chapter 8 earthquakes. i. what are earthquakes? seismology is the science devoted to studying...

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Chapter 8 Earthquakes

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Page 1: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

Chapter 8Earthquakes

Page 2: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

I. What are Earthquakes?• Seismology is the science devoted to studying

earthquakes•Most take place near the edges of tectonic

plates• Earthquakes are caused by elastic deformation• Rocks stretch to a certain point and then

suddenly return to its original shape in elastic rebound• Energy is released and some of this energy

travels as seismic waves that cause earthquakes

Page 3: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

A. Faults at Tectonic Plate Boundaries• A specific type of motion takes place at

different tectonic plate boundaries• Each motion creates a particular kind of fault

- Transform strike-slip fault- Convergent reverse fault- Divergent normal fault

Page 4: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

1. Earthquake Zones• Places where a large number of faults are

located• Some earthquakes however happen along

faults in the middle of tectonic plates

Page 5: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

B. How do Earthquake Waves Travel?• Seismic waves that travel through the Earth’s

interior are called body waves- P waves- S waves• Seismic waves that travel along the Earth’s

surface are called surface waves

Page 6: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

1. P Waves (primary waves)• Travel through solids, liquids, and gases• Fastest waves; travel ahead of other seismic

waves•Move rock back and forth, squeezing and

stretching the rock

Page 7: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

2. S Waves (sear, or secondary waves)• Cannot travel through parts of the Earth that

are completely liquid• Second-fastest seismic waves• Shear rock side to side

Page 8: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

3. Surface Waves• Produce motion mostly in the upper few

kilometers of Earth’s crust• Travel more slowly and are more destructive• Produces motion up, down, and around or

back-and-forth

Page 9: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

II. Earthquake MeasurementA. Locating Earthquakes• Seismographs are instruments located at or

near the surface of the Earth that record seismic waves•When the waves reach a seismograph, the

seismograph creates a seismogram

Page 10: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

1. Determining Time and Location of Earthquakes• The start time is determined by comparing

seismograms and noting the differences in arrival times of P and S waves• Seismograms are also used to find the

earthquake’s epicenter- An epicenter is the point on the Earth’s surface

directly above an earthquake’s starting point

Page 11: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

• A focus is the point inside the Earth where an earthquake begins

Page 12: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

2. The S-P Time Method• Seismograms from different locations are

compared• Seismograms are placed on a time-distance graph• The horizontal axis tells the distance between a

station and the earthquake’s epicenter

Page 13: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

• A circle is drawn around three seismograph stations with the radius of the circle coming from the horizontal axis of the time-distance graph• The point where all three circles intersects is

the earthquake’s epicenter

Page 14: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

B. Measuring Earthquake Strength and Intensity1. The Richter Magnitude Scale• Charles Richter created the scale in the

1930s• Compares earthquake’s by measuring

ground motion recorded by seismograms

Page 15: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

2. Earthquake Ground Motion•Magnitude is a measure of the strength of an

earthquake•Magnitude values are from 2 to 7• Each time the magnitude increases by one unit,

the measured ground motion becomes 10 times largerEx) Magnitude of 5 is 10x greater than

magnitude of 4 and 100x greater than magnitude of 3

Page 16: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

3. Modified Mercalli Intensity Scale• Intensity is a measure of the degree to which

an earthquake is felt by people and the amount of damage• Scale of Roman numerals from I to XII

- An earthquake not felt by people to total damage of an area

• Intensity values are usually higher near an earthquake’s epicenter

Page 17: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

III. Earthquakes and SocietyA. Earthquake Hazard• A measure of how likely an area is to have

damaging earthquakes in the future• The West Coast has a high earthquake-

hazard level because it has a lot of seismic activity

Page 18: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

B. Earthquake Forecasting1. Strength and Frequency• Strength of earthquakes is related to how

often they occur

Page 19: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

2. The Gap Hypothesis• A hypothesis that states that sections of

active faults that have had relatively few earthquakes are likely to be the sites of strong earthquakes in the future• The areas along a fault where relatively few

earthquakes have occurred are called seismic gaps

Page 20: Chapter 8 Earthquakes. I. What are Earthquakes? Seismology is the science devoted to studying earthquakes Most take place near the edges of tectonic plates

C. Earthquakes and Buildings• The process of making older structures more

earthquake resistant is called retrofitting- Securely fastening buildings to their foundation- Steel can be used to strengthen structures made of

brick• Architects and engineers

use the newest technologyto design and construct buildings and bridges to better withstand earthquakes