Non-isotropic nano-seismic sources detected at Transition zone pressures in Serpentine.

Abstract:

We collect nano-seismic emissions from high pressure serpentine as it undergoes amorphization. We used an array of 4 conical piezo-electric sensors sampling at 40 MHz attached to the diamond anvil cell to detect acoustic emissions; 3 sensors are attached to the side of the diamond cell, in-plane at 60 degree angles from one another, and a fourth sensor is placed on the bottom of the diamond cell, orthogonal to the 3 in-plane sensors. We determine first motions of acoustic emissions collected from serpentine between 6 and 12 GPa, pressures corresponding to the upper mantle and transition zone in the earth, representing a new pressure record for this diagnostic technique. All observed nano-seismic events have significant deviatoric components based on first-motions analysis, similar to findings from deep focus earthquakes on the kilometer scale at these pressures.