Download
1 / 53
530 likes | 596 Views
Shakin' Things Up With. Earthquakes. What is an earthquake?. An earthquake is the rapid vibration of the earth created by a sudden movement of large sections of rock. Earthquakes are caused by tectonic forces. When plates move, stress is put on rocks.
E N D
Shakin' Things Up With... Earthquakes
What is an earthquake? An earthquake is the rapid vibration of the earth created by a sudden movement of large sections of rock
Earthquakes are caused by tectonic forces. When plates move, stress is put on rocks. Eventually, these rocks break, forming faults.
The “Scientific Explanation”…. • The Earth releases its internal heat by convecting, (boiling) much like a pot of pudding on the stove. • Hot asthenospheric mantle rises to the surface and spreads laterally, transporting oceans and continents as on a slow conveyor belt (a.k.a. “tectonic movement). • The speed of this motion is a few cms per year (about as fast as your fingernails grow). • The pressure from this movement creates a fault (large crack in the rocks making up the earth’s crust). • Rocks moving along these faults create vibrations, known as earthquakes!
Earthquake Vocabulary Fault: a surface between two regions of rock, along which there has been rupture and movement in the past San Andreas Fault
Earthquake Vocabulary Cont’d Shear Strength: The force that is needed to break a solid material Elastic Rebound: The return of a bent elastic solid to its original shape after the deforming process is removed Friction: The force that resists the motion of one surface against another surface
The following diagram illustrates the process of elastic rebound. Start at the bottom. • A straight fence is built across the San Andreas fault. • - As the Pacific plate moves northwest, it gradually distorts the fence. • Just before an earthquake, the fence has an "S" shape. • - When the earthquake occurs the distortion is released and the two parts of the fence are again straight; but now there is an offset.
This is a picture of the offset fence along the San Andreas Fault after the 1906 San Francisco Earthquake Offset by 8.5 feet!
Big Quake or Small Quake? • How would you measure the strength of an earthquake? • The Seismograph • For centuries different societies have designed many creative ways to measure the shaking of the earth. • Nearly 2000 years ago, for example, the ancient Chinese made a special vase that had several sculpted dragons mounted all around the sides of the vase. • Each dragon held in its mouth a metal ball. When the ground shook, some of the balls would fall from the mouths of the dragons into the waiting mouths of the sculpted frogs to show how the ground had moved.
Modern Seismograph Today’s geologists measure earthquakes with a seismograph A typical seismograph works in a very simple way…
A heavy weight is fastened to a horizontal rod as shown in the diagram
This rod hangs from a pole (and is free to swing from side to side when the ground shakes. • At the other end of the rod (away from the pole) is an ink pen • directly underneath the pen is a piece of paper rolled around a cylinder .
This cylinder rotates so that the pen continuously draws an ink line along the moving paper. • If the ground does not move, the rod does not swing, and the pen stays in place, so the ink line is smooth and straight. • If the ground shakes, however, the row swings and so the pen draws a zigzag line as the paper turns. • The stronger the shaking, the sharper the zigzags. This zigzag picture made on the paper roll is called a seismogram.
Earthquake Vocabulary Cont’d • Seismic Waves: • The shock waves created at the focus of an earthquake and sent out in all directions through the earth. • Seismograph: • A device that records seismic waves • Seismogram • The picture drawn by a seismograph.
Types of Seismic Waves: • Body waves (P and S waves) • travel through the earth’s interior • Surface waves: • travel along theearth’s outer layer
Primary Waves (P waves): • Fastest moving (6 km/s) • First to be recorded by a seismograph • Can travel through solids and liquids • Effect: Push & Pull--cause rocks to move back and forth in the same direction the wave is moving
Secondary Waves(S waves): • Second waves to be recorded on a seismograph (4 km/s) • Can ONLY travel through solid material (NOT liquid) • Effect: Side-to-Side--Cause rocks to move in right angles to the wave
Both S and P waves travel throughout the body of the earth. However, it turns out that S waves cannot travel through the core, and only P waves are recorded in some places
Surface Waves (a.k.a Long waves; L waves) • Slowest moving wave • Last to be recorded on a seismograph • Move through liquid & solid • Effect: cause the earth’s surface to rise and fall • THESE ARE THE MOST DESTRUCTIVE WAVES!
Review of Seismic Waves • S wavescannot travel through the liquid outer core. • They can travel through the mantle because the mantle behaves more like a solid than a liquid. • The S waves curve as they move through the mantle due to refraction as the density of the mantle changes. • P waves can travel through the whole planet. • They also curve with the changing density of both the mantle and the core. • The P waves change direction at the boundary between the different layers of the Earth. • This is due to refraction caused by the different densities of the layers.
