EARTHQUAKES

Amanda Embrey and Steven BomarChapter 8

WHAT ARE EARTHQUAKES?

Even though we believe that earthquakes are just ground tremors, they are way more complex than that. In order to understand them more, we use seismology (the study of earthquakes).

WHERE DO EARTHQUAKES OCCUR?

Earthquakes happen along tectonic plates. In order for an earthquake to happen, though, the plates must slide against and past each other. Due to this movement, faults (breaks in the Earth’s crust) may occur.

           

WHAT CAUSES EARTHQUAKES?

As tectonic plates move against each other, stress builds up along the faults. Rocks may change, which is a process called deformation (the change in the shape of rock in response to stress). In some circumstances, elastic rebound (the sudden return of elastically formed rock) may happen. This is when a rock stretches out but doesn’t break. Deformed rock also returns to it’s original state.

DIAGRAM OF ROCK DEFORMATION AND ELASTIC REBOUND

TRANSFORMING

Transforming occurs where two plates slip past each other. During this motion, strike-slip faults may form. These faults cause moderate and shallow earthquakes.

CONVERGING

Converging occurs where two plates push together. This movement creates reverse faults. Along these faults, strong and deep earthquakes occur.

DIVERGING

Diverging occurs where two plates pull away from each other. This motion causes normal faults. Earthquakes that are weak and shallow form along these faults.

HOW DO EARTHQUAKES TRAVEL?

After rock releases energy, the energy travels in waves called seismic waves (waves of energy that travel through the Earth). The two types of waves are P waves (travel through solids, liquids, and gases, and are the fastest) and S waves (second-fastest seismic wave that move rock back and forth).

LOCATING EARTHQUAKES

To locate earthquakes, instruments called seismographs (located at for near the surface of the Earth that record seismic waves) measure the waves. A seismogram (another instrument that measures waves) traces the motion of the earthquake.

WHERE IN THE EARTH DO THEY HAPPEN?

The epicenter (the point on the Earth’s surface directly above an earthquake’s starting point) is where scientists measure the power of the earthquake. The focus is where the earthquake begins.

MEASURING EARTHQUAKE STRENGTH

Richter Scales are used to measure the intensity of an earthquake. This scale ranges from 2.0 to 10.0. When the measurement is high, the power of the earthquake is high.

EARTHQUAKE HAZARD

Certain areas are more prone to earthquakes. In the U.S., the west coast is more prone than the east. This is because California etc. sits near the tectonic plates. California experiences an earthquake every day.

EARTHQUAKE HAZARD (CONTINUED)

The Gulf Coast and Midwest have a low vulnerability to earthquakes. Areas that are not near the tectonic plates do not experience many.

EARTHQUAKE FORECASTING

Predicting earthquakes is difficult to do. Scientists must monitor active faults regularly in order to predict them. The strength of earthquake is related to how often they occur.

THE GAP HYPOTHESIS

The gap hypothesis is another way of predicting earthquakes. This hypothesis states that active faults that have recently had an earthquake are likely to have one again and will be strong. An area of a fault that has very few earthquakes is called a seismic gap.

EARTHQUAKES AND BUILDINGS

The damage done to a building during an earthquakes varies with its strength. Some buildings are modified to resist a certain amount of damage from earthquakes. Even though, the most strong buildings may crumble if the strength is too high.

DISCOVERIES IN EARTH’S INTERIOR

A point in the Earth called a Moho has been discovered. This point is where the speed of seismic waves increase. A shadow zone is a point on the Earth where seismic waves cannot be detected when an earthquake occurs.

QUAKES AND SHAKES ON OTHER COSMIC BODIES

Earthquakes are known to occur on the sun and moon. On the moon, asteroid impacts can cause moonquakes. On the sun, solar flares cause sunquakes. Sunquakes are stronger than earthquakes and moonquakes.

ARE YOU PREPARED FOR AN EARTHQUAKE?

If an earthquake is about to occur, it is advised to put heavier objects on a lower shelf so that nothing falls on your head. Also, it is best to find shelter immediately under a table or in a doorway.

VOCABULARY USED

Seismology Fault Deformation Elastic Rebound Seismic Waves P Waves S Waves Seismograph

Seismogram Epicenter Focus Gap Hypothesis Seismic Gap Moho Shadow Zone