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drscottI heard something on the news last night about a study of the southern San Andreas fault; locked for 300 years, overdue for a Big One. I wasn't too alarmed, but the more thorough text stories are scary. It appears that some scientific wishful thinking about the network of faults in the Coachella Valley gradually releasing the accumulating stress is ruled out by the study, which used detailed GPS and satellite data to show that the fault is truly locked along a segment from San Bernardino to the Salton Sea. This implies that the yearly probability of a massive (1906-SF-level) quake along this segment is very high, and if it unlocks from south to north, it will send a wave of focused energy into the Los Angeles basin, with resulting destruction and death on a scale never seen in this country.
It may not happen for another 20 years, or it could be this afternoon.
[detailed report in Science here, but it may be behind a wall]
East of Los Angeles, the San Andreas fault dangerously traverses rapidly growing areas of the Inland Empire (San Bernardino-Riverside). In a great earthquake (magnitude 8.0 or greater) along the San Andreas fault, northern Los Angeles County and the Palm Springs area will likely be the hardest hit. Because there is a greater density of older structures in these areas, many buildings will completely collapse, potentially killing thousands. All southern California communities will be subjected to some level of damage; aid for emergency response will have to come from much farther away and will take much longer to arrive.
The level of damage in Los Angeles will likely be higher than current models predict. Existing building codes have been designed largely based on the ground shaking generated by moderate earthquakes. A recent California Institute of Technology study concluded that the energy produced in a magnitude 8 earthquake on the San Andreas fault could cause one or more high-rise buildings in downtown Los Angeles to collapse.
Just as the collapse of the levees in New Orleans turned a disaster into a catastrophe, the secondary effects of an earthquake can also be more calamitous than the earthquake event itself. Any of the major earthquakes that will strike the Southern California region could trigger a range of secondary effects depending upon the exact fault, weakened infrastructure nearby, and the weather. The potential secondary effects include:
* Fires. Fires have always been a major problem after earthquakes. Ruptured gas lines and failed water delivery systems combine to make firefighting very difficult. Fires destroyed much of San Francisco in 1906, and contributed to the loss of 100,000 lives in the great Tokyo earthquake of 1923. If an earthquake strikes Los Angeles during a time of hot, dry winds such as when the wildfires of 2003 occurred, firestorms could erupt throughout the City.
* Landslides. Landslides are another common result of earthquakes. If the earthquake happens during heavy winter rains, landslides could be widespread. One landslide triggered by an earthquake in the Soviet Union in 1957 covered a city, killing 50,000 people. There are even secondary effects from the landslides – for example, over 1,000 cases of Valley Fever, an emerging and sometimes deadly fungus infection, were caused by the dust raised by landslides during the 1994 Northridge earthquake.
* Dam failures. The San Gabriel Mountains, north of the Los Angeles basin contain many old dams built in the 1920s and 1930s. The failure of even one of these structures could flood tens of thousands of homes and result in significant loss of life.
* Aftershocks. Large earthquakes trigger other earthquakes, sometimes at significant distance away from the main shock. A large San Andreas event could easily trigger an aftershock of magnitude 6.5 – 7 in Los Angeles. Aftershocks can be even more damaging to buildings already weakened by the main shock. A disaster similar to the 1994 Northridge earthquake could occur as a consequence of a single aftershock.
It may not happen for another 20 years, or it could be this afternoon.
[detailed report in Science here, but it may be behind a wall]
East of Los Angeles, the San Andreas fault dangerously traverses rapidly growing areas of the Inland Empire (San Bernardino-Riverside). In a great earthquake (magnitude 8.0 or greater) along the San Andreas fault, northern Los Angeles County and the Palm Springs area will likely be the hardest hit. Because there is a greater density of older structures in these areas, many buildings will completely collapse, potentially killing thousands. All southern California communities will be subjected to some level of damage; aid for emergency response will have to come from much farther away and will take much longer to arrive.
