Seismology

Earthquakes have inspired fear and awe since beings on Earth possessed the capacity to feel these emotions. Earlier mystical explanations for earthquakes have been replaced in the modern era by natural, mechanistic explanations informed by observational science.

Stresses in the rock that make the Earth are usually in a state of equilibrium – all the forces acting on a chunk of rock are balanced by opposing forces. The overall stress levels can increase slowly as the rock deforms slowly, but nothing dramatic happens – nothing accelerates.

But occasionally that equilibrium is disturbed, producing a stress imbalance, usually because the strength of a weak area in the rock (a fault) is exceeded. During the temporary loss of equilibrium, the rock on either side of the fault accelerates until it relieves the pent-up elastic stresses, then decelerates and stops moving, and equilibrium is re-established. When this movement occurs along a fault, we call the rupture an earthquake.

The sudden, temporary imbalance of forces in the Earth generates seismic waves that radiate outward, sharing a fraction of the energy released by the rupture with the rest of the world. Seismologists detect those waves and use them to understand the fascinating details of what produced them.

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