What natural disasters occurred in Vancouver earthquakes

America’s northwest is threatened with a strong earthquake

A devastating strong earthquake comparable to the Chile earthquake or the Haiti earthquake at the beginning of this year could hit the Pacific Northwest of America within the next 50 years. Geologists have re-examined the seismic past of the Cascadia fault there and determined a 37 percent probability of a strong earthquake of magnitude 9 in the next 50 years.

The Cascadia subduction zone in the northwest of the American continent is considered to be a mega-class earthquake generator. Because if it crashes here, then it's right: 41 quakes of magnitude 8.2 and higher have occurred at this plate boundary in the last 10,000 years alone, in which several oceanic plates collide with the North American crustal plate. The last major quake occurred in January 1700 and sent a tsunami across the Pacific that caused waves nine meters high in Japan. Actually, seismologists previously thought that such a strong earthquake in the Cascadia Zone, which stretches from Vancouver Island to Northern California, was only due every 500 years, but as it now turns out, they could have been wrong.

Marine sediment as an earthquake indicator

New analyzes by marine geologist Chris Goldfinger and colleagues at Oregon State University have opened up new insights into the seismic history of the American Northwest, suggesting a much more complex geology. The researchers found important evidence of this hundreds of meters below the surface of the sea, in the deep-sea canyons of the North American continental margin. When a major earthquake occurs along the coast, large amounts of sand and debris slide down these submarine gorges and form characteristic deposits on the sea floor. Due to their coarser structure, they can be easily distinguished from the finer sediments of normal, earthquake-free times.

Segments of different earthquake activity

By dating the earthquake deposits in different areas along the subduction zone, the geologists were now able to determine with a high degree of accuracy when and where major earthquakes occurred. It also showed that previous ideas about the structure of the tectonic fault are imprecise. "We found that when it comes to earthquakes, Cascadia is not a large subduction zone, but rather consists of several segments - at least four," explains Goldfinger. "The earthquake activity differs depending on where the quake originated."

“The strongest earthquakes occur in the north and usually break the entire fault. These are strong earthquakes with a magnitude of 9, but they do not occur that often, ”the geologist continues. “At the southern end of the fault, however, the earthquakes are somewhat weaker but more frequent. But these are still events of magnitude 8 or even higher, which corresponds to the earthquake in Chile - the potential for destruction is therefore very real. "

Earthquake accumulations at certain times

The chronological sequence of the quakes along the Cascadia Zone is also much less linear than expected. In the northern part, the researchers discovered a cluster formation: Sometimes around 1,000 years passed without a quake, then again there were phases in which one occurred every 250 years. "We are only just beginning to understand the whole idea of ​​clusters and there is still no consensus on whether we are currently in such a cluster or not," said Goldfinger. "But the possibility exists, which suggests that we will see a major earthquake sooner rather than later."

37 percent risk of strong earthquakes in the southern part

Based on the new data, the geologists reassessed the risk of a strong earthquake in the near future. According to this, there is even a 37 percent chance of a strong earthquake in the next 50 years for the southern end of the subduction zone - e.g. from Newport in Oregon to Northern California. For the northern part of the Cascadia fault, on the other hand, the risk is significantly lower: the researchers estimate the probability of a megaquake within this period of time to be only ten to 15 percent.

"Perhaps even more impressive than the probabilities is that we can now say that we have remained without a quake for longer than was the case in 75 percent of all interquake periods of the last 10,000 years," said Goldfinger. "And in 50 years this number will have increased to 85 percent."

Destructive power comparable to Haiti

Should a strong earthquake of magnitude 9 occur in the Cascadia subduction zone, the entire Pacific Northwest would be endangered. The destructive power of the tremors would match or even exceed that of the Haiti quake in January 2010 or Chile in February 2010. According to Goldfinger, the tremors could last several minutes and cause buildings to collapse, destroy highways and bridges. If the epicenter were just off the coast, the residents of the region would only have a few minutes to get to safety from the resulting tsunami.

"It is not a question of whether there will be a major earthquake," said Goldfinger. “It's a question of 'when'. And this 'when' looks like it might not be too far in the future. "

(Oregon State University, May 26, 2010 - NPO)

May 26, 2010