Post by blackcrowheart on Jan 10, 2006 12:18:50 GMT -5
The orphan wave
John Driscoll
www.times-standard.com/local/ci_3383126
Three hundred and six years ago on Jan. 26, the massive earthquake fault that runs from Vancouver Island, British Columbia, to Cape Mendocino slipped.
The quake registered about 9 on the Richter scale, a rare giant like the one in December 2004 off Sumatra.
American Indians on the then-uncharted West Coast felt the quake, but it wasn't recorded in writing. So until the 1990s, the capacity of the Cascadia subduction zone -- where one huge plate plunges under another -- to produce a huge earthquake was unknown.
In an amazing blend of scientific, literary and anthropological disciplines, researchers began to pin down the big quake. Geologists looked at coastal peat and tsunami sand deposits along the West Coast, including Humboldt Bay. Others began delving into Indian stories of earthquakes. Using the information as references and backing it up with radiocarbon dating, scientists figured the quake happened between 1680 and 1720.
All along, researchers in Japan were puzzled over a tsunami -- a huge earthquake-generated wave -- that struck coastal towns there in January 1700. The Japanese were, and still are, well acquainted with tsunamis, but this one was not preceded by an earthquake.
It was Japan's orphan tsunami, and it was the key to Cascadia.
The story of how scientists put together the puzzle is recorded in a fascinating new book called “The Orphan Tsunami of 1700: Japanese Clues to a Parent Earthquake in North America.”
Its authors include five Japanese writers -- linguists and scientists -- and geologist Brian Athingyer of the University of Washington. Pinning down the exact date of the earthquake, he said, is vital.
”If you define the hazard that exactly,” Athingyer said, “it gives the earthquake a reality.”
Such an event today could have disastrous consequences. Not only would severe shaking cause lots of damage in West Coast cities, but a huge tsunami is likely to rise up and wash ashore within minutes, not with hours of warning granted by a distant tsunami.
Some of the evidence for the huge 1700 quake was found in the Mad River Slough and other bays and river mouths on the West Coast. Geologists more than 20 years ago found evidence that spruce trees in those areas were killed quickly, not from a gradual rise in sea level. That bolstered the case for sudden subsidence, or an immediate lowering of coastal land.
Sheets of sand laid down right after the coastal plunge showed that tsunamis overran the areas, in some places burying native campsites in Oregon and Washington.
But how big was the Cascadia quake that gave birth to the tsunamis? How much of the 1,000-mile-long subduction zone had to slip to create the earthquake?
Geologists started a series of experiments using radiocarbon dating to determine when different areas along the coast dropped. But all they could figure was that places from Southern Washington to Northern California dropped within the same few decades, between about 1695 and 1720. That might have happened all at once, or it might have happened through a series of smaller -- though still major -- earthquakes of around magnitude 8.
Without a time machine, how could scientists figure out if the whole fault ruptured, or if parts of it slipped over time?
”It's difficult to imagine how you could get that kind of information for an event that would be considered prehistoric,” Athingyer said.
All along, Tsuji Yoshinobu and Ueda Kazue were growing intimately familiar with Japan's record of tsunamis. They were developing a catalog of tsunamis, and they couldn't escape the mystery of the quake-less tsunami of Jan. 26, 1700.
Kenji Satake was at Caltech for post-doctorate work in the 1980s, then moved to the University of Michigan, as the geology of Cascadia began to be unraveled.
Satake was interested in Japanese historical records, and came to realize that the 1700 tsunami was of greater importance to the North Americans' work than anybody's.
”A Pacific tsunami flooded Japanese shores in January 1700,” the book reads. “The waters drove villagers to high ground, damaged salt kilns and fishing shacks, drowned paddies and crops, ascended a castle moat, entered a government storehouse, washed away more than a dozen buildings and spread flames that consumed 20 more.”
The ruling samurai, merchants and peasants in several towns on Japan's east coast recorded the event. Most were perplexed; they called it a flood, or an extreme high tide. But some accounts called it what it was, a tsunami, despite the strange truth that there hadn't been an earthquake.
Of course, the Japanese calendar is different than the Western calendar, and it took some figuring to determine when the tsunami was recorded. Coupled with accounts suggesting the wave was several meters high -- though different between towns -- computer modelers were able to simulate a great earthquake that gave birth to a tsunami that engulfed the Pacific Ocean.
