Chapter 5:Eartquakes

Chapter 5:Eartquakes

1. Section 1:Forces in Earth's Crust

   • Types of Stress
     • Tension
       • It pulls the crust and it stretches rocks so that it thinner in the middle
     • Compression
       • It squeezes rock until it folds or breaks.
     • Shearing
       • Pushes a mass of rock in two opposite ways. It can cause rocks to break and slip apart or to change its shape.
   • Kinds of Faults
     • Normal Faults
       • Normal faults cause things like hanging wall and a footwall. A hanging wall is the block of rock that lies above. A footwall is a rock that  lies below
       • Reverse Faults
         • It has the  same structures as a normal fault, but the blocks move in the opposite directions. The rock forming the hanging wall slides up and over the footwall. 
       • Strike-Skip Faults
         • In a strike-slip fault,the rocks on either side of the fault slip past each other sideways,with little up and down motion.
   • Changing Earth's Surface
     • Folding Earth's Crust
       • Much as the rug wrinkles,rock stressed by compression may bend without breaking. Folds are bends in rock that form when compression shortens and thickens Earth's crust.
     • Stretching Earth's Crust
       • When two of these normal faults form parallel to each other,a block of rock is left lying between them. As the hanging wall of each normal fault slips downward,the block in between moves upward,forming a fault-block mountain.
     • Uplifting Earth's Crust
       • Some plateaus form when forces in Earth's crust push up a large,flat block of rock.It is wider than it is tall.
       • Plateau
         • It is a large area of flat land elevated high above sea level.

2. Section 2:Earthquakes and Seismic Waves

   • Types of Seismic Waves
     • P Waves
       • They are seismic waves that compress and expands the ground like an accordion
     • S Waves
       • They are seismic waves that vibrate from side to side as well as up and down.
     • Surface Waves
       • Surface Waves move more slowly than P Waves and S Waves,but they can produce severe ground movements.
   • Measuring Earthquakes
     • The Mercalli scale
       • The Mercalli scale was developed to rate earthquakes according to their intensity, or strength at a given place.
     • The Richter Scale
       • The Richter scale assigns a magnitude number to an earthquake based on the size of the seismic waves.
     • The Moment Magnitude Scale
       • A moment magnitude scale is a rating system that estimates the total energy released by an earthquake.
   • Locating the Epicenter
     • To tell how far the epicenter is from the seismograph, scientists measure the difference between the arrival times of the P waves and the S waves.

3. Section 3:Monitoring Earthquake's

   • The Seismograph
     • Measuring Seismic Waves
       • All seismographs make use of a basic principle of physics:Whether it is moving or at rest, every object resists any change to its motion. A seismograph's heavy weight resists motion during a quake. But the rest of the seismograph is anchored to the ground and vibrates when seismic waves arrived.
     • Reading a Seismogram
       • The height of the jagged lines drawn on the seismograph's drum is greater for a more severe earthquake or for an earthquake close to the seismograph.
       • Seismograph
         • The pattern of lines,called seismogram, is the record of an earthquake's seismic waves produced by a seismograph.
   • Instruments That Moniter Faults
     • Tiltmeters
       • A tiltmeter measures tilting or raising of the ground.If the land rises or falls slightly, the liquid will flow from one light bulb to the other.
     • Creep Meters
       • A creep meter uses a wire stretched across a fault to measure horizontal fault movement of the ground.
     • Laser-Ranging Devices
       • A laser-ranging device uses a large beam to detect horizontal fault movements. The device can detect any change in distance to the reflector.
     • GPS Satellites
       • GPS, the Global Position System, was developed to help ships and planes find their routes.
   • Use Seismographic Data
     • Mapping Faults
       • When seismic waves hit a fault, the waves are reflected off the fault. Seismoghraphs can detect these reflected seismic waves. Geologists then use the data to map the fault's length and depth.
     • Monitoring Changes Along Faults
       • Geologists study the types of movement that occur faults. 
     • Trying To Predict Earthquakes
       • Even with data from many sources, geologists can't predict when and where a quake will strike. Usually, stress along a fault increases until an earthquake occurs.

4. Section 4:Earthquake's Safety

   • Earthquake Risk
     • Plate Boundaries and Faults
       • Plates meet along the Pacific coast, causing many active faults. In California, the Pacific plate and North American plate meet along the San Andreas fault.
     • Mapping Earthquake Intensity
       • Geologists can use Mercalli scale data to map the intensity of an earthquake.
     • History Earthquakes
       • Geologists learn about past earthquakes is from historic reports. The reports describe where the quake was strongest and what damage it caused.
   • How Earthquakes Cause Damage
     • Shaking
     • Liquefaction
       • In 1964,when a powerful earthquake roared through Anchorage,Alaska,wide cracks opened in the ground.The cracks were made by liquefaction.
     • Aftershocks
       • Sometimes, buildings weakened by an earthquake collapse during an aftershock.
   • Steps to Earthquake Safety
     • If you are indoor, crouch down beneath a sturdy table or desk and hold on to it. If no table or desk,crouch against an inner wall,away from the outside of a building.
   • Designing Safer Buildings
     • Protecting Srtuctures
       • The only buildings you need is a building that can withstand.
     • Making Utilites Safer
       • Earthquakes can cause fire and and flooding when gas pipes and water mains break.Flexible joints can be installed in gas and water lines to keep them from breaking. Automatic shut-off vales can be installed on these lines to cut off gas and water flow.