Earthquakes

Midterm

What is an earthquake?

The sudden release of energy in Earth’s crust that produces seismic waves.

What are seismic waves?

Energy waves that travel through Earth during an earthquake.

What are primary (P) waves?

Fastest seismic waves; compressional waves that travel through solids, liquids, and gases.

What are secondary (S) waves?

Slower than P-waves; shear waves that travel only through solids.

What are surface waves?

Seismic waves that travel along Earth’s surface and cause the most damage.

Which seismic waves are considered body waves?

P-waves and S-waves (they travel through Earth’s interior).

What is the order of seismic wave arrival?

P-waves first, S-waves second, surface waves last.

What is the focus of an earthquake?

The point inside Earth where the earthquake begins.

What is the epicenter of an earthquake?

The point on Earth’s surface directly above the focus.

What is a seismometer?

An instrument that detects and measures seismic waves.

What is a seismograph?

The recording produced by a seismometer showing wave motion.

What is triangulation?

A method used to locate an earthquake’s epicenter using data from three seismograph stations.

Why are three seismograph stations needed?

Each station narrows the epicenter to a circle; three circles intersect at one point.

What is stress?

The total force acting on rocks in Earth’s crust.

What is compression stress?

Stress that squeezes rocks together.

What is tension stress?

Stress that pulls rocks apart.

What is shear stress?

Stress that causes rocks to slide past each other.

What is deformation?

The change in shape or volume of rock due to stress.

What is strain?

The amount of deformation experienced by rocks due to stress.

What is elastic deformation?

Temporary deformation where rock returns to its original shape when stress is removed.

What is plastic deformation?

Permanent deformation where rock does not return to its original shape.

What does a stress–strain curve show?

How rocks respond to stress, including elastic limit, plastic deformation, and failure.

What causes tsunamis to occur?

Sudden displacement of the seafloor, usually from underwater earthquakes at convergent boundaries.

Why are tsunamis not usually caused by surface waves?

They require vertical movement of the seafloor to displace large volumes of water.