Melt squirt in the asthenosphere

Abstract

The interpretation of the seismic low‐velocity zone as a region of partially molten rock is extended to explain the transient displacements following the 1946 Nankaido earthquake. Three partial melt models are considered to account for the observed time constant of 3–5 years: large‐scale diffusion of melt through a porous matrix can decay over thousands to billions of years and is much too slow. Simple shearing in ‘penny‐shaped’ cracks happens on a seismic time scale and is much too rapid. Interconnected penny‐shaped cracks at different orientations with respect to the principal stresses respond on an intermediate time scale by short‐range melt squirt from one crack to another, providing a reasonable mechanism to account for the transient deformation at Nankaido, while components of shear parallel to each individual crack relax quickly according to the better‐known mechanism for seismic attenuation in the low‐velocity zone.

A review of shear-wave splitting in the compliant crack-critical anisotropic Earth

“…First identified for isotropic (random) crack distributions [49], squirt flow was analysed for distributions of aligned cracks by Pointer et al [48]. The effects can be significant but are controlled by the ratio of wavelength to crack size.…”

Simultaneous Measurements of the Compressional-Wave Velocity and the Electrical Conductivity in a Partially Molten Material.

“…This elastic effect of the melt is independent of the frequency. In addition to this effect, relaxation mechanisms related to the melt can decrease the velocity depending on the frequency: the fluid flow (Mavko and Nur, 1975;O'Connell and Budiansky, 1977) and the phase transform (Vaisnys, 1968). Mavko (1980) studied the relaxation mechanisms in partially molten regions and estimated their relaxation frequencies.…”

Computation of Wave Attenuation and Dispersion, by Using Quasi-Static Finite Difference Modeling Method in Frequency Domain

“…Several analytical solutions are also put forward to estimate wave attenuation and velocity dispersion due to WIFF at microscopic scale [Mavko et al 1975, Mavko et al 1979, Budiansky et al 1976, Palmer et al 1980, Dvorkin et al 1995, Chapman et al 2002, Pride et al 2003, Gurevich et al 2009. Apart from the ability to precisely predict wave attenuation and velocity dispersion at sonic frequency frequencies, investigations reveal that the microscopic scale theories lack to predict wave attenuation and velocity dispersion within seismic frequency band.…”

“…In order to compute wave attenuation and velocity dispersion at grain (microscopic) scale Mavko and Nur [Mavko et al 1975, Mavko et al 1979, Dvorkin et al 1995 presented the concept of fluid flow from soft crack to stiff pores, that eventually causes wave attenuation and velocity dispersion. Several analytical solutions are also put forward to estimate wave attenuation and velocity dispersion due to WIFF at microscopic scale [Mavko et al 1975, Mavko et al 1979, Budiansky et al 1976, Palmer et al 1980, Dvorkin et al 1995, Chapman et al 2002, Pride et al 2003, Gurevich et al 2009.…”