EARTHQUAKES

SEISMOLOGY- The study of earthquakes waves and how they move through the body and around the

surface of the earth.

Seismic Waves - vibrations generated in the earths interior that carry energy away from the focus point of the earthquake towards the surface of the earth

which is what we feel.

What are Earthquakes?

The shaking or trembling caused by the sudden release of energy.

Usually associated with the faulting or breaking of rocks along tectonic plates or faults (cracks in the plates)

What is Elastic Rebound?

Energy is stored-up in rocks

Rock bend and stretch until the strength of the rock is exceeded.

Rupture occurs and the rock quickly snap back to the shape they were before the rupture

Energy WAVES are released and travel outward.

What is Elastic Rebound?

Prefix “Seis” - is from the Greek word “Seien” which means “to shake”

Seismologist - a scientist who studies earthquakes

Seismic Waves- waves of energy caused by the sudden breaking/releasing of rock or an explosion.

Seismograph/Seismometer - an instrument used to record seismic activity

Seismogram - a record (paper or electronic) produced by a seismograph.

Old School Seismograph

Seismogram Sample

Two main categories of seismic waves:

1. Body Waves - travel through the Earth’s interior only - two types of these:

A. Primary Waves (P Waves)

B. Secondary Waves (S Waves)

2. Surface Waves - travel along the Earth’s surface only - also two types of these:

A. Love Waves (L Waves)

B. Rayleigh Waves ( R Waves)

Seismogram Sample

Body Waves

A. PRIMARY WAVES (P Waves):

Called Primary waves because they are the first to arrive at a seismograph station.

the fastest of the seismic waves

can travel through solids or liquids

Seismogram Sample

Body Waves

A. PRIMARY WAVES (P Waves):

“Compressional”/push-and-pull wave action like someone at the back of a line pushing and a chain reaction results

The sound waves of thunder travel in the same way...pushing and pulling on the air, shaking the windows and walls of your house.

Body Waves - Secondary Waves

B. SECONDARY WAVES (S Waves):

Slower than P Waves

Can only move through solid rock, not liquids

Second Type- Surface WavesA. LOVE WAVES (L Waves)

Fastest of the two types of surface waves

Cause the surface to move in a side-to-side manner

Surface Waves - Rayleigh Waves

B. RAYLEIGH WAVES (R Waves):

cause a “rolling” action across the surface making the ground go up-and-down, and side to side.

Most of the shaking felt during an earthquake is caused by Rayleigh Waves.

Seismogram Example - Labeled

How are Earthquakes Measured?

The “size” of earthquakes is commonly expressed in two ways: magnitude and intensity.

The Richter Scale

Magnitude is a measure of the total energy released during an earthquake. It is determined from a seismogram, which plots the ground motion produced by seismic waves. As devised by C.F. Richter in 1935, the magnitude scale allows us to compare earthquakes in relative terms. It’s known as The Richter Scale.

The Richter Scale

The important thing to remember about magnitude is that the scale is logarithmic, which means that each step in magnitude represents a TEN times increase in amplitude of wave motion. Therefore, an earthquake of magnitude 6.0 has ten times the wave amplitude of an earthquake of magnitude 5.0, a hundred times the strength of a magnitude 4.0 earthquake, and one thousand times the strength of a magnitude 3.0 earthquake.

The Richter Scale

What are the Epicenter and Focus?

FOCUS - The point within the Earth where the faulting begins, also known as the HYPOCENTER

EPICENTER - The point directly above the focus on the surface

How are the Focus & Epicenter located?

These are located in much the same way a GPS (global positioning system) knows where you are and how fast you’re moving in a car. However, instead of using satellites the way a GPS does, seismologist use seismographs and seismic waves to determine the focus & epicenter locations through a process known as TRIANGULATION.

Triangulation

In all honesty, the jobs of seismologist has been made much simple with the invention of networked, computerized sensors.

Instead of having to wait days or weeks for data to be gathered from seismographs and then the information be interpreted and calculations be made, seismologist can get real-time results and we can too at......

http://earthquake.usgs.gov

U.S. Geological Survey Earthquake Hazards Program

This website has enough information and incoming data to keep ANY seismologist busy.

The END