Do First Questions: What mechanical layer of the Earth are plates made of? What mechanical layer of the Earth is moving causing the plates to move?
Agenda Quiz on these notes on Thursday Earthquake Notes Mercalli Scale Practice
EARTHQUAKES: WHY? AND HOW?
Video http://tinyurl.com/q37fmlb
What are Earthquakes? The shaking or trembling caused by the sudden release of energy due to the movements of plates Usually associated with faulting (movement) or breaking of rocks at plate boundaries
Where do Earthquakes occur? Earthquakes occur along fault lines where two plates meet Earthquakes can occur at all three types of plate interactions The most violent earthquakes occur at convergent boundaries In the US, most earthquakes occur along the San Andreas fault in California 80% of all Earthquakes occur an area of the Pacific Ocean known as the “Ring of Fire”
Where Do Earthquakes Occur and How Often? ~80% of all earthquakes occur in the circum-Pacific belt most of these result from convergent margin activity ~15% occur in the Mediterranean-Asiatic belt remaining 5% occur in the interiors of plates and on spreading ridge centers more than 150,000 quakes strong enough to be felt are recorded each year
http://tinyurl.com/mshzd9f or
The Focus and Epicenter of an Earthquake The focus or hypocenter is the point within Earth where faulting begins The epicenter is the point directly above the focus on the surface
Elastic Rebound Theory Explains how energy is spread during earthquakes Rocks on opposite side of the fault are under pressure due to the force and shifting of the plates Rocks bend until the strength of the rock is exceeded Rupture occurs and the rocks quickly rebound /return to their original shape Energy is released in waves that radiate outward from the fault
Elastic Rebound Theory
Elastic Rebound
Seismic Waves Seismic are energy waves released by earthquakes There are two types: Body waves - P and S Surface waves
Seismic Waves
Body Waves: P and S waves Body waves travel through the interior of the Earth P or primary waves fastest waves travel through solids, liquids, or gases compressional wave, material movement is in the same direction as wave movement S or secondary waves slower than P waves travel through solids only shear waves - move material perpendicular to wave movement
Earthquake Waves P waves move through solids & liquids Notes: Surface waves cause most damage (“L” waves – feel like ocean waves) Body waves move through the earth p & s are Body waves – move through the earth http://earthquake.usgs.gov/learning/animations/ S waves move through solids only!!!
Surface Waves Surface Waves Travel just below or along the ground’s surface Slower than body waves; rolling and side-to-side movement Most destructive type of wave
Are you listening? Lets test your understanding!! Is this a P or an S wave? P wave! S Wave Surface waves cause most damage (“L” waves – feel like ocean waves) Body waves move through the earth Surface waves move along surface – not felt opposite side of earth
Effects of Earthquakes Building Collapse Avalanches and Landslides Fire Tsunamis Liquefaction occurs when water-logged soil acts like a liquid and causes sections of ground to sink or slide
Damage in Oakland, CA, 1989
Liquefaction
How are Earthquakes Measured? Seismographs record earthquake waves Seismograms show: Amplitude of seismic waves (how much rock moves or vibrates) Distance to the epicenter Earthquake direction Surface waves move along surface – not felt opposite side of earth
How Seismographs Work
Scales of Measurement 1. Richter Scale 2. Mercalli Scale Measure the energy released by an earthquake Measures magnitude using seismic wave data from a seismograph 2.0 to 10.0 +, each increase in number is a 10 times increase 2. Mercalli Scale Measures the effects of an earthquake Measures intensity using observation data I (not felt) to XII (total destruction)
MERCALLI VS. RICHTER
MERCALLI VS. RICHTER
DYL What are two effects of Earthquakes? Where in the world do most Earthquakes occur?
Resources https://www.youtube.com/watch?v=VMrqhVW5k6Y