California residents are conversant with February 9, 1971, precisely at 6:01 AM PST. What was to be the dawn of another usual day turned out to be an uneventful day following the occurrence of an earthquake that stands as one of the worst to have hit the California region. The earthquake came to be known as the San Fernando earthquake of 1971. With a magnitude of 6.6 and a maximum Mercalli intensityof XI.
What caused the San Fernando Earthquake?
The San Andreas Fault and the Transverse ranges were the main geographic features that geologists established as being involved in causing the earth movements.The main visible feature affected by San Fernando was the San Gabriel Mountains which is a 60 km portion of the Transverse ranges.
Geologists assert that paleomagnetic forces lead to the formation of the Transverse Ranges at the time the Pacific Plate was moving northward along the North American Plate. With the Pacific Plate moving to the north, a part of the terrane which was parallel to the coast got to be rotated in the clockwise direction leaving it positioned in an east-west orientation.A series of basins are found along the Transverse range. On the eastern side, there are two basins, the San Gabriel Basin and the Ventura Basins. The San Gabriel Basin has active reverse faults which are actually responsible for movements that have led to the occurrence of a number earthquakes in the region.
How did the San Fernando Earthquake happen?
San Fernando which lasted for nearly 12 seconds was attributed to a reverse faulting process. As stated, the earthquake occurred at 6:01,PST (which is 14:01 UCT). The epicenter of earthquake was traced to be an estimated five miles to the north of the San Fernando Valley, which is actually where the active faults are located. All features around the San Fernando were the first in the line of damage with there being massive earth movements in the valley and in the San Gabriel Mountains right above the fault block. Geologists least expected the occurrence of this earthquake owing to the fact that the fault which moved causing the movement had initially been treated as one posing no threat.
The impacts of the San Fernando earthquake
Buildings, structures and social amenities
The earthquake, which was seen to have quite a number of similarities with the Northbridge earthquake of 1994 which occurred in the same region, hit the areas lying north of Los Angeles. From a geographicalperspective those areas bounded by the San Fernando Valley on the northern side( located at the base of the San Gabriel Mountains) were the most affected areas.
Even in the areas that stood as less susceptible to damage, the tremors were able to make their way there and some substantial damage was experienced. A perfect example is in the unincorporateddistricts (Saugus, Newhall) where new buildings had been erected. Unfortunately, the engineering specifications were not enough to cater for the magnitude of the tremors.
Geologists were able to make out the important role played out by the geographical features around the areas where human life was present during the earthquake. Those living in the areas bound by the Los Angeles River, the Santa Monica Mountains, the Santa Susana mountains and the Verdugo Mountains were shielded from the possible massive damage that would have affected them.
With most of the buildings, institutions(Hubbard Street Elementary School, Los Angeles High School), dams (Van Norman dam), and bridges(Golden State Freeway) that were worst affected being locates on loose sedimentary material, there were absolutely minimal chances of these structures surviving the damages. A large number of the social amenities in the region could barely be of service right after the earthquake occurred. The Sylmar Juvenile Hall, gas systems, sewers, underground water pipes and hospitals (Foothill Medical Building, Indian Hills Medical Centre and Pacoima Lutheran Professional building) were among the many listed social amenities that experienced heavy damage.
After the earthquake subsided, medics were able to ascertain that more than 50 lives had been lost in causes directly linked to the tremors. The total number of deaths was a higher number since other people eventually succumbed to injuries later on. The Olive View hospital and the Veterans hospital contributed the highest number of deaths to the eventual tally of the deaths. The rest of the deaths were distributed in different locations.
What intervention measures resulted from the earthquake?
Following the San Fernando Earthquake, the senate legislated the Alquist-Priolo Special Studies Zone Act and embarked on the development of program called the California Strong Motion Instrumentation Program both of which were geared towards ensuring readiness in case a similar earthquake hit the region.