Seismologists stress importance of monitoring small earthquakes
While large damaging earthquakes get a lot of attention, researchers at the Alaska Earthquake Center say small earthquakes that some might think are insignificant can tell researchers important information about seismic activity in specific areas around the state.
“For many decades we have tracked earthquake activity around the state, but most all of our instrumentation was in the southern portions of the state. As a result, things that happened on the north slope, Seward Peninsula, throughout the Brooks Range... we were maybe vaguely aware of but couldn’t really see,” said Michael West, state seismologist with the Alaska Earthquake Center.
The USArray is a network of permanent and portable seismographs that record local, regional and distant earthquakes. In 2014 the Transportable Array started to deploy in Alaska, and West says this gave them the ability to monitor the activity in the northern region of the state better.
“It’s kind of been like turning on the lights, and we’ve finally been able to see and track seismic activity -- earthquake activity -- through those parts of the state,” said West.
The USArray stations in Alaska are scheduled to be demobilized this spring. “The USArray project has given us that ability to see these earthquakes but it was temporary. It was a science project not unlike a science fair project for school. You go out, you collect your data, [and] when it is all done you pack up and you go home. That was always the intention of this project. It was not driven by Alaska’s long term earthquake awareness needs,” said West.
Although it was not the original intent of the project, West says the data has been useful for larger earthquake monitoring efforts in Alaska. Seismologist Natalia Ruppert with the Alaska Earthquake Center says they have tracked some interesting earthquake activity in the northern region of the state.
Ruppert says that in August of 2018 there was a magnitude 6.4 earthquake south of Kaktovik that produced a very active aftershock sequence. Beginning in the summer of 2018, swarm-like activity was identified in the northeastern region of the Brooks Range. Swarm activity refers to events where there is not one single large earthquake but multiple earthquakes of similar size. Ruppert says the activity has been ongoing since last year.
Another site of activity Ruppert says is in the southcentral part of the Brooks Range. This swarm activity had four magnitude 5.2 and 5.3 earthquakes and many smaller earthquakes. This activity began in February of 2019 and is still ongoing. “It’s hard to tell if it’s truly unique or if it’s something that has been going on previous years because we didn’t really have a comprehensive seismic network in the Brooks Range network region until Earthscope project arrived in Alaska and installed 200 new seismic stations. So only with this additional seismic network now are we able to record seismic events in the Brooks Range with much higher accuracy and see earthquakes to a much lower magnitude,” said Ruppert.
However, she says they observed an earthquake in Kaktovik that was the largest earthquake north of the Brooks Range that they have recorded.
West fears that having the USArray in Alaska demobilized will be a step backwards scientifically. “It seems like a once in a generation opportunity to bring the capabilities in Alaska a little bit more in alignment with what the rest of the country already has. It will not come as a surprise, I would think, to know that earthquake monitoring capabilities in Alaska, despite our large earthquakes, are not the same as elsewhere,” said West.
When someone in Alaska goes to build a road, pipeline, building, or mine, West says there are engineering considerations to follow that account for earthquakes. “The best way that we can forecast the kinds of earthquakes we expect in the future is to have a good understanding of what’s happened in the past. So we spend a lot of time tracking what seem like irrelevant earthquakes -- little magnitude 2 and 3 earthquakes. But we use those little earthquakes to paint in the picture of what we should expect in the way of large damaging earthquakes,” said West.
“By the time you have a large earthquake it might be too late. If you do not know anything about the region, you cannot forecast how it is going to behave in the future. So small earthquakes help us to describe behavior of the faults,” said Ruppert.
West and colleagues have been working over the last few years to partner with federal and state agencies to retain a portion of the USArray infrastructure in Alaska. “We have been successful along sort of the southern swath of Alaska, and we will be keeping and operating much of the USArray instrumentation. Right now, everything in the north and west is still planned for removal starting next summer, but we remain very much engaged at the state level and the federal level in attempts to retain those,” said West.
West adds they are anxiously awaiting the governor’s proposed budget. “The University Board of Regents has included in the university’s request this year, one and only one research initiative... and it is seed monies, if you will, to spur this larger adoption of USArray equipment in northern and western Alaska. While we will work with the legislature through the spring on that, we hope very much to gain the governor’s support,” said West.