F. Bella

Hydrogeochemical anomalies in Kamchatka (Russia)

Abstract Data concerning discharge, melted iones and gases from underground waters obtained in Kamchatka during the last ten years are presented. Some hydrogeochemical parameters from a volcanic site reveal clear coseismic and postseismic anomalies on the occasion of five earthquakes with magnitude M > 6.5 that occurred at distances closer than 250 km from the measurement site. Hydrogeochemical parameters from a tectonic site show anomalies on the occasion of three of the above earthquakes. Such earthquakes are characterized by the highest values of the deformation parameter ϵ and the corresponding anomalies are preseismic ones, starting from 1 to 4 months prior to the earthquake. Also, some hydrogeochemical parameters from another tectonic site show clear preseismic anomalies on the occasion of just one of these earthquakes. This last one is located inland while the epicentres of the other earthquakes are well offshore. Models able to explain the phenomenologies we described are proposed.

Electromagnetic Propagation of GPR Signals in Martian Subsurface Scenarios Including Material Losses and Scattering

A study on the electromagnetic propagation in various models of the Martian subsurface is performed with a relevance to ground penetrating radar (GPR) operating onboard rover missions. Measurements of the electromagnetic properties of Mars soil simulants are obtained; on this basis, the attenuation features of the GPR signals are estimated, including both electric and magnetic losses. The effect on propagation of inhomogeneities inside the soil is also taken into account by means of a specific model with randomly distributed scatterers. The GPR performance in terms of resolution and maximum penetration depth is evaluated in the considered scenarios for different operating frequencies, thus providing a basic information for the design of systems for future subsurface sounding investigations on Mars

Field strength variations of LF radio waves prior to earthquakes in central Italy

Abstract The electric field strength of the LF radio broadcasting RMC (Principality of Monaco) which operates at 216 kHz has been recorded since January 1991 by two receivers in central Italy. During the monitoring period we observed two evident attenuations of the field strength in one receiver, with durations of 6–10 days. The geomagnetic and ionospheric observations carried out in the same time interval do not seem able to explain the attenuation of the radio signal. An analysis of the seismic activity occurring in the area between transmitter and receiver has revealed that some days after the attenuations the energy released by earthquakes reaches a maximum. The observed attenuation might therefore be precursors of earthquakes. We also checked meteorological conditions and found that advections of warm air occurred during both the two anomalous periods. It seems possible that these conditions can help the action of preseismic effects in generating irregularities in the vertical gradient of the tropospheric radio refractivity able to produce defocusing of LF radiobroadcast propagation.

Very slow-moving crustal strain disturbances

Abstract A model of discrete crustal blocks, separated by a thin weak transition zone whose stress-strain relations contain derivatives of real order implying a memory mechanism in the medium, seems to give a good explanation for the low velocity values (0.03–15 cm/s) of slow moving crustal strain disturbances. Tilt and strain anomalies observed before moderate and large earthquakes are thought to be generated in the focal zone of the forthcoming earthquake, due to the spatial and temporal redistribution of the physical processes that occur during the preparation time of the earthquake. On the basis of experimental results it has been assumed that these anomalies propagate from the hypocentral area. In addition post-seismic deformations show the effects of propagation. The anomalies observed have a duration and a velocity ranging from minutes to months and from O.O5 cm/s to 10 cm/s, respectively. The velocity of migration of post-seismic deformation also lies in this range. The velocity of propagating strain disturbances is obtained as a function of the frequency and of the linear dimension of the oscillating blocks. The velocity values calculated using this model range from 0.1 cm/s to 10 cm/s, for viscosities of 10 9 –10 11 ) g cm −1 s −2+z (0.1≤ z ≤ 0.5) and blocksizes (1–4) · 10 6 cm, at frequencies of 10 −5 -10 −8 s −1 .

Anomalies in geophysical and geochemical parameters revealed on the occasion of the Paravani (M = 5.6) and Spitak (M = 6.9) earthquakes (Caucasus)

Abstract On the occasion of the Paravani (May 13, 1986) and Spitak (December 7, 1988) earthquakes, which occurred in the Caucasus, irregularities in several geophysical and geochemical parameters were revealed. In this paper, data on anomalies in the water level in deep wells, in the helium content in thermal waters, in electromagnetic signals revealed by surface and underground antennae, and in an F ( σ gt ) function based on traveltimes of P and S waves, are presented. Data were collected from sites located in the Georgian S.S.R. In the case of the Spitak earthquake, the anomalies in all the presented parameters can be attributed to the processes that preceded and accompanied the earthquake. For the Paravani earthquake, no significant precursory phase seems to have been reflected in the helium content in thermal waters, though this phase can be observed in the other parameters. In general, it would appear that the magnitude of the earthquake and the distance from the epicentre exert a significant control on the appearance of the anomalies.

