Connected Californian Fault Lines can Cause Havoc

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San Andreas is a movie that describes the imaginary effect of a huge earthquake in California – but scientists say the tsunami threat to the West coast of the United States could be greater than was previously thought.

Geologists have pinpointed a number of major faults that have the potential to send tsunamis crashing into San Diego and Los Angeles. Mark Legg, lead researcher and geologist from a consulting firm Legg Geophysical says, “in the last few hundred years, there have been large magnitude 7-plus earthquakes on these offshore faults. So we should not be surprised if we have another one.”

Though geologists knew about these faults, Legg and his team have studied them in greater detail, and found evidence of upward and sideways movement by measuring seafloor depth along a 4,500 km-stretch of the Santa Cruz-Catalina Ridge Fault and the Ferrelo Fault. Movement of the Earth’s Pacific plate – sliding away from California – against the North American plate has caused these faults as well as the more well-known San Andreas one.

Scientists have confirmed that two California fault lines – the Calaveras Fault and the Hayward Fault – are connected. The 70-km-long Hayward Fault is “already known as one of the most dangerous in the country as it runs through densely populated areas.” The line begins near Santa Rosa in the north, passes east of San Francisco, and ends near San Jose in the south.  A tsunami could still wreak havoc on cities, beaches and ports along the Californian coast.

The group’s findings have just been published in the Journal of Geophysical Research. And now that they know it’s connected to the 123-km-long Calaveras Fault, they say the risk it poses could be even greater.

The lead researcher and seismologist, Estelle Chaussard said “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.”   The findings reported in the journal Geophysical Research Letters convey that the next stage of the research is to refine their “magnitude estimates” for specific spots along the fault line to help predict potential damage and take suitable precautions.

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