Massive earthquake rocked Seattle area 1,100 years ago, it may happen again

A new study suggests that a massive earthquake — around magnitude 7.8 — rocked the Seattle area around 1,100 years ago when a series of hidden faults ruptured simultaneously. Something like that may happen again, and the implications would be catastrophic.

Earthquakes happen when the tectonic plates get stuck at their edges due to friction and when the stress on the edge overcomes the friction. Such movement releases energy in waves that travel through the earth's crust, which leads to the trembling that we feel.

The Seattle fault is among other fault lines and associated folds in the United States. It runs along the northern border of Seattle and extends up to the Olympic Peninsula.

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The latest study published in the journal Science Advances on Wednesday (Sep 27) analysed theearth-shifting event which happened more than a millennium ago in the Puget Sound region, which is comprised of metropolitan areas such as Seattle and Tacoma.

According to the study, the quake led to landslides, upliftment of fault scraps, and a local tsunami, as a result of which a lot of local trees were drowned and buried across an area of 193 square miles.

Several reports claim that the region is a structurally complex, seismically active trough between the Coast Range and the Cascade volcanic arc. In the mentioned region, the Seattle municipality said that deep quakes of magnitude more than six have occurred in 1909, 1939, 1946, 1949, 1965, and 2001.

The government website said that earthquakes are the most serious hazard facing Seattle and unlike other potentially catastrophic hazards, Seattle has had and will experience powerful earthquakes.

Scientists urge authorities to take appropriate actions to mitigate the implications as the latest study discusses the multifault earthquake threat for the Seattle metropolitan region.

The study noted that researchers used dendrochronological dating and a cosmogenic radiation pulse to constrain the death dates of earthquake-killed trees along two adjacent fault zones near Seattle, Washington within a 6-month period between the 923 and 924 CE growing seasons.

"Our narrow constraints conclusively show linked rupturing that occurred either as a single composite earthquake of estimated magnitude 7.8 or as a closely spaced double earthquake sequence with estimated magnitudes of 7.5 and 7.3," the authors of the study said.

Researchers hired divers to bring to the surface a tree sample collected from an earthquake-downed tree in Washington's Price Lake. Using radiocarbon and tree-ring dating, the team determined when the trees died.

They found that the trees had died between 923 and 924 AD, within a six-month period. It suggests that the earthquakes across the Puget Sound region took place in a short period of time.

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The press release mentioned that the researchers estimated that a single multi-fault earthquake could have had a magnitude of around 7.8, however two earthquakes within that six-month period would each have exceeded 7.3.

The study further added that these scenarios, which are not recognised in current hazard models, increase the maximum earthquake size needed for seismic preparedness and engineering design within the Puget Sound region of >4 million residents.

(With inputs from agencies)

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