The damage was greatest near and well north of the surface faulting , and at the foot of the mountains . The hospital buildings , the freeway overpasses , and the Sylmar Juvenile Hall were on coarse alluvium that overlay thousands of feet of loosely consolidated sedimentary material . In the city of San Fernando , underground water , sewer , and gas systems suffered breaks too numerous to count , and some sections were so badly damaged that they were abandoned . Ground displacement damaged sidewalks and roads , with cracks in the more rigid asphalt and concrete often exceeding the width of the shift in the underlying soil . Accentuated damage near alluvium had been documented during the investigation of the effects of the 1969 Santa Rosa earthquakes . A band of similarly intense damage further away near Ventura Boulevard at the southern end of the valley was also identified as having been related to soil type
1969 Santa Rosa earthquakes
1969 Santa Rosa earthquakes
1971 San Fernando earthquake