Earthquakes 1

What are earthquakes and where do they occur Lesson 1: What are earthquakes and where do they occur 2

Where do Earthquakes Occur? Earthquakes can occur near the Earth’s surface or far below the surface. Most earthquakes occur at plate boundaries, but some happen at faults located in the middle of tectonic plates. 3

PLATE BOUNDARIES 4

Earthquake Locations Around the World 5

What Causes Earthquakes? Earthquakes are caused by movement along faults. When stress is placed on rocks it deforms, or changes. This is called Elastic Deformation (remember faults and folds, tension and compression) Rock is stretched and bent until it can no longer take the stress. When enough stress builds up in the rock it, it slips and energy is released. The rock then returns to its original shape. This is called Elastic Rebound. Think of a rubber band, you can only stretch it so far until it breaks and return to its original shape. This energy is felt as an earthquake. 6

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Earthquakes in St Louis?? Do we live near a plate boundary? Do we live near a fault? 8

The New Madrid Fault If there is no plate boundary in the middle of the United States, why did these earthquakes take place? Geologists are beginning to understand the answer. The New Madrid Fault Zone is part of an ancient plate boundary. In this area, the North American Plate tried to form a divergent plate boundary about 500 million years ago. The splitting stopped before new plates could form. The faults in the New Madrid Zone are remnants of this old event. Earthquakes occur because the North American Plate is still "settling down". The faults in the New Madrid Zone do not reach the Earth’s surface. They are buried beneath thousands of feet of rock and sediment deposited by the Mississippi River. Geologists have located them by looking at the patterns of earthquakes in the zone. 9

Several of the largest earthquakes ever recorded in the United States occurred in the Midwest, far from any plate boundary. These earthquakes took place in an area called the New Madrid Fault Zone, named after the town of New Madrid, Missouri. 10

New Madrid Fault Over a three-month period in the winter of 1811 to 1812, the New Madrid Fault Zone was struck by three huge earthquakes estimated to be greater than magnitude 8.0 The New Madrid Fault is what causes Alabama to experience earthquakes. 11

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3 Types of Faults associated with Earthquakes PLATE MOTION FAULT TYPE Transform Strike –Slip Fault Convergent Reverse Fault Divergent Normal Fault 13

Strike-Slip Fault occurs at a Transform Boundary 14

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Reverse Fault occurs at a Convergent Boundary 16

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Normal Faults occur at Divergent Boundaries 18

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How do Earthquake Waves Travel? Energy released from moving plates and faults travels through the Earth as waves. These waves are called seismic waves. 22

Depending on what kind of material they are moving through. Types of Seismic Waves 1. BODY WAVES: Seismic waves that travel through the Earth. 2. SURFACE WAVES: Seismic waves that travel along the surface. WAVES TRAVEL: 1.At different speeds and 2 In different ways Depending on what kind of material they are moving through. 23

Body Waves There are two types of body waves: P-waves S-waves 24

P-waves P-waves are primary waves. P-waves travel through solid, liquids and gases. P-waves are the fastest waves. P-waves are the first waves to be detected and the first waves to arrive. P-waves are called primary waves because they arrive first. P-waves cause rock to squeeze and stretch. Imagine a slinky! The area of the Earth that does not receive seismic energy is called the shadow zone. 25

1.P-Waves 26

2. S-waves S-waves are the second fastest waves. S-waves are also called secondary waves because they arrive second. S-waves are slower than P-waves. S-waves move rock from side to side. S-waves can’t travel through parts of the Earth that are completely liquid. 27

S-Waves 28

3. Surface Waves Surface waves move along the surface of the Earth. Surface waves can move up, down and around or side to side. Surface waves move the slowest and cause the most destruction. 29

Surface Waves 30

Seismic Wave Arrival First- P-waves Second- S-waves Third- Surface Waves 31

Quiz 1. Most Earthquakes occur along ________________. 2. The first seismic waves to arrive are______________. 3. The second seismic waves to arrive are _____________. 4. The last seismic waves to arrive are_______________. 5. Which seismic waves travel the fastest?___________ 6. Which type of seismic wave can move through a solid, liquid or a gas?________________ 7. Which seismic wave cannot travel through material that is completely liquid?______________ 8. Which seismic waves are the slowest and the most destructive?_______________ 32

Seismograph A seismograph is an instrument used by scientists to measure earthquakes. Seismologists who study earthquakes can determine when an earthquake started by noting the arrival times of P-waves and S- waves. A seismograph records vibrations in the Earth and determines the strength and location of an earthquake. Ancient Chinese Seismograph. The ball would drop from the dragon to the frog. It told the people which direction the earthquake come from. 33

