Tectonic plates move slowly, but faults at their boundaries and within plates can remain locked by friction. Stress builds in the surrounding rock until part of a fault slips. The sudden movement releases energy as seismic waves: an earthquake.
Where shaking begins
The rupture starts underground at the hypocenter, also called the focus. The epicenter is the point on the surface directly above it. P waves arrive first and can travel through solids and liquids. S waves follow and travel only through solids. Surface waves often contribute strongly to damaging ground motion.
Magnitude estimates the size of an earthquake at its source. Intensity describes shaking and effects at a particular place. The same earthquake can produce very different intensities because distance, rupture direction, depth, local soil and building design all matter. Soft sediments may amplify shaking, while steep slopes can fail in landslides. Underwater movement that vertically displaces the seafloor can generate a tsunami.
Prediction, forecasting and warning
Scientists cannot currently predict the exact time, location and magnitude of a major earthquake. Claims based on weather, animal behavior or vague time windows are not reliable predictions.
What researchers can do is estimate long-term probabilities by studying faults, past earthquakes and plate motion. Seismic hazard maps show where specified levels of shaking are more likely over time. Early-warning systems are different: they detect an earthquake after rupture begins and may send alerts before the strongest waves reach locations farther away. Depending on distance, that can provide seconds to take protective action.
Reducing risk
Earthquake-resistant construction, secured utilities, emergency planning and public education save lives. Hazard is the natural phenomenon; risk also depends on who and what is exposed and how vulnerable structures are.
Earthquakes cannot be stopped, but their consequences can be reduced through sound engineering, realistic hazard assessments and preparation grounded in evidence.
Sources
- USGS, Can You Predict Earthquakes?: https://www.usgs.gov/faqs/can-you-predict-earthquakes
- USGS, Earthquake Hazards: https://www.usgs.gov/programs/earthquake-hazards/hazards