Earthquakes Ch. 8

Earthquakes Earthquake: –shaking and trembling that results from the sudden movement of the rock along the fault. Energy is released What is the study of Earthquakes called?

What causes Earthquakes? Deformation: change in shape due to stress There is an elastic limit to the amount a rock can bend and stretch before it will break. –Elastic rebound: when it returns to its original shape

Faults Tension-normal fault Compression- reverse fault Strike-slip-transform fault

Seismic Waves The waves of energy generated by an earthquake are called seismic waves. 3 types: –Primary (P waves) –Secondary (S waves) –Surface (L waves)-most destructive

Primary Waves Seismic waves that travel fastest are P waves. –Travel through solids, liquids and gases. –Deeper in the Earth the faster they move P waves are push-pull waves.

Secondary Waves Seismic waves that do not travel through the Earth as fast as P waves are called secondary or S waves. –S waves travel through solids but not liquids or gases. –S waves cause particles to move from side to side

P and S Waves

Warm-up: What are Earthquakes?

8.2: Locating Earthquakes How do scientists know when and where Earthquakes occur? –Use 2 things: 1.) Seismograph: instrument that records seismic movements 2.) Seismograms: is the tracing of Earth’s motion how_seismograph_works.htmhttp:// how_seismograph_works.htm

Epicenter Directly above the starting point Earthquake waves reach the epicenter first. Most violent shaking is found here

Focus Point inside the Earth where an earthquake begins w- hill.com/sites/ /student_view0/c hapter16/animations_ and_movies.html# w- hill.com/sites/ /student_view0/c hapter16/animations_ and_movies.html#

S-P Time Method: Finds epicenter Uses many seismogram readings to estimate beginning of epicenter

Triangulation Scientists can use readings from three or more stations to find epicenter

Scales Used to Measure Earthquakes The Richter scale is used to calculate the strength (magnitude) of an earthquake. The Modified Mercalli is used to measure the intensity (amount of destruction) of an earthquake.

The Richter Scale measures the strength or magnitude An increase of one on the Richter scale = 10 times more energy An earthquake of magnitude 6 is how many times larger than a magnitude 3?

The Modified Mercalli Scale measures the amount of damage Describes the intensity of an earthquake

Warm-up: How do we exist with Earthquakes?

8.3: Earthquakes and Society 1.) Forecasting: –Seismic risk maps –Gap Hypothesis Few = strong 2.) Technology: –Retrofitting: making buildings Earthquake resistant 3.) Education:

Seismic Risk Map of the U.S.

Warm-up: What is a volcano?

Ch. 9: Volcanoes It is an opening in the Earth that erupts gases, ash and lava. –Kilauea is the world’s most active volcano.

1.) Magma Deep within the Earth rock exists as a hot liquid called magma. –This molten rock is found in pockets called magma chambers.

2.) Lava When the magma reaches the surface, it is called lava. The opening from which lava erupts is the vent. –Volcanoes often have more than one vent.

4 Lava Types : 1.) Aa: –This lava is thin and runny –Forms brittle crust 2.) Pahoehoe: –Slow flowing –Looks glassy

Continued… 3.) Pillow Lava: –Forms underwater –Looks like pillows 4.) Blocky Lava: –Cool, stiff lava –Forms sharp blocky chunks

Volcanic Eruptions: kaboom! During volcanic eruptions, many rock fragments are blown into the air. –Smallest particles are called volcanic dust. –Vol. Ash (.25 -5mm) falls forms small rocks. –Volcanic bombs (5 mm-3 m) harden in air and form cannon balls

9.2 Effects of Eruptions

Types of Volcanoes Different types of volcanic eruptions form different types of volcanoes. –Cinder cones –Shield volcanoes –Composite volcanoes

1.) Cinder Cones Made of cinders and other rock particles that have been blown into the air ar Form from explosive eruptions. They have a narrow base and steep sides, not very tall –Ex.) Paricutin in Mexico.

Cinder Cone Volcano

2.) Shield Volcanoes Volcanoes composed of quiet flows The lava flows over a large area. After several eruptions, a dome-shaped mountain is formed –Ex.) Mauna Loa in the Hawaiian Islands.

3.) Composite Volcanoes Volcanoes built up of alternating layers of rock particles and lava –A violent eruption first occurs, hurling volcanic bombs, cinder and ash out of the vent. –Then a quiet eruption, produces lava flow that covers the rock particles. After alternating eruptions, a cone-shaped mountain forms Ex.) Mount Vesuvius (Erupted 79 AD)

Mount Vesuvius

Crater There is often a funnel-shaped pit or depression at the top of a volcanic cone. If the crater becomes very large as a result of the collapse of its walls, it is called a caldera.

Volcanic Activity Volcanoes are unpredictable Some erupt regularly, others have not erupted in modern history Scientists classify them as: –active, dormant or extinct.

1.) Active Volcanoes Erupts continually or periodically –Ex.) Mount Katmai in Alaska –Ex.) Mount St. Helens in the Cascade Range.

2.) Dormant Volcano A volcano that has been known to erupt within modern times but is now inactive. –Ex.) Mount Rainier in Washington state

3.) Extinct Volcano A volcano not known to have erupted within modern history. –They have been worn away almost to the level of their magma chamber. Scientists can be wrong. Mount St. Helens was considered to be dormant but erupted after long periods of inactivity.

Volcano and Earthquake Zones Most major earthquakes and volcanic eruptions occur in three zones of the world. Scientists believe that there is a great deal of movement and activity in the Earth’s crust in these three zones.

1.) Ring of Fire One major earthquake and volcano zone extends nearly all the way around the edge of the Pacific Ocean. This zone goes through New Zealand, the Philippines, Japan, Alaska and along the western coasts of North and South America. The San Andreas fault is part of this zone.

Ring of Fire

2.) Mediterranean Zone A second Major earthquake and volcano zone is located near the Mediterranean Zone Extends across Asia into India. Many countries in the zone, including Italy, Greece and Turkey, have violent earthquakes. Many volcanic eruptions also occur in this zone.

3.) Mid-Atlantic Ridge Zone The third major earthquake and volcano zone extends through Iceland and to the middle of the Atlantic Ocean. There is under the ocean a long range of volcanic mountains called the Mid-Atlantic Ocean Range.