The earthquake occurred at just about 9 p.m. on Jan. 26, 1700.
The authors retie the loose ends by comparing other earthquakes and resulting tsunamis, and go back over the geological evidence and American Indian accounts of a huge quake of magnitude 9. They also ask the necessary question, if the tsunami could have come from somewhere beside Cascadia.
”By elimination,” as one chapter starts, “no other place rivals Cascadia as the orphan tsunami's source.”
”The Orphan Tsunami of 1700” is a detailed description of the detective work that unlocked one of the final vaults of Cascadia. But it is also a warning.
It tells us that what happened after the Indonesian earthquake in December 2004 could happen here, said Humboldt State University geologist Lori Dengler.
”Knowing a specific date matters in the sense that it makes it easier for people to visualize, to understand,” Dengler said.
Shaking from a magnitude-9 quake would do significant damage and probably kill people in Humboldt County, but it would devastate big cities like Portland, Seattle, San Francisco and Sacramento. Those cities would get the attention of disaster officials first, and isolated Humboldt County would likely have to survive on its own for days at least.
The following tsunami would put about 2,000 people at risk, those who live or work in the medium- to high-risk tsunami zone.
”What you know and what you do really can make an enormous difference,” Dengler said.
While the Sumatran quake and tsunami claimed about 220,000 lives, some areas equally devastated by the giant waves saw little or no death. Residents of the Simuelue Islands saved themselves by following a simple rule: When you feel a big quake, run to and stay on high ground.
The preparation people do prior to such a disaster will factor heavily in how comfortable they will be after such a disaster, Dengler said. Disaster plans and disaster kits will make a difference.
”The discoveries thrilled and astonished us -- and they still do,” the authors write. “But they also bring to mind the Indian Ocean disaster. How many actual orphans did the tsunami of 1700 create?”
For complete information on earthquakes and tsunamis, go to www.humboldt.edu/~geodept/earthquakes/eqk_info.html
John Driscoll covers natural resources/industry. He can be reached at 441-0504 or jdriscoll@times-standard.com
John Driscoll
www.times-standard.com/local/ci_3383126
Three hundred and six years ago on Jan. 26, the massive earthquake fault that runs from Vancouver Island, British Columbia, to Cape Mendocino slipped.
The quake registered about 9 on the Richter scale, a rare giant like the one in December 2004 off Sumatra.
American Indians on the then-uncharted West Coast felt the quake, but it wasn't recorded in writing. So until the 1990s, the capacity of the Cascadia subduction zone -- where one huge plate plunges under another -- to produce a huge earthquake was unknown.
In an amazing blend of scientific, literary and anthropological disciplines, researchers began to pin down the big quake. Geologists looked at coastal peat and tsunami sand deposits along the West Coast, including Humboldt Bay. Others began delving into Indian stories of earthquakes. Using the information as references and backing it up with radiocarbon dating, scientists figured the quake happened between 1680 and 1720.
All along, researchers in Japan were puzzled over a tsunami -- a huge earthquake-generated wave -- that struck coastal towns there in January 1700. The Japanese were, and still are, well acquainted with tsunamis, but this one was not preceded by an earthquake.
It was Japan's orphan tsunami, and it was the key to Cascadia.
The story of how scientists put together the puzzle is recorded in a fascinating new book called “The Orphan Tsunami of 1700: Japanese Clues to a Parent Earthquake in North America.”
Its authors include five Japanese writers -- linguists and scientists -- and geologist Brian Athingyer of the University of Washington. Pinning down the exact date of the earthquake, he said, is vital.
”If you define the hazard that exactly,” Athingyer said, “it gives the earthquake a reality.”
Such an event today could have disastrous consequences. Not only would severe shaking cause lots of damage in West Coast cities, but a huge tsunami is likely to rise up and wash ashore within minutes, not with hours of warning granted by a distant tsunami.
Some of the evidence for the huge 1700 quake was found in the Mad River Slough and other bays and river mouths on the West Coast. Geologists more than 20 years ago found evidence that spruce trees in those areas were killed quickly, not from a gradual rise in sea level. That bolstered the case for sudden subsidence, or an immediate lowering of coastal land.
