A geological reorganization off the coast of Japan may have helped form the Gulf of California and, ultimately, the Grand Canyon, according to a study published Oct. 29 in Science, Live Science reported. The birth of the gulf, which rifted from Mexico and created the Baja Peninsula 6 million to 8 million years ago, was accelerated by the formation of a double subduction zone more than 6,000 miles (9,600 kilometers) away. That change transferred tectonic force across the Pacific Plate, the authors said. "It's more than a regional curiosity," co-author Thorsten Becker, a geophysicist at the University of Texas at Austin, told Live Science. "It's a reminder of the global connectedness of mantle convection and plate tectonics."
The Gulf of California is a rift zone, where continental crust pulls apart until ocean water can fill the low spot, similar to the Red Sea today. Rifting can slow, speed up, or stop. In the gulf, it not only continued but sped up, taking about 6 million to 13 million years, much quicker than a typical 30 million to 80 million years. Co-author Guido Gianni, a geophysicist at the Czech Academy of Sciences, wanted to know why. No earlier work fully explained the burst of speed, which also transferred Baja California to the Pacific Plate and gave the developing Colorado River an outlet to the sea, allowing it to carve the Grand Canyon on its way to sea level.
Gianni and Becker's doctoral student at UT Austin, Xiang He, ran a global plate-tectonics model on supercomputers at the Texas Advanced Computing Center. Around the same time the gulf was opening, a single subduction zone off Japan, where the Pacific Plate pushes under the Eurasian Plate, transitioned into two separate zones about 10 million to 12 million years ago. That change at the western end of the Pacific Plate altered pulling stresses on the other side. "It turned out — ta-da! — [with] the change in this pulling stress, Baja California was one of the few places outside the Japan region that were affected," Becker said. The team tested the result under different assumptions about stresses and mantle properties, and it held.
The gulf was already rifting because the Farallon Plate, once under the West Coast of North America, had stretched and thinned the crust. Without the extra "oomph" from Japan's reorganization, the authors said, that rift might have ended as little more than a valley. Becker argued the work matters for how scientists think about plate boundaries and earthquake-generating faults, including the San Andreas and the Cascadia megathrust, which can produce quakes larger than magnitude 9. "If I'm asking what is the mantle doing underneath Cascadia so I get our megathrust correct," he said, "I need to include these effects." The verified claim is a model-based explanation linking distant plates, not a new crack in the canyon itself.