Chapter 19 Earth Science Riddle Earthquakes Chapter 19 Earth Science Riddle

Stress and Strain Stress and Strain earthquakes result of movement in Earth’s crust Plate tectonics Along plate boundaries plate resist movement Build up stress Stress the total force acting on crustal rocks per unit of area When stress overcomes the strength of rocks, movement occurs along fractures in the rocks. The vibrations are earthquakes

Stress Three types of stress Compression: stress decreases the volume of material Tension: pulls material apart shear: causes material to twist

Deformation Elastic Material is bent for stretched. Low stress Like pulling the ends of a rubber band When stress released, it goes back to original size Plastic Stress builds to a certain point- elastic limit. Strain the causes permanent deformation. Does not go back to original size when stress is reduced to zero

Faults Reverse Movement partly horizontal and partly vertical compression Squeezes rock Shortens crust One side of fault is pushed up relative to the other.

Normal Fault Partly horizontal and partly vertical Pulls rocks apart and stretches the crust Vertical movement when stretching causes rock to move down relative to the other side of the fault.

Strike-Slip Fault Caused by horizontal shear. Movement is horizontal in opposite directions. San Andreas is an example of a Strike-Slip fault

Earth Quake Waves Seismic Waves The vibrations of the ground produced during an earthquake Three types of seismic waves Primary Waves Secondary Waves Surface Waves

Primary Waves P-Waves Squeeze and push rocks in the direction the waves are moving. The first wave Passes through Earth’s interior

Secondary Waves S Waves Second to arrive Slower than P waves Motion causes rocks to move at right angles in relation to the wave Passes through the Earth’s interior

Surface Waves Slowest type of wave Travel only Earth’s surface Causes ground to move sideways and up and down Most destructive Take the longest to pass

Generation of Seismic Waves The point at which the waves generate is the focus. Epicenter is the point on Earth’s surface directly above the focus.

Seismic Waves and Earth’s Interior Chapter 19 Section 2 Earth Science

Seismometer An instrument that can detect movement in Earth’s crust. Rotating drum with a suspended pen and mass. Records the movement on the paper on the drum.

Seismogram The record produced by seismometer

Travel Time Curves Using seismogram data, scientists have been able to construct a global travel time curves for the arrival for P and S waves. Curves provide average travel time of each wave.

Distance from Epicenter P waves arrive first S waves arrive second Distance between P and S waves increases as distance form the epicenter increase This data is used to determine the distance from the epicenter

Clues to Earth’s Interior Internal Structure Seismic waves change speed and direction at boundaries between different materials. P and S waves initially travel through mantle on fairly direct paths. P waves are refracted when they hit the core and other boundaries of Earth’s layers Travel times between refractions give information about Earth’s interior Data about paths and travel times gave evidence that Earth’s core was at least partially liquid Outer core mostly liquid Inner core mostly solid

Earth’s Composition

Measuring and Locating Earthquakes Chapter 19 Section 3 Earth Science

Earthquake Magnitude and Intensity Richter scale Numerical rating system measures the height largest seismic waves Magnitude: energy of the largest seismic waves Amplitude: height of the largest seismic wave Each successive number represents an increase in the amplitude of a seismic wave by a factor of 10 Example: Magnitude of 8 is 10x larger than a magnitude of 7.

Moment Magnitude Scale Measures the energy released by an earthquake Used by seismologists Takes into account the size of the fault and the rocks’ stiffness

Modified Mercalli Scale Describes the earthquake with respect to the damage they cause. Listed in Roman numerals to designate degree of intensity The larger the numeral, the more damage.

Earthquake Intensity Depends on amplitude of surface waves Surface waves decrease as they move away from the focus Intensity decreases with distance Maximum intensity at epicenter

Depth of Focus Earthquakes classified as Shallow Intermediate Deep Catastrophic earthquakes are almost always shallow-focus events Deeper focus event produce smaller vibrations at the epicenter. Mercalli scale affected by depth of focus- based on damage. Richter scale is not affected by depth of focus.

Distance to an Earthquake Scientists look at the difference between the arrival times of the P and S waves. The longer the time between the two- the farther they are from the epicenter Use Travel Time curves to calculate distances based on the arrival times of the P and S waves.

Seismic Belts Earthquake epicenters reveal a pattern Majority of earthquakes occur on narrow seismic belts Example Ring of Fire Correspond closely with tectonic plates boundaries

Earthquakes and Society Chapter 19 Section 4 Earth Science

Earthquake Hazards Factors that determine the severity of damage are called Earthquake Hazards Identifying the hazards in an area can prevent damage

Structural Failure Ground beneath structures shake Supporting walls fail and cause upper levels to fall and collapse Tall structures collapse or sway violently before falling

Land and Soil Failure Landslides are triggered on sloped areas. Soil liquefaction: vibrations cause ground to behave like liquid Can cause trees and houses to sink

Tsunami Large ocean wave generated by vertical motions on the ocean floor Displace entire column of water overlying the fault

Tsunami