main shocks. The weak-seismic regions contain most of the interseismic activity and aftershocks, but also «creep seismically», that is, most of the weak-seismic area slips aseismically, actuating the seismicity on the remaining area. This «mixed» frictional behavior can be obtained from a sufficiently heterogenous distribution for the critical slip distance. The interseismic slip provides an inherent rupture resistance: dynamic rupture fronts decelerate as they penetrate into these unloaded compliant or creeping weak-seismic areas, diffusing into broad areas of accelerated afterslip. Aftershocks occur in both the weak-seismic and compliant areas around the fault, but most of the stress is diffused through aseismic slip. Rapid afterslip on these peripheral areas can also produce aftershocks within the main shock rupture area, by reloading weak fault areas that slipped in the main shock and then healed. We test this frictional model by comparing the interevent seismicity and aftershocks to the coseismic slip distribution for the 1966 Parkfield, 1979 Coyote Lake, and 1984 Morgan Hill earthquakes.
A model for frictional sliding instability on a heterogeneous fault
Authors: M. Dragoni  , A. Piombo
Published: June 2021

An instability of frictional sliding driven by tectonic stress is assumed to be the source of earthquakes. Empirical slip laws indicate that, under constant ambient conditions, friction depends on time, slip rate and slip history. Regular stick slip behaviour is induced by velocity weakening, a decrease of friction with slip rate. Velocity weakening is introduced into a model for a propagating Somigliana dislocation under slowly increasing shear stress in an elastic space. Two distributions of static friction are considered, characterized by asperities with sharp borders and smooth borders respectively. The instability occurs when the rate at which friction decreases becomes greater than the rate at which the applied stress must increase to produce an advance of fault slip. The possibility that this condition is fulfilled depends on the velocity dependence and on the spatial distribution of friction on the fault. In the case of sharp asperity borders, instability can take place only when some amount of slip has occurred on the fault, while this condition is not required in the case of smooth borders.
Transient stresses al Parkfield, California, produced by the M 7.4 Landers earthquake of June 28, 1992: implications for the time-dependence of fault friction
Authors: P. Spudich  , L. K. Steck  , M. Hellweg  , J. B. Fletcher  , L. M. Baker
Published: June 2021

he M 7.4 Landers earthquake triggered widespread seismicity in the Western U.S. Because the transient dynamic stresses induced at regional distances by the Landers surface waves are much larger than the expected static stresses, the magnitude and the characteristics of the dynamic stresses may bear upon the earthquake triggering mechanism. The Landers earthquake was recorded on the UPSAR array, a group of 14 triaxial accelerometers located within a 1-square-km region 10 km southwest of the town of Parkfield, California, 412 km northwest of the Landers epicenter. We used a standard geodetic inversion procedure to determine the surface strain and stress tensors as functions of time from the observed dynamic displacements. Peak dynamic strains and stresses at the Earth's surface are about 7 microstrain and 0.035 MPa, respectively, and they have a flat amplitude spectrum between 2 s and 15 s period. These stresses agree well with stresses predicted from a simple rule of thumb based upon the ground velocity spectrum observed at a single station. Peak stresses ranged from about 0.035 MPa at the surface to about 0.12 MPa between 2 and 14 km depth, with the sharp increase of stress away from the surface resulting from the rapid increase of rigidity with depth and from the influence of surface wave mode shapes. Comparison of Landers-induced static and dynamic stresses at the hypocenter of the Big Bear aftershock provides a clear example that faults are stronger on time scales of tens of seconds than on time scales of hours or longer.
From tomographic images to fault heterogeneities
Authors: C. Chiarabba  , A. Amato
Published: June 2021

