Introduction
Earthquake lights—also termed earthquake lightning or earthquake flash—are luminous optical phenomena reported in close temporal and spatial association with seismic and volcanic events. They typically appear in the sky near areas of crustal strain such as active faults, earthquake epicenters, or erupting vents and arise during, immediately before, or shortly after episodes of seismicity and tectonic deformation rather than as persistent atmospheric features. Observers describe them as brief, localized lightning-like flashes or sustained glows; they are visual phenomena without direct mechanical or structural expression.
The physical origin of earthquake lights remains contested: multiple explanatory hypotheses have been advanced, but no single mechanism has achieved broad scientific consensus. It is important to distinguish these phenomena from bright flashes caused by damaged electrical infrastructure (for example, arcing power lines) or from ordinary meteorological lightning, which are secondary effects of shaking or storms and not the same phenomenon. While documented instances can draw attention to zones of intense tectonic stress or volcanism in observational records, the inconsistent occurrence and unresolved causation mean earthquake lights are not presently reliable as predictive or diagnostic tools in seismology or volcanic monitoring.
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Appearance
Earthquake lights are transient luminous phenomena observed in the atmosphere in temporal association with seismic activity. They most commonly resemble auroral displays with white to bluish hues but have been reported across a broader color range, including yellow, and may appear as brief flashes lasting seconds or as sustained glows persisting for tens of minutes. Their temporal relationship to earthquakes is variable: reports cluster around the period of ground shaking but include well‑documented cases that occurred before or after seismic ruptures. Many compilations suggest a rough magnitude threshold near Mw ~5 for frequent occurrence, although exceptions and variability in reporting—particularly of pre‑seismic ball‑like lights—are noted.
Historical chronicles extend the record of such sightings back at least to the 869 Jōgan earthquake in Japan, and modern accounts document occurrences at considerable lateral distances from rupture zones (for example, luminous reports up to ~110 km from the 1930 Idu epicenter and about 400 km from the 2008 Sichuan event). Video and eyewitness documentation now exist from multiple tectonic settings worldwide, including colorful sky lights recorded during the 2003 Colima quake, filmed displays above the sea in the 2007 Peru event, footage from the 2009 L’Aquila and 2010 Chile earthquakes, and numerous recent recordings across North America, New Zealand, Mexico and Asia (notable examples include events in Napa/Sonoma 2014, Wellington 2016, Mexico City 2017, Acapulco/Mexico City 2021, Qinghai 2022, and multi‑angle footage from the 2022 Fukushima earthquake). Increasingly ubiquitous recording devices and webcam networks have improved preservation of these transient phenomena. Recent work has also begun to link some luminous flashes to contemporaneous geophysical signals (for instance, a 2023 case in which flashes coincided with a geomagnetic disturbance and power‑system failures were ruled out), while large, high‑magnitude ruptures in 2023 produced repeated or persistent lights in several regions, reinforcing a recurring association between strong seismic events and atmospheric luminescence.
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Types
The model situates earthquake‑light generation within an Andean‑type, interplate orogenic setting—a subduction‑zone environment where plate‑interface deformation and elevated mountain‑belt relief concentrate crustal stresses. For clarity, conceptual cross‑sections often exaggerate vertical relief to emphasize the topographic and structural contrasts that influence stress distribution and electrical behaviour of the crust.
Deforming rocks are treated as media that can generate and transport electronic charge carriers. Positive electron holes (denoted +) and electrons (e′) are invoked as the principal mobile species, and lithologic differences are described using an extrinsic‑semiconductor analogy: some rock volumes behave as “P‑type” (hole‑dominated) domains and others as “N‑type” (electron‑dominated). These contrasts in dominant carriers and conductivity across lithologic boundaries facilitate charge separation, current flow, and localized field intensification when the rocks are stressed.
Stress accumulation and release in this tectonic context can activate these carriers and drive their migration through P‑ and N‑type domains. The resulting currents and concentrated electric fields may produce luminous manifestations at or above the surface when charge release or ionization processes occur, linking electrical activity in the faulted crust to observed lights.
