Southeast residents felt the tremors of two earthquakes that struck on Friday night.
Two quakesat first, one of magnitude 5.1 followed by one of magnitude 5.3 occurred about 45 minutes apart, near Glacier Bay National Park. They were felt across communities as far from Juneau in the state of Whitehorse. Smaller aftershocks were felt throughout the weekend, averaging 40 at this point.
Scientist senior Natalia Ruppert with the Alaska Earthquake Center said that moderately-sized earthquakes like these aren’t unusual for the area.
Its style=”font-weight 400 ;”>”These are quite common however they’re not frequent,” Ruppert said. “Maybe one or two times a year. It disappears from the minds of people.”
In the last decade some significant quakes have caused a lot of damage to Southeast Alaska. In 2017, two magnitude 6+ quakes close to Haines caused damage in Whitehorse. In 2013 an earthquake of magnitude 7.5 earthquake close to Craig could be felt as as Seattle.
In 1958 in the year 1958, a magnitude 7.8 earthquake damaged bridges and docks in Yakutat and caused the landslide which created the death of a wave at Lituya Bay — the largest ever recorded.
In Southeast Alaska often happen near two faults: the Denali Fault which extends to the south of to the Alaska Range through Southeast Alaska as well as the Fairweather Fault which runs along the coastline. In this instance the quakes originate from a land strip between the two faults.
Both are strike slip faults that are fractures between two pieces of earth moving horizontally. The earth that is on either end of the fault travels at a different rate. Ruppert stated that it’s like two cars moving at slightly different speeds on parallel lanes along the highway.
span style=”font-weight 400 ;”>”If you wrap an elastic band over those two vehicles, the band will continue stretching, stretching,” Ruppert said. “And this is how pressure increases.”
When the rubber band cracks the pressure releases. The result is a quake.
Strike-slip faults tend to be near to their surface meaning even minor or moderate earthquakes are more easily observed. The residents who felt the earthquake are encouraged to complete an “Did the earthquake feel like that it was there?” form from the U.S. Geologic Survey, to aid scientists in their analysis of follow-up.