To find the epicenter of an earthquake, scientists analyze the difference between the arrival times of the P waves and S wave. • Scientists know that: • P waves travel 1.7 times faster than S waves Therefore: ·If the S waves arrive shortly after the P waves, then the earthquake must have occurred nearby ·If the S waves arrive a long time after the P waves, then the earthquake must be further away • So……… scientists simply use a graph to plot the arrival times of the 2 waves. Then they translate the difference in times to distance.
Earthquake Measurement: • Richter Scale- scale that expresses magnitude of an earthquake • Magnitude- measure of the energy released by an earthquake. • Each whole number increase in magnitude represents a tenfold increase in measured amplitude (height of the wave on seismograph) • As an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31.7 times more energy than the amount associated with the preceding whole number value.
Mercalli Scale- Scale that expresses the intensity of an earthquake Intensity- the amount of damage caused • Any given earthquake can be described by only one magnitude, but many intensities: • the earthquake effects vary with circumstances such as distance from the epicenter, quality of buildings and local soil conditions. • Because there is some room for interpretation in the scale, the Mercalli scale is not often used in modern detection of quakes
Shaking Earth There are thousands upon thousands of earthquakes annually. They range, on average, from 18 major quakes to more than 2 million very minor ones per year (approximately 8,000 per day). On average, we can expect one exceptionally big one (with a magnitude of 8 or higher) each year.
Statistics: The largest earthquake ever recorded was an 9.5 on the Richter scale • Great: 8 or higher ·Major earthquake: 7 -8 • Strong earthquake: 6-7 ·Moderate earthquake: 5-6 • Light: 4-5 • Minor: 3-4 • Microquake: lower than 2.5 and is usually not felt by people • Location, location, location
Eq Vocabulary Cont’d Focus: The location within the earth where under-ground rock moves and sends out earthquake waves. Epicenter: The location on the surface of the earth directly above the focus of an earthquake. The relationship between the focus and the epicenter of an earthquake
FocusDepths • Shallow Focus Earthquake: • within 70km of the earth’s surface • Intermediate Focus Earthquake: • between 70km and 300km deep • Deep Focus Earthquake: • 300km-650kmdeep Which one do you think causes the most amount of damage?
That’s RIGHT!!!! • Shallow Focus Earthquakes cause the most amount of damage, because the strongest vibrations reach the earth’s surface more quickly • Deep Focus Earthquakes are the weakest, because the vibrations lose a lot of energy as they travel great distances to the earth’s surface. • Intermediate Focus Earthquakes are somewhere in-between!
Secondary Effects of an EQ • Fires • Land Slides • Tsunamis • Floods • Avalanche
Earthquake of August 18, 1959, Hebgen Lake, Montana. The magnitude 7.1 earthquake killed 28 people and caused $11 million property damage
Great Chilean Earthquake -May 22, 1960Magnitude 9.5 The earthquake caused a tsunami that hit the Chilean coast severely, with waves up to 25 meters high, ran through the Pacific Ocean and devastated Hilo, Hawaii, 10,000 kilometers (6,200 miles) from the epicenter, as well as coastal regions of Japan. The total number of fatalities from the earthquake/tsunami combination was estimated to have been as many as 3,000.
Good Friday Earthquake- March 27, 1964Magnitude 9.2 131 people were killed as a result of the earthquake: nine in the earthquake itself, 106 from tsunamis in Alaska, and 16 from tsunamis elsewhere. Property damage was estimated at over $300 million (1964 dollars), or $1.8 billion 2006 U.S. dollars.
Earthquake of June 16, 1964, Niigata, Japan. The magnitude 7.4 earthquake killed 26 and destroyed 3,018 houses and moderately or severely damaged 9,750 in Niigata
Earthquake of November 23, 1980, Campani, Italy. The magnitude 6.8 earthquake killed over 3,000, injured 7,750, and caused severe property damage. An additional 1,575 were reported missing and presumed dead. Two hundred fifty thousand were reported to be homeless. Twenty five thousand square kilometers of southern Italy were devastated.
Earthquake of February 9, 1971, San Fernando, California. The magnitude 6.7 earthquake killed 66 and caused $0.5-1.0 billion property damage.
Loma Prieta earthquake October 17, 19897.1 Magnitude This major earthquake caused 63 deaths, 3,757 injuries, and an estimated $6 billion in property damage.
August 1999 7.4 Turkey EQ More than 15,000 people are dead, 23,000 injured, and 500,000 homeless after this earthquake.
Dec. 26, 2004 Indian Ocean EarthquakeMagnitude 8- 9.2* Its tsunami killed more than 230,000 people, making it one of the deadliest disasters in modern history. * the earthquake's magnitude was first reported as 8.1 by the U.S. Geological Survey After further analysis, this was increased to 8.5, 8.9, and 9.0. In February 2005, some scientists revised the estimate of magnitude to 9.3. The most definitive estimate so far has put the magnitude at 9.15.
