Why & How So…why do earthquakes happen? Tectonic plates are always moving The boundary between 2 tectonic plates is called a fault Faults are areas where earthquakes happen…how?
Why & HowThe rocks on each side of the fault are moving slowly.As they move, sometimes they get stuck. If they stay stuck for a while, a lot of pressure builds up.When the rocks finally get un-stuck they break (fracture) and move again, and the rocks “rebound” past the place where they were stuck and keep moving slowly past each other.This is the Elastic Rebound Theory
Mechanics of an Earthquake Where the plates actually get stuck is where the earthquake begins…called the focus. The point on Earth’s surface directly above the focus is the epicenter. Which plate boundary would have deeper focus earthquakes?
Seismic GapsSometimes the plates get stuck for a long timeWhy could this be bad?We identify these places because they haven’t released any seismic waves in a long time.This is a “gap” in the record of seismic activity
What makes an EarthquakeDangerous?So, plates get stuck and then move quickly…what does this really do?This creates vibrations (waves) that travel through the ground.What does a wave look like?
Seismic WavesThere are 4 types of seismic waves released in an earthquake.The first two move deep within the Earth, and are called Body WavesThe second two move through the surface of the Earth and are called Surface Waves
Seismic Waves Use Arrows Amount of Time in Describe Wave to Describe Damage Earthquake Movement Movement CausedP WaveS WaveLoveWaveRayleighWave
WhereWhat kinds of plate boundaries usually create earthquakes?
Quick Quiz #1The place underground where an earthquake actually begins.The seismic wave that arrives first in an earthquakeLove and Rayleigh waves are the two types of ____________ waves.Why is a seismic gap dangerous?
WhereWhat kinds of plate boundaries can create earthquakes?ANY kind of plate boundary!Boundaries are places where tectonic plates rub against each other.How are their earthquakes different?
Transform Boundary EarthquakesForm where the plates move past one anotherUsually begin near the surface…why?Create lots of vibrations near the surface, which cause a lot of damageLargest in the world is along the coast of California
Convergent Boundary EarthquakesWhere one plate subducts beneath another plateUsually begin deep underground…why?Their vibrations are felt over a large areaIf they are totally underwater, they form: Underwater volcanoes, which can make island arcs Tsunamis Example: Aleutian IslandsIf they are on land, they form: Terrestrial volcanoes Example: West coast of South America
Terrestrial Convergent Boundary Andes Mountains, South America
The Pacific Ring of FireOne of 3 major earthquake zones in the worldSurrounds the Pacific OceanContains Transform & Convergent boundaries.
The Eurasian-MelanesianMountain Belt One of the 3 major earthquake zones in the world Mountains that extend from Europe into Asia Contains mostly Convergent Boundaries
Divergent BoundaryEarthquakes Form where the plates spread apart Usually begin near the surface Usually too small to be felt by people Most found on the Ocean Floor
The Mid-Atlantic Ridge One of 3 major earthquake zones in the world Splits the Atlantic Ocean Mostly underwater
Magnitudes of Earthquakes The Richter Scale: Measures Energy Released Measures from 1-12, with 1 being the smallest and 12 being the highest. Major Earthquake: over 7 Moderate Earthquake: 6-7 Minor Earthquake: 2.5-6 Microquake: less than 2.5 (cannot be felt by people) The Mercalli Scale Measures in Roman numerals from 1-12 (I – XII)
Magnitudes of EarthquakesThe largest earthquake ever recorded was estimated at 9.6 on the Richter scale, and caused massive damage. It is the only earthquake ever recorded over 9.Most major earthquakes are between 7 and 8, and most scientists believe only 1 or 2 earthquakes over 8 will happen in 100 years.Most scientists do not believe that an earthquake larger than 10 on the Richter Scale could ever happen.On the Richter Scale, the highest number (12) is described as “total destruction of the Earth, where the Earth would be split in two.
Quick Quiz #2The deepest earthquakes are found at ________________ boundaries.The west coast of North America is part of an earthquake zone known as the ___________________.To find the epicenter of an earthquake, you need to know the arrival time of the ______ wave from 3 recording stations.A ________________ earthquake has a Richter magnitude between 6 & 7.
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