It's news that no one wants to know, but few can resist reading about: We here in the Pacific Northwest are living in territory that can...

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It’s news that no one wants to know, but few can resist reading about: We here in the Pacific Northwest are living in territory that can generate giant earthquakes on par with those that struck Alaska in 1964 (magnitude 9.2) and Chile in 1960 (magnitude 9.5).

This wasn’t always thought to be the case. Our recorded history shows few seismic events of a magnitude higher than 6 or 7. But recorded history in this region begins only in the 1770s with the first European explorations.

By the mid-1990s, geologists at the University of Washington and earthquake historians in Japan, pursuing separate investigations, were closing in on the truth about the seismic potential of subduction quakes triggered by the Juan de Fuca Plate, as it slips at four meters per century beneath the North American Plate.

The story of how that truth emerged is laid out in vivid instruction-book style in “The Orphan Tsunami of 1700: Japanese Clues to a Parent Earthquake in North America” by Brian F. Atwater, Musumi-Rokkaku Satoko, Satake Kenji, Tsuji Yoshinobu, Ueda Kazue and David K. Yamaguchi (United States Geological Survey/University of Washington Press, 133 pp., $24.95).

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Author Appearance

Brian F. Atwater reads from “The Orphan Tsunami of 1700,” 7 p.m. Thursday, University Book Store, 4326 University Way N.E., Seattle; free (206-634-3400 or www.ubookstore.com).

I say “instruction-book style” because “The Orphan Tsunami of 1700” is not exactly a narrative. Instead, UW-based USGS geologist Brian Atwater and his Japanese and American colleagues have chosen to approach their subject by using a format busy with charts, graphs, sidebar texts, footnotes galore, archival photographs and handsome reproductions of old maps and paintings. The result is that you don’t so much read the book as pick your way through it.

Still, the materials on offer here are fascinating, as Atwater and company outline the steps by which they established “precedent for a giant Cascadia earthquake and its tsunami.” The stateside research involved studying sunken forests and bayside sediments along the coast between British Columbia and California. By the early 1990s, they were sure that Cascadia had been hit by one huge earthquake or “a swift series of merely great earthquakes” between 1695 and 1720.

In Japan, the problem was different. The Japan of the late 17th century was stable, prosperous, literate — and meticulously documented. There survive 100,000 pages of administrative records for the period 1644-1840, including a record of 366 “earthquake days” between 1650 and 1700. Records of tsunamis were also kept, and one tsunami in particular grabbed earthquake historians’ interest: an “orphan tsunami” in 1700. (Most tsunamis in Japan come preceded by an earthquake — but “orphans” arrive without warning.)

Detailed accounts of its character and the damage it did survive in records from six different villages and make clear it was an unusual event — “something like a very high tide” that, in one village, peaked seven times between dawn and mid-morning. Evidence suggests it was generated by a distant earthquake, like the tsunami triggered by the 1960 Chilean earthquake.

By 1996, Japanese and American researchers, working together, were able to establish that an earthquake between 8.7 and 9.2 in magnitude struck Cascadia on the evening of Jan. 26, 1700, triggering a tsunami that reached Japan nine or 10 hours later.

The calculations resulting in this remarkably precise verdict involved taking into account differences between Japanese “hours” (“120 minutes on average”) and our 24-hour day, along with differences between Japanese and Western calendar systems, and the confusion resulting from Europe’s piecemeal changeover from the Julian to the Gregorian calendar during this period.

Of course, the news that we’re vulnerable to such a large earthquake isn’t good. The authors outline how it would affect us: Highway 101 would be “largely impassable” and east-west routes to and from the coast could be cut off by landslides. The skyscrapers of Seattle, Portland and Vancouver, B.C., may also have trouble holding up to a prolonged subduction earthquake.

That warning alone makes the book valuable. What’s missing here is an effort to convey what it was like to be on the hunt for what must have felt, at times, like a phantom event. But that’s probably a separate book — a first-person narrative that one of this volume’s authors may some day be inspired to write on his own.