ENGINEERING OBSERVATIONS ON GROUND MOTION AT THE VAN-NORMAN-COMPLEX AFTER THE 1994 NORTHRIDGE EARTHQUAKE

During the 1994 Northridge earthquake, the Van Norman Complex yielded an unprecedented number of recordings with high acceleration, in the c lose proximity of the fault rupture. These strong-motion recordings ex hibited 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 val ues comparable with those of the horizontal acceleration. The accelera tion response spectra in the longitudinal and transverse directions we re significantly different. Such a difference, which is not yet well d ocumented in the field of geotechnical earthquake engineering, indicat es that the amplitude and frequency content of the ground motion was d irectionally dependent in the Van Norman Complex.