The Orphan Tsunami of 1700: Japanese Clues to a Parent Earthquake in North America
by Brian Atwater
How to Date an Earthquake
A review by Doug Brown
Over the last thirty years, evidence has been slowly amassing for recurrent major earthquakes in the Pacific Northwest (what geologists call the "Cascadia" region). Particularly in coastal regions, every few hundred years there appears to be sudden subsidence, resulting in drowned forests. In several places along the Oregon and Washington coast roots of these dead forests can be seen in outcroppings. In the 1990s, the most recent of these subsidences was radiocarbon dated to the years 1699-1700. However, while the dead trees certainly pointed towards major quakes, they did not in themselves constitute a smoking gun.
Then Japanese researchers began finding mentions in old documents of a tsunami in January 1700, for which there was no earthquake in Japan. Tsunamis of this type were called orphans, as there was no obvious parent earthquake. Once these Japanese accounts and the PNW data were brought together, the picture became clear: sometime between 9 and 10 pm on the night of January 26, 1700, a magnitude 9 earthquake hit the Cascadia region, causing 3-5 feet of subsidence along the coast. This earthquake generated a tsunami that sped across the ocean as fast as a jet airliner, arriving in Japan around 10 hours later on January 27.
The Orphan Tsunami of 1700 gathers pretty much all of the known data on the event, from both sides of the Pacific. All of the tree ring data, all the radiocarbon data, all of the Japanese accounts, and more are presented. The Japanese accounts are engagingly presented with translations beside each handwritten Kanji symbol, and summary translations at the top of the page. Contemporary maps of affected areas and other documents from the time offer a window into what the life in affected communities was like.
Some might complain of the profusion of data in this book, but speaking as a data junkie, I think this is one of the coolest science books in a long time. Each page is packed with charts, diagrams, beautiful old maps, watercolors, translations, and photos. This is a wonderful interdisciplinary work, as it covers cultural history, geology, oceanography, and the fine art of translation. Anyone interested in tsunamis, earthquakes, Japanese history, old maps, or anyone who simply lives in the Pacific Northwest (particularly along the coast) will find items of interest in The Orphan Tsunami of 1700.