A newly trained machine learning system has detected for the first time thousands of previously unrecognized small earthquakes, exposing the well-defined boundaries of the Yakutat microplate as it subsides beneath the North American plate.
The Yakutat Oceanic Plateau is effectively trapped in a complex tectonic collision zone, wedged between major plate systems as subduction continues beneath North America. This dense “tectonic traffic jam” shapes the broader geodynamic environment of southcentral Alaska.
The precise shape and interaction of these plates strongly influences how stress builds and releases across the region, directly influencing earthquake frequency and volcanic activity. By analyzing this fine-scale seismicity, researchers can get a clearer picture of how deformation is distributed along one of North America’s most active and structurally complex subduction systems.
Rebuilding our understanding of Yakutat plate edges
Detailed new analysis Earthquake records Meghan Miller and her colleagues at the Australian National University have sharply refined the mapping extent and boundaries of the Yakutat Plate in southern Alaska.
To build this high-resolution image, the team combined data from both permanent seismic stations and a temporary network deployed between 2018 and 2021. Using a machine learning workflow, we generated an expanded earthquake catalog that significantly increases the number of events detected in this region.
The results revealed a previously unrecognized linear cluster of about 1,750 small earthquakes stretching about 255 miles from northwest to southeast. This continuous seismic zone delineates the plate boundaries much more clearly than previous conventional studies have been able to achieve.
By analyzing ambient seismic noise and imaging deeper structures, the researchers determined that this seismic line marks the edge of the Yakutat microplate, which subducts directly beneath the North American plate at a shallow angle, especially when the separating mantle wedge typically found in many subduction zones is absent. This revised geometry places the Yakutat microplate directly beneath the curvature apex of the Alaska Range and aligns it with the Denali fault system, a major continental-scale fault network in southcentral Alaska.
New Alaska plate map matches deep tremor signals and major fault zones
Researchers suggest that stresses created by the collision of the Yakutat microplate with the North American plate may have transmitted through the upper crust to the Denali fault, contributing to the 2002 magnitude 7.9 Denali earthquake.
They also note that the newly identified boundary is in close agreement with previous studies based on tectonic signals that had already suggested that the Yakutat plate extended further east than previously mapped. Miller said the newly revealed linear structure coincides with the endpoint of that tremor activity, a previously unobserved feature that exactly matches independent seismic evidence.
Therefore, the combination of earthquakes and tremors may reflect differences in rock composition along the plate. To the west of the sharp boundary, the shaking suggests that ductile rocks slide slowly, releasing stress without causing earthquakes. At edges defined by earthquakes, the rock appears more brittle, allowing stress to build up and rupture in small earthquakes.
Looking ahead, the researchers plan to extend their analysis further back, to before 2018, to identify additional earthquakes along the Yakutat boundary and better understand the structure of the highly compressed tectonic zone near Alaska’s southern coast. They also emphasized that machine learning approaches are key to revealing previously invisible edges of the Yakutat plate.
