Abstract

During the 1994 Northridge earthquake, the Van Norman Complex yielded an unprecedented number of recordings with high acceleration, in the close proximity of the fault rupture. These strong-motion recordings exhibited the pulses of the main event. One station recorded the largest velocity ever instrumentally recorded (177 cm/sec), resulting from a 0.86 g peak acceleration with a low frequency. Throughout the complex, the horizontal accelerations reached peak values ranging from 0.56 to 1.0 g, except for the complex center, where the peak acceleration did not exceed 0.43 g. The vertical acceleration reached maximum peak values comparable with those of the horizontal acceleration. The acceleration response spectra in the longitudinal and transverse directions were significantly different. Such a difference, which is not yet well documented in the field of geotechnical earthquake engineering, indicates that the amplitude and frequency content of the ground motion was directionally dependent in the Van Norman Complex.

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