Northridge, California, earthquake of 1994: density of pipe breaks and surface strains

Empirical scaling equations are presented which relate the average number of water pipe breaks per km², , with the peak strain in the soil or intensity of shaking at the site. These equations are based on contour maps of peak surface strain evaluated from strong motion recordings, and observations of intensity of ground shaking and damage following the Northridge, California, earthquake of 17 January 1994. Histograms for the number of pipe breaks per km², n, are presented for several ranges of values of the horizontal peak strain and for several values of the site intensity. The observed distribution of pipe breaks is also used to speculate on possible more detailed geographical distribution of near surface strains in the San Fernando Valley and in central Los Angeles. The results can be used to predict number of pipe breaks in the San Fernando Valley and in Los Angeles, for a scenario earthquake or in probabilistic seismic hazard calculations, considering all possible scenarios that contribute to the hazard and the likelihood of their occurrence during specified exposure. Such predictions will be useful for emergency response planning (as the functioning of the water supply is critical for sanitation and in fighting fires caused by earthquakes), to estimate strains during future and past earthquakes in areas where no strong motion was recorded and in defining design guidelines for pipelines and other structures and structural systems sensitive to strains in the ground.