Local Earthquake Tomography (LET) is a useful tool for imaging lateral heterogeneities in the upper crust. The pattern of P- and S-wave velocity anomalies, in relation to the seismicity distribution along active fault zones. can shed light on the existence of discrete seismogenic patches. Recent tomographic studies in well monitored seismic areas have shown that the regions with large seismic moment release generally correspond to high velocity zones (HVZ's). In this paper, we discuss the relationship between the seismogenic behavior of faults and the velocity structure of fault zones as inferred from seismic tomography. First, we review some recent tomographic studies in active strike-slip faults. We show examples from different segments of the San Andreas fault system (Parkfield, Loma Prieta), where detailed studies have been carried out in recent years. We also show two applications of LET to thrust faults (Coalinga, Friuli). Then, we focus on the Irpinia normal fault zone (South-Central Italy), where a Ms = 6.9 earthquake occurred in 1980 and many thousands of attershock travel time data are available. We find that earthquake hypocenters concentrate in HVZ's, whereas low velocity zones (LVZ s) appear to be relatively aseismic. The main HVZ's along which the mainshock rupture bas propagated may correspond to velocity weakening fault regions, whereas the LVZ's are probably related to weak materials undergoing stable slip (velocity strengthening). A correlation exists between this HVZ and the area with larger coseismic slip along the fault, according to both surface evidence (a fault scarp as high as 1 m) and strong ground motion waveform modeling. Smaller wave-length, low-velocity anomalies detected along the fault may be the expression of velocity strengthening sections, where aseismic slip occurs. According to our results, the rupture at the nucleation depth (~ 10-12 km) is continuous for the whole fault lenoth (~ 30 km), whereas at shallow depth, different fault segments are activated due to lateral heterogeneities in the sedimentary cover. This finding confirms that the rupture process is controlled by lithologic and structural discontinuities in the upper crust, and emphasizes the contribution that LET can make to the study of fault mechanics.
A comparison of two methods for earthquake source inversion using strong motion seismograms
Authors: B. P. Cohee  , G. C. Beroza
Published: June 2021

In this paper we compare two time-domain inversion methods that have been widely applied to the problem of modeling earthquake rupture using strong-motion seismograms. In the multi-window method, each point on the fault is allowed to rupture multiple times. This allows flexibility in the rupture time and hence the rupture velocity. Variations in the slip-velocity function are accommodated by variations in the slip amplitude in each time-window. The single-window method assumes that each point on the fault ruptures only once, when the rupture front passes. Variations in slip amplitude are allowed and variations in rupture velocity are accommodated by allowing the rupture time to vary. Because the multi-window method allows greater flexibility, it has the potential to describe a wider range of faulting behavior; however, with this increased flexibility comes an increase in the degrees of freedom and the solutions are comparatively less stable. We demonstrate this effect using synthetic data for a test model of the Mw 7.3 1992 Landers, California earthquake, and then apply both inversion methods to the actual recordings. The two approaches yield similar fits to the strong-motion data with different seismic moments indicating that the moment is not well constrained by strong-motion data alone. The slip amplitude distribution is similar using either approach, but important differences exist in the rupture propagation models. The single-window method does a better job of recovering the true seismic moment and the average rupture velocity. The multi-window method is preferable when rise time is strongly variable, but tends to overestimate the seismic moment. Both methods work well when the rise time is constant or short compared to the periods modeled. Neither approach can recover the temporal details of rupture propagation unless the distribution of slip amplitude is constrained by independent data.
A deep geoelectrical survey in the Southern Central Alps
Authors: L. Alfano  , G. Lorenzoni  , C. Melandri  , M. Mocchi  , G. Nuttini  , F. Pirera  , M. F. Soffientini
Published: June 2021

A deep geoelectrical survey was carried out on the Southern Central AIps, to the north of Bergamo, by means of the continuous polar dipole-dipole electrode array. Among the 6 profiles executed, 4 revealed the existence of a substratum with very high resistivity values (15 000-40 000 ohm.m) and a flat not very deep upper boundary; its thickness exceeds the maximum expIoration depths of the soundings (1 to 6 km). On the grounds of general considerations and resistivity field data set, it is possible to infer that the high values should be ascribed to endogenous rather than to sedimentary rocks. A problem arises since these geophysical results are not in agreement with some geological models.
Geomagnetism, volcanoes, global climate change, and predictability. A progress report
Authors: G. P. Gregori
Published: June 2021

A model is investigated, by which the encounters of the solar system with dense interstellar clouds ought to trigger either geomagnetic field reversals or excursions, that produce extra electric currents within the Earth dynamo, that cause extra Joule's heating, that supplies volcanoes and endogenous processes. Volcanoes increase the Earth degassing into the atmosphere, hence the concentration of the minor atmospheric constituents, including the greenhouse gases, hence they affect climate temperature, glacier melting, sea level and global change. This investigation implies both theoretical studies and observational data handling on different time scales, including present day phenomena, instrumental data series, historical records, proxy data, and geological and palaeontological evidences. The state of the art is briefly outlined, mentioning some already completed achievements, investigations in progress, and future perspectives.
Anisotropies of anhysteretic remanence and magnetic susceptibility of marly clays from Central Italy
Authors: A. Winkler  , L. Sagnotti
Published: June 2021

