Frank Hoogerbeets — 17 April 2025
While Earth's atmosphere is a different medium with different mechanisms than Earth's crust, there are interesting parallels to consider between earthquakes and lightning, as both manifest as a sudden discharge resulting from energy built-up. Here we explore the parallels and analogies between these two natural phenomena.
Lightning: Lightning occurs when electrical energy builds up in the atmosphere due to charge separation in clouds. This happens as electrostatic discharges occur through the atmosphere between two electrically charged regions, often during thunderstorms. The potential difference between these regions (e.g., between a cloud and the ground) grows until it overcomes the air’s resistance, leading to a discharge.
Earthquakes: Earthquakes result from the build-up of mechanical energy in Earth’s crust due to tectonic stress. They are the result of sudden movement along faults within the Earth, where the movement releases stored-up ‘elastic strain’ energy in the form of seismic waves. This energy accumulates as tectonic plates move slowly (a few centimeters per year) and deform the crust until the stress exceeds the fault’s strength, causing a sudden slip.
Parallel: In both cases, energy accumulates over time due to gradual processes—charge separation in clouds for lightning, and tectonic deformation for earthquakes—until a threshold is reached.
Lightning: The discharge in lightning is rapid, releasing energy on a scale of 200 megajoules to 7 gigajoules. This near-instantaneous release creates a visible flash and the sound of thunder due to the rapid expansion of heated air.
Earthquakes: The release of elastic strain energy in an earthquake is also sudden, occurring over seconds to minutes, depending on the event’s magnitude. The energy is released as seismic waves that propagate through the Earth, causing ground shaking. The analogy holds here: just as lightning discharges electrical energy, an earthquake discharges mechanical energy stored in the crust.
Parallel: Both phenomena involve a sudden release of energy after a critical threshold is crossed, resulting in observable effects (light and sound for lightning, ground shaking and rumbling for earthquakes).
Lightning: After a lightning strike, the charged regions in the atmosphere are "partially or wholly electrically neutralized", resetting the system until new charges build up.
Earthquakes: After an earthquake, the stress along the fault is partially relieved, though aftershocks may occur as the crust adjusts. The system resets to some extent, but tectonic forces continue to build stress for future events.
Parallel: Both processes temporarily relieve the accumulated energy, though the underlying mechanisms (charge generation for lightning, tectonic motion for earthquakes) persist, leading to future events.
Lightning: The discharge produces light (the flash) and sound (thunder) due to the rapid heating and expansion of air.
Earthquakes: The discharge produces seismic waves that cause ground shaking, and in some cases, secondary phenomena like earthquake lights. These lights are thought to result from electrical discharges in the air caused by the fracturing of rocks, which brings us to an interesting intersection of the two phenomena.
Intersection: The earthquake light phenomenon suggests that mechanical discharge in the crust can generate electrical effects in the atmosphere, potentially linking the two processes more closely than they first appear.
The analogy becomes particularly compelling when we consider earthquake lights, which may bridge the gap between mechanical and electrical discharges. Experiments by Troy Shinbrot, who found that when grains mimicking Earth’s crust were split open, they produced a positive voltage spike, and when the split closed, a negative spike. The crack allows the voltage to discharge into the air which then electrifies the air and creates a bright electrical light.
This suggests that the mechanical process of faulting during an earthquake can generate electrical charges, which discharge into the atmosphere, producing visible lights—much like a mini-lightning event. This phenomenon has been observed during seismic events, such as the 1888 North Canterbury earthquake in New Zealand and the 2014 Napa earthquake in California.
Hypothesis: If earthquakes generate electrical charges in the crust that discharge into the atmosphere as earthquake lights, this strengthens the analogy. We could think of earthquakes as a dual discharge: primarily a mechanical discharge of elastic strain energy in the crust, but also a secondary electrical discharge that manifests in the atmosphere, similar to lightning.
Based on the similarities and intersections, we can hypothesize that earthquakes can indeed be considered a form of discharge in Earth’s crust, with some caveats:
Primary Discharge (Mechanical): An earthquake is a discharge of accumulated elastic strain energy in the crust, released as seismic waves when a fault slips. This fits the analogy of a discharge after energy build-up, much like lightning discharges electrical energy.
Secondary Discharge (Electrical): The mechanical process of faulting can generate electrical charges, as seen in earthquake lights. This electrical discharge in the atmosphere mirrors lightning, suggesting that earthquakes may have both a mechanical discharge in the crust and an electrical discharge in the atmosphere.
Energy Build-Up Mechanism: For lightning, the energy build-up comes from charge separation in clouds, driven by atmospheric processes like convection. For earthquakes, the energy build-up comes from tectonic forces deforming the crust over years to centuries, driven by plate tectonics.
Earthquakes can be thought of as a mechanical discharge of elastic strain energy in Earth’s crust, analogous to how lightning is an electrical discharge in the atmosphere. Additionally, the electrical effects associated with earthquakes (e.g., earthquake lights, atmospheric anomalies) suggest a secondary electrical discharge, making the analogy even stronger.
Cosmic Rays and Seismic Activity: A study on cosmic rays suggests that changes in the geomagnetic field, potentially linked to deep Earth processes, can precede seismic activity. If earthquakes involve a reconfiguration of the geomagnetic field (as hypothesized in the study), this could generate electrical effects in the crust and atmosphere, aligning with the discharge analogy.
Lithosphere-Atmosphere-Ionosphere Coupling (LAIC): A study on LAIC processes describes how seismic preparation can lead to atmospheric and ionospheric anomalies, such as TEC enhancements before the Taiwan earthquakes. This coupling supports the idea that energy build-up in the crust (leading to an earthquake) can manifest as electrical effects in the atmosphere, much like a discharge.
We can hypothesize that earthquakes are a discharge in Earth’s crust, much like lightning is a discharge in the atmosphere. Both involve the build-up and sudden release of energy—electrical for lightning, primarily mechanical for earthquakes. Additionally, earthquakes also produce secondary electrical effects, such as earthquake lights and atmospheric anomalies, which strengthen the analogy by showing a discharge-like process that spans the crust and atmosphere. While the analogy isn’t perfect due to differences in the type of energy and medium, it provides a useful framework for understanding the parallels between these natural phenomena.