Tiny Earthquakes Reveal Hidden Faults Under Northern California

Why this matters: Understanding the underlying tectonic processes is crucial for predicting seismic hazards and mitigating the impact of potential earthquakes. This research provides a more accurate model of the region, improving our ability to assess earthquake risks.

The study, published in *Science*, used data from a network of seismometers to track low-frequency earthquakes in the Pacific Northwest. By analyzing these tiny tremors, researchers identified five moving pieces within the Mendocino Triple Junction. These include the Pacific plate, the North American plate, the Gorda plate, a fragment of the North American plate being pulled down with the Gorda plate, and the Pioneer fragment (a remnant of the Farallon plate) being dragged under the North American plate by the Pacific plate.

The discovery of these hidden tectonic structures challenges previous assumptions about the region's geology and helps explain the unexpected shallowness of the 1992 Cape Mendocino earthquake. The findings suggest that the fault boundary may be shallower than previously estimated, potentially increasing the area of contact between the Pacific Plate and the subduction zone. This could also mean that faults not currently in hazard models might be capable of generating large earthquakes.

Researchers confirmed their model by observing how the plates respond to tidal forces. The gravitational forces of the Sun and Moon exert tidal forces on tectonic plates, and when these forces align with the direction a plate is moving, more small earthquakes occur.

It's the meeting point of three tectonic plates: the Pacific, North American, and Gorda plates.

They are very small earthquakes that occur where tectonic plates rub against each other, thousands of times less intense than earthquakes felt at the surface.

A remnant of the ancient Farallon plate that is now stuck to the Pacific plate and is being dragged under the North American plate.

Do you think this new understanding of the Mendocino Triple Junction will lead to better earthquake predictions? Share your thoughts in the comments!

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