USAcross - Parkfield, CA

Imaging of the structure of a fault zone is currently done passively by earthquake monitoring and actively by explosion tomography. A better, more repeatable method is required if seismologists are to observe temporal changes in the soils and rock surrounding the fault zone. In Japan, large eccentric mass shakers have been used for this kind of study. At the well-monitored Parkfield segment of the San Andreas Fault, the NEES@UCLA shaker will provide the repeatable source and IRIS-provided seismic instrumentation will provide the receivers for an active imaging experiment. The 100,000-lb shaker force will be mounted on a permanent foundation and operated at both sine sweeps and sine dwells for periods up to 24 hours. Sensitive seismometers will monitor ground motions at distances up to 15km from the shaker in various array configurations designed to look at specific areas of the fault zone. In addition to these seismologically-oriented instruments, NEES@UCLA will provide strong-motion instrumentation for installation around the shaker foundation to record near-field ground motion patterns. The Project Team will use these data for imaging of the fault zone. If successful, the testing may be repeated at intervals of low years to attempt to image changes in the fault. In addition, per the requirements and spirit of both IRIS and NEES, all of the experimental data will be made available to the community.


Famous Parkfield Cafe


Shaker at the Middle Mountain site


Shaker at the Lake site


Waiting for shaker run to finish