The 1906 San Francisco Earthquake
Quake in Bay Area Among Worst Natural Disasters Recorded in US
A severe rupture occurred along the San Andreas Fault near San Francisco and tremors were felt in Oregon, southern California and central Nevada.
Statistics of the 1906 San Francisco Earthquake
On April 18th 1906 at 5:12am an earthquake with a magnitude of approximately 7.7 to 8.3 struck San Francisco with the epicenter near Daly City which is a suburb south of San Francisco. Approximately 25 seconds prior to the major earthquake, there was a foreshock felt in the San Francisco Bay area. The main tremor lasted 45 to 60 seconds. At 8:14am, a major aftershock struck which caused the collapse of many damaged buildings.
Immediately after the quake, many fires broke out and this added further destruction and death. The total death toll from the 1906 San Francisco earthquake was believed to be 3,000 and damage was estimated to be $5 million dollars using 1906 prices. There were over 250,000 homeless people.
Damage Caused by the 1906 San Francisco Earthquake
Over 30 fires caused by ruptured gas mains destroyed approximately 25,000 buildings in 490 city blocks. With water in short supply due to water mains breaking, it was almost impossible to extinguish the fires. Many buildings were purposely blown up with dynamite in order to create a fire break. The fires burned on for 3 or 4 more days before they were extinguished.
Many property owners deliberately set fire to their buildings that were damaged by the earthquake because most insurance companies did not cover losses from earthquakes but covered for fires.
Structures built in the valleys endured vigorous shaking due to the soil turning to liquid. This is a process called liquefaction. Buildings on bedrock were subjected to less shaking. The strongest shaking occurred in areas where the ground was reclaimed from San Francisco Bay.
The earthquake ruptured the ground for 296 miles along the northern section of the San Andreas Fault. The ground surfaces on either side of the rupture showed a slippage up to 20 feet away from each other in certain places.
What Was Learned From the 1906 San Francisco Earthquake
There were no strict building codes that made provision for earthquake damage. In fact, it wasn’t until the 1950s where a high level of building standards was established. Unfortunately, many of the pre-1950 buildings still exist in San Francisco which may prove dangerous when the next earthquake hits.
With the rupturing of the San Andreas Fault, it provided scientists an opportunity to further their studies in plate tectonics and the effects of earthquakes on the earth’s crust. On the eastern side of San Francisco Bay lies the Hayward Fault which runs through Oakland and Berkeley. There is a strong likelihood that activity on this fault will cause an earthquake in upcoming decades.
Sources:
- Berkeley Seismology
- US Geological Survey
- Wikipedia (has Pictures)
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The 1989 San Francisco Earthquake
The Great Alaskan Earthquake 1964
