EARTHQUAKES

TYPES OF STRESS

Tension- pulls on the crust stretching rock so that it becomes thinner in the middle.

Compression- Squeezes rock together until it folds and breaks.

Shearing – Pushing rock in opposite directions causing it to break and slip apart.

TYPES OF STRESS

TYPES OF STRESS

KINDS OF FAULTS

Normal Fault – occurs when earths crust is being pulled apart (tension). In normal faults the hanging wall slips down relative to the footwall.

Reverse Fault- occurs when earths crust is being pushed together (compression). In reverse faults the hanging wall slips upward relative to the footwall.

Strike-slip Fault- occurs in places where plates move past each other. (shearing)

NORMAL FAULT

REVERSE FAULT

STRIKE-SLIP FAULT

ANATOMY OF A EARTHQUAKE

The FOCUS is the area beneath the Earth’s surface where the rock that is under stress breaks and causes the earthquake.

The EPICENTER is the point on the surface of the crust directly above the focus.

SEISMIC WAVES

Once an earthquake occurs it produces seismic waves.

There are three types :P waves S waves Surface waves

P WAVES

- P waves are compressional waves. They are the first waves to arrive from an earthquake. Only travel through solids.

S waves are transverse waves. They are the second waves to arrive from an earthquake. They travel through both solids and liquids.

Surface waves- When S waves reach the surface they become surface waves. These waves are responsible for the damage caused during earthquakes. They can make the ground roll like ocean waves.

COMPRESSION WAVE

TRANSVERSE WAVE

MEASURING EARTHQUAKES

Mercalli Scale- measures earthquakes according to the level of damage at a given place. Has 12 steps in the scale to rate the earthquake. Same earthquake can have different ranking with this scale at different places based on the damage cause in each place.

RICHTER SCALE

This is a measure of an earthquakes magnitude based on the size of the earthquakes seismic waves.

Uses a seismograph to measure the waves.

This scale doesn’t work well for earthquakes that occur far away.

MOMENT MAGNITUDE SCALE

Scale that geologist often use today. This scale estimates the total energy released by a earthquakes of all sizes, near or far away.

Geologist use seismographs to look at how big the waves were and how strong they were.

This helps them determine how far the fault moved, and they use all of this information to determine the moment magnitude scale for a specific earthquake.