How distant forces may have accelerated the opening of the Gulf of California

Geodynamic models suggest that a reorganisation of subduction zones in the western Pacific may have helped accelerate the opening of the Gulf of California, already weakened by its tectonic history.

Can geological opening be accelerated by forces exerted thousands of kilometres away? That is the question posed by a study published in “Science” on 29 October 2026. Geodynamic models link the reorganisation of subduction zones in the western Pacific to the rapid extension of the Gulf of California, without reducing this history to a single cause.

The finding describes neither a recent earthquake nor a tremor originating in Japan. It concerns tectonic forces transmitted across an immense plate over millions of years. To understand the proposed link, we need to follow three elements: the configuration of the plates, the strength of the lithosphere and the already weakened state of the Californian margin.

A gulf widening between two pieces of a continent

The Gulf of California separates the Baja California peninsula from mainland Mexico. In this region, the continental crust has stretched and thinned; further south, the separation has allowed new oceanic crust to form. This transition from a continental rift to an ocean basin is called “rift-to-drift”.

A rift is an area where the lithosphere—the rigid outer layer made up of the crust and the upper part of the mantle—stretches. When it thins sufficiently and breaks, ocean floor can form. The rift was already under way before the acceleration studied: the authors focus mainly on the rapid phase of its opening, around 6 to 8 million years ago.

This chronology matters. The reorganisation of the western Pacific subduction zones began around 10 million years ago, while the acceleration of rifting is documented later, between around 8 and 3 million years ago. This was therefore a gradual tectonic change and a regional evolution, not a one-off event off the coast of Japan.

Why a second subduction zone changes the forces

Subduction is the process by which one oceanic plate sinks beneath another plate, towards the mantle. The part that sinks exerts a pull on the rest of the plate. When the configuration of subduction zones changes, the forces acting on the plate can change too, even far from the trenches where it sinks.

The researchers studied this mechanism using three-dimensional geodynamic models, calculated with the ASPECT software. They compared single- and double-subduction configurations in a framework representing the current geometry of the plates. The calculation estimates the stress fields associated with these configurations. It does not directly measure a force that would have been recorded in Californian rocks several million years ago.

In the models, double subduction in the western Pacific can transmit extensional stresses of around 5 to 15 megapascals across the Pacific Plate. The pascal measures pressure; these values are neither an earthquake magnitude nor an opening rate. The authors find increased mechanical loading in the Gulf region and in the southern part of the San Andreas Fault system.

The key point is the comparison: the question is not just what stresses exist in one configuration, but how they change when moving from single to double subduction. The authors thus investigate whether the reorganisation in the western Pacific can provide a mechanical contribution to rifting in the east.

An additional force does not act on an intact margin

The same stress does not necessarily produce the same deformation everywhere. The lithosphere resists, and its strength depends on its structure and history. Before the acceleration, the margin of the Gulf had already undergone extension and magmatism, which had weakened it. It was therefore more prone to concentrating deformation than a region that had remained more robust.

The mechanism can be compared to an additional load applied to a structure that has already been weakened. The image helps distinguish the force received from the capacity to withstand it, but it does not literally represent the lithosphere as a simple object that would break under a single blow. In the model, the addition of stresses can help push the system past a threshold at which deformation becomes localised: extension concentrates, thinning increases, and feedbacks that weaken the system can then accelerate the process.

That is why the study does not say that double subduction alone opened the Gulf. It proposes an external contribution to a system already primed by its history. The result depends on the model parameters, including the strength and viscosity assigned to the materials. The authors’ sensitivity tests preserve the general trend, but the precise stress values can vary depending on the assumptions.

What the calculation can establish

The model shows that a long-distance mechanical link is plausible in the configurations examined. It does not explicitly simulate the entire historical transition from single to double subduction. The researchers compare a state before double subduction with a modern configuration in which the system is fully active, then assess the difference in stress. This method tests a mechanical capacity; it does not reconstruct every stage in the margin’s evolution.

The coincidence in timing offers a lead; the simulation adds a possible mechanism. The distant force remains a proposed contribution, associated with the local conditions of the margin.

The San Andreas Fault provides another geological reference point for the region. A transform fault is a boundary where two plates slide horizontally past one another; on its own, it neither creates nor destroys lithosphere. In Mexico, movement involves both divergent boundaries, associated with opening, and transform boundaries. The US National Park Service describes this combination around the Gulf and distinguishes the lateral movement of the San Andreas Fault.

The study therefore forms part of a broader question: how far can forces acting at the boundaries of a plate influence the deformation of a distant margin? The authors mention other ancient episodes of rifting as avenues for comparison, not as cases already demonstrated by this work. For the Gulf of California, their contribution is to show how a distant reorganisation can impose an additional load on an already weakened lithosphere, and why this interaction deserves to be included in explanations of its opening.