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Fault System Enables Larger Quakes In California
Taco Cowboy writes Researchers have mapped the land at the southern end of the Hayward Fault and found that the creep continued 15 km beyond to merge with the Calaveras Fault, which was thought to be independent. "The maximum earthquake on a fault is proportional to its length, so by having the two directly connected, we can have a rupture propagating across from one to the other, making a larger quake," said lead researcher Estelle Chaussard, a postdoctoral fellow in the Berkeley Seismological Laboratory. "People have been looking for evidence of this for a long time, but only now do we have the data to prove it". The 70-kilometer-long Hayward Fault is already known as one of the most dangerous in the country because it runs through large population areas from its northern limit on San Pablo Bay at Richmond to its southern end south of Fremont. Last month the U.S. Geological Survey estimated a 14.3 percent likelihood of a magnitude 6.7 or greater earthquake on the Hayward Fault in the next 30 years, and a 7.4 percent chance on the Calaveras Fault, but there is one problem — the estimate was based on the assumption that the two faults are independent systems, and that the maximum quake on the Hayward Fault would be between magnitudes 6.9 and 7.0. Given that the Hayward and Calaveras faults are connected, the energy released in a simultaneous rupture could be 2.5 times greater, or a magnitude 7.3 quake.
Laws requiring all structures to withstand an 8.0? Let's move past the enforcement nightmare that would be and look at the reality of building that strong, It would cost close to million US dollars to build a single floor, single family dwelling to those specifications. You would need a foundation between 36"-48", fully steel enforced, likely 6"x12" studs throughout 16" on center and 12'x12' or larger corner posts. The roof structure would weigh 5 to 7 times what a normal roof would, and every single wood joint would have to be reinforced with 1" thick steel plate, bolted through the stud and beam centers.
In California structural laws are designed to preserve human life, and structures are designed to survive the shaking enough to allow people to exit, but we take the Japanese mentality that natural disasters will do damage, and it's better to rebuild every few decades.
Besides, California is a transverse zone (primarily, north of Mendocino is subduction with divergent off shore, and some divergence from the Salton Sea south) and we deal with shallow M7-M9 earthquakes, while Chile runs along a subduction zone, with deep M15+ quakes. Your quakes have much more energy dispersed over a larger area, while ours tend to be more localized and focused. We get at most 3-5 minutes of shaking, with less than a minute of intense damaging waves, while you can have 5min+ of building-toppling destruction,