Marly clays from an Upper Pliocene unit at Valle Ricca (Rorne) were investigated for their Anisotropy of Anhysteretic Remanence (AAR) and Anisotropy of Magnetic Susceptibility (AMS). The study of AAR was accomplished for the first time in ltaly, developing a suitable laboratory technique and adapting a standard statistical procedure. The comparison between anhysteretic remanence and magnetic susceptibility anisotropies discriminates the fabric of the ferromagnetic fraction from that of the paramagnetic matrix of the rock. The separation of fabric components was applied to distinguish subsequent geological processes that affected the total rock fabric. The results indicate that the clayey units are particularly suitable for the empirical investigation of fabric to strain relationship in weakly deformed rocks.
The Canadian National Seismograph Network
Authors: R. G. North
Published: June 2021

The Canadian National Seismograph Network currently consists of 5 very-broadband (VBB) and 15 broadband (BB) stations across Canada, supplemented by 6 short period (SP) stations. When it is completed by the end of 1995, a further 1 VBB, 12 BB and over 40 SP stations will have been added. Data from all sites are telemetered in real time to twin network acquisition, processing and archiving centres in Eastern and Western Canada. All data are continuously archived in SEED format on optical disk and access to the most recent three days of data is provided through a mail-based AutoDRM system. Continuous data from the VBB sites are sent to the FDSN Data Management Centre approximately one month after being recorded.
The GEOFON Program
Authors: W. Hanka  , R. Kind
Published: June 2021

Following the long tradition in broadband seismology in Germany, the GedForschungsZentrum (GFZ) at Potsdam, an institution for interdisciplinary research in geosciences, founded in 1992 by the Federal Ministry of Research and Technology, has started a program for the establishment of a network of globally distributed broadband seismic stations. The program, called GEOFON (GEOFOrschungsNetz), is dedicated to Emst von Rebeur-Paschwitz who recorded the first teleseismic seismogram, 1889 in Potsdam and proposed a global seismograph network and an earthquake reporting system. Our program will, after its completion, consist of three parts: a permanent network of about 30 stations, a portable broadband network and a comprehensive data archive. It is planned for two three-year periods (1993-1995 and 1996-1998). The funding for the first period has already been provided almost completely. An Advisory Board with members from German Universities and the GFZ guides the operation of GEOFON. The main task of the program is to serve the seismological community with high quality broadband data for all kinds, of scientific tasks. The research projects at the GFZ itself, to be carried out with GEOFON and other broadband data, are presently dealing mainly with lithospheric and upper and lower mantle 3D structure.
GSETT 3: a test of an experimental international seismic monitoring system
Authors: F. Ringdal
Published: June 2021

The UN Conference on Disarmament's Group of Scientific Experts (GSE) was established in 1976 to consider international co operative measures to detect and identify seismic events. Over the years, the GSE has developed and tested several concepts for an International Seismic Monitoring System (ISMS) for the purpose of assisting in the verification of a potential comprehensive test ban treaty. The GSE is now planning its third global technical test. (GSETT 3) in order to test new and revisled concepts for an ISMS. GSETT 3 wili be an unprecedented global effort to conduct an operationally realistic test of rapid collection, distribution and processing of seismie data. A global network of seismograph stations will provide data to an International Data Center, where the data will be processed an results made available to participants. The full scaIe phase of GSETT 3 is scheduled to begin in January 1995.
Seismic signals detection and classification using artiricial neural networks
Authors: G. Romeo
Published: June 2021

Pattern recognition belongs to a class of Problems which are easily solved by humans, but difficult for computers. It is sometimes difficult to formalize a problem which a human operator can casily understand by using examples. Neural networks are useful in solving this kind of problem. A neural network may, under certain conditions, simulate a well trained human operator in recognizing different types of earthquakes or in detecting the presence of a seismic event. It is then shown how a fully connected multi layer perceptron may perform a recognition task. It is shown how a self training auto associative neural network may detect an earthquake occurrence analysing the change in signal characteristics.
Solar cycle and seasonal behaviour of quasi two and rive day oscillations in the time variations of fOF2
Authors: E. M. Apostolov  , L. Alberca  , D. Altadill
Published: June 2021

