f orces within earth
DESCRIPTION
Chapter 19.1 EARTHQUAKES. F orces within earth. 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 - PowerPoint PPT PresentationTRANSCRIPT
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