# Earthquakes and Seismic Waves

## 14 terms

### Earthquake

Shaking and trembling that results from movement beneath the surface. Most are to small to notice. But some are large and can cause great changes and damage.

### Focus

The area beneath the Earth's surface where rock that is under stress breaks, triggering an earthquake.

### Epicenter

The point on the surface directly above the focus.

### Seismic Waves

Waves that carry energy from an earthquake away from the focus, through Earth's interior, and across the surface in all directions.

### P Wave

The first seismic wave to arrive. They compress and expand the ground like and accordion. Can damage buildings.

### S Wave

The second seismic wave to arrive. Vibrate side to side n up n down. Shakes the ground back n forth. Shakes the ground violently. Cannot move through liquid.

### Surface Wave

P n S waves when they reach the surface. Moves slower than P n S waves but can produce severe ground movement. Can move like an ocean waver or side to side.

### Most used methods of measuring earthquakes

Mercalli Scale, Richter Scale, and Moment Magnitude Scale.

### Mercalli Scale

Rates earthquakes according to level of damage at a given place. Isn't very reliable because the same earthquake can have different ratings because it causes different amounts of ground motion at different locations.

### Magnitude

A number geologists assign an earthquake based on its size. They determine magnitude by measuring the seismic waves and fault movement.

### Richter Scale

Rating of an earthquake's magnitude based on the size of an earthquakes seismic waves. Works for small, nearby EQs but not large distant EQs.

### Seismograph

An instrument that records and measures seismic waves.

### Moment Magnitude Scale

A rating system that estimates the total energy released by an earthquake. Can be used to rate EQs of all sizes, near or far. To get this geologists study data from seismographs. This shows what kinds of waves the EQ produced n how stong it was.

### How do you Locate Epicenter

To tell the distance, measure the difference of arrival time between S P waves. Then draw AT LEAST THREE circles of seismograph locations. Where they intersect is where the epicenter is.