This grant will support in situ measurements of the mechanical properties of an active fault zone (the San Andreas fault in southern California). The measurements are made using a long-base laser strainemeter to measure the earth tides inside the fault zone, which are compared against the tides expected for a homogeneous Earth. Differences between the measured and predicted tides indicate that the fault zone has different elastic properties than the material around it. This project was originally supported by EAR Instruments and Facilities, which supported construction of a "portable" strainmeter for measuring tides. This first installation showed clear evidence of tidal distortion; the present grant is to relocate the strainmeter to a new azimuth, so as to determine the full strain tensor and better constrain the nature of the fault zone elastic properties.
