[1] The geomagnetic field is chaotic and can be characterized by a mean exponential time scale < t > after which it is no longer predictable. It is also ergodic, so time analyses can substitute the more difficult phase space analyses. Taking advantage of these two properties of the Earth's magnetic field, a scheme of processing global geomagnetic models in time is presented, to estimate fluctuations of the time scale t. Here considering that the capability to predict the geomagnetic field is reduced over periods of geomagnetic jerks, we propose a method to detect these events over a long time span. This approach considers that epochs characterized by relative minima of fluctuations in time scale t, i.e., those periods when a geomagnetic field is less predictable, are possible jerk occurrence dates. We analyze the last 400 years of the geomagnetic field (covered by the Gufm1 model) to detect minima of fluctuations, i.e., epochs characterized by low values of the time scale. Most of the well known jerks are confirmed through this method and a few others have been suggested. Finally, we also identify some short periods when the field is less chaotic (more predictable) than usual, naming these periods as steady state geomagnetic regime, to underline their opposite behavior with respect to jerks.

No abstract

In this study we have applied spectral techniques to analyze geomagnetic field time-series provided by observatories, and compared the results with those obtained from analogous analyses of synthetic data estimated from models. Then, an algorithm is here proposed to detect the geomagnetic jerks in time-series, mainly occurring in the eastern component of the geomagnetic field. Applying such analysis to time-series generated from global models has allowed us to depict the most important space-time features of the geomagnetic jerks all over the globe, since the beginning of XXth century. Finally, the spherical harmonic power spectrum of the third derivative of the main geomagnetic field has been computed from 1960 to 2002.5, bringing new insights to understand the spatial evolution of these rapid changes of the geomagnetic field

In this study we have applied spectral techniques to analyze geomagnetic field time-series provided by observatories, and compared the results with those obtained from analogous analyses of synthetic data estimated from models. Then, an algorithm is here proposed to detect the geomagnetic jerks in time-series, mainly occurring in the Eastern component of the geomagnetic field. Applying such analysis to time-series generated from global models has allowed us to depict the most important space-time features of the geomagnetic jerks all over the globe, since the beginning of XXth century. Finally, the spherical harmonic power spectra of the third derivative of the main geomagnetic field has been computed from 1960 to 2002.5, bringing new insights to understanding the spatial evolution of these rapid changes of the geomagnetic field

&lt;p&gt;The paper is mainly aimed at presenting some results of the geophysical investigations focused on the Gurghiu Mountains volcanism.&lt;/p&gt; &lt;p&gt;The Gurghiu Mountains are located in the central inner (western) part of Eastern Carpathians, Romania. They represents the middle segment of the approx. 160 km long Neogene to Quaternary volcanic chain C&amp;#259;limani-Gurghiu-Harghita (CGH), the southeastern end of the magmatic arc adjoining the Carpathians from Slovakia to Romania. CGH is a typical andesite-dominated calc-alkaline volcanic range. As part of it, Gurghiu Mountains exhibits (with minor exceptions) monotonous volcanic rocks, clearly dominated by andesites and pyroxene andesites.&lt;/p&gt; &lt;p&gt;Several years ago, CGH volcanism was subject to research within a specific project funded by the Romanian National Agency for Scientific Research. During the project, gravity and geomagnetic investigations were conducted in the Gurghiu Mountains areal to help unveiling the composition and structure of the volcanic edifices. Thus, consistent gravity and geomagnetic data sets over the studied area were obtained. Furthermore, various data mining techniques (e.g., Bouguer anomaly for various reference densities, geomagnetic and reduced-to-the-pole geomagnetic anomaly, regional-residual separation through upward/downward continuation and/or polynomial regression, high-order derivatives) were applied in order to create more intuitive images helping in the qualitative interpretation of the geophysics results.&lt;/p&gt; &lt;p&gt;In a second stage, quantitative approaches were employed for unveiling the hidden structure of the shallow part of the crust. Consequently, 2D and 3D models of the density and magnetic structure of the main volcanic forms in the area (e.g., F&amp;#226;ncel-L&amp;#259;pusna caldera, Seaca-T&amp;#259;tarca, Sumuleu and Ciumani-Fier&amp;#259;straie crater areas) were inferred from joint inversion of gravity and geomagnetic data.&lt;/p&gt; &lt;p&gt;Finally, based on the inversion results, attempts to construct 3D models of the shallow crust architecture were made by employing the forward modelling approach under constraints provided by rock physics studies and exploration wells.&lt;/p&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;p&gt;Key words:&amp;#160; gravity, geomagnetism, density, magnetic susceptibility, inversion, forward modelling, volcanism, Gurghiu Mountains, Eastern Carpathians&lt;/p&gt;