A newly trained machine-learning system has, for the first time, picked out thousands of previously unrecognized small earthquakes, exposing the sharply defined boundary of the Yakutat microplate as it descends beneath the North American plate.

The Yakutat oceanic plateau is effectively trapped in a complex tectonic collision zone, where it is being squeezed between major plate systems as subduction continues beneath North America. This tightly packed “tectonic traffic jam” shapes the broader geodynamic environment of south-central Alaska. 

The precise geometry and interaction of these plates strongly influence how stress builds and is released across the region, directly affecting its earthquake frequency and volcanic activity. By resolving this fine-scale seismicity, researchers gain a clearer picture of how deformation is distributed along one of North America’s most active and structurally complex subduction systems.

Reshaping the understanding of the Yakutat plate edge

A detailed new analysis published in The Seismic Record by Meghan Miller of Australian National University and her colleagues has sharply refined the mapped extent and boundary of the Yakutat plate in southern Alaska.

To build this high-resolution picture, the team combined data from both permanent seismic stations and a temporary network deployed between 2018 and 2021. Using a machine-learning workflow, they generated an expanded earthquake catalog that significantly increased the number of detected events in the region.

The results revealed a previously unrecognized linear cluster of roughly 1,750 small earthquakes stretching about 155 miles from northwest to southeast. This continuous seismic band outlines the plate boundary with far greater clarity than earlier conventional studies had been able to achieve.

By analyzing ambient seismic noise to image deeper structures, the researchers determined that the earthquake line delineates the edge of the Yakutat microplate as it subducts at a shallow angle directly beneath the North American plate, notably without a separating mantle wedge typically seen in many subduction zones. This revised geometry places the Yakutat microplate directly beneath the apex of curvature of the Alaska Range and aligns it with the Denali Fault system, a major continental-scale fault network in south-central Alaska.

New Alaska plate map aligns with deep tremor signals and major fault zone

The researchers suggest that stress generated by the collision between the Yakutat microplate and the North American plate could be transmitted through the overriding crust all the way to the Denali Fault, potentially contributing to the 2002 magnitude 7.9 Denali earthquake.

They also note that the newly identified boundary aligns closely with earlier research based on tectonic tremor signals, which had already implied the Yakutat plate extends farther east than previously mapped. According to Miller, the newly revealed linear structure matches the end point of that tremor activity, describing it as a feature that had not been observed before but fits precisely with independent seismic evidence.

Thus, the mix of earthquakes and tremor likely reflects differences in rock composition along the plate. West of the sharp boundary, tremor suggests ductile rocks that slip slowly and release stress without earthquakes. At the earthquake-defined edge, the rock appears more brittle, allowing stress to build and rupture in small quakes.

Looking ahead, the researchers plan to extend their analysis further back in time, or before 2018, to identify additional earthquakes along the Yakutat boundary and to better resolve the structure of the highly compressed tectonic zone closer to Alaska’s southern coast. They also emphasized that the machine-learning approach was key to revealing the previously unseen edge of the Yakutat plate.

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