Cornell Notes

Earthquakes Poseidon

Earthquakes Worldwide

Loss of Life and Economic Costs Northridge, California 1994 E:\HHS_2010\METROPOLI TAN.WMV Should we care?

Earthquakes Since 1900

Montana Earthquakes

What is an Earthquak e?

Seismic Waves rohan.sdsu.edu/~rmellors/lab8/l8awa v2.htm ves.html

What happens to seismic wave in Earth’s interior?

Shadow Zones

Locating & Measuring Earthquakes Seismograms Seismograph

Seismographs

A modern seismograph station usually has three seismographs. The first one records up-and-down motions, the second one records side-to-side motions in a north/south direction, and the third one records side-to-side motions in an east/west direction. Seismograph station at Cornell University

Measuring quakes.

Where are Earthquakes found? 10_largest_world.php

Locating an Earthquake Epicenter - Step 1- Analyzing 3 Seismograms

Step 2- Read Time-Travel Graph

Step 3 – Triangulate to find Epicenter.

Depth of Focus. Yellow = shallow, Red = intermediate, Black = deep

Depth of Earthquakes Divergent boundaries earthquakes occur at shallow depths about 30 Km. Transform boundaries earthquakes occur at shallow depths. Subduction boundaries, the focus of the earthquake can be very deep up to 700 kilometers. The depth at which an earthquake originates depends upon the type of plate boundary involved.

Measuring Earthquakes –Magnitude is a quantitative measurement that estimates the energy released. Richter Scale Moment Magnitude –Intensity is a qualitative measurement that evaluates the degree of earthquake shaking perceived by individuals Modified Mercalli Scale

Richter Scale (Magnitude) Developed by Charles F. Richter in Measurement of ground movements. Each increase of one whole number in Richter magnitude is a 10 x increase in shaking (32 x increase in energy release). For example, a magnitude 6 earthquake is about 10 times more powerful than a magnitude 5 earthquake. A magnitude 7 earthquake is more than 100 times (10x 10) more powerful than a magnitude 5 earthquake.

Magnitude Magnitude is a measure of the amount of energy released in an earthquake.

Reading a Nomogram

Richter Scale (Magnitude) Richter ScaleDescription Less than 3.5Not generally felt by humans Slight damage to structures 7.0 – 7.9Serious damage 8.0 and greaterTotal destruction of nearby communities

Moment Magnitude (Magnitude) Moment Magnitude is the current method used for measuring earthquakes (especially large ones) and uses three measurements: 1. Average area of slip along the fault; 2. Distance traveled; and 3. Considers the strength of the rock.

Example Magnitudes LocationDateRichter Magnitude Moment Magnitude San Francisco Alaska Alaska released at least twice as much energy because it involved greater movements along a much larger fault plane.

Mercalli Scale (Intensity) Mercalli Scale (Giuseppi Mercalli 1902) measures the intensity of a quake by using observed affects of ground movement.

Earthquake Risk Where in the United States is the risk for earthquakes the greatest? Alaska and California are high risks since they are found near plate boundaries. The middle of the country by Missouri is also at a higher risk, because many faults are buried deep beneath sediments deposited by the Mississippi, Missouri, and Ohio rivers.

Damage from Earthquakes Ground shaking Foundation failure Aftershocks Fire Tsunamis

Ground Shaking Ground shaking is produced by the waves set in motion by an earthquake’s sudden release of energy. Some of the ground vibrations are up-and-down, but the largest are side-to-side motions. Most buildings can withstand fairly violent up-and-down shaking; however, few buildings can survive violent side-to-side shaking, and as a result many buildings collapse.

Foundation Failure As a result of severe ground shaking, soils under buildings may settle or even liquefy. Liquefaction occurs when loose soil temporarily takes on some of the properties of a liquid. A building located on soil that settles is no longer safely supported and may collapse. For example, buildings located on bog muds or soil landfill can suffer severe damage or can collapse because of foundation failure.

Foundation Failure Liquefaction caused the building in the front to tip nearly 22°. The arrow points to a building that is tipped almost 70°.

Aftershocks A large earthquake may be followed by a smaller earthquakes. Aftershocks are a series of smaller earthquakes originating close to the focus of the large earthquake. Aftershocks can be as great as 1000 per day, though the frequency usually diminishes quickly over time.

Fire One of the most damaging effects of an earthquake may be the fires caused by the rupturing of gas lines by ground movement.

Tsunami Underwater earthquakes and landslides sometimes cause huge ocean waves called tsunami. Tsunami can travel very quickly across large expanses of water. Its speed depends on the depth of the water.

Tsunami When a tsunami reaches shallower water near a shoreline, it will slow down and increase dramatically in height. A tsunami warning system is now in place for regions in the Pacific Ocean. Scientists monitor wave activity at various stations throughout the Pacific.

Tsunami Animation

Elastic Rebound Theory Stress is released and crust is occassionally cracked called the elastic-rebound theory normally occuring at faults. Stresses: Plate Tectonics Thermal expansion and contraction. Gravitational attraction Mineral phases

Tensional stress pulls rock away from adjacent rock thinning crust. Normal faults occur when rock along one side of the fault slide down relative to the other. Divergent Boundary

Reverse faults occur when rocks are pushed together and one side of the fault moves up. Compressional stress pushes rock together causing. Convergent Boundary

Rocky Mountain Front

Shearing stress pushes rock in two different directions adjacent to one another. Strike-slip faults occur when blocks of rock on each side of the fault move in opposite directions. TRANSFORM PLATE BOUNDARY