Geomagnetic depth sounding in the Northern Apennines (Italy)

Abstract

A Geomagnetic Depth Sounding (GDS) survey covering the Northern Apennines of Italy has been carried out in the period 1992-94. Induction arrows maps and hypothetical event Fourier maps were constructed to obtain an electromagnetic imaging of this area. Since the two dimensional (2-D) character comes out from those maps for periods greater than 32 minutes, a 2-D inverse modeling was carried out. The model responses show that a deep conductive layer (>5000 S) underlies the Apennine chain at about 20 km depth. The transition between the Adriatic and the Tyrrhenian domains is marked by a rather sharp vertical offset in this conducting layer. In the northwest sector of the studied area an anomalous high conductivity behavior is superimposed on the regional trend, which corresponds to the geothermal field of Larderello-Travale.

Magnetic transfer function entropy and the 2009 <i>M</i><sub>w</sub> = 6.3 L'Aquila earthquake (Central Italy)

“…The upward instability propagation could have been accentuated by upward fluid migration, in a fashion similar to the F-D model (Stefánsson et al, 2011). This model would be supported by the conductivity structure proposed by Armadillo et al (2001) using independent magnetic data, of a consistent conductive volume beneath L'Aquila at depths between 20 and 40 km. This volume could be interpreted as the possible reservoir releasing the fluids upward, in some way analogous to what was found for Iceland, supporting the F-D model there (Stefánsson et al, 2011).…”

“…By applying Eq. (1) for those frequencies and considering a plausible average crustal conductivity of σ = 0.02 S m −1 (an intermediate value of the conductivity beneath Central Italy among those given by Armadillo et al, 2001), we have found that the range for skin depth δ corresponding to them is a little deeper than the main shock hypocentre. This outcome has been the starting point for a more detailed study in order to verify whether (i) the adopted conventional method had succeeded in removing some unwanted sources which may have biased the analysis; and in case of success, (ii) whether the suggestive hypothesis about their possible seismogenic origin may have a foundation.…”

Evaluation of seismo-electric anomalies using magnetic data in Taiwan

“…When the Parkinson vectors are employed in surveying the momentary existence of earthquake-related high conductivity materials, influences of the coast effect and inhomogeneous conductivity of subsurface structure have to be considered. The coast effect (Parkinson and Jones, 1979;DeLaurier et al, 1983;Parkinson, 1983) is caused by an induction field resulting from differing conductivity properties of sea water, the oceanic and continental lithosphere and has been observed in countries such as Japan (Ogawa et al, 1986), Italy (Armadillo et al, 2001) and Australia (Hitchman et al, 2000). The coast effect causes that the induction arrows point toward the high conductivity sea water and remain simultaneously orthogonal to the nearby coastline.…”

“…The magnitude of an induction arrow is related to both the proximity of the conductor and its conductivity contrast with the background structure (Hitchman et al, 2000). Thus, the magnetic transfer function is usually applied to survey sites where the conductivity is higher than in the nearby areas (Parkinson, 1962;Parkinson and Jones, 1979) and it is widely utilised to study time-varying conductivity due to earthquakes (Zeng et al, 1995) and magnetic coast effects (Ogawa et al, 1986;Armadillo et al, 2001;Hitchman et al, 2000).…”

CalMagNet – an array of search coil magnetometers monitoring ultra low frequency activity in California

“…Geomagnetic depth sounding (GDS) techniques use triaxial magnetic measurements to obtain orientations to nearby conductivity anomalies (Gregori and Lanzerotti, 1980;Schmucker, 1985). Typical GDS measurement examples include the survey of northern Italy by Armadillo et al (2001) and a survey of North America by Neal et al (2000).…”