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The Pioneer Fragment is located at the Mendocino Triple Junction, an especially complex point where the Santo André fault and the Cascadia subduction zone converge.
A trace of the extinct Farallón plate, which sank beneath the North American plate during the breakup of Pangea, has reappeared. Scientists considered it impossible that a fragment had survived.
A tectonic plate that disappeared more than 200 million years ago has once again captured the attention of the scientific community after being identified under western North America.
The discovery, presented in a published on Thursday in the magazine Sciencereopens the debate on the internal dynamics of the planet and its current seismic implications.
The study documents the existence of what it calls Pioneer Fragmenta remnant of an ancient oceanic plate associated with the extinct, which began to sink beneath the North American plate during the breakup of the supercontinent.
For decades scientists assumed that these remnants of the supercontinent had been completely absorbed by the Earth’s mantle. The new seismic data now analyzed indicates that this fragment not only persistsas continues to influence the current tectonic configuration.
Your unexpected behavior brings a new perspective on how very old geological structures can continue to condition seismic activity millions of years after their formation, notes .
The missing sign is located on the Mendocino Triple Junctiona particularly complex point where the Saint Andrew fault and the Cascadia subduction zone. In this region, lateral and subduction movements interact, capable of generating sisms of great magnitude and difficult to predict.
Unlike other Farallón fragments, such as , which is “dying” beneath Oregon, the Pioneer Fragment it’s not sinking under the continent.
According to the study authors, the Pioneer Fragment remains close to the Pacific plate, moving northwest and brushing the continental crust instead of disappearing beneath it.
The discovery was made possible thanks to microearthquake analysis low-frequency and deep tremors, recorded using high-precision seismic instrumentation. This approach allowed the USGS team to detect subtle displacements that are not visible on the surface.
The results suggest that the presence of ancient fragments, together with remains of the Gorda plate, could explain seismic anomalies observed in the past, such as the 1992 Cape Mendocino earthquake.
Furthermore, scientists warn of the possible existence of a fault almost horizontal not yet included in risk models, a factor that requires a review of the region’s seismic assessment.
