### EarthQuakes

1. EARTHQUAKES
2.  What are Earth Quakes?  Where do Earth Quakes occur?  How do Earth Quakes occur?  What are effects of Earth Quake?  How are Earth Quakes measured? Objectives
3. What are Earthquakes?  The shaking or trembling caused by the sudden release of energy  Usually associated with faulting or breaking of rocks  Continuing adjustment of position results in aftershocks
4.  Most earthquakes occur along the edge of the oceanic and  Along faults: normal, reverse, transform Where do earthquakes occur:
5. Fractures, faults Energy released and propagates in all directions as seismic waves causing earthquakes How do earthquakes occur? focus epicenter
6. Earthquake = Vibration of the Earth produced by the rapid release of energy Seismic waves = Energy moving outward from the focus of an earthquake Focus= location of initial slip on the fault; where the earthquake origins Epicenter= spot on Earth’s surface directly above the focus Definitions
7. - Earthquakes and Seismic Waves
8. Types of SeismicWaves P-waves: • called compressional, or push-pull waves • Propagate parralel to the direction in which the wave is moving • Move through solids, liquids S-waves: • Called shear waves • Propagate the movement perpendicular to the direction in which the wave is Moving Surface waves (L-waves or long waves). • Complex motion • Up-and-down and side-to-side • Slowest • Most damage to structures, buildings
9. Locating the shaking Measure time between P and S waves on a seismogram Need at least 3 seismographs
10. What is the Elastic Rebound Theory? Explains how energy is stored in rocks • Rocks bend until the strength of the rock is exceeded • Rupture occurs and the rocks quickly rebound to an undeformed shape • Energy is released in waves that radiate outward from the fault
11. How is an Earthquake’s Epicenter Located? • P waves arrive first, then S waves, then L • Average speeds for all these waves is known • After an earthquake, the difference in arrival times at a seismograph station can be used to calculate the distance from the seismograph to the epicenter.
12.  Three seismograph stations are needed to locate the epicenter of an earthquake  A circle where the radius equals the distance to the epicenter is drawn  The intersection of the circles locates the epicenter
13.  Earthquakes are measured based on three different scales.  The first measures the actual size or magnitude of the quake.  The second measures the effects or damage of the quake.  The third measures the total energy of the quake. How are Earthquakes Measured?
14.  A seismograph is the the tool used to measure the strength of an earthquakes  The seismograph prints out a seismogram that scientists read to determine the strength of the quake.  The data from the seismogram is translated into a 1-10 rating on the Richter Scale. Each step in the scale represents a tenfold increase in the size of the quake! How is the Magnitude of Earthquakes Measured?
15. Seismic waves cause the seismograph’s drum to vibrate. But the suspended weight with the pen attached moves very little. Therefore, the pen stays in place and records the drum’s vibrations. What is a Seismograph
16. 1) Magnitude: Richter Scale • Measures the energy released by fault movement • related to the maximum amplitude of the S wave measured from the seismogram • Logarithmic-scale; quantitative measure • For each whole number there is a 31.5 times increase in energy eg. an increase from 5 to 7 on the Richter scale = an increase in energy of 992 times!! Earthquake Effects : two ways to measure
17. 2) Intensity: Mercalli Scale: •Assigns an intensity or rating to measure an earthquake at a particular location (qualitative) •I (not felt) to XII (buildings nearly destroyed) •Measures the destructive effect •It is a linear scale Intensity is a function of: • Energy released by fault • Geology of the location • Surface substrate: can magnify shock waves e.g. Mexico City (1985) and San Francisco (1989)
18. Largest earthquake in the world Chile : 1960 May 22 Magnitude 9.5 More than 2,000 killed, 3,000 injured, 2,000,000 homeless, and \$550 million damage in southern Chile tsunami caused 61 deaths \$75 million damage in Hawaii; 138 deaths and \$50 million damage in Japan; 32 dead and missing in the Philippines; and \$500,000 damage to the west coast of the United States.
19. Measuring Earthquakes The Mercalli scale was developed to rate earthquakes according to the amount of damage at a given place.
20. Preferred by scientists and seismologists to the Richter scale because moment magnitude is more precise. not based on instrumental recordings of a quake, but is based on the area of the fault that ruptured in the quake. • calculated by multiplying the area of the fault's rupture surface by the distance the earth moves along the fault….this calculation is more precise than a tool or scientist opinion! Moment Magnitude Scale
21. Comparison between the Richter and Moment Magnitude Scales Earthquake Richter Scale Moment Magnitude Scale New Madrid, MO, 1812 8.7 8.1 San Francisco, CA, 1906 8.3 7.7 Prince William, AK, 1964 8.4 9.2 Northridge, CA, 1994 6.4 6.7
22. Shaking and ground rupture  Shaking and ground rupture are the main effects created by earthquakes, principally resulting in more or less severe damage to buildings and other rigid structures.  The severity of the local effects depends on the complex combination of the earthquake magnitude, the distance from the epicenter, and the local geological and geomorphological conditions, which may amplify or reduce wave propagation. How Earthquakes Cause Damage
23. Landslides and avalanches  A landslide is a geological phenomenon that includes a wide range of ground movements.  Rockfalls, deep failure of slopes and shallow debris flows were common.  Although the action of gravity is the primary driving force for a landslide to occur, there are other contributing factors affecting the original slope stability.  Typically, pre-conditional factors build up specific sub- surface conditions that make the area/slope prone to failure, whereas the actual landslide often requires a trigger before being released.
24. Earthquakes can cause fires by damaging electrical power or gas lines. In the event of water mains rupturing and a loss of pressure, it may also become difficult to stop the spread of a fire once it has started. Fires of the 1906 San Francisco earthquake Fires
25. Soil liquefaction occurs when, because of the shaking, water-saturated granular material (such as sand) temporarily loses its strength and transforms from a solid to a liquid. Soil liquefaction may cause rigid structures, like buildings and bridges, to tilt or sink into the liquefied deposits. For example, in the 1964 Alaska earthquake, soil liquefaction caused many buildings to sink into the ground, eventually collapsing upon themselves. Soil liquefaction
26. Tsunami  Tsunamis are long-wavelength, long-period sea waves produced by the sudden or abrupt movement of large volumes of water.  Large waves produced by an earthquake or a submarine landslide can overrun nearby coastal areas in a matter of minutes.  Tsunamis can also travel thousands of kilometers across open ocean and wreak destruction on far shores hours after the earthquake that generated them.  Ordinarily, subduction earthquakes under magnitude 7.5 on the Richter scale do not cause tsunamis, although some instances of this have been recorded.  Most destructive tsunamis are caused by earthquakes of magnitude 7.5 or more.
27. A flood is an overflow of any amount of water that reaches land. Floods occur usually when the volume of water within a body of water, such as a river or lake, exceeds the total capacity of the formation, and as a result some of the water flows or sits outside of the normal perimeter of the body. However, floods may be secondary effects of earthquakes, if dams are damaged. Earthquakes may cause landslips to dam rivers, which collapse and cause floods. Floods
28. Base-isolated buildings can sway back and forth. Fixed-base building absorb the energy of seismic waves Construction Methods
29. Gas and water pipes should be flexible so they don’t break open. Construction Methods
30. Drop, cover, and hold Cover your head and things that could break or fall over. Protecting Yourself
31. When outdoors, move to open areas without trees and sit down. Put together an earthquake kit with food and first aid supplies. Protecting Yourself