In the early hours of February 9 in the year 1971, the foothills of San Gabriel Mountains located in the southern area of California was rudely awaken by a sudden violent shaking of the ground. The earthquake was soon to be known as “the Sylmar Earthquake”. The totally unexpected earthquake was measured to have the magnitude of 6.5 up to 6.7 as done by seven different independent institutions; and had the maximum intensity of XI or in other words extreme according to the Mercalli scale. The occurrence was one that had an effect in Los Angeles in the late parts of the 20th century.
A study was then conducted on the Sierra Madre Fault and the results indicate that earthquakes had occurred in the past located near its Transverse ranges. The casualties were severe in the local northern San Fernando Valley. The fault on the surface was extensive and was to the south of the epicenter that was in the mountains along with the urban settings, city streets and the neighborhoods. The uplift and the other effects of the earthquake had affected most private homes and business.
The earthquake had caused damage to some medical care facilities in Sylmar, located in San Fernando; not only that but the densely populated parts of Central Los Angeles also suffered damages. One of the infrastructures that were damaged was the Olive View Medical Center and the Veterans Hospital. These two structures had suffered very heavy and major damage. The buildings around and in both sites also experienced structural failure, this was the cause of the majority of death casualties in the tragic event.
The infrastructures were both constructed differently, but unfortunately the engineers had failed to thoroughly inspect the responses of the buildings because they weren’t outfitted with the instruments used to record strong ground motions. Because of that the Veterans Administration was prompted to install seismometers at sites that are high risk or are highly likely to be most vulnerable to ground movements.
The other sites all throughout Los Angeles were then instrumented as the result of local ordinances to reduce earthquake casualties. Due to that, extraordinary amounts of data regarding strong ground motion was recorded, more than any other occurrence up until that point in time. The success in spreading awareness in this area had prompted the start of a Strong Motion Instrumentation Program in California.
The transportation in Los Angeles was severely problematic due to the roadway failure and the collapse of seven major freeway interchanges. The Lower Van Norman Dam had nearly experience complete and total failure, this resulted to the evacuation of thousands of residents in the downstream area. But it was believed that the early choice to maintain the water at a low level may have had contributed to salvation of the dam from being topped over. Schools in the area were also affected just as they were in the prior earthquake in Long Beach California. Though at this time, the construction styles were amended and the damage the schools that taken were significantly lower.
Other casualties due to the earthquake were a methane seep that had emanated from the Pacific Ocean’s floor that was near Malibu for seven days and many landslides were recorded in the San Gabriel mountains.