1700 Cascadia Earthquake

The 1700 Cascadia earthquake occurred along the Cascadia subduction zone on January 26, 1700, with an estimated moment magnitude of 8.7–9.2. The megathrust earthquake involved the Juan de Fuca plate from mid-Vancouver Island, south along the Pacific Northwest coast as far as northern California. The plate slipped an average of along a fault rupture about long.

The earthquake caused a tsunami which struck the west coast of North America and the coast of Japan. Japanese tsunami records, along with reconstructions of the wave moving across the ocean, put the earthquake at about 9:00 PM Pacific Time on the evening of 26 January 1700.

Japanese records

The earthquake took place at about 21:00 PT on January 26, 1700 ( NS). Although there are no written records for the region from the time, the timing of the earthquake has been inferred from Japanese records of a tsunami that does not correlate with any other Pacific Rim quake. The Japanese records exist primarily in the modern-day Iwate Prefecture, in communities such as Tsugaruishi, Miyako (Kuwagasaki) and Ōtsuchi. The fact that the waves were recorded as striking Ōtsuchi and Kuwagasaki on the same day and hour helped researchers pinpoint the estimated date, time, and place of origin of the earthquake.M 9.0 - The 1700 Cascadia Earthquake
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According to Japanese records, destructive waves hit towns along the Pacific Coast of Japan on the 8th and 9th days of the 12th month of Genroku 12, which would be equivalent to January 27 and 28, 1700. Based on the damage reports in Japanese records, the maximum wave heights were estimated to be in the range of 2-5 meters. At Kuwagasaki, 13 houses were destroyed by flooding and 20 in a subsequent fire, with this representing about 10% of all buildings in the town. At Ōtsuchi, two buildings, two salt kilns, and some fields and paddies were damaged. At Miho, the village headman observed the waves and warned the villagers to flee to higher ground. No damage was reported there. At Nakaminato, where oceangoing ships unloaded their cargoes to smaller vessels to travel by river to Edo (now Tokyo), a ship carrying 28 metric tons of rice was unable to enter the port due to high waves. Later that evening, a storm drove it onto a rocky shore, killing two sailors and destroying the cargo. In the Tanabe area, the waves destroyed wheat fields and rice paddies, flooded a storehouse, and ascended the moat of Tanabe Castle.

As no one in Japan had felt an earthquake before the waves struck, many writers were reluctant to call them a tsunami, with some referring to them as merely high tide or high waves. An observer at Kuwagasaki called it a tsunami while the village headman of Miho was puzzled after observing that the waves behaved like a tsunami but no earthquake had been felt in the area.

Scientific research

The most important clue linking the tsunami in Japan and the earthquake in the Pacific Northwest comes from studies of tree rings (dendrochronology), which show that several "ghost forests" of red cedar trees in Oregon and Washington, killed by lowering of coastal forests into the tidal zone by the earthquake, have outermost growth rings that formed in 1699, the last growing season before the tsunami. This includes both inland stands of trees, such as one on the Copalis River in Washington, and pockets of tree stumps that are now under the ocean surface and become exposed only at low tide."Jan. 26, 1700: How Scientists Know When The Last Big Earthquake Happened Here"
Oregon Public Broadcasting, January 26, 2015.

Sediment layers in these locations demonstrate a pattern consistent with seismic and tsunami events around this time. Core samples from the ocean floor, as well as debris samples from some earthquake-induced landslides in the Pacific Northwest, also support this timing of the event. Archaeological research in the region has uncovered evidence of several coastal villages having been flooded and abandoned around 1700.

Cultural research

The contemporary indigenous groups of Cascadia had no known written documentation like that of the Japanese tsunami, but numerous oral traditions describing a great earthquake and inundation exist among indigenous coastal peoples from British Columbia to Northern California. These do not specify a date, and not all earthquake stories in the region can be ascribed to the 1700 quake; however, virtually all of the native peoples in the region have at least one traditional story of an event of unmatched destructive power.

Some of the stories contain temporal clues—such as a time estimate in generations since the event—which suggest a date range in the late 1600s or early 1700s, or which concur with the event's timing in other ways. For instance, the Huu-ay-aht legend of a large earthquake and ocean wave devastating their settlements at Pachena Bay places the event on a winter evening shortly after the village's residents had gone to sleep (consistent with the 9:00 PM reconstructed time). Every community on Pachena Bay was wiped out except for Masit on a mountainside above sea level. The only other Panchena Bay survivor was a young woman named Anacla aq sop, who happened to be staying that day at Kiix-in, located on the less-tsunami-impacted Barkley Sound.

Kwakwakaʼwakw (Kwakiutl) stories from the north end of Vancouver Island report a nighttime earthquake that caused virtually all houses in their community to collapse; Cowichan stories from Vancouver Island's inner coast speak of a nighttime earthquake, causing a landslide that buried an entire village. Makah stories from Washington speak of a great night-time earthquake, of which the only survivors were those who immediately fled inland before the tsunami hit. The Quileute people in Washington have a story about a flood so powerful that villagers in their canoes were swept inland all the way to Hood Canal

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