f orces within earth

FORCES WITHIN EARTH

Chapter 19.1 EARTHQUAKES

Earthquakes Natural vibrations of

the ground caused by movement along fractures in the crust or volcanic eruptions

Fractures form when stress exceeds the strength of the rock

Types of Stress Tension- pull Compression-

push Shear- twist

Strain- deformation caused by stress

Ductile Deformation Elastic deformation

occurs as a result of low stress

Ductile deformation occurs when stress is high

When does fracture occur?

Faults Fractures in the Earth’s crust along

which movement occurs

Types of Faults Normal- tension Reverse- compression Strike-slip- shear

Seismic Waves (Primary) P-waves-

squeeze and pull rocks in the same direction of the waves

(Secondary) S-waves- cause rock to move at right angles to the direction of the waves

Surface waves- cause rock to move up & down

Focus- point where an earthquake originates Epicenter- point on surface directly above the

focus

SEISMIC WAVES & EARTHS INTERIOR

Chapter 19.2 EARTHQUAKES

Seismology Study of earthquake waves Seismograph/seismometer- register the vibrations Seismogram- the record of vibrations

Travel- time Travel time for P and

S waves differ Can you tell which

ones reach a location first?

Where is the biggest difference in the time one wave arrives before the other?

Clues to Earth’s Interior P waves are

refracted in the core

S waves can not travel through liquids

Behavior of waves provide details of Earth’s interior structure and composition

MEASURING & LOCATING

EARTHQUAKES

Chapter 19.3 EARTHQUAKES

Earthquake Magnitude and Intensity

Magnitude- the amount of energy released during an earthquake

Richter scale- earthquake rating based on the size of the largest seismic waves

Increases by power of 10 for each magnitude

Moment Magnitude Scale Most used today Based on the

size of the fault rupture, amount of movement along the fault, and the rocks’ stiffness

Modified Mercalli Scale Based on the

amount of damage done to structures

Measure of intensity

Intensity Relates to Magnitude

Locating an Earthquake Distance from

epicenter is calculated by comparing the separation time between P and S waves

3 locations are needed to accurately determine the epicenter of the earthquake

Why?

Seismic Belts 80% occur in the Circum-Pacific Belt 15% occur in the Mediterranean-Asian Belt

EARTHQUAKES & SOCIETY

Chapter 19.4 EARTHQUAKES

Earthquake Hazards Structural Failure

PancakingCollapse

1999 Izmit earthquake in Turkey2010 Pichilemu earthquake in Chile

Earthquake Hazards Land and Soil Failure

LiquifactionSeismic wave amplification

Liquifaction in Christchurch, NZ

Earthquake Hazards Fault Scarps

Vertical offset

Earthquake Hazards Tsunamis

Seismic Risk

Earthquake Prediction History Strain

Accumulation