The level of damage in Los Angeles will likely be higher than current models predict. Existing building codes have been designed largely based on the ground shaking generated by moderate earthquakes. A recent California Institute of Technology study concluded that the energy produced in a magnitude 8 earthquake on the San Andreas fault could cause one or more high-rise buildings in downtown Los Angeles to collapse.
Just as the collapse of the levees in New Orleans turned a disaster into a catastrophe, the secondary effects of an earthquake can also be more calamitous than the earthquake event itself. Any of the major earthquakes that will strike the Southern California region could trigger a range of secondary effects depending upon the exact fault, weakened infrastructure nearby, and the weather. The potential secondary effects include:
* Fires. Fires have always been a major problem after earthquakes. Ruptured gas lines and failed water delivery systems combine to make firefighting very difficult. Fires destroyed much of San Francisco in 1906, and contributed to the loss of 100,000 lives in the great Tokyo earthquake of 1923. If an earthquake strikes Los Angeles during a time of hot, dry winds such as when the wildfires of 2003 occurred, firestorms could erupt throughout the City.
* Landslides. Landslides are another common result of earthquakes. If the earthquake happens during heavy winter rains, landslides could be widespread. One landslide triggered by an earthquake in the Soviet Union in 1957 covered a city, killing 50,000 people. There are even secondary effects from the landslides – for example, over 1,000 cases of Valley Fever, an emerging and sometimes deadly fungus infection, were caused by the dust raised by landslides during the 1994 Northridge earthquake.
* Dam failures. The San Gabriel Mountains, north of the Los Angeles basin contain many old dams built in the 1920s and 1930s. The failure of even one of these structures could flood tens of thousands of homes and result in significant loss of life.
* Aftershocks. Large earthquakes trigger other earthquakes, sometimes at significant distance away from the main shock. A large San Andreas event could easily trigger an aftershock of magnitude 6.5 – 7 in Los Angeles. Aftershocks can be even more damaging to buildings already weakened by the main shock. A disaster similar to the 1994 Northridge earthquake could occur as a consequence of a single aftershock.
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no subject
Date: 2006-06-22 10:28 pm (UTC)Curious that the Science article refers to the 1906 earthquake that left the nascent gold-rush city in smouldering ruins. Maybe I'm being too picky, but I think it was the fire, not the quake, that left the city in smouldering ruins, 'though, of course, the quake cause the fire. See for example here for the usual line about most of the damage being attributable to the fire.
I know it is dangerous to tangle with the Dr. on a scientific matter...
no subject
Date: 2006-06-23 04:16 am (UTC)There was an effort by Chamber of Commerce types to minimize the reported number of deaths in 1906, and the fire was played up somewhat to make the disaster seem less threatening. There were probably a lot of frame structures in reasonable shape after the quake which were then destroyed by the fire. But it's far from clear that the city would avoid the same fate if the quake hit today, since they allowed rebuilding in wood and much of the city is rent-control-anti-development-locked into contiguous blocks of wood-frame construction.
no subject
Date: 2006-06-23 09:55 pm (UTC)While I would love to somehow find comfort in your relative comparison to the situation in LA, I'm not going to bet on it. I think we could easily get a 7+ along the Hayward or one of the other Bay Area faults in our lifetimes.
The SF city spin machine definitely did try to minimize the death toll of '06. I think it has been pretty clearly established that there were several times the 500 or so deaths the city officials tried to claim.
Not sure what better practical alternatives there are to wood (rebuild the Victorians with steel frame perhaps?). At least wood bends and flexes when the earth shakes. If you were around in Loma Prieta you probably saw that by far the worst damage was anything in brick or masonry, especially when built on soft soil.
no subject
Date: 2006-06-23 10:21 pm (UTC)The complete aversion to highrises and the lack of redevelopment of the square miles of typical wooden flat blocks is unfortunate for all sorts of city planning reasons, not just fire. And the codes put in place after 1906 do specify better firewalls. But still, if the city had evolved as Vancouver's West End did, to mix (steel-framed) highrise flats with older houses and open space, it would be less likely to support a firestorm today.