Unit 10: Earthquakes Chapter 8

Understand how an earthquake epicenter is determined (be able to find an epicenter from seismograph data)

The difference in speeds of P & S waves provides a way to locate the epicenter. The formula given distance between P&S waves and Max Amplitude is: The greater the interval between the arrival of the first P wave and the First S wave-the greater the distance to the earthquake epicenter.

Describe the Elastic Rebound Theory.

The rocks on each side of a fault are moving slowly. The fault doesn't move due to friction-the stress in the rocks increases and they bend. Stress overcomes friction=blocks move on either side of fault move (unlocked). The rocks then rebound (snap) back to their original shape but in a new position. The rebound/snap releases energy as seismic waves.

Distinguish between earthquake magnitude and intensity, Richter vs Mercalli and Moment Magnitude.

1). Magnitude is a measure of the energy released by an earthquake. Magnitude is expressed by using a Richter Scale. Richter scale can only measure small shallow earthquakes, it is outdated. Today scientist use Moment Magnitude-based on the amount of displacement that occurs along a fault. Moment Magnitude is calculated by calculating the average amount of movement along the fault;area of surface break; and strength of broken rock. INTENSITY is the measure of the amount of shaking at a given location based on damage.This is measured by a modified mercali scale. It uses roman numerals and a verbal description of earthquake damage.

Be able to draw and label the parts of a wave (crest, trough,wavelength, amplitude)

1). Wavelength-the distance over which the waves shape repeats (one complete cycle or horizontal distance from one crest to the next). 2). Crest-the position at which the disturbance of a wave attains its highest positive value (highest point) 3).Trough-the position at which the disturbance of a wave attains its highest negative value (lowest point) 4).Amplitude-the vertical distance from the resting position to the crest or trough. 5). Frequency-how oftern a vibration or pulse happens (vibrations per second).

What is a wave and which ways can they move throughout their medium?

A disturbance in a medium (the material the wave travels through) that transmits energy but no matter. 1) Transverse Waves: a wave in which the medium moves at right angles (90 degrees to the direction the wave moves). 2)Longitudinal Wave: a wave in which the medium moves in the same direction as the wave.

Understand where most earthquakes occur (I.E. what explains the pattern of earthquakes that we see)?

An earthquake is the vibration of Earth produced by a rapid release of stored energy. They usually occur when rocks under stress suddenly shift along a fault (break in the crust of the earth along which movement occurred). Energy released radiates in all directions from its source (or focus). Energy is in the form of seismic wave.

What are the 3 types of seismic waves and which causes the most destruction?

Body waves: 1) P wave-fastest moving (high frequency);first to be recorded by seismographs; travels through both solids and liquids through the earth; longitudinal (causes rock particles to move in the same direction that the wave (energy) is traveling. 2) Secondary (S) Waves. -Travel slower than P waves;only travels through solids;transverse waves-cause rock marticles to move at right angles to the direction in which the wave (energy) is traveling. Surface Waves: 3). L Waves. Slowest, last to reach a seismograph station; can travel like ocean waves along the earth's surface;surface waves cause the outer layer of the earth to rise and fall; Surface waves cause the most damage. ** The damage is reduced in deeper focused quakes.

How does a seismograph work and the scientific principle that it is based upon.

Consist of 3 separate sensing devices that that records motion in 3 different planes. Vibrations are recorded as wave shaped tracings or translated into electronic signals. It is BASED ON INERTIA: body at rest remains at rest unless acted on by outside force. Highly sensitive to vibrations. The suspended mass remains at res while the entire instrument moves up and down and side to side as the waves pass.

Understand the difference between a fault, earthquake focus, and epicenter.

Fault-break in the crust of the earth along which movement has occurred. Focus-The source of the earthquake-where the earthquake originates. Epicenter-The location on the Earth's surface directly above the focus of an Earthquake.

Understand how an Earthquake magnitude is calculated and what it means that it is a logarithmic scale: How much more ground shaking does a magnitude 6 earthquake cause as compared to a magnitude 4?How much more energy does a magnitude 6 earthquake release as compared to a magnitude 4?

Increase in 1 unit=10 times more shaking. Increase in 1 unit=30 times more energy released. A magnitude 6 earthquake causes 20 times more shaking than a magnitude 4. A magnitude 6 earthquake releases 60 times more energy than a magnitude 4.

What do we have more of each year-magnitude 2 earthquakes or magnitude 8?

Magnitude 2 there are 1,000,000 per year. Magnitude 8 there are only around 3.