Development of Multi-Channel Ultrasound Recording System for a High-Pressure, High-Temperature Rock Deformation Apparatus

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

Movement of rocks in Earth's interior results in the build-up of stress. Depending on a variety of factors such as temperature, pressure and stressing rate a rock can either fail abruptly in an earthquake or deform slowly by creep. Experimental rock deformation studies provide fundamental insights into the processes that accommodate plate tectonic movement at different depths in the Earth and quantify the strength and stability of tectonic plates. Development of new capabilities open new horizons for experimental geophysics and provide tools for studying many poorly understood phenomena such as intermediate and deep-focus earthquakes as well as non-impulsive slow-slip events, low frequency earthquakes and non-volcanic tremor in the laboratory at relevant pressure and temperature conditions. The aim of this proposal is to develop and integrate a multi-channel ultrasound recording system into an existing state-of-the-art solid medium rock deformation apparatus. The apparatus is capable of deforming large volume samples (~380 cubic mm) at pressures of up to 2.5 GPa and temperatures of up to ~1400 degrees C and is specifically designed to allow for the integration of an ultrasound recording system. It is planned to use several miniature needle piezoelectric sensors in the frequency range of 1 - 10 MHz to monitor the sample. Triggered acoustic emission data will be recorded at sampling speeds of up to 50 Ms/s per channel and continuous data will be recorded at sampling speeds of up to 10 Ms/s. A high-energy pulser will be synchronized with the recording system and will generate known pulses that will travel through the deforming sample and will be used to characterize the microstructural evolution in-situ. The investigator will be able to locate acoustic emissions within the sample volume and measure the evolution of p-wave velocities. These data will give us fundamental new insights into a number of natural phenomena ranging from seismicity, influence of stress and strain on metamorphic reactions, to the influence of stress on melt alignment and acoustic wave propagation to name just a few possible applications. The PecLab, where the apparatus will be installed, is part of a Collaborative Organization for Rock Deformation (CORD) which was formed between MIT and Brown University. The goal of CORD is to encourage and facilitate participation in experimental rock deformation studies by a broader spectrum of scientists within the Earth science community. The newly developed experimental capabilities will serve the geoscience community by enabling new, previously impossible studies to any interested visitors. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.