'Seismic champagne effect' may explain why fires break out long after earthquakes

'Seismic champagne effect' may explain why fires break out long after earthquakes Gaby Clark Scientific Editor Robert Egan Associate Editor Following the devastating urban fire that broke out in Wajima City after Japan's 2024 Noto Peninsula earthquake, investigators struggled to identify a clear ignition source, despite widespread destruction and unusual reports of flames emerging from areas with no visible combustible material. While previous studies have linked earthquakes to secondary disasters such as tsunamis and infrastructure failures, the possible role of underground methane release has remained poorly understood. Now, a new study by Professor Emeritus Yuji Enomoto of the Faculty of Textile Science and Technology at Shinshu University, Japan, published in Natural Hazards on April 22, 2026, proposes a previously unrecognized earthquake-related hazard mechanism involving methane gas trapped within soft sediment layers beneath the city. The study introduces what the author calls the "delayed seismic champagne effect." The work examines why a major fire broke out in Kawai-machi, Wajima City, nearly an hour after the magnitude-7.6 earthquake struck on Jan. 1, 2024, despite widespread power outages and no confirmed surface ignition source. A possible methane-driven fire "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 of Japan Meteorological Agency (JMA) seismic intensity 6 or greater, potentially contributing to fire occurrence with a time delay relative to the mainshock," explained Prof. Enomoto. The fire in Wajima destroyed approximately 240 buildings and burned nearly 49,000 square meters. While tsunami-related fires have historically occurred after earthquakes, investigators were unable to identify a conventional ignition source for this event. Earlier observations had already suggested the possible involvement of underground methane, including footage showing flames erupting from a parking lot with no visible combustible materials. To investigate the delayed timing of the fire, Enomoto analyzed seismic waveform data, geological records, groundwater gas measurements, historical earthquake reports, media footage, and field observations collected from the affected area. The study focused particularly on an unusual aftershock that occurred at 5:21 p.m., almost simultaneously with the reported outbreak of the fire. Clues from the aftershock Although the aftershock measured only magnitude 3.5, seismic instruments in Wajima recorded unexpectedly intense and highly localized shaking. The study found that the shaking exhibited unusually high-frequency signals between 10 and 15 Hz, differing from the lower-frequency resonances typically associated with soft sediment layers during large earthquakes. The observed frequency band is consistent with a Helmholtz-type resonance mechanism that may occur in shallow gas-filled fracture systems. According to the paper, the sequence likely began when the mainshock caused strong resonance within the soft alluvial deposits beneath Wajima. This shaking may have driven methane dissolved in groundwater into a supersaturated state, forming microscopic gas bubbles. Over the following hour, the bubbles likely grew, migrated upward through porous sediments, and accumulated beneath shallow low-permeability layers, with the estimated timeline closely matching the observed delay between the earthquake and the outbreak of the fire. As pressure increased underground, localized ruptures and rapid gas releases may have occurred, potentially contributing to the localized anomalous ground shaking observed shortly before the fire. The released methane may then have ignited near the surface. The study also connects this proposed mechanism to several unusual post-earthquake phenomena observed in Wajima, including uplifted manholes, seafloor bubble emissions offshore, and widespread ground fissures. In one case, sealed manholes reportedly rose more than one meter above road surfaces. The author argues that gas pressure buildup beneath the surface may better explain these observations than conventional liquefaction alone. Prof. Enomoto explains, "The concept of the delayed seismic champagne effect presented in this study provides a fundamental framework for reassessing secondary hazard risk evaluation and evacuation planning during the post-earthquake phase." Broader risks after earthquakes The findings may have implications far beyond Japan. Many coastal cities worldwide are built on soft, organic-rich alluvial sediments capable of storing dissolved methane and other gases underground. According to the study, these environments could face overlooked secondary hazards after major earthquakes, even after the initial shaking has ended. The study emphasizes that dangerous conditions may continue to develop for tens of minutes or even hours after the evacuation begins. The author suggests that future earthquake preparedness plans in gas-bearing regions should include monitoring for flammable gases, improved ventilation at evacuation shelters, and revised risk communication strategies. While the study does not conclusively prove that methane caused the Wajima fire, it presents a detailed physical framework consistent with observed seismic, geological, and chemical evidence. The author hopes the work will encourage further investigation into delayed subsurface hazards following major earthquakes. More information Yuji Enomoto, Amplified ground shaking from subterranean gas expansion: a new geohazard in the 2024 Noto earthquake, Natural Hazards (2026). DOI: 10.1007/s11069-026-08124-7 Provided by Shinshu University