A Skyquake is the name given to loud, distinct booming sounds, somewhat like cannon fire, appearing to originate from the sky. The phenomenon can last for several hours, with hundreds of booms, and has been widely reported, from the 1800s onwards, by reliable observers on every continent except Antarctica. (Example )

To qualify as a skyquake event, there must be no clouds or lightningplugin-autotooltip__plain plugin-autotooltip_bigLightning

High powered lightning discharges are happening somewhere on Earth around 100 times every second.

A possible mechanism for the very substantial electrical charges within the clouds was put forward in 1978. Following lab-based experiments, it was suggested that the charges arise from the static-electric interactions of graupel (slush) and ice crystals moving within the cloud (due to convection currents caused by widely differing air temperatures) . strikes in the area - and, since the 1940s, no supersonic aircraft.

There is currently no agreement about the cause of the sounds. Theories include :

• Coronal mass ejections
• Meteor impacts
• Escaping bio-gas
• Escaping gas from caves
• Shallow earthquakes
• Underwater geological collapses
• Magnetic interactions with the atmosphere
• Volcanic eruptions
• Avalanches
• Acoustic focussing of distant storms

See : Wikipedia