Duration of strong ground motion during Northridge, California, earthquake of January 17, 1994

Contours of spatial variations of the duration of strong earthquake ground motion during the 1994 Northridge, California earthquake are smooth over distances as large as tens of kilometers. Visual comparison of those contours with the depth of sediments and with vertical offsets of the basement rocks along the faults in the Los Angeles basin are in excellent qualitative agreement with the trends predicted by the previously published empirical scaling equations of strong-motion duration. It is argued that if the source-to-station distances were measured along the three-dimensional wave paths through the sedimentary wave-guides, rather than along straight lines as is common at present, the accuracy of empirical scaling equations could be improved significantly.

► Contours of strong motion duration are presented for 1994 Northridge earthquake. ► It is shown that distances for regressions should be measured along the wave paths. ► Earthquake specific contours provide better accuracy for attenuation equations.