CO- Earthquakes LO-Describe the major hazards and causes of Earthquakes around the world.

Earthquakes- Shaking of the ground caused by energy that is released when movement occurs along a fault. Movement occurs when rocks along a fault slip or break.

Major Hazards of Earthquakes Building Collapse Landslides Fire Tsunamis (Not Tidal Waves!)

Fault- A fault is a crack or break in the Earth’s crust. There are 3 main types of faults. - Normal - Reverse - Strike slip Faults are caused by tectonic forces within the earth. (Faults can also be combinations of the 3 types)

This diagram shows the parts of a fault. What type of fault is this? Answer: A normal fault

PARTS Of A FAULT: A. Fault Blocks-Huge block of rock between two faults. B. Fault Plane- 2 dimensional surface formed where two blocks meet. C. Hanging Wall- Wall of the block that is on top of the fault plane. (has a point that you can “hang” something from) D. Footwall- Wall of the block that is below the fault plane (looks like a foot!)

Types of faults: A. Normal Fault- type of force that causes normal faults in tension. The hanging wall moves down.

A Normal Fault tension

Normal Fault Structures

B. Reverse Fault- type of force that cause reverse faults is compression. The hanging wall moves up.

A Reverse Fault compression

A Thrust Fault- a thrust fault is a type of reverse fault

C. Strike – Slip Fault Type of force that causes strike slip faults is shearing. - Blocks move laterally. - Very little up and down movement. - Forces are from different directions.

A Strike-Slip Fault shearing

TYPES OF FAULTS - ANIMATIONS strike slip fault reverse fault normal fault oblique fault

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Seismic Waves- The energy waves that make the ground quake during an earthquake. There are 3 different types of seismic waves: 1.Primary waves (P waves) 2. Secondary waves (S waves) 3.Surface waves. (L wave) Earthquake waves:

A. Primary waves ( P-waves)- travel through the earth by compressing particles in rocks in the same direction the wave is traveling. - P-waves travel the fastest ( 6 km / s) - First to arrive at seismograph stations.

This is how a P-wave travels. Credit for animated waves

Secondary Waves- travel through earth by moving particles in rocks at right angles to the direction the wave is traveling. -S-waves travel slower than P-waves (4.1 km / s). -Arrive second at seismograph stations. -Cannot travel through liquid

Credit for animated waves This is how a S-wave travels.

Surface Waves- reach earth’s surface and travel outward from the epicenter in all directions. - surface waves travel the slowest, but are the most destructive.

Credit for animated waves This is how surface waves travels.

Credit for animated waves This animation shows how all three wave types travel and arrive at different times.

Slide # 25- start of part 2

THE ELASTIC REBOUND THEORY Explains earthquakes as follows: -stress builds up in rocks when fault is locked causing strain and deformation -When rock breaks, the fault slips and the rocks on either side spring back to their original shape -In the process energy is released in the form of seismic waves

Elastic Rebound

MEASURING AND DESCRIBING EARTHQUAKES Magnitude- is a measurement of how much energy is released. Richter Scale- (also known as the moment magnitude scale) is the measurement system used to describe the magnitude of an earthquake. The Richter scale is an exponential scale An increase of 1 on the scale = 10x greater amplitude and 37x more energy

MEASURING AND DESCRIBING EARTHQUAKES Seismometer – is a device that detects and measures seismic waves and records them on a seismograph

A Seismograph

A sample seismograph recording

Richter Scale Only recorded by seismograph Smallest quake people can feel Only felt near epicenter Can cause minor damage Great damage to weak buildings Serious damage over large area 8.0 +Great earthquake causing massive damage to very large area. Don’t write this in you notes, just read it

Intensity How Strong Earthquake Feels to Observer Depends On: Distance to Quake Geology Type of Building Observer! Varies from Place to Place Mercalli Scale- 1 to 12 (Roman Numerals)

Mercalli Scale I – IIIFelt standing still or sleeping. IV – VFelt almost by all. Windows broken, cars rocked, items knocked off shelf. VIFelt by all, many frightened. Some heavy furniture moved. VIILight damage to strong buildings and great damage in poor buildings. Don’t write this in you notes, just read it

Mercalli Scale VIIIMajor damage to most buildings not specially designed for large earthquakes. Chimneys and walls collapse. IXSpecially designed buildings damaged. Partial collapse of buildings. X – XIVery few buildings standing, bridges destroyed, and rails bent. XIITotal damage. Don’t write this in you notes, just read it

The location of an earthquake is described using the following terms: Epicenter Focus

The focus of an earthquake is the spot inside the earth where the earthquake actually occurred.

The epicenter of the earthquake is the spot on the earth surface directly over where the earthquake occurred ( over the focus). It is described in two ways: Latitude and longitude Distance from a major city or landmark

When an earthquake occurs, seismic waves travel outward in all directions from the focus.

P- wave arrives 1:15 ( 75 seconds) S- wave arrives 3:30 ( 210 seconds) So.. The difference between the P-wave and S-wave arrival time is 135 seconds- this is called the “lag time” Distance? Because distance = speed x time ( d = st) 1.9 km/sec. x 135 sec. = km ** NOTE 1.9 km/sec is the difference in speed between the P and S waves

Location of the seismograph Dist. From Earthquake km Using the difference between the P-wave and S-wave arrival times you can determine the distance from the seismograph but NOT the direction. So… the earthquake occurred somewhere on the circle.

It takes a minimum of three (3) seismograph stations to locate the epicenter of an earthquake.

Locating Earthquakes

Paricutin, Mexico Location: 19.5N, 102.2W Elevation: 10,400 feet (3,170 m)