Earthquakes and Volcanoes

Chapter 12: Section 1

A. How and Where Earthquakes Happen1. earthquake a movement or trembling of the ground that is caused by a sudden release of energy when rocks along a fault move2. elastic rebound the sudden return of elastically deformed rock to its undeformed shape = what causes earthquakes

B. Anatomy of an Earthquake1. focus - the location within Earth along a fault at which the first motion of an earthquake occurs2. epicenter - the point on Earth’s surface above an earthquake’s starting point, or focus3. 90% of continental earthquakes have a shallow focus.4. Seismic Waves

a. body wave a seismic wave that travels through the body of a medium

b. surface wave a seismic wave that travels along the surface of a medium and that has a stronger effect near the surface of the medium than it has in the interior

5. Body Wavesa. P wave a primary wave, or compression

wave; a seismic wave that causes particles of rock to move in a back-and- forth direction parallel to the direction in which the wave is traveling

b. P waves are the fastest seismic waves and can travel through solids, liquids, and gases.

c. S wave a secondary wave, or shear wave; a seismic wave that causes particles of rock to move in a side-to-side direction perpendicular to the direction in which the wave is traveling

d. S waves are the second-fastest seismic waves and can only travel through solids.

• e. Surface waves form from motion along a shallow fault or from the conversion of energy when P waves or S waves reach Earth’s surface.

f. surface waves are the slowest-moving seismic waves, they can cause the greatest damage during an earthquake

The diagram below shows the different tectonic boundaries where earthquakes occur

Chapter 12 Section 2

A. Studying Earthquakes1. The study of earthquakes and seismic waves is called seismology.2. seismograph an instrument that records vibrations in the ground3. Seismographs record three types of ground motion—vertical, east-west, and north-south.

B. Earthquake Measurement1. magnitude a measure of the strength of an

earthquake2. While the Richter scale was widely used for

most of the 20th century, scientists now prefer to use the moment magnitude

scale.3. intensity the amount of damage caused by

an earthquake

4. The modified Mercalli scale expresses intensity in Roman numerals from I to XII and provides a description of the effects of each earthquake intensity.

C. Earthquake Safety1. Before an Earthquake

a. Be prepared. Keep an adequate supply of food, water, batteries, flashlights and a radio.

b. Prepare an earthquake plan and discuss it with your family.

c. Learn how to turn off the gas, water, and electricity in your home.2. During an Earthquake

Protect yourself from falling debris by standing in a doorway or crouching under a desk or a table.

3. After an Earthquake• Be cautious.

• Check for fire and other hazards.

• Always wear shoes when walking near broken glass.

• Avoid downed power lines and objects touched by downed wires.

Chapter 13: Section 1 Volcanoes and Plate Tectonics

A. Volcanoes and Plate Tectonics1. Some volcanic eruptions can be more powerful than the explosion of an atomic bomb.2. The cause of many of these eruptions is the

movement of tectonic plates.3. The movement of tectonic plates is driven

by Earth’s internal heat

B. Formation of Magma1. magma - liquid rock produced under Earth’s surface2. Magma can form under three conditions:

#1) if the temperature of the rock rises above the melting point of the minerals the rock is composed of, the rock will

melt.#2) rock melts when excess pressure is removed from rock that is above its

melting point.#3) the addition of fluids, such as water, may decrease the melting point of some minerals in the rock and cause the rock

to melt

C. Volcanism1. volcanism any activity that includes the movement of magma toward or onto Earth’s surface2. lava magma that flows onto Earth’s surface;

the rock that forms when lava cools and solidifies

3. volcano a vent or fissure in Earth’s surface through which magma and gases are

expelled4. As bodies of magma rise toward the surface, they become larger

D. Major Volcanic Zones1. A major zone of active volcanoes encircles

the Pacific Ocean.a. called the Pacific Ring of Fireb. formed by the subduction plates along

the Pacific coasts2. Mid-Ocean Ridges

The largest amount of magma comes to the surface where plates are moving

apart at mid-ocean ridges.3. hot spot a volcanically active area of Earth’s

surface, commonly far from a tectonic plate boundary

Section 2 Volcanic EruptionsA. mafic describes magma or igneous rock that

is rich in magnesium and iron and that is generally dark in color (oceanic crust)

B.felsic describes magma or igneous rock that is rich in feldspar and silica and that is generally light in color (continental crust)

C. Magma that contains large amounts of trapped, dissolved gases is more likely to produce explosive eruptions than is magma that contains small amounts of dissolved gases

D. Explosive Eruptions

pyroclastic material - fragments of rock that form during a volcanic eruption

E. Predicting Volcanic Eruptions1. One of the most important warning signals

of volcanic eruptions is changes in earthquake activity around the volcano.2. Before an eruption, the upward movement

of magma beneath the surface may cause the surface of the volcano to bulge

outward.3. Predicting the eruption of a particular volcano also requires some knowledge of its previous eruptions