Notepack # 11 November 8, 201 AIM: What are the features of Earthquakes and where are they located? Do Now: What are some words that are associated with earthquakes?
What are Earthquakes? The shaking or trembling caused by the sudden release of energy (pressure). As a result of the tectonic plate movement. Usually associated with faulting or breaking of rocks Continuing adjustment of crust position results in aftershocks
What causes an Earthquake? The plates of the crust are always being pushed or pull by the convection currents of the Asthenosphere. Sometimes these plates push or rub against each other; causing the plates not to move freely. The plates become stuck.
What causes an Earthquake? Cont. Because the convection currents are continuing to push against the plates, pressure starts to build. Sooner or later too much stress (pressure) has build up causing rocks to crack and the plates begin to violently and suddenly move. This movement (earthquake) takes place along a fault. A fault is a place where two plate boundaries meet.
Results of Earthquakes
Earthquakes
Earthquakes
Earthquakes
Parts of an Earthquake Focus: The focus is the point in the Earth where the release of energy originates. Most of the time it is under ground. Epicenter: The epicenter is the location on the surface of the crust directly above the focus.
Parts of an Earthquake
The Two types of waves an Earthquake Produces Earthquakes release a lot of energy. This energy is released in the form of waves. Seismic waves are the waves of energy caused by the sudden breaking of rock within the Earth. This energy travels through the earth and are recorded on a machine called a seismographs. The two types are P-waves and S-waves We feel both of these waves during an Earthquake but at different times.
Seismographs record earthquake events
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What are P waves and S waves? Seismic waves P or primary waves fastest waves 1 st wave felt in an earthquake travel through solids, liquids, or gases Move in a linear direction S or secondary waves slower than P waves 2 nd wave of an earthquake travel through solids only Moves in an up and down direction
Push/pull waves Can travel through solids and liquids Fastest wave Slower Move in an S motion Travel only through solids
MAJOR DIFFERENCES P WAVES Can go through liquid (magma) and solid Primary wave, arrives first, travel quicker Travels parallel S WAVES Can only go through solid (No Liquid - Magma) Second wave, travels slower Travels perpendicular
How to read a Seismograph P wave arrives Magnitude of quake S wave arrives
Seismograph
What can a Seismograph tell us? When looking at a seismograph, there is a lot of information you can get. The distance between the P-wave and the S-wave tells how close the earthquake is to your location. When the P-wave and the S-wave are close together, that means that the earthquake is relatively close to your location. When the P-wave and the S-wave are far apart, that means that the earthquake is relatively far from your location. The size of the S-wave can tell you how strong the earthquake was. The wider the S-wave the stronger the earthquake. The narrower the S-wave the weaker the earthquake.
How do Seismic Waves react with the Earth s Interior Layers The Earth is made up of 4 main layers: the crust, mantle, outer core and inner core. Each layer has its own density. Seismic wave traveling speed is affected by the density of material.
How do Seismic Waves react with the Earth s Interior Layers (cont) P wave can travel though any material: solid, liquid and gas. S waves can ONLY travel through solid objects. S waves CANNOT travel through the mantle because the mantle is made up of magma (liquid rock).
Earthquakes Push/pull waves Can travel through solids and liquids Fastest wave Earthquakes by depth. Notice that the deep earthquakes occur only at subduction zones.
Earthquakes Location of worldwide earthquakes
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
The Economics and Societal Impacts of EQs Building collapse Fire Tsunami Ground failure Damage in Oakland, CA, 1989
Regents Question: Why do geologists infer that the Earth's outer core is a liquid? S-waves do not pass through the outer core of the Earth. Instruments indicate that the Earth's temperature increases with depth. P-waves can travel through the core of the Earth. S-waves travel faster than P-waves in the outer core.
Regents Question What is the relationship between the velocity of compressional waves (P-waves) and the velocity of shear waves (S-waves) as they travel through the same material? P-waves and S-waves have the same velocity. P-waves have a greater velocity. S-waves have a greater velocity.
How is an Earthquake s Epicenter Located? Seismic wave behavior P waves arrive first, then S waves, then L and R Average speeds for all these waves is known After an earthquake, the difference in arrival times at a seismograph station can be used to calculate the distance from the seismograph to the epicenter.
How is an Earthquake s Epicenter Located? Time-distance graph showing the average travel times for P- and S-waves. The farther away a seismograph is from the focus of an earthquake, the longer the interval between the arrivals of the P- and S- waves
How is an Earthquake s Epicenter Located? Three seismograph stations are needed to locate the epicenter of an earthquake A circle where the radius equals the distance to the epicenter is drawn The intersection of the circles locates the epicenter
Can Earthquakes be Predicted? Earthquake Prediction Programs include laboratory and field studies of rocks before, during, and after earthquakes monitor activity along major faults produce risk assessments
Slower Move in an S motion Travel only through solids
How are the Size and Strength of an Earthquake Measured? Intensity subjective measure of the kind of damage done and people s reactions to it isoseismal lines identify areas of equal intensity Modified Mercalli Intensity Map 1994 Northridge, CA earthquake, magnitude 6.7
How are the Size and Strength of an Earthquake Measured? Magnitude Richter scale measures total amount of energy released by an earthquake; independent of intensity Amplitude of the largest wave produced by an event is corrected for distance and assigned a value on an open-ended logarithmic scale
Can Earthquakes be Predicted? Earthquake Precursors changes in elevation or tilting of land surface, fluctuations in groundwater levels, magnetic field, electrical resistance of the ground seismic dilatancy model seismic gaps