Electromagnetic propagation features of ground penetrating radars for the exploration of martian subsurface

In this work, the effects of magnetic inclusions in a Mars-like soil are considered with reference to the electromagnetic propagation features of ground-penetrating radars (GPRs). Low-frequency and time-domain techniques, using L-C-R meters and TDR instruments, respectively, are implemented in laboratory experimental set-ups in order to evaluate complex permittivity and permeability and wave velocity for different scenarios of a dielectric background medium (silica) with magnetic inclusions (magnetite). Attenuation and maximum detection ranges have also been evaluated by taking into account a realistic GPR environment, which includes the transmitting/receiving antenna performance and the complex structure of the subsurface. The analysis and the interpretation of these results shed new light on the significant influence of magnetic inclusions on the performance of Martian orbiting and rover-driven GPRs.

Possible Creep-related Tilt Precursors Obtained in the Central Apennines (Italy) and in the Southern Caucasus (Georgia)

Daily averaged tilt component data from two sites of the Central Apennines (Italy) and of the Southern Caucasus (Georgia), respectively, revealed intermediate-term tilts as possible precursors to earthquakes (M=3.0÷4.7) which occurred in the above-mentioned seismic areas within a distance of 50 km from the sites. A good temporal correlation as well as a fair spatial correspondence between these residual tilts (with amplitude and duration of some microradians and months, respectively) and main shocks were pointed out, by removing both secular trends and seasonal thermoelastic effects from the raw tilts. An attempt was made to justify the above-mentioned results, based on the assumption that the observed intermediate-term preseismic tilts are the manifestation of aseismic creep episodes of comparable duration in the fault materials of thrust faults close to the tilt sites. The mechanism refers to a strain field slowly propagating from the preparation focal area to the tilt site, through crustal blocks separated by weak transition zones. This propagation is thought to be the cause of the local aseismic fault slip recorded by the tiltmeters. Previously, both discrete structures and strain propagation effects were revealed in the Central Apennines and are thought also to exist in the Southern Caucasus. As in the past, the rheological properties of fault materials are revealed as viscoelastic ones. In fact, creep equations obtained by applying several viscoelastic models on our data, proved to fit quite well some of the observed tilt precursors, producing viscosity and rigidity values very similar to those reported in literature.

Helium content in thermal waters in the Caucasus from 1985 to 1991 and correlations with the seismic activity

Abstract A wide data set of groundwater helium content collected in the Caucasus from 1985 to 1991 has been analyzed. The strongest earthquakes that occurred in this area during the helium measurement period were the: Paravani (May 13th, 1986, M = 5.6), Spitak (December 7th, 1988, M = 6.9) and Georgian (April 29th, 1991, M = 6.9) earthquakes. The analysis of the helium content data revealed statistically significant increases in this parameter on the occasion of the Paravani and Spitak earthquakes and no increase on the occasion of the Georgian earthquake. These results corroborate those obtained by the analysis of scanty helium content data presented in previous papers. With the exception of the anomalous increases, the helium content data were subjected to randomness tests and spectral analysis and cross correlation with meteorological parameters and areal seismicity were also attempted. The main result obtained is that the destructive Spitak earthquake produced some statistical changes in the groundwater helium content fluctuations some years before and after its occurrence.

A digital recording system of electromagnetic emissions

SummaryA new equipment able to reveal the electric component of electromagnetic emission and suitable for underground deployment has been made. The system enables to measure the absolute value of integrated voltage of signals. Data are recorded by a solid-state memory circuit. The system is performed as a plug-in modular design and it can be also used in diverse fields of application.RiassuntoÈ stata realizzata una nuova strumentazione per la rivelazione della componente elettrica delle emissioni elettromagnetiche in laboratori sotterranei. Il sistema è in grado di misurare i valori assoluti della tensione integrata dei segnali. I dati vengono registrati su un circuito di memoria a stato solido. Il sistema è stato realizzato con caratteristiche modulari e può essere utilizzato anche in altri campi di applicazione.РезюмеСконструировано новое оборудование для регистрации электрической компоненты электромагнитных излучений в подземных лабораториях. Система позволяет измерять абсолютную величину суммарного напряжения сигналов. Данные регистрируются в схеме с твердотельной памятью. Предложенная система собрана на специальных сменных модулях и может быть использована для различным прикладных задач.

No preseismic evidence from hydrogeochemical parameters on the occasion of the April 29, 1991, Georgian earthquake, Caucasus

Abstract The behaviour of helium content in thermal waters and of water level in deep wells was investigated on the occasion of the strong (M = 6.9) Georgian earthquake which occurred in the Caucasus on April 29, 1991. Data were collected from a measurement network located in Georgia. Just one significant preseismic variation appeared in the water level which seemed to be connected with the Georgian earthquake. In other wells, only some co-seismic and post-seismic effects are visible. No statistically viable variation was noted in the helium content. In contrast, clear anomalies in these parameters were observed on the occasion of the 1988 Spitak earthquake with the same magnitude which occurred in the Caucasus. We prepose that the location of the epicentre with respect to the measurement network was the reason for this disagreement. We therefore suggest the introduction of a coefficient c into relationships that give the size of the premonitory area as a function of the magnitude of the forthcoming earthquake. This coefficient, ranging from 0 to 1, can take into account the extent to which the focal zone belongs to different tectonic structures and the extent to which the measurement network coincides with these structures.