Abstract
<p>Modeling non-double-couple earthquakes and surficial deformation in volcanic and geothermal areas usually involves expansion sources. Given an ensemble of ellipsoidal or tensile expansion sources and double-couple ones, it is straightforward to obtain the equivalent single moment tensor under the far-field approximation. On the contrary, the moment tensor interpretation is by no means unique or unambiguous. If the far-field approximation is unsatisfied, the single moment tensor representation is inappropriate. Here we focus on the volume change estimate in the case of single sources, in particular finite pressurized ellipsoidal sources, presenting the expressions for the computation of the volume change and surficial displacement in a closed analytical form. We discuss the implications of different domains of the moment-tensor eigenvalue ratios in terms of volume change computation. We also discuss how the volume change of each source can be obtained from the isotropic component of the total moment tensor, in few cases of coupled sources where the total volume change is null. The new expressions for the computation of the volume change and surficial displacement in case of finite pressurized ellipsoidal sources should make their use easier with respect to the already published formulations.</p>
Highlights
IntroductionModeling non-double-couple (non-DC) earthquakes and surficial deformation in volcanic and geothermal areas usually involves expansion sources, e.g. microcracks, magma chambers, and dikes
Modeling non-double-couple earthquakes and surficial deformation in volcanic and geothermal areas usually involves expansion sources, e.g. microcracks, magma chambers, and dikes.Observations of non-DC earthquakes include earthquakes related to landslides and volcanic eruptions, long-period volcanic earthquakes, short-period volcanic and geothermal earthquakes, earthquakes at mines, deep-focus earthquakes, and other shallow earthquakes [for a review, see e.g. Miller et al 1998]
As regards shallow earthquakes in volcanic or geothermal areas and mines, isotropic components are consistent with failure involving both shear and tensile faulting, which may be facilitated by high-pressure, high-temperature fluids, and with cavity closing in mines
Summary
Modeling non-double-couple (non-DC) earthquakes and surficial deformation in volcanic and geothermal areas usually involves expansion sources, e.g. microcracks, magma chambers, and dikes. The library of available analytical (approximate or exact) solutions for surface displacements includes few finite cavity shapes [spheres, McTigue 1987; prolate spheroids, Yang et al 1988; fluid-pressurized closed pipes or dislocating open pipes, Bonaccorso and Davis 1999; circular horizontal cracks, Fialko et al 2001; finite triaxial ellipsoids, Amoruso and Crescentini 2011] and very small (with respect to depth) cavities [spheres, Mogi 1958; generic triaxial ellipsoids, through its representation in terms of a single moment tensor, Davis 1986]. We give explicit analytical expressions for computing surficial displacements from a pressurized ellipsoidal cavity, under the quadrupole approximation
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