Presentation on theme: "Earthquakes Chapter 2 book F page 44. Vocabulary for section 1 page 44 book F Stress Tension Compression Shearing Normal fault Reverse fault Strike-slip."— Presentation transcript:
Vocabulary for section 1 page 44 book F Stress Tension Compression Shearing Normal fault Reverse fault Strike-slip fault
Earthquakes Earthquakes: the shaking that results from the movement of rock beneath the Earth’s surface. –An Earthquake is a release of tension at a high stress point causing the shaking. There three different types of stress. –Tension –Compression –shearing
Tension Tension : this type of stress pulls on the crust, stretching rock so that it becomes thinner in the middle. –This type of stress is found where twp plates are being pulled apart.
Compression Compression : this type of stress squeezes rock until it folds or breaks. –This type happens at plate boundary's where one plate pushes against another.
Shearing Shearing : stress that pushes rock in two different directions. –Shearing can cause rock to break and slip apart or to change its shape.
Faults Fault : a break in Earths crust where masses of rock slip past each other. –Most faults occur along plate boundaries, where the forces of plate motion push or pull the crust so much that the crust brakes. There are three main types of faults Normal Reverse Strike-slip
Normal Normal fault: is when the crust is pulls apart. Reverse fault: is when the rock is pushed together compression causes these kind of faults. Strike-slip fault: when plates move past each other, shearing causes this type of fault.
Where Earthquakes happen Most Earthquakes happen in the lithosphere within about 100 kilometers of Earths surface. –The focus: is the area beneath Earths surface where rock that is under stress breaks, triggering an earthquake. Epicenter: The point on the surface directly above the focus,
Types of waves Seismic waves carry energy out from the focus in all directions during an Earthquake.
P waves P waves : a type of seismic wave that compresses and expands the ground. –P waves or primary waves are so named because they are the first waves to arrive
S waves S waves : a type of seismic wave that moves the ground side to side, up and down. –When S waves reach the surface they shake structures violently, causing damage and destruction.
Surface waves Surface waves : when P&S waves reach the surface they can become surface waves. –So what makes them different? – these type of waves move more slowly than the other two but they can cause Sevier ground movements causing the ground to roll like ocean waves and to move from side to side.
Measuring an Earthquake When an Earth quake happens everybody wants to know how big it was. –To determine this there are about 20 different measures for rating Earthquakes. Each with its strengths and weaknesses. The one used most often is the Richter scale. Richter scale: is a rating of the Earthquakes magnitude based on the size of the seismic waves.
Instrument for measuring Seismograph : a device that measures and records ground movement caused by seismic waves as they move through Earth.
Where to look How do we find where the Earthquake originated from? –Geologist use seismic waves to locate an Earthquakes epicenter. P waves arrive at the seismograph first followed by S waves, to tell how far away the Earthquake is from the seismograph scientist measure the difference in arrival times.