It's Earthquake Day today, so there's lots in the media.
Here are a few very interesting links:
- San Francisco’s Big
San Francisco lives with the certainty that the Big One will come. But the city is also putting up taller and taller buildings clustered closer and closer together because of the state’s severe housing shortage. Now those competing pressures have prompted an anxious rethinking of building regulations. Experts are sending this message: The building code does not protect cities from earthquakes nearly as much as you might think.
- The HayWired Earthquake Scenario
The HayWired scenario is a hypothetical earthquake sequence that is being used to better understand hazards for the San Francisco Bay region during and after an earthquake of magnitude 7 on the Hayward Fault. The 2014 Working Group on California Earthquake Probabilities calculated that there is a 33-percent likelihood of a large (magnitude 6.7 or greater) earthquake occurring on the Hayward Fault within three decades. A large Hayward Fault earthquake will produce strong ground shaking, permanent displacement of the Earth’s surface, landslides, liquefaction (soils becoming liquid-like during shaking), and subsequent fault slip, known as afterslip, and earthquakes, known as aftershocks.
The most recent large earthquake on the Hayward Fault occurred on October 21, 1868, and it ruptured the southern part of the fault. The 1868 magnitude-6.8 earthquake occurred when the San Francisco Bay region had far fewer people, buildings, and infrastructure (roads, communication lines, and utilities) than it does today, yet the strong ground shaking from the earthquake still caused significant building damage and loss of life.
- News from the HayWired fault
Today, though, I wanted to provide some details from the original quake. In 1868 a committee was convened to create a report on the event, but it never finished a report, so whatever work they did was lost. We only know as much as we do because after the San Francisco earthquake of 1906, the commission set up under UC Berkeley’s Andrew Lawson to investigate it decided to add a chapter on previous earthquakes. There were enough survivors of 1868 at the time to record quite a bit of detail. So here are some tidbits from the famous Lawson Report of 1908 about the Hayward quake of 1868.
- The California earthquake of April 18, 1906. Report of the State Earthquake Investigation Commission
The fact that the California earthquake of April 18, 1906; occurred a little after 5 A. m., before people in general were up, is one cause why we have so little reliable information regarding the exact time at which it occurred. In answer to questions sent out by the Earthquake Commission, a very large number of replies were received, but it is quite evident, from the variations among them and from the fact that many only gave the time to minutes, that these times are very unreliable. The general descriptions show that the earthquake began with a fairly strong movement which continued with increasing strength for an interval variously estimated, but which really amounted to about half a minute; then very violent shocks occurred, and quiet was restored about 3 minutes later.