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Earth of fire

Actualité volcanique, Article de fond sur étude de volcan, tectonique, récits et photos de voyage

Publié le par Bernard Duyck
Publié dans : #Mythes et légendes., #Sismologie

On January 26, 1700, a strong earthquake strikes the west coast of North America and engenders a transpacific tsunami.
With a magnitude around 9 on the Richter scale, it occurred in the subduction zone of the Cascades.

The date of January 26 could be fixed by comparing the growth rings of the ghost forest trees along the west coast and inland ranges.
The correspondence with historical accounts that describe high waves of 1.8 to 3 meters on the coast of Japan on 27 and 28 January 1700, and the use of computer models for tsunamis, helped to determine the time taken by the tsunami to cross the Pacific: a dozen hours ... which specifies the time of the earthquake, around 9.30 pm on January 26.

Simulation of the tsunami of the year 1700 - Doc. USGS / Japan Geological Survey / via Wired

Simulation of the tsunami of the year 1700 - Doc. USGS / Japan Geological Survey / via Wired

Neskowin Ghost Forest on the north coast of Oregon -photo robertchaen

Neskowin Ghost Forest on the north coast of Oregon -photo robertchaen

The Amerindian legends tell terrifying stories and the reaction of the natives who refused to leave.

"The earth would quake and quake again and quake again," said the Yurok people. "And the water was flowing all over. The people went to the top of a hill, wearing headbands of woodpecker feathers, so they could dance a jumping dance that would keep the earthquake away and return them to their normal lives. But then they looked down and saw the water covering their village and the whole coast; they knew they could never make the world right again".

The earthquake and tsunami of 1700: legends and tectonics.

"The same night, farther on the coast at a place known today as Washington, the thunderbird and the whale had a terrible fight, shaking the mountains and uprooting the trees" say the Quileutes and The Hoh. "The ocean rose and covered the whole country".


Further north on Vancouver Island, the Nuu-chah-nulth people report that "dwarves living on a mountain invited a person to dance around their drum, which accidentally kicked the drum , acquired an "earthquake-foot" and then, at every step, he caused an earthquake. Earth trembled and the ocean overflowed ... people did not have time to wake up and to enter their canoes ... all to derivative, everything was lost and disappeared ".

The history of the "earthquake-foot" and earthquakes - by a Nuu-chah-nulth artist, Tim Paul Royal / BC

The history of the "earthquake-foot" and earthquakes - by a Nuu-chah-nulth artist, Tim Paul Royal / BC

The geologic-tectonic interpretation:


The west coast of north america was hit by earthquakes from northern California to southern Vancouver Island. At this level, the tectonic plate Juan de Fuca meets the North American plate. Its subduction, blocked, broke and violently released ... the earthquake(s) was of maximum magnitude. The coast has dropped by nearly two meters and a tsunami caused floods more than 300 meters inside the US side, and transpacific waves.

Origin of earthquakes in the Cascades - doc. Oxford geology

Origin of earthquakes in the Cascades - doc. Oxford geology

Geologists today know that the Pacific Northwest experienced earthquakes and tsunamis irregularly every 500 years or so.
The evidence is massive: submerged marshes, ghost forests, sediment layers showing enormous landslides that flowed over the ocean floor (listed over 10,000 years), seismic profiles of the Juan de Fuca plate, and satellite measurements of a coast distorted by the stress of a plate again blocked.
Over the next 50 years, the probability of another earthquake of magnitude 9 is 1 in 10.

The subduction zone of the Cascades and summary of the historical earthquakes of the last 10,000 years - Doc. Goldfinger et al.2012

The subduction zone of the Cascades and summary of the historical earthquakes of the last 10,000 years - Doc. Goldfinger et al.2012

There has not been a major earthquake in the Cascades subduction area for 300 years, and many people who live in the area are unaware of the danger or are not prepared for a strong earthquake. Many buildings in the cities on and near the coast, such as Portland, have not been renovated to withstand a major jolt.
 
Sources:
- Hakai magazine - Coastal science and societies: the Great Quake and the Great Drowning - link
- Wired - Jan. 26, 1700: Northwest Quake Unleashes Trans-Pacific Tsunami - link
- Science Daily - Japanese Shipwreck Adds To Great Cascadia Earthquake In 1700 - link

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