Earthquakes & seismicity in Iceland: a tectonic saga Iceland Seminar Marianne Karplus 6 March 2009.
Earthquakes. Earthquakes A natural vibration of the ground caused when the stress built up between...
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![Page 1: Earthquakes. Earthquakes A natural vibration of the ground caused when the stress built up between tectonic plates is suddenly released. There are three.](https://reader033.fdocuments.in/reader033/viewer/2022052702/56649f435503460f94c62c70/html5/thumbnails/1.jpg)
Earthquakes
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Earthquakes
A natural vibration of the ground caused when the stress built up between tectonic plates is suddenly released.
There are three types of stress:◦Compression – caused by two plates being push
together.◦Tension – Pulls plates apart.◦Shear – causes plates to twist.
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Types of faults
There are three types of Faults1. Normal fault
caused by tension.
2. Reverse fault caused by compression.
3. Strike-slip fault caused by shearing.
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Three Types of Seismic Waves
1. Primary waves (p-waves)◦ Longitudinal waves – these vibrate by the
compression of material in the direction of the wave’s motion. These can travel through the core.
2. Secondary waves (s-waves)◦ Transverse waves (Like in water) – these vibrate by
moving the particles perpendicular to the direction of wave’s motion. These cannot travel through the core.
3. Surface waves◦ Vibrate in all directions.
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Measuring Earthquakes
Richter Scale◦Based on size of the largest seismic waves
generated by the Earthquake.◦Each level increase represents an increase of
energy by a factor of 32 and a wave size of 10 times.
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Measuring Earthquakes
Moment of Magnitude Scale◦Based size of fault rupture, amount of
movement, and rock characteristics.◦More accurate than Richter scale.
Modified Mercalli Scale◦Measures the amount of damage caused by the
Earthquake.
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Strongest Earthquakes of 2010
1. Chile (Feb 27th) Mag. 8.82. Indonesia (April 6th) Mag. 7.73. Vanuatu (May 27th) Mag. 7.74. Indonesia (May 9th) Mag. 7.25. Mexcali Valley, California (April4th) Mag. 7.26. Solomon Islands (Jan 3rd) Mag. 7.17. Haiti (Jan 12th) Mag. 7.08. Ryukyu, Japan (Feb 27th) Mag. 7.0
There have been 7460 earthquakes so far this year. Most are below a magnitude of 4.9.
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Chili
7th Strongest in History130 after shocks over the next
week.The focus ground at epicenter
moved 3.0 up and 10 m west. 500 times more powerful than
HaitiCalled a megathrust quake
because it is in a subduction zone
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Location of the Earthquake
Focus ◦The location in the Earth’s crust where the
earthquake occurs.◦It can occur anywhere between the surface and
a depth of 700 km. The closer to the surface it occurs, the more powerful the earthquake is.
Epicenter ◦The location on the Earth’s surface above the
focus.
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Finding the Epicenter
Epicenters are found using triangulation from three or more seismograph stations.
P-waves travel a lot faster than s-waves. The difference between the arrival time of each type of wave tells you the distance to the epicenter.
The speed of each wave is a constant factor.
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Steps for finding the Epicenter
1. Determine the difference in time between the arrival of the s & p waves.
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Steps for finding the Epicenter
1. Use the travel-time graph at which the p-curve and s- curve have the same separation.
2. Record this distance.
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Steps for finding the Epicenter
1. Repeat the steps #1-3 for two other stations
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Steps for finding the Epicenter
1. Use a compass to draw a circle around each station with the radius in step #3.
2. The epicenter is located where all three circles intersect.
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Homework
P. 499 #1-4p. 504 #2, 4P. 510 #1-4