Friday has arrived, and the "A Taste of Science for the Weekend" corner is back again - number 104.
This time about Mie scattering, positive holes, and their connection to earthquake lights.
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The earthquake in Venezuela left behind devastation and destruction on an enormous scale, which this unfortunate country will struggle greatly to cope with. A few days after the disaster, the skies turned a crimson red, giving the remains of the collapsed buildings a stunning yet horrifying apocalyptic look.
The common explanation for the phenomenon was that these were "earthquake lights" - lights that emerge from the ground during earthquakes. But although this is a real phenomenon, in this case the explanation is likely different.
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Even though sunlight is white, we see the sky as blue because of Rayleigh scattering.
Rayleigh scattering occurs when light waves strike particles in the air that are smaller than their wavelength, and the up-and-down motion of the light waves causes these particles to repeatedly change their orientation, like tiny magnets, and release light.
Since short light waves carry more energy and change orientation far more times per second, the result is enhanced emission of light at wavelengths that skew toward blue, which is why the sky is blue when the air is clean.
Mie scattering occurs when the particles in the air are larger than the wavelength of the light - for example, grains from a sandstorm, dust, or fog. In such a case, the movement of electrons within the particle in response to the light is irregular, and the result is an equal scattering of all wavelengths of visible light.
The air in Venezuela was full of sand from a storm that arrived from Africa, and dust from the rubble of buildings that collapsed in the earthquake. At sunset, light always tends toward red because it travels a longer path through the atmosphere on its way to our eyes, and Mie scattering caused the sunset colors to spread across the entire sky and turned it red.
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Earthquake lights typically appear as flashes or flame-like glows near the occurrence of an earthquake. The explanation for the phenomenon isn't completely clear, but one theory is called the "peroxy defect" theory.
The rocks in the Earth's crust crystallized from molten magma in an environment rich in water. During the crystallization process of the rocks, water first bonds to silicon, and as the mixture cools, the hydrogen atoms separate and turn into hydrogen gas, while the remaining oxygen atoms bond to each other with a loose bond.
When an earthquake forms, tectonic plates are crushed against each other with great force, and this pressure suddenly breaks the bonds between the oxygen atoms, tearing electrons away from them.
Each oxygen atom whose shell is missing a negatively charged electron becomes positively charged. The atoms themselves remain trapped in place, but the empty spot in the atom's shell becomes a positive hole that pulls in an electron from a neighboring atom, filling the gap. The atom that gave up the electron then pulls in another electron from the next atom in line, and so on. In this way, the hole itself effectively travels very quickly from atom to atom.
On their way upward, these positive holes combine to create an enormous positive charge, and when it reaches the ground's surface, it ionizes the air until a voltage discharge similar to lightning occurs. The flashes that result from this are earthquake lights.
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The process by which earthquake lights form holds significant potential for early-stage earthquake prediction.
Currently, detection is based on identifying the first seismic wave, which allows a warning of a few seconds or minutes before the second, destructive wave.
Detecting earthquake light flashes is also, admittedly, too late - but it's possible that detecting the infrared light emitted from the buildup of positive holes at the ground's surface could enable much earlier detection and save many human lives.
Shabbat Shalom 😊
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👋 Hi, I'm Shlomo Shtraus, and my posts are not written by artificial intelligence.
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