Sheets of sand laid down right after the coastal plunge showed that tsunamis overran the areas, in some places burying native campsites in Oregon and Washington.
But how big was the Cascadia quake that gave birth to the tsunamis? How much of the 1,000-mile-long subduction zone had to slip to create the earthquake?
Geologists started a series of experiments using radiocarbon dating to determine when different areas along the coast dropped. But all they could figure was that places from Southern Washington to Northern California dropped within the same few decades, between about 1695 and 1720. That might have happened all at once, or it might have happened through a series of smaller -- though still major -- earthquakes of around magnitude 8.
Without a time machine, how could scientists figure out if the whole fault ruptured, or if parts of it slipped over time?
”It's difficult to imagine how you could get that kind of information for an event that would be considered prehistoric,” Athingyer said.
All along, Tsuji Yoshinobu and Ueda Kazue were growing intimately familiar with Japan's record of tsunamis. They were developing a catalog of tsunamis, and they couldn't escape the mystery of the quake-less tsunami of Jan. 26, 1700.
Kenji Satake was at Caltech for post-doctorate work in the 1980s, then moved to the University of Michigan, as the geology of Cascadia began to be unraveled.
Satake was interested in Japanese historical records, and came to realize that the 1700 tsunami was of greater importance to the North Americans' work than anybody's.
”A Pacific tsunami flooded Japanese shores in January 1700,” the book reads. “The waters drove villagers to high ground, damaged salt kilns and fishing shacks, drowned paddies and crops, ascended a castle moat, entered a government storehouse, washed away more than a dozen buildings and spread flames that consumed 20 more.”
The ruling samurai, merchants and peasants in several towns on Japan's east coast recorded the event. Most were perplexed; they called it a flood, or an extreme high tide. But some accounts called it what it was, a tsunami, despite the strange truth that there hadn't been an earthquake.
Of course, the Japanese calendar is different than the Western calendar, and it took some figuring to determine when the tsunami was recorded. Coupled with accounts suggesting the wave was several meters high -- though different between towns -- computer modelers were able to simulate a great earthquake that gave birth to a tsunami that engulfed the Pacific Ocean.
The earthquake occurred at just about 9 p.m. on Jan. 26, 1700.
The authors retie the loose ends by comparing other earthquakes and resulting tsunamis, and go back over the geological evidence and American Indian accounts of a huge quake of magnitude 9. They also ask the necessary question, if the tsunami could have come from somewhere beside Cascadia.
”By elimination,” as one chapter starts, “no other place rivals Cascadia as the orphan tsunami's source.”
”The Orphan Tsunami of 1700” is a detailed description of the detective work that unlocked one of the final vaults of Cascadia. But it is also a warning.
It tells us that what happened after the Indonesian earthquake in December 2004 could happen here, said Humboldt State University geologist Lori Dengler.
”Knowing a specific date matters in the sense that it makes it easier for people to visualize, to understand,” Dengler said.
Shaking from a magnitude-9 quake would do significant damage and probably kill people in Humboldt County, but it would devastate big cities like Portland, Seattle, San Francisco and Sacramento. Those cities would get the attention of disaster officials first, and isolated Humboldt County would likely have to survive on its own for days at least.
The following tsunami would put about 2,000 people at risk, those who live or work in the medium- to high-risk tsunami zone.
”What you know and what you do really can make an enormous difference,” Dengler said.
While the Sumatran quake and tsunami claimed about 220,000 lives, some areas equally devastated by the giant waves saw little or no death. Residents of the Simuelue Islands saved themselves by following a simple rule: When you feel a big quake, run to and stay on high ground.
The preparation people do prior to such a disaster will factor heavily in how comfortable they will be after such a disaster, Dengler said. Disaster plans and disaster kits will make a difference.
”The discoveries thrilled and astonished us -- and they still do,” the authors write. “But they also bring to mind the Indian Ocean disaster. How many actual orphans did the tsunami of 1700 create?”
For complete information on earthquakes and tsunamis, go to www.humboldt.edu/~geodept/earthquakes/eqk_info.html
John Driscoll covers natural resources/industry. He can be reached at 441-0504 or jdriscoll@times-standard.com