Fundamental and Applied Investigations in Rock Physics and Mechanics

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The Experimental Geophysics Group (EGG) investigates the factors that control the physical properties of earth materials and applies this knowledge in next generation interpretation of geophysical observations. Investigations are carried out both in controlled laboratory conditions and in the field with surface and borehole measurements. A major interest focusses on measurement of the stresses in the earth, both their directions and their strength. The students working with EGG have the opportunity to participate in the field activities that are increasingly rare. This proposal seeks support to allow us to continue collaboration in scientific drilling programs and to carry out novel rock physics laboratory experiments. We are part of the science team for two upcoming scientific drilling programs. In the first, a 1.5 km deep borehole will be drilled through the Alpine Fault on the South Island in New Zealand. The Alpine Fault bounds the Pacific and the Australian plates and is a significant crustal feature accommodated by significant uplift, it is feared that this fault can produce a major earthquake with devastating. The borehole, with drilling expected to begin in late 2014, is slated to intersect the fault at a depth of about 1 km. EGG will take significant responsibilities for the logging program that provides baseline physical property data along the borehole that will be used by the entire science team to correlate core and to assist in understanding in situ conditions. This work will have implications for the understanding of plate boundary fault motions leading to large earthquakes.We are also in the science team for drilling at Coulman High, a seafloor area that has collected sediments from Antarctica for much of the Cenozoic. Again, we are tasked with logging operations and we expect to send a trained Ph.d. student to carry out this work. In this case, the logging data will be key to locating in proper depth the core materials. The logs will look for patterns in sedimentation that switch from open ocean to ice covered; this information reveals patterns of past climate changes as indicators of open ocean in this part of the world strongly suggest that when the sediment was deposited the planet was generally warmer everywhere. Our primary interest, however, will focus on determination of stress states in the borehole. Our laboratory studies will concentrate on two topics. The first examines seismic reflections from anisotropic layers. While this work is of a more fundamental nature, having a good understanding of how the reflections change with both angle of incidence and azimuth is necessary for the proper interpretation of industrial seismic surveys that seek to indicate the patterns of in situ fracturing. Such knowledge is key to the planning of drilling for hydrocarbons in low permeability formations and for long term injection of geologically sequestered greenhouse gases. We will use a specialized instrument called an acoustic goniometer to measure the variations in the amplitudes of ultrasonic pulses reflected from anisotropic blocks of materials in order to simulate in situ conditions. Finally, we will continue laboratory research on seismic dispersion, i.e. the changes in the seismic wave speeds and attenuation with frequency. The purpose is to determine how to reconcile laboratory measurements taken at very high frequencies of 1 MHz with field seismic observations acquired at frequencies of 100 Hz. We are currently developing new instrumentation to measure directly the bulk modulus at low frequencies. This differs from all other measurements in the and as such the new instrumentation should provide a new tool for studying frequency dispersion.