This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). It will support the design and construction of a new instrument capable of measuring with high sensitivity the torsional oscillations of the Earth?s surface induced by earthquakes and other disturbances. In recent years, there has been a recurring clarion call for the development of suitable instruments to record rotations over a wide frequency band of interest from ~ 0.37 mHz corresponding to the lowest normal mode of the Earth, up to about ~1Hz, corresponding to the highest frequency of interest in the near-field strong-motion seismology, and in the engineering of structures like buildings, dams, bridges and pipelines. The development of precisely such an instrument will be undertaken at the Washington University, St. Louis, based on an innovative idea which has played an important role in Physics. The essence of the new idea stems from the study of the response of torsion balances to torques generated by seismic rotations about the local zenith. At frequencies larger than the natural frequency of the torsion balance, its response drops quadratically and rapidly becomes negligible. Thus, the balance bob offers an immovable target for being viewed by an optical lever, which, being attached to the Earth, will record the seismic rotational oscillations with high fidelity. The optical lever with a sub-nanoradian resolution has been developed at the Washington University. In order to meet the need of a large number of field instruments needed for studies in close proximity to faults prone to generate earthquakes, a robust instrument will also be developed. These instruments will help in the understanding of the interior structure of the Earth, and the seismic processes.
Among the six seismological observables comprising translations along the three axes and rotations about these axes, it is the translations that have led to much of the developments thus far the field of Seismology and Earth Sciences, both in terms of theoretical studies and observations. All the same, there is no doubt that rotational motions, once measured carefully, will bring a wealth of information that will not only complement and accentuate that obtained from translations but are also likely to reveal new phenomena specific to rotations. Also the highly interdisciplinary aspect of these studies involving activities across the fields of seismology and earth sciences, physics, instrumentation and computer technology, provides an excellent training ground in science and engineering, not only for the undergraduate and graduate students of the university, but also to the instructors and students of the community colleges and under-represented groups who will be invited to participate in the project activities right from the beginning. Such training will increase our competitiveness in technology and innovations. Because the rotational seismometers, especially the robust strong-motion near-field sensors, are required in large numbers for deployment in earthquake-prone zones, they will have a potential as commercial products, especially because of their moderate cost. More importantly, they will tend to mitigate the damage caused to people and property by earthquakes.