Seasonal and solar cycle variations of the quasi-two- and five-day oscillation amplitudes off f0F2 are evaluated by moving periodogram analysis. The 23 year time series (1964-1986) of fOF2 hourly values of Kaliningrad (54.7°N, 20.62°E), covering the solar cycles 20 and 21, is used for the analysis. Long term variations of these amplitudes are modulated by the 11-year solar cycle and are simultaneously influenced by the geomagnetic activity. The annual variation of the quasi-two- and five-day oscillation amplitudes has very clear maxima near the equinoxes. The mechanism of the influence of the travelling planetary waves in the meteor wind region by vertical plasma drift to the F2-layer electron density maximum is discussed.
On the possibilities of coordinated ionospheric soundings and GPS measurements
Authors: L. Bányai  , J. Kalmár  , P. Bencze
Published: June 2021

onospheric soundings carried out at the same site and simultaneously with GPS measurements could contribute to the better understanding of the variations of the total electron content. However, for this purpose the total electron content deduced from GPS measurements must be converted to the place of observation. A method based on an interpolation considered as boundary value problem is recommended for this conversion. Furthermore, the possibilities of the application of datapobtained by ionopheric soundiings in GPS measurements are discussed and also preliminary results of model calculations are presented.
Comparison of inversion methods in seismic tomography: application to tectonic structures in Northwestern Italy
Authors: F. Maggio  , F. Malfanti  , M. Bertero  , M. Cattaneo  , C. Eva
Published: June 2021

In this paper we apply various inversion methods to a set of teleseismic data collected by a network operating along the Ligurian Belt in the transition region between Alps and Apennines. In particular, we consider the regularization method, the truncated singular value decomposition, the Landweber method (with the Related Simultaneous Iterative Reconstruction Technique) and the conjugate gradient method. All the methods provide rather similar velocity models which are well approximated by that provided by back-projection (used with an appropriate normalization constant). A drawback of these models seems to be the large discrepancy (of the order of 40%) between the observed time residuals and those computed from the model itself. However, for each station of the network, the azimuth dependence of the computed time residuals reproduces rather well the observed one so that it is believable that the most significant information contained in the data has been expIoited. The computed velocity models indicate strong heterogeneities in the first 200 km below the Apennines.
Introduction to the volume (1, 36, 1993)
Authors: E. Boschi  , D. Pantosti  , D. Slejko  , M. Stucchi  , G. Valensise
Published: June 2021

In the file
Ground based observations of Pc3-Pc5 geomagnetic pulsation power at Antarctic McMurdo station
Authors: P. Ballatore  , M. J. Engebretson  , C. G. Maclennan  , M. Candidi
Published: June 2021

The two horizontal geomagnetic components and, measured by a fluxgate magnetometer at Antarctic McMurdo station (corrected geomagnetic coordinates 80.0° S, 327.5° E), are analyzed for the period May-June 1994; the spectral powers are calculated and integrated over three frequency intervals corresponding to the nominal ranges. The time dependence of those integrated powers and their correlations with northern auroral indices and solar wind speed are considered. The observations are compared with previous results reported from Terra Nova Bay station (located near McMurdo at the same corrected geomagnetic latitude) during Antarctic summer intervals. The differences found between the two stations are discussed in terms of the seasonal dependence of geomagnetic field line configurations in the near cusp region.
Is the illite group the cause of high electrical conductivityin certain lithospheric areas?
Authors: G. Losito  , M. Muschietti
Published: June 2021

This article discusses the problem of the mineralogical-petrographic interpretation of the "anomalous" conductive layer inside the lithosphere, which has resulted from electromagnetic deep soundings. Three situations can be found: 1) a resistivity of less than 1 ? ·m in the Very High Conductivity Layer (VHCL); 2) a resistivity of 1÷100 ? ·m in the High Conductivity Layer (HCL); 3) a resistivity of 102 ÷ 103 ? ·m in the Continental Lower Crust (CLC). We have focused our attention on the HCL because of its widespread distribution. Most authors attribute HCL conductivity to the presence of salt water or graphitic materials, that are uniformly and continuously distributed inside rocks. Other hypotheses from the literature are the presence of oxides and/or sulphides, rock melting, and brine-bearing rocks. Each one of these elements can cause high electrical conductivity, depending on the petrophysical conditions, but much discussion involves the necessary physical continuity of the conductive elements. We forward one more hypothesis as follows. By means of experiments on rock samples from different geographical and deep areas, under simulated in situ physical conditions (e.g., pressure, temperature, saturation), we have found resistivity values similar to the in situ ones. Chemical, mineralogical, and petrographic analyses have shown the presence of large amounts of phyllosilicate minerals, such as illite. These minerals act in two ways: they produce the physical continuity of associated conductive minerals, and they decrease the resistivity of rocks. This second hypothesis is consistent with both the very widespread diffusion of illite inside the Earth's crust, and with the good conductivity found in depth.
An analysis of working days contamination in micropulsation measurements
Authors: U. Villante  , M. Vellante
Published: June 2021

A long term analysis of the power of geomagnetic variations in the micropulsations band at L'Aquila (Italy) revealed a weekly variation represented by an increased level of power in the working days with respect to Sundays. The maximum increase, by a factor of ~1.2, occurs during morning hours in the 100-500 Hz band. A daily-light-saving time effect has been also identified. Some implications on a wider scientific context are discussed.
Neogene and Quaternary geodynamic evolution of the Italian peninsula: the contribution of paleomagnetic data
Authors: Antonio Meloni  , Laura Alfonsi  , Fabio Florindo  , Leonardo Sagnotti  , Fabio Speranza  , Aldo Winkler
Published: June 2021

Paleomagnetism has played an important role in the development of geodynamic models for the Italian peninsula.

