Most of our attention here at Hot Air is devoted to politics and cultural issues, but I came across some stories this week that have me worried about something else: Earthquakes.
I’ve been living here since 1997 and in that time I’ve experienced at least half a dozen earthquakes. Most of them are small. Maybe your chair rocks in place a little bit. It’s unnerving, partly because you don’t know how long it will last or if what you’re feeling will suddenly get a lot worse.
I’ve only experienced two earthquakes that I’d describe as scary. The worst one happened sometime around 1999. I was upstairs in the townhouse I owned at the time and the entire thing started to rock violently back and forth, hard enough that I could see the walls bending and hear them creaking. For a moment it genuinely felt like the floor might just break apart and dump me down a long way. And then it was over.
So that’s probably why I notice stories like this one saying that the slip rate of the San Andreas fault is faster than previously estimated.
The speed at which the Santa Cruz Mountains portion of the northern San Andreas Fault moves — also known as the fault’s slip rate — is faster than earlier estimates suggested, according to research by San Jose State University professor Kim Blisniuk, an earthquake geologist. Faster faults generally have more frequent earthquakes than equivalent slower-moving faults.
Previous research into slip rates in the area spanned a time period of up to 1,000 years, according to Blisniuk. Her study — which is not yet published, though she hopes to present the findings at a conference in October — stretched over the last 10,000 years.
Scientists previously theorized that the slip rate of the northern San Andreas would slow down further south along the fault, with one hypothesis being that “slip is then being transferred onto other faults” along the way, such as the Calaveras or Hayward faults, Blisniuk said. But her research found that the slip rate — and therefore the likelihood of an earthquake — did not decrease but actually stayed the same from the North Coast section to the Santa Cruz Mountains section.
The story is careful to point out that while this makes future earthquakes along the fault more likely, it doesn’t necessarily mean they will be more powerful. That depends on how deep the eventual quake happens and how powerful it is cannot be estimated by the slip rate. So more quakes but not necessarily worse ones.
But there’s also this other story I came across which suggests the fault has been relatively quiet for quite a long time. There have been some massive quakes in the past, but nothing at quite that scale since.
There is no simple answer for why California’s longest fault, responsible for some of America’s most powerful earthquakes, has produced so few in the last century.
But it is clear that the quiet period is only increasing strain on the San Andreas, as well as on the state’s second-longest fault, the San Jacinto.
A new study underscores the concern. Researchers estimated that key sections of the fault in Southern California are at their highest level of tectonic strain in the last 1,000 years…
The computer model “found that tectonic stress has now reached higher levels than at any point in that entire record. From the model, we see that the conditions that historically preceded large joint ruptures crossing both fault systems are now approaching,” said Liliane Burkhard, the lead author of the study and a scientist at the University of Bern in Switzerland and the Hawaii Institute of Geophysics and Planetology at the University of Hawaii.
In 1857, a 7.9 earthquake located near Bakersfield is still considered a “Big One.” Almost no one was killed, mostly because it was relatively isolated and there weren’t many people in the area. But obviously if we had something like that today near a major city the outcome would be very different.
In 1924, a 7.9 quake hit San Francisco. It destroyed 80 percent of the city and killed 3,000 people at a time when the total population of the city was about 400,000. The current population is now double that and there are a lot more tall buildings.
What’s coming could be on that scale. By contrast the last big earthquake most people remember is the Northridge quake in 1994, which was relatively limited.
The computer model “found that tectonic stress has now reached higher levels than at any point in that entire record. From the model, we see that the conditions that historically preceded large joint ruptures crossing both fault systems are now approaching,” said Liliane Burkhard, the lead author of the study and a scientist at the University of Bern in Switzerland and the Hawaii Institute of Geophysics and Planetology at the University of Hawaii.
The last major temblor to strike urban Southern California, the magnitude 6.7 Northridge earthquake of 1994, resulted in severe damage and the deaths of about 60 people. But it was also mostly limited to a relatively small area of Los Angeles County.
So if you’re not here, you have nothing to worry about but if you are here you find yourself wondering occasionally when the next one will happen and how big it will be.
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