Visitors to the Bay area are curious about, if not fearful of earthquakes. They have seen pictures of earthquake aftermath, understand that another quake is inevitable, and want to know how Bay area natives live with this threat.
I usually reply with an old saying, “earthquakes don’t kill people; buildings do”.
Major quakes in 1868, 1906 and 1989 tested building techniques in the Bay area. Each failure has produced corresponding remedies. These remedies form the basis for building practices and seismic safety codes in widespread use today.
The 1868 earthquake, centered in Hayward, registered 6.8 on the Richter scale and shook for 1 minute. Buildings on landfill were the hardest hit. The best performing buildings were bolted to their foundations and/or had internal bracing. Reports following the earthquake publicized these successes, though building codes did not change. Since San Francisco was also subjected to devastating fires, many new buildings were constructed of fire retardant materials such as brick or cement.
In 1884 San Francisco engineer Ernest Ransome invented and patented reinforced concrete. Ransome added twisted iron rods to poured concrete to increase its strength. His Alvord Lake Bridge in Golden Gate Park (1889) was the first bridge in North America made of reinforced concrete. By 1894 Stanford University used reinforced concrete in several of its buildings, including the Junior Museum. Ransome’s methods became more widely used after fire and earthquake proved they worked.
The 1906 earthquake in San Francisco registered 7.8 on the Richter scale and killed an estimated 3,000 people. One fatality, fire chief Dennis Sullivan, died from his injuries when a chimney fell on the firehouse. With the failure of the water mains, fires consumed the city and 250,000 persons became homeless.
Those structures that withstood the 1906 earthquake featured steel or iron frames or bracings. The Palace Hotel, for example, was constructed to be “earthquake resistant”. Its structure contained multiple crosswalls, belted with iron, and strengthened with cement mortar. (It survived the earthquake but, unfortunately, suffered massive damage in the fire that followed.)
Rebuilding rapidly, San Francisco became a city of “rising steel”. Many buildings of this era survive today. The latest earthquake-resistant construction emphasized static buildings, trussed, braced and bolted.
In 1925 John Blume experienced a severe earthquake in Santa Barbara, and vowed to look for solutions to poor construction. In the 1930’s he was a young student at Stanford University studying earthquake engineering. Blume rejected the theory of static buildings and advocated “dynamic” building, stressing design and materials with flexibility and ductility. With the help of Professor Lydik Jacobsen, Blume constructed a shaking machine to simulate an earthquake and its effect on various landforms and buildings. He tested replica buildings for inertia, ductility, resilience and strength. He promoted the use of materials and techniques to allow a building to move in an earthquake. Blume’s work led to his reputation as “the father of modern earthquake engineering”.
The Alexander Model is Blume’s replica of a 16-story building and allows 5 degrees of movement in all directions without damage. Blume used this model to test various seismic conditions. Today the Alexander Model is on display at the Blume Earthquake Engineering Center at Stanford.
New techniques in earthquake design allow for movement, intentional break points, and flexible utilities. San Francisco’s City Hall sits on a moat and a basement of shock absorbers. These “base isolators” allow the whole structure to move as a unit in an earthquake.
One of the most recent examples of cutting edge earthquake design in San Francisco is the Exploratorium Museum. In 2013 the Museum opened at its new Pier 15 location. The architects of the new museum exposed the flexible utilities inside in long, looping cables, and designed a prominent (300 foot long) “seismic joint” which attaches the pier to the bulkhead. This joint will allow the pier and the wharf to move without damaging each other.Among these successes are still some cautionary notes. Many vintage buildings in San Francisco have first stories that are considered “soft”. These buildings are vulnerable to collapse in the next big earthquake. Yes, they urgently need retrofitting but at what cost? Landlords and homeowners risk property and even life by delaying improvements.
Earthquakes are a feature of the Bay area, but the dangers of earthquakes can be mitigated with good design. So if you are a visitor to the Bay area and you experience an earthquake, my advice is to step inside a new building for shelter and safety.