By GARLAND KENNEDY
Sentinel Staff Writer
Beneath the Pacific Ocean not far to the west of Sitka, the Queen Charlotte Fault runs north to south along the Continental Shelf.
As part of an effort to better understand the fault and the earthquake and tsunami hazards that it poses, an international team of researchers has created a detailed and comprehensive map of the fault, marine geologist Gary Greene said in an online seminar hosted by the Sitka Sound Science Center Monday evening.
“Very few (undersea faults) have been imaged well,” Greene said in his presentation, adding, “the Queen Charlotte Fault is one of the first and most imaged faults now that exists in the world. So we’re really highlighting a very interesting fault indeed.”
The seminar took place one day after the 58th anniversary of the 1964 Alaska Earthquake, which inflicted significant damage on Southcentral Alaska.
Greene, a professor emeritus at San Jose State University in California, is one of the principal investigators on the Queen Charlotte Fault project.
The multi-year research project has involved the National Science Foundation, the Sitka Sound Science Center, the U.S. and Canadian geological surveys and a number of universities, as well as other groups.
Unlike many fault lines, the Queen Charlotte Fault is unusually straight, which could result in a large earthquake, Greene said.
“The straighter the fault is, the more rupture that can take place,” he told the Zoom audience of about 60 viewers.
He cited the magnitude 7.8 2012 Haida Gwaii quake off the Canadian coast just south of the Alaska border.
Although the quake caused minimal damage and no casualties, he said its force was demonstrated by the 130-foot undersea scarp it created.
“That just gives you an idea of the amount of displacement that can take place,” he said.
Using a pair of research vessels, the research team used high energy sound to image the seafloor.
“Last year there was a major seismic survey that was done using airguns, using low frequency, high-energy sound to image the sea floor,” Greene said.
Not all of his local work has involved earthquakes, however. Greene noted that Sitka’s local dormant volcano, Mt. Edgecumbe, is part of the Queen Charlotte Fault. Part of the imaging project has been aimed at learning the age of the volcano so as to understand its patterns of activity.
“We in a sense start to anchor the age of Mt. Edgecumbe,” Greene said. “And it appears that it is at least one million years old and most likely older than one million years old. So this volcano has been active for one million years. Now the question is, when is it going to be reactivated? … If we can start to assign ages to that, between those (active) time periods, we might be able to come up with a good estimate of when the next eruption might take place. So that’s one of the things we’re looking at right now.”
Pointing to undersea images, he showed a number of volcanic cones on the seafloor that stretch to the north along the fault line. Stretching from the southern end of Haida Gwaii, formerly known as the Queen Charlotte Islands, northward to the north end of Chichagof Island, the fault moves about two inches each year, which has acted as a sort of conveyor belt for these volcanic cones, he said.
Two of these ancient volcanic cones, the 19- and 34-fathom pinnacles located southwest of Kruzof Island, are the Edgecumbe Pinnacles Marine Reserve, where fishing is prohibited.
As far as public safety is concerned, he said earthquakes along the Queen Charlotte Fault pose the greatest risk to Sitka.
“The hazard that I think you should be most worried about of course is an earthquake,” Greene said. “Let me point out one thing: should Sitka be more concerned about an earthquake than Seattle? My answer to that is no.”
The likelihood of a catastrophic tsunami in Seattle, he added, is much higher due to the nature of the nearby Cascadia Fault, whereas the linear nature of the Queen Charlotte Fault involves lower tsunami risk.
However, an underwater landslide on the Queen Charlotte Fault off Sitka or in Dixon Entrance could trigger a significant tsunami, possibly with minimal warning, the marine geologist said.
“The other thing that a transform fault earthquake could cause could be a big failure on the slope, like a landslide. And if it’s shallow enough it could produce a very substantial tsunami,” he said. In areas of significant underwater erosion, a tsunami could occur without an earthquake, an event he called a “silent tsunami.”
Separate from Greene’s seminar, the Sentinel interviewed Craig Warren, Sitka Fire Chief and Emergency Response Coordinator, about the public-safety aspect of seismic activity that could affect Sitka.
He said the Cascadia Fault concerns him more than does the Queen Charlotte, because a major seismic event on the Cascadia could shut down the barge traffic that sustains Sitka.
“That one’s a very scary fault line, that’s going to interrupt some serious shipping for us...all our heating fuel in the winter, all of our food, all of our supplies – everything from the sodas that you don’t really need to the toilet paper that’s going to make it uncomfortable, this is a serious issue,” Warren said. “My opinion is that 99 percent of Sitkans do not have the capability to self-sustain for 14 days and that is what we would like. We would like a food cache.”
There could also be communication infrastructure breakdowns, he said.
“The second problem that I think Sitkans have is we have become so used to phones and the convenience of talking to anybody we want whenever we want that most people don’t understand these cell towers have four hours of battery. After four hours if your plan is not made and communicated and possibly you may not even have a line to be able to communicate… Have a plan, know where everybody is going,” he said.
Watch out for your neighbors, too, he urged.
“The best thing for me is if each individual Sitkan made a plan and that plan, I would love if it included some vulnerable neighbors, the little old lady next door that you talk to just in passing on the sidewalk, a special needs family,” he said.
In the event of a disaster, Sitka could run short of water, fuel oil and other essentials, he said. While some disasters such as tsunamis or earthquakes might force some people from their homes, Warren said everyone should stay at home if possible and safe.
“Every person that I can keep in their house is going to extend our abilities to provide food and shelter to those that don’t have a house anymore,” he said.
Gary Greene will spend the remainder of the week in Sitka. Today from 5 to 7 p.m. he will be at the Bayview Pub to answer public questions, and from 8 to 9 a.m. Wednesday he will be available at the Backdoor Cafe.
For Sitkans interested in learning about local geology, Greene will host a walk from 5 to 7 p.m on Thursday.
It will begin at Whale Park and follow the multi-use trail to view rock formations near Eastern Channel and Silver Bay.