Earthquake lights are commonly classified by their timing relative to rupture. Preseismic lights arise from precursory stress changes and carry timescales from a few seconds up to several weeks before rupture; they are typically observed close to the eventual epicentral zone and are interpreted as signals of local charge activation and migration preceding failure. Coseismic lights appear during the mainshock and can be generated either locally—by earthquake‑induced stress concentrations near the source—or remotely, when transient stresses associated with the propagating seismic wavefield (notably S waves) activate charge carriers in distant rock volumes.
This distinction produces differences in spatial extent: preseismic phenomena tend to be spatially confined near the impending rupture, whereas coseismic lights may be spatially decoupled from the epicenter by wave‑induced transient stress pulses that trigger luminous effects at considerable distances. Observationally, luminous occurrences associated with smaller aftershock sequences are uncommon, suggesting that the production of visible lights depends on the magnitude of stress perturbation, the spatial scale of rock volumes activated, and the intensity of the underlying charge‑generation mechanisms, which are typically greater in larger ruptures.
Possible explanations
Earthquake lights are a well-documented but poorly understood phenomenon for which several physical mechanisms have been proposed; no single hypothesis currently accounts for the full range of observations, and some proposals lack direct experimental confirmation. A prominent geochemical–electrical model invokes stress-induced rupture of peroxy (O–O) bonds in certain rock types (for example, dolomite and rhyolite). Bond rupture produces mobile oxygen anions that can migrate through fracture networks; when these charged species reach the near-surface they may ionize pockets of air and produce visible plasma emissions. Laboratory work has demonstrated that some rocks emit oxygen-derived charge carriers when subjected to high stress, lending empirical support to this pathway.
Fault geometry appears relevant under the peroxy/anion framework: subvertical faults, particularly in extensional (rifting) settings, are disproportionately associated with reported light events, a pattern consistent with steeper fault angles facilitating upward migration of stress-generated charges to the atmosphere. A distinct but related hypothesis emphasizes piezoelectricity in quartz-rich lithologies (notably granite): mechanical deformation of quartz under rapid tectonic loading generates strong electric potentials that can ionize air and produce luminous discharges.
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A further class of explanations invokes perturbations of the geomagnetic field and the ionosphere in regions of concentrated tectonic stress. Such disturbances could, in principle, induce luminous phenomena either by causing ionospheric recombination at anomalously low altitudes or via auroral-type processes; however, this mechanism does not account for all observations and remains difficult to verify experimentally at crustal scales.
Laboratory experiments have also demonstrated crack- and friction-related electrical effects that may be relevant. At the American Physical Society meeting in 2014, experiments using granular layers of varied materials showed reproducible voltage spikes associated with grain fracture and sliding (positive spikes when grains split open, negative when contacts closed). Those crack-mediated discharges were sufficient to electrify the surrounding air and produce bright flashes consistent with triboluminescence. While such laboratory results suggest plausible mesoscale sources of luminous emission during rock failure, scaling these processes to natural fault systems and determining their relative importance among competing mechanisms remain active areas of research.
Despite numerous anecdotal reports and a substantial body of literature, the existence of earthquake lights (EQL) as a distinct seismogenic phenomenon remains disputed. Critics note a lack of unambiguous, direct evidence tying luminous atmospheric displays causally to seismic ruptures, and they emphasize that the published record is internally inconsistent. Prominent commentators in 2016 argued that researchers should first establish that a reproducible phenomenon exists before attempting mechanistic explanations, and they documented cases in which images claimed as EQL were visually indistinguishable from ordinary atmospheric optics such as iridescent clouds.
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Skeptics also point to the wide range of morphologies attributed to EQL—from small, mobile globes to lightning‑like flashes and cloud‑like luminous patches—which increases the risk that observers will project an earthquake association onto heterogeneous, ambiguous displays. From a geographic and methodological standpoint these critiques imply two priorities: (1) rigorous differentiation of seismically linked lights from common atmospheric optical events, particularly in mountainous or other tectonically active regions where such optics are frequent; and (2) adoption of standardized, well‑documented observational protocols (for example, precise spatiotemporal correlation with seismic data, spectrometric or other instrumental verification, and thorough contextual reporting) before asserting a seismogenic origin for reported luminous phenomena.