Chapter 6

Earthquakes pg 123

Seismometer- an instrument that measures

earthquakes Earthquake- is a series of low frequency shock

waves traveling through earth Tectonic plate motion builds up stress at plate

boundaries and within the plates themselves. Stress- is a force exerted inside a material. Shear- exits when forces are acting in opposite

directions on different parts of the same object.

Tectonic Forces

Divergent boundaries- Plate sections that are

moving part. Convergent boundaries- plates moving

towards each other. Transform boundaries- where plates slide past

each other.

Strain- any change in shape of a solid under

stress. Ductility- the amount of strain a material can

endure without breaking Some Rocks have elasticity. These rocks store

energy which can cause a more serious earthquake.

Strain and fracture

Joints- cracks in rocks Faults- occurs when the sections of rock on

opposite sides of the crack move relative to each other

Most major fault lines in the United States are in mountain Ranges.

Dip slip fault- parallel to its dip Normal fault- block above fault surfaces drops. Reverse fault- upper block rises above lower

block

Section 6b Faults and Joints

Most earthquakes we feel happen at depths

less than 45 miles. Secondary earthquakes are called aftershocks. Aftershocks result from potential energy still

being stored in the rocks. The fault slips again which causes the after shock.

Aftershocks can go one for days, weeks or even months after the initial earthquake.

Faults and earthquakes

Seismometer are instruments that detect

seismic waves (earthquake waves). Seismographs include a seismometer and a way

to record the wave changes During normal activity the seismograph will

draw a straight line. During a earthquake the straight line turns into a zigzag. The height (amplitude) of the zigzag (wave) shows how strong the earthquake was.

The bigger the amplitude the stronger the earthquake

6c Earth waves and Seismology

Body waves- earthquake waves that pass right through the

earth. P waves- Fastest body waves. Have small amplitude and short

wavelengths. They can travel through both solid and liquid rock S waves- have larger amplitude. Stronger and slower than P

waves. They can travel through solid rock. Surface waves- travel through earths surface. Have to basic

waves Rayleigh and Love waves. Rayleigh and Love waves are more destructive waves because

they affect human structures. ( house buildings, roads, etc.)

Epicenter – Center; spot on earths surface directly Focus- the center of an earthquakes activity . This is deep

underground

Type of Seismic Waves

Richter scale- how the strengths of earthquakes are reported. Magnitude- indicates the energy released by the earth movement. This scale does not work well on earthquakes that have a magnitude over 7.

Effects of Earthquakes

Intensity- is a measure of how much damage

actually results from the earthquake. Earthquakes can last from a few seconds to a

few minutes. Modified Mercalli Intensity scale- Measures

the destructiveness of an earthquake. The scale is 1- 12.

1 is a earthquake that leaves no visible damage. A 12 is total destruction to the whole building.

Earthquake Intensity

Building collapse, fire, tsunamis, and landsides

are all hazards of earthquakes. Many cities are enforce earthquake proof

buildings and strict building codes. Many cities have sensors in their gas lines.

These sensor will turn the gas off if there is a break in the line.

Earthquake Hazards