Section: 1: Forces inside Earth Chapter 5: Earthquakes Section: 1: Forces inside Earth Objectives: Explain how earthquakes result from buildup of energy in rocks Describe how compression, tension, and shear forces make rocks move along faults Distinguish among normal, reverse, and strike-slip faults

Rough Outline Earthquake Causes A. Fault Formation B. What Causes Faults C. How Earthquakes Occur Type of Faults A. Normal Faults B. Reverse Faults C. Strike-Slip Faults

Frequency of occurrence Richter magnitudes Description Earthquake effects Frequency of occurrence Less than 2.0 Micro Microearthquakes, not felt. About 8,000 per day 2.0-2.9 Minor Generally not felt, but recorded. About 1,000 per day 3.0-3.9 Often felt, but rarely causes damage. 49,000 per year (est.) 4.0-4.9 Light Noticeable shaking of indoor items, rattling noises. Significant damage unlikely. 6,200 per year (est.) 5.0-5.9 Moderate Can cause major damage to poorly constructed buildings over small regions. At most slight damage to well-designed buildings. 800 per year 6.0-6.9 Strong Can be destructive in areas up to about 160 kilometers (100 mi) across in populated areas. 120 per year 7.0-7.9 Major Can cause serious damage over larger areas. 18 per year 8.0-8.9 Great Can cause serious damage in areas several hundred miles across. 1 per year 9.0-9.9 Devastating in areas several thousand miles across. 1 per 20 years 10.0+ Epic Never recorded; see below for equivalent seismic energy yield.

Haitian Capital, Port-au-Prince January 14, 2010

Earthquake measured 7.2

More than 100,000 died

Injured people outside the Villa Creole the day after the earthquake

An aerial view of the UN headquarters in Haiti shows how the office complex was devastated by the earthquake

The Haitian national palace shows heavy damage following the earthquake. The city's airport was operational, opening the way for international relief aid to be ferried in

People search for survivors under the rubble of a collapse building the day after the quake

A women and her injured baby are seen at a makeshift field hospital in Port-au-Prince

A shanty town on the outskirts of Port-au-Prince where thousands of dwellings were either completely destroyed or badly damaged

Haitians set up impromtu tent cities thorough the capital after the earthquake

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Earthquake in Chili February 27, 2010

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Is it likely we will encounter an earthquake of this magnetite? NO Take a look at the plate boundaries and take a look at where we are located!!

Earthquake Causes Fault Formation Elastic limit: the limit to how far something can bend Elastic Deformation: the forces that cause rocks to bend and stretch. Faults: Surface along which rocks move when they pass their elastic limit and break.

What causes faults? The forces inside the Earth cause plates to move and shift – causes earthquakes. Earthquake: The vibrations produced by the breaking of rock Earthquakes are most likely to happen near the plates because most stress in as boundaries where plates meet.

How Earthquakes Occur 1. As plates move past each other their rough surfaces sometimes catch. 2. Forces continue to build up where the rocks are stuck 3. The stress causes rocks to bend and change shape 4. When the rocks are stressed beyond their elastic limit they break and move along a fault to return to their original shape 5. THIS CREATES AN EARTHQUAKE!!!!!

Earth’s crust is in constant motion Places stress on rocks Rocks bend & stretch like a rubber band Break Produces vibrations called EARTHQUAKE

II. Types of Faults A. Normal Fault Force – tension Plates move apart Rock moves downward

On the east coast of California Sierra Nevadas On the east coast of California

B. Reverse Fault Force – compression Plates come together Rocks at the surface are forced up & over the ones below the surface

Rocky Mountain National Park

C. Strike-slip Fault Force – shear Plates move sideways past each other Rocks on either side move past each other

San Andreas Fault http://pubs.usgs.gov/gip/earthq3/