How can the Chignik, Alaska, earthquake assist predict future threat?

Earthquakes are brought on by the motion of the tectonic plates that make up Earth’s crust. Off the coast of Alaska, the Pacific plate thrusts beneath the North American plate creating monumental strain on the Alaska-Aleutian fault. Between 2020 and 2021, the 2 plates slipped alongside this fault, producing a sequence of earthquakes, together with the Chignik, Alaska, earthquake on July 29, 2021, which registered an 8.2 in magnitude—the most important earthquake inside U.S. territory in 58 years.

Jeffrey Freymueller, a professor within the School of Pure Science at Michigan State College, is researching this earthquake to study extra about precisely the place that slip occurred (and the way a lot) to higher perceive how faults work and to assist consider the danger of future earthquakes and tsunamis. Freymueller is an internationally acknowledged knowledgeable in geodesy, or the research of Earth’s dimension and form, and serves as MSU’s Endowed Chair for Geology of the Strong Earth. This analysis appeared just lately within the journal Science Advances.

What are the challenges with learning the Alaska-Aleutian fault?

The most important problem is that the fault involves the floor on the ocean backside far offshore, and there are kilometers of water in the way in which! We have to measure how the Earth was completely moved by the earthquake, and we actually want measurements which might be made proper above the a part of the fault that slipped.

On land, we will arrange International Positioning Methods or International Navigation Satellite tv for pc Methods—GPS and GNSS, respectively—devices and document the positions of the plates pretty simply, however the a part of the fault that slipped within the earthquake is situated fairly distant from land. Radio indicators from the GPS satellites won’t journey via water, so to get any information we should mix the GPS positioning of a floating platform with acoustic, or sound wave, positioning of the identical platform relative to an array of transponders, which choose up and emit indicators on the seafloor. This system is known as GPS-acoustic positioning, and by repeating the survey measurements earlier than and after the earthquake, we will measure how a lot the seafloor moved, and use that to higher decide how the fault moved.

Why is learning the Chignik, Alaska, earthquake vital to earthquake analysis?

A very powerful factor we realized is that the entire motion on the GPS-acoustic website offshore was a lot bigger than had been predicted by earlier fashions for the earthquake. Giant earthquakes are vital to check as a result of they produce the most important motions and trigger the most important adjustments in stress throughout the Earth. Which means a big sign for us to measure, which is all the time useful. The GNSS-acoustic place measurements of the seafloor’s movement are fairly noisy as a result of the velocity of sound via the water could be very delicate to ocean temperature and varies so much with time. Which means it’s laborious to measure the acoustic vary as exactly as we will measure the GPS half. So, it helps to have a bigger movement to measure when the noise stage is excessive.

How does this analysis assist with assessing tsunami hazard threat?

This analysis helps with assessing hazard and threat. One of many fascinating options of this earthquake is that it did NOT generate a big tsunami. Why did not it? The reason being that a lot of the slip on the interface between the plates occurred solely on the a part of the interface that was nonetheless fairly deep—the earthquake did not rupture to the seafloor and even near it.

However we actually have to know the way near the floor it obtained, and whether or not the shallower a part of the fault that did not slip on this earthquake is able to doing so sooner or later. Whether it is, then the danger of a future giant tsunami is excessive. If the shallow a part of the fault simply would not slip in earthquakes, however as an alternative creeps alongside steadily, then the danger of a big tsunami from this a part of the fault is way decrease. We’re nonetheless undecided, however now we all know greater than we did earlier than about what occurred within the earthquake. We’re persevering with to take a look at different information, and we hope we’ll get extra GPS-acoustic information as properly to determine how the shallowest a part of the fault behaves.