(ORDO NEWS) — The study of two powerful earthquakes in the surrounding areas off the Alaska Peninsula in 2020 and 2021 shows a connection between them. This also suggests that they may be part of an 80-year cascade of faults along the fault.
The study was published today in the journal Science Advances by University of Alaska Fairbanks Geophysical Institute Associate Professor Ronnie Grapentine and Michigan State University Associate Professor Julie Elliott. Also among the co-authors was UAF researcher Revati M. Parameshwaran.
The researchers also concluded that two deep earthquakes on the Aleutian-Alaska megathrust fault, where the Pacific Plate slides under the North American Plate, may have brought shallow fault sections closer to failure. They add that their study will help scientists better understand stress transfer and earthquake occurrence in the region and in general.
“One strong earthquake increases the load on the adjacent part of the megathrust.
This section then ruptures and increases the load on the next section of the fault, like delayed knuckles of knuckles,” Grapentin said. And that’s what we’re seeing here.
The first of two major earthquakes, known as the Simeonovo earthquake, occurred on July 21, 2020. It had a magnitude of 7.8, occurred near the Shumaginsky Islands to the south of the Alaska Peninsula and spread to the west.
The second earthquake, Chignik, occurred just over a year later, on July 28, 2021. It was recorded with a magnitude of 8.2, was located south of the Alaska Peninsula and northeast of the Simeonovsky earthquake, and spread eastward.
Two earthquakes and their aftershocks occurred in the Shumaginsky Gorge, a place not far from the Shumaginsky Islands in a well-known historical fault belt. This 1,900-mile subduction zone, where the Pacific tectonic plate slides under the North American plate, begins at the tip of the Aleutian Islands.
It continues along the south side of the islands and the Alaska Peninsula, curving upward through the Kenai Peninsula and enclosing the Anchorage area and Prince William Sound.
Prior to the 2020 and 2021 earthquakes, the Shumaginsky Gorge, an expanse of about 100 miles in the subduction zone, had no major earthquakes recorded.
“This could be a case study to understand how nearby sites of an earthquake can be activated by a significant release of energy stored in plate movement,” said Parameswaran.
The researchers examined the data to evaluate the impact of stress changes caused by the 2020 Simeonov earthquake, especially as they may be related to the rupture site of the Chignik earthquake.
Stress build-up simulations of the Simeonov earthquake show that the Chignik hypocenter, the location inside the earth where an earthquake starts, is in an area of increased stress variation, consistent with what scientists know about how earthquakes occur.
The paper also noted some notable areas of “very high” stress load on the fault, especially in smaller areas of the fault plane model. According to the study, this area did not rupture during the earthquake.
The researchers added that the two earthquakes may be part of an 80-year cascade of large subduction earthquakes along this main plate boundary, and that this cascade has now ended, with the most recent major event before the 2020 Simeonof earthquake having a magnitude of 8.7 in 1965. . Earthquake near the Rat Islands of the Aleutian Ridge.
Prior to 1965, over a period of 30 years, five earthquakes of magnitude 8 or more occurred from the outermost Aleutian Islands to south-central Alaska.
“In the concept of cascades, the entire Aleutian-Alaska megathrust has now ruptured and released much of the stress accumulated since this most recent cascade occurred,” Grapentin said.
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