Paleomagnetic data from this area have been increasingly reported since the late 1960s, placing important constraints on geodynamics. A brief outline of the main concepts underlying a paleomagnetic study is provided in the first part of this paper. We also discuss the criteiia for the assessment of the reliability of paleomagnetic data. Finally,the data collected over the past 25 years in peninsular and insular Italy are synthetically reviewed, discussing the main implications for the geodynamic evolution of the Tyrrhenian - Apennines foreland system.
Regularities in discrete hierarchy seismo-acoustic mode in a geophysical field
Authors: Kamel Baddari  , Anatoly D. Frolov
Published: June 2021

Some regularities in seismo acoustic mode have been studied during the preparation and development of dynamic events generated during the deformation at different scales in a geophysical field. The time-space behavior of certain auto similarity parameters: the slope of the recurrence plot c, the fractal dimension of the hypocenters set D, the relationship D-3c and the crack concentration parameter Ksr in laboratory and field experiments in Algerian seismoactive zone have been analyzed as well. Precursory stage and local failure evolution in rock samples and in natural conditions were studied. It is shown that the regularities in the behavior of the parameters under study do not qualitatively depend on the dimension of the object being loaded. The quoted examples above speak of inhomogeneity and self-similarity of seismicity distribution in space-time. This suggests that the evolution of cracking process at different scales, from rock samples to Earth crust, is controlled by the same physical mechanism. The further development of these studies consolidates the physical basis of the prediction of the dynamic events.
The seisniicity of Iran. The Silakhor (Luristan) earthquake of 23rd Ianuary, 1909 (Part II)
Authors: N. N. AMBRASEYS
Published: June 2021

This paper shows t h a t given certain conditions it is perfectly feasible to study an earthquake that occurred three-quarters of a century ago in a remote part of the world. Also, it shows that there are many large earthquakes which, because of lack of interdisciplinary efforts to study such events, have remained hitherto little known or totally unknown. The case of the Silakhor earthquake revealed deficiencies in the determination of epicentres by ISS and Gutenberg; the difference between macroseismic and instrumental position for the Silakhor earthquake is 380 kilometres, a difference which lias caused a serious problem in the assessment of seisniicity of Iran. Accurate macroseismic d a t a may be used to minimize bias in t h e instrumental relocation of the larger events and to study source mechanisms. Untili this study was undertaken, the faulting associated with the Silakhor earthquake was totally unknown. Even more important t h a n the value of recent faulting for its significance in resolving ambiguities in t h e choice of the t r u e source parametres, is the information that can be gleaned from evidence for the mechanism of earthquakes that occurred long before t h e advent of modern seismology and in particular, for the pattern of recent tectonic activity.
Repeat station data compared to a global geomagnetic field model
Authors: Monika Korte  , Vincent Lesur
Published: June 2021

Geomagnetic repeat station surveys with local variometers for improved data reductions have been carried out in Germany for about ten years. For nearly the same time interval the satellites Ørsted and CHAMP have provided a good magnetic field data coverage of the whole globe. Recent global field models based on these satellite data together with geomagnetic observatory data provide an improved description of the core field and secular variation. We use the latest version of the GFZ Reference Internal Magnetic Model to compare the magnetic field evolution predicted by that model between 2001 and 2010 to the independent repeat station data collected over the same time interval in Germany. Estimates of crustal bias at the repeat station locations are obtained as averages of the residuals, and the scatter or trend around each average provides information about influences in the data from field sources not (fully) described by the global model. We find that external magnetic field signal in the order of several nT, including long-term trends, remains both in processed annual mean and quiet night time repeat station data. We conclude that the geomagnetic core field secular variation in this area is described to high accuracy (better than 1 nT/yr) by the global model. Weak long-term trends in the residuals between repeat station data and the model might indicate induced lithospheric anomalies, but more data are necessary for a robust analysis of such signals characterized by very unfavorable signal-to-noise ratio.