Alaskan Megathrust Earthquakes: Sedimentary records provide new data and a look 2000 years into the past

In 1964, a historically unprecedented magnitude 9.2 earthquake struck the Aleutian Islands of Alaska. The earthquake prompted scientists to figure out that the Aleutians lie along a unique form of fault, now known as a “megathrust” fault. During a megathrust earthquake, large swaths of land suddenly rise or sink, depending on their location relative to the fault rupture. Over long periods of time, as tectonic plates slide under one another, compression causes the top plate to buckle and rise up along the coast. When enough energy is accumulated, a slip eventually occurs. In places that were being uplifted, the land suddenly falls a few meters as the strain is released, otherwise known as an earthquake. It has been thought that areas of uplift and subsidence remain constant, always rising or falling in exactly the same place with every earthquake. However, a recent study suggests that these areas are not constant, further complicating our understanding of how “megathrust” earthquakes occur.

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