ABSTRACT Because of the wide deployment of fiber with cables often carrying 100,000 or more voicecircuits, even a one minute interruption in telecommunication service can totally disrupt theaffected communities. Therefore, service reliability of the telecommunication network is essential in an information-intensive society. One of the major reliability issues is the serviceability of telecommunication systems following a major earthquake. In this paper, we analyzed the mechanical failures of optical fibers from a cable subjected to a major earthquake.1. INTRODUCTION Little is known from laboratory testing or field performance of the seismic resistance of fiberoptic cables. An earthquake measuring 7.1 on the Richter scale rocked Northern California in October 1 989. A span of the Bay Bridge between San Francisco and Oakland collapsed. One of Pacific Bell's major fiber optic cables ran the length of the Bay Bridge. The active networks continued to provide uninterrupted service. Because of the major renovation to the bridge, the1 0,774 feet of cable had to be removed. It was sent to Bellcore for analysis to determine if any