When the ground finally stopped shaking on New Year's Day 2024, residents of Wajima City on Japan's Noto Peninsula thought the worst was over. Then, nearly an hour later, flames erupted across the city, destroying buildings even though power had been cut and no clear ignition source could be found. Now, a new study reveals a surprising culprit: methane bubbles trapped underground, released and ignited by the earthquake's lingering effects—a phenomenon a Japanese researcher calls the "delayed seismic champagne effect."
Professor Emeritus Yuji Enomoto of Shinshu University's Faculty of Textile Science and Technology has proposed that the magnitude 7.6 earthquake shook loose dissolved methane stored in groundwater beneath the city's soft alluvial sediments. Over the next hour, microscopic gas bubbles grew, migrated upward, and accumulated beneath shallow underground layers. When pressure finally ruptured these pockets, methane escaped upward and ignited near the surface—producing fires where no fire should logically exist.
The fire that followed consumed approximately 240 buildings and burned nearly 49,000 square meters of Wajima's urban core. "Urban areas developed on soft alluvial deposits rich in organic matter may inherently be susceptible to the exsolution of flammable gases dissolved in groundwater during strong seismic shaking," Enomoto explained. The unusual timing and location of the blaze—which appeared to emerge from areas with no visible combustible material—had puzzled investigators for months.
Clues to the mechanism came from an aftershock that struck at 5:21 p.m., almost precisely when the fire was reported. Though the aftershock registered only magnitude 3.5, seismic instruments recorded unexpectedly intense, high-frequency shaking between 10 and 15 Hz—a signature consistent with gas-filled fracture systems rather than typical sediment resonance. The study argues this aftershock may have been the final trigger that released the accumulated underground pressure.
The evidence extends beyond the fire itself. Sealed manholes reportedly rose more than one meter above road surfaces. Bubble emissions appeared offshore on the seafloor. Widespread ground fissures cracked through streets and foundations. Enomoto contends that gas pressure buildup may explain these observations more completely than conventional soil liquefaction alone.
The implications stretch far beyond Japan's coastline. Coastal cities worldwide sit on soft, organic-rich sediments capable of storing dissolved methane and other gases underground. If the delayed seismic champagne effect proves widespread, it would add an entirely new category of risk to post-earthquake emergency planning. "The concept of the delayed seismic champagne effect presents a fundamental framework for reassessing secondary hazard risk evaluation and evacuation planning during the post-earthquake phase," Enomoto wrote—meaning cities may need to keep watching the skies long after the ground has gone quiet.