Episode 125: Earthquakes

Faults

James Fodor begins by explaining the concept of faults, which are breaks in rocks where movement occurs, often serving as sites for earthquake generation. These faults can be part of larger fault zones, consisting of multiple interconnected cracks, and can exist both at tectonic plate boundaries and within the plates themselves 1. Fault ruptures occur when stress forces build up due to friction and the rigidity of rocks, eventually leading to a break when the stress exceeds a threshold 2.

It's not exactly going to slide smoothly. Also, there's just friction between the rock surfaces at the fault.

--- James Fodor

This rupture releases accumulated strain, causing significant changes in the landscape, such as the formation of mountains or cliffs.

   

Seismic Waves

Seismic waves are crucial in understanding how energy from earthquakes travels through the Earth. James Fodor describes these waves as either body waves, which travel through the Earth's interior, or surface waves, which move along the Earth's surface 3. Body waves include P-waves, which can travel through both solids and liquids, and S-waves, which only move through solids 4.

Love waves are basically the same as S waves, except they're trapped on the surface of the earth.

--- James Fodor

Surface waves, such as Love and Rayleigh waves, are particularly damaging due to their side-to-side and rolling motions, respectively.

   

Causes

Earthquakes are primarily caused by the movement of tectonic plates, where stress builds up at faults until it is released in a sudden rupture. This process is explained by the elastic rebound theory, which describes how stress from tectonic forces causes rocks to deform until they snap back to a less stressed state, releasing energy as seismic waves 5. James Fodor notes that while this theory is widely accepted, it doesn't fully explain all earthquake phenomena, such as weak faults that show gradual deformation 6.

The release of this energy at the focus then propagates outwards in seismic waves.

--- James Fodor

After the initial quake, aftershocks occur as the crust adjusts to a new equilibrium.