Aftershocks took place over the following 36 hours. It also took place over rush hour in the city. The San Andres fault ruptured bilaterally, that is in two directions, from the centre of the fault line, causing a relatively short shock. If the fault had ruptured unilaterally, along the entire fault line, the shock would have lasted for almost double the time.
The underlying geology of California causes most of its earthquakes. Much of San Francisco is based on clay, some areas are built on reclaimed soft soil, e.g. the Marina district was built on reclaimed marshland in 1915. During the past years, the Santa Cruz Mountains have moved 6 ft northwards along a 25 mile section of the San Andres fault.
The problem comes when the quake occurs. The hard rock of the area provides resistance to the shock waves, and they are reduced in intensity. The clays and soft soils magnify the wave’s power, and can cause them to behave lick quicksand, an effect known as liquefaction. Under this, buildings can sink, intact, under their own weight. What made the earthquake even worse, was that the quake was predicted and the areas which suffered most were known to be at risk, and yet nothing was done.
All of the following events were caused by the earthquake of ’89:
- For some time, TV was the main means of communicating with the outside world.
- Local power supplies were cut, and the government emergency radio system had failed.
- People stayed at home, and isolated themselves.
- Relief efforts for the “Bay Area” were a national response.
- Media takes some responsibility for public education.
- The government were slow to respond. The media respond much faster.
- Total economic damage of around $10 billion.
- 42 died in Oakland, 60 miles from the epicentre. Are there were 400 injuries from the Cypress structure alone.
- 59 water mains burst, and over 100 gas mains were ruptured.
- 10,000 were left homeless, 63 died.
-
The Nimitz highway, and Cypress structure, and sections of the Bay Bridge collapsed, due to structural failure. They were subject to ten times the amount of force for which they were designed
