Open AccessTime dependent piezomagnetic fields in viscoelastic medium
Author(s) -
Currenti G.,
Del Negro C.,
Sasai Y.
Publication year - 2008
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.2007.03679.x
Subject(s) - viscoelasticity , rheology , standard linear solid model , materials science , shear modulus , viscosity , elastic modulus , mechanics , physics , composite material
SUMMARY We investigated time dependent piezomagnetic fields due to volcanic sources embedded in a viscoelastic, homogeneous half‐space. Especially in volcanic areas, the presence of inhomogeneous materials and high temperatures produce a lower effective viscosity of the Earth's crust that calls for considering anelastic properties of the medium. Piezomagnetic properties are carried by grains of titano‐magnetite, which occupy only a small fraction of ordinary rock volume and are supposed to be elastic, while the non‐magnetic surrounding matrix is assumed to be viscoelastic. From all the possible rheological models, we investigated two cases in which the bulk modulus is purely elastic and the shear modulus relaxes as: (i) a Maxwell solid and (ii) a standard linear solid (SLS). We applied the Correspondence Principle to the analytical elastic solutions for pressurized spherical sources and dislocation sources in order to determine the time dependent piezomagnetic fields in a viscoelastic medium. The piezomagnetic field completely vanishes after the relaxation process for a Maxwell rheology, whereas it is found to decrease over time and reach some finite offset value for a SLS rheology. These different behaviours provide helpful hints in understanding the temporal evolution of piezomagnetic anomalies in volcanic regions.