3 Whose Fault is it?Faults are fractures in Earth where movement has occurredBecause earthquakes occur when two plates rub together, they are often said to occur on fault lines.Faults occur because forces inside the Earth cause Earth’s plates to move placing stress on or near the plate edge
4 What are the types of Faults? To relieve this stress, the rocks tend to bend, compress, or stretchIf the force is great enough the rocks will break.This breaking produces an earthquake.An earthquake is vibrations produced by breaking rock or rock sliding past each other.Abrupt shakings of the Earth is caused bythe release of built up pressure on theEarth’s surface
5 What are the 3 types of Faults? 3 types of forces act on rocks: tension, compression, and shearNormal Fault- caused by rock above the fault moving downward in relation to the rock below the fault
6 What are the 3 types of Faults? Reverse faults result from compression forces that squeeze rock.If rock breaks from forces pushing from opposite directions, rock above a reverse fault surface is forced up and over the rock below the fault surface.
7 What are the 3 types of Faults? At a strike-slip fault, rocks on either side of the fault are moving past each other without much upward or downward movementThe San Andreas Fault is the boundary between two of Earth’s plates that are moving sideways past each other.
8 What are the features of an Earthquake? Seismic Waves- waves generated by an earthquake, can move the ground forward and backward, up and down, and side to sideFocus- an earthquake’s point of energy releaseThis is the point within Earth where the earthquake startsEpicenter- is the point on the earth’s surface directly above the earthquake focus
9 What are the types of Seismic Waves that are produced? Primary Waves (P-Waves)- cause particles in rocks to move back and forth in the same direction that the wave is travelingSecondary Waves (S-waves)- move through Earth by causing particles in rocks to move at right angles to the direction of wave travel.Surface Waves- are seismic waves that travel along Earth’s outer layerThese waves cause most of the destruction resulting from earthquakes
11 How do we locate an Earthquake? The different speeds of seismic waves allow scientist to determine the epicenterPrimary waves move fastestSecondary waves followSurface waves move slowest and arrive at the seismograph station lastThe difference in arrival times is used to calculate the distance from the seismograph station to the earthquake epicenter
12 How do we locate an Earthquake? Seismic waves from earthquakes are measured with an instrument known as a seismographConsists of a rotating drum of paper and a pendulum with an attached penThe paper record of a seismic event is called a seismogram
14 How do we measure an earthquake? We can measure earthquakes by its:Intensity – a measure of the effects on an earthquake at a particular locationORMagnitude: a measure of the strength or amount of energy released during an earthquake
15 How do we measure an earthquake? The Richter scale is used to describe the strength of an earthquake and is based on the height of the lines on the seismograph
16 How do we measure an earthquake? The Mercalli Scale is based on actual observations of damage
18 Earthquake dangers…Most earthquake damage occurs when surface waves cause building, bridge, and roads to collapseHowever, an earthquake under the ocean causes a sudden movement of the ocean floorThe movement pushes against the water, causing a powerful wave that can travel thousands of kilometers in all directionsThese ocean waves caused by earthquakes are called seismic sea waves, or tsunamis