The San Francisco earthquake of 1868
A home in Hayward, California
Background
In the years 1827, 1829, and 1839, California experienced a multitude of earthquakes. At the time there were reports that buildings had collapsed, and certain areas of California had become flooded. San Francisco was once a small town with a population of about 800 people. After gold was discovered in the area that number quickly shot up to around 20,000 individuals.
After about two decades, the inhabitants of San Francisco would find themselves complaining of the frequency of these earthquakes. There was one earthquake that occurred in 1865 that shook San Francisco. The reported magnitude of said earthquake was around a 6.8 on the Richter scale. The citizens of San Francisco were incredibly concerned as at the time there was no way to predict when an earthquake would occur. People were also very curious as to why these earthquake had been happening in such frequency.
On October 21st, 1868 the city suffered another major earthquake. This time the damage was even more serious. Whole buildings could not stand up to the forces produced by the earthquake. As such buildings made from masonry crumbled and fell to pieces. It was calculated that this earthquake has 7.0 magnitude.
Flour Mill in Hayward
House in Hayward
What was lost
Deaths: 5
Injuries: 30
Property Damage: Excess of $300,000 in 1868, equivalent to $5,000,000 in 2019.
Alameda County Courthouse
Closeup of Courthouse
What was learned
- Surprisingly it was found that ballon framed buildings actually held up the forces of the earthquake.
- This was due to the nails that held the structure together. The nails allowed for the structure to move thereby rendering the force of the earthquake ineffective.
- Interestingly, buildings that were contracted from masonry or concrete, do not handle well under tensile forces. As such when the earthquake hit these buildings they simply broke apart.
Estudillo Home
Warehouse in Hayward
Bush & Market
significance
- Improvements to earthquake resistant designs are slow, however codes are constantly changing to meet with the specific needs of each kind of disaster.
- "As of the 2006 International Building Code, the current earthquake formula utilized to calculate the amount of shaking force that a buildings base must resist is, V= Cs W."
Where,
V = the "seismic base shear", this is how strong the base of the building needs to be in order to resist shearing.
Cs = the "seismic response coefficient", this is usually found in tables and charts which can tell a designer how well the building will perform given specific conditions.
W = the "effective seismic weight", this is the total weight building.
Reimstein Clothing