Cascadia's Fault - Jerry Thompson [98]
When I met Kenji Satake in a small city on the southeast coast of Japan several years later to interview him, he explained why the date had jumped out at him. “If the earthquake happened in Cascadia, and if it was large enough, it must have generated a tsunami which would propagate across the Pacific. And 1700 is not very long ago for Japan. So if such a tsunami arrived in Japan and caused damage that must have been documented in historic documents.”
No such written record existed in North America. The only cultural evidence of a huge earthquake around 1700 would be the oral histories of the Yurok or the Makah or the Huu-ay-aht people of Pachena Bay. And their stories did not include exact dates. By then a few European explorers had come and gone but the rest of the world knew little about the northwest coast of America and nothing at all about its earthquakes. Even the geography was a yellowing parchment void on most existing maps. The Spanish had outposts in Chile, Peru, Mexico, and southern California, but Cascadia was still terra incognita.
By comparison the Japan of 1700 already had a long history of writing things down. The damage reports of earthquakes, tsunamis, and volcanic eruptions were usually kept at temples or in the ledgers of local merchants and public officials. When Kenji Satake returned in 1995, he started looking for catalogs compiled by various teachers and scholars who had been working on a history of ruptures and tsunamis going back more than a thousand years. He knew that some of the tsunamis recorded would have no earthquake listed alongside them because the plate motion that caused the waves would have happened so far away—in places like Chile or Alaska or Siberia’s Kamchatka Peninsula—that local residents would not have felt the shaking. Without “parent” earthquakes, the “orphan” tsunamis should stand out and be relatively easy to spot in the seismologists’ catalog.
He approached Kunihiko Shimazaki, Yoshinobu Tsuji, and Kazue Ueda, colleagues who had begun studying Japan’s historical earthquakes and tsunamis in the 1970s. Together they searched backward chronologically through the list. “Soon after we started looking,” Satake said, “we found that there were some documents describing a tsunami from an unknown origin in the year 1700.” A series of waves swept down the Japanese coast after midnight on January 27 and into the early morning hours of January 28, to be exact.
“The people studying the history of Japanese earthquakes—for them it was a strange event. There wasn’t an earthquake, so they didn’t care,” Satake explained. “They didn’t care what the origin was because they were interested only in Japanese earthquakes—and this wasn’t a Japanese earthquake.”
While this may have seemed like a eureka moment, plenty of work remained before Satake could say for sure this wave of unknown origin had come from Cascadia. Perhaps it was caused by a typhoon or some other big storm. Maybe the orphan wave had come from a rupture in Alaska or Chile. So Satake and his colleagues quickly moved to the next stage of their investigation.
Fairly easily they ruled out the storm surge idea. “We knew that the tsunami waves were documented in many places along the Japanese coast,” Satake continued, pointing to a map that showed nearly 560 miles (900 km) of affected shoreline, “which is too large an area—too wide—for a meteorological origin.” Add to this the fact that most typhoons hit Japan between August and October. These mystery waves had arrived in the dead of winter. “We examined the weather of that day and we found that the weather wasn’t that bad,” he said, with sunny or cloudy skies reported in most of central and northern Japan on January 27, 1700.
Having ruled out storms, they were convinced it had to be a tsunami and it must