This action is to support the installation of a vertical seismic array on the UC Berkeley campus. Two instrumented boreholes will be installed on either side of the Hayward Fault. Each borehole will consist of 3-component accelerometer units, a rate gyroscope, magnetometer, and pore pressure sensor. The sensors will be an array of MEMS-based devices, including an all-digital 24-bit accelerometer. The sensors will be incorporated into an intelligent networked sensor Mote. An event driven TinyOS is used to multiplex the concurrent flows of information across this single controller, which is connected to a transceiver, a secondary storage device, a sensor oriented I/O system, and a power management subsystem. The noise floor of the array is expected to be approximately 30 ng/root(Hz), and the cost about 2 magnitudes less than current vertical arrays.
In recent years, vertical arrays have come on-line in several sites in California, Taiwan, and Japan. They are changing the understanding of seismic ground motion by allowing for the 3-D evaluation of seismic wave propagation. Downhole recordings of ground motion provide a glimpse of how waves are propagating near the surface of the earth. By comparing multiple downhole recordings and a related surface recording, it is possible to observe how the waves change as they progress through the ground and are affected by materials in the soil profile. The arrays allow the estimation of experimental Greens functions for a site, with the estimation made using the rich field of system identification. Perhaps most importantly, the project will also introduce civil engineering students to new developments in sensor, communications, and information technologies, and to help them to become familiar with multi-disciplinary tools, and to become aware of the implications of advances in other fields of engineering, and how these technologies might help them solve civil engineering problems.
