True six-degree-of-freedom (6DOF) measurement of free-field strong ground motion has been accomplished using a prototype 6DOF accelerograph system. This system consists of a traditional triaxial translational accelerometer, three new rotational velocity sensors, and a digital data logger.

Rotational and translational ground motions at a single free-field location were measured successfully during the recent NPE event, a very large (1 kton) chemical explosion. Peak vertical acceleration at the near-field measurement site exceeded 1g for this event; the peak measured rotational velocity was 2.2°/sec. Earthquake strong-ground-motion measurements are currently in progress.

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