Seismograms 1. How many minutes did it take for the P-Waves to arrive? 0 1 2 3 4 5 6 7 8 Time in Minutes 1. How many minutes did it take for the P-Waves to arrive? 2. How many minutes did it take for the S-waves to arrive? 3. How long did the surface waves last? 34

Epicenter The epicenter is the point on the Earth’s surface directly above an earthquake’s starting point. 35

Focus The focus is the point inside the Earth where the earthquake begins. The epicenter is located directly above the focus. 36

Measuring Earthquakes There are two major ways earthquakes are measured: Richter Scale 2. Mercalli Scale 37

Richter Scale/Measures Magnitude The Richter Scale measures magnitude. The measurements are given in numbers. Measures the energy released by an earthquake Earthquake Severity-Energy released by an earthquake. Richter Earthquake Magnitudes Effects Less than 3.5 Generally not felt, but recorded. 3.5-5.4 Often felt, but rarely causes damage. Under 6.0 At most slight damage to well-designed buildings. Can cause major damage to poorly constructed buildings over small regions. 6.1-6.9 Can be destructive in areas up to about 100 kilometers across where people live. 7.0-7.9 Major earthquake. Can cause serious damage over larger areas. 8 or greater Great earthquake. Can cause serious damage in areas several hundred kilometers across. 38

Vents Volcanoes form around vents that release magma onto the Earth’s surface. Lava Magma chamber 40

The Composition of Magma Determines whether it is explosive or not! High water content More likely to be !!! High content More likely to be !!! Why? Silica has a thick, stiff consistency Flows slowly Tends to Harden in the volcano’s vent EXPLOSIVE silica EXPLOSIVE The Earth is made of many different and distinct layers. The deeper layers are composed of heavier materials; they are hotter, denser and under much greater pressure than the outer layers. Core: The Earth has a iron-nickel core that is about 2,100 miles in radius. The inner core may have a temperature up to about 13,000°F (7,200°C = 7,500 K), which is hotter than the surface of the Sun. The inner core (which has a radius of about 750 miles (1,228 km) is solid. The outer core is in a liquid state and is about 1,400 miles (2,260 km) thick. 41

Quiz Part 2 a. What physical event causes explosive eruptions? b. Would high water content increase the likelihood of having an explosive eruption? c. Would high silica content increase the likelihood of having an explosive eruption?

What Erupts from a Volcano? Blocky lava Lava can be thick or thin. Pahoehoe Aa Pillow lava 43

What Erupts from a Volcano? Pyroclastic material Rock fragments created by eruptions magma explodes from volcano and solidifies in the air existing rock is shattered by powerful eruptions EXPLOSIVE Lapilli Volcanic bombs Volcanic blocks Volcanic ash 44

How do volcanoes affect the Earth? Flows and Fallouts hot ash can flow really quickly Knock down buildings Dam rivers (flooding/drought) Kill crops and livestock Climatic Changes Ash & Gases can block sunlight Drop average global temperature noticeably 45

Types of Volcanoes Shield volcano Cinder cone volcano Composite volcano 46

Craters, Calderas, and Lava Plateau From explosions of material out of the vent and the collapse of material back into vent Caldera Much larger depression that forms when magma chamber empties and its roof collapses Lava Plateau Forms when lava erupts from long cracks, or fissures, and spreads out evenly (thousands of km) 47

What causes volcanoes? The Formation of Magma Mantle rock melts when the temperature increases or the pressure decreases. There are lots of uncertainties about why volcanoes form, because scientists have to rely on models based on rock samples and other data. 48

What causes volcanoes? Where Volcanoes Form Tectonic Plate Boundaries!!! There are lots of uncertainties about why volcanoes form, because scientists have to rely on models based on rock samples and other data. ~75% world’s active volcanoes in Ring of Fire 49

What causes volcanoes? 50

What causes volcanoes? Hot Spots 51

How do volcanologists predict eruptions? Measuring Small Quakes Before eruption, increase in number & intensity Measuring Slope Bulges may form with magma (tiltmeter) Measuring Volcanic Gases Outflow of volcanic gases Sulfur dioxide, carbon dioxide Measuring Temperature from Orbit Measure changes in temperature over time

You should not be a Volcanologist if…. You don’t like hiking, backbacking, rockclimbing, etc. You are not interested in experiencing extreme temperatures and heights. If you don’t like to travel to incredible places and see breathtaking views of the world. Robert McGimsey USGS A. Ozerov

Volcano Quiz What are the types of pyroclastic material? Define crater, caldera and lava plateau. What causes volcanoes? Where are 75% of the world’s volcanoes found? How does a volcano form at a hot spot? How can volcanoes be predicted? Would you want to be a volcanologist? Why or why not?