Presentation on theme: "1.Tension – stretches rock, they become thin in the middle 2. Compression – pushes rock together, squeezes rock until it folds or breaks 3. Shearing –"— Presentation transcript:
1.Tension – stretches rock, they become thin in the middle 2. Compression – pushes rock together, squeezes rock until it folds or breaks 3. Shearing – masses of rock slip, they move past in opposite directions
Earthquakes 8.1 What Is an Earthquake? Focus is the point within Earth where the rock breaks. Epicenter is the location on the surface directly above the focus. An earthquake is the shaking & trembling of rock produced by the rapid release of energy Focus and Epicenter Faults are fractures in Earth where movement has occurred. Faults
1.Normal – due to tension, fault is at an angle, at diverging boundaries, hanging wall slips down footwall 2.Reverse or thrust – due to compression, fault is at an angle, hanging wall slides up and over footwall 3.Strike-slip or transform – due to shearing, 2 plates slip past each other sideways, at transform boundaries
Normal Fault: The hanging wall has slipped down in comparison to the foot wall. Gravity causes the hanging wall to slip down. Normal Faults are from layers being pulled apart. Also known as a GRAVITY FAULT.
ReverseFault: The hanging wall has slipped up in comparison to the foot wall. When layers are pushed together this is the kind of fault that occurs. Also known as a THRUST FAULT.
Strike Slip Fault: Two layers of rock are shifted horizontally or parallel to the fault plane.
Focus, Epicenter, and Fault
Slippage Along a Fault
1.Fault-block mountains – uplifted block of rock created between 2 normal faults 2.Anticlines – upward fold = ridges 3.Synclines – downward fold = valleys
Fault-block mountains in Juniper Canyon and Yosemite
Cause of Earthquakes 8.1 What Is an Earthquake? Elastic Rebound Hypothesis Most earthquakes are produced by the rapid release of elastic energy stored in rock that has been subjected to great forces. When the strength of the rock is exceeded, it suddenly breaks, causing the vibrations of an earthquake.
Elastic Rebound Hypothesis
Earthquake Waves 8.2 Measuring Earthquakes P waves -Have the greatest velocity of all earthquake waves -a.k.a. primary waves - Are push-pull waves that push (compress) and pull (expand) in the direction that the waves travel - Travel through solids, liquids, and gases
Earthquake Waves 8.2 Measuring Earthquakes S waves - Seismic waves that travel along Earth’s outer layer - a.k.a. secondary waves - Slower velocity than P waves - Shake particles at right angles to the direction that they travel or back & forth - Travel only through solids
Surface waves are seismic waves that travel along Earth’s outer layer. -Make most severe ground movements. ka/aeic/waves/index. html ence/terc/content/vis ualizations/es1002/es 1002page01.cfm
Earthquake Waves 8.2 Measuring Earthquakes Seismographs are instruments that record earthquake waves. Seismograms are the drawn records
Measuring Earthquakes 8.2 Measuring Earthquakes Mercalli Scale Rates damage at a given place Uses Roman numerals 1-12 Richter Scale Does not estimate adequately the size of very large earthquakes Based on the amplitude of the largest seismic wave Each unit equates to roughly a 32-fold energy increase
Modified Mercalli Scale IntensityVerbal DescriptionMagnitudeWitness Observations IInstrumental1 to 2Detected only by seismographs IIFeeble2 to 3Noticed only by sensitive people IIISlight3 to 4Resembling vibrations caused by heavy traffic IVModerate4 Felt by people walking; rocking of free standing objects VRather Strong4 to 5Sleepers awakened and bells ring VIStrong5 to 6 Trees sway, some damage from overturning and falling object VIIVery Strong6General alarm, cracking of walls VIIIDestructive6 to 7Chimneys fall and there is some damage to buildings IXRuinous7 Ground begins to crack, houses begin to collapse and pipes break XDisasterous7 to 8 Ground badly cracked and many buildings are destroyed.There are some landslides XIVery Disasterous8 Few buildings remain standing; bridges and railways destroyed;water, gas, electricity and telephones out of action. XIICatastrophic8 or greater Total destruction; objects are thrown into the air,much heaving,shaking and distortion of the ground Modified Mercalli Scale
Richter scale no.No. of earthquakes per year Typical effects of this magnitude < Detected only by seismometers Just about noticeable indoors Most people notice them, windows rattle Everyone notices them, dishes may break, open doors swing Slight damage to buildings, plaster cracks, bricks fall Much damage to buildings: chimneys fall, houses move on foundations Serious damage: bridges twist, walls fracture, buildings may collapse Great damage, most buildings collapse. > 8.0One every 5 to 10 years Total damage, surface waves seen, objects thrown in the air.
Measuring Earthquakes 8.2 Measuring Earthquakes Moment Magnitude Scale Derived from the amount of displacement that occurs along the fault zone most widely used measurement for earthquakes because it estimates the energy released by earthquakes. Scale ranges from Measures very large earthquakes
Some Notable Earthquakes
2009 Sichuan, China – 70,000 dead, 10 million homeless magnitude 6.7 Northridge Earthquake
Port au Prince, Haiti, Jan. 2010
1.Shaking – landslides, avalances, building & bridge topples, gas & water mains break 2.Liquefaction – loose, soft soil turns into Liquid mud, buildings fall & sink 3. Aftershocks – smaller eqs that occur after the larger one 4. Tsunami – giant wave created by displaced water Earthquake Dangers
Liquefaction /learn/animations/animatio n.php?flash_title=Liquefa ction+Flash+Animation&f lash_file=liquefaction&fla sh_width=450&flash_heig ht=200 Earthquake animation th/animations/earthquakes/index.ht ml Haiti clip HgQd0K5W0vI Photo gallery rthquake-pictures.htm Loma Prieta earthquakes/lomaprieta.htm
Transamerica Building in San Francisco, CA Building design to minimize EQ damage
Locating an Earthquake 8.2 Measuring Earthquakes Earthquake Distance Travel-time graphs from three or more seismographs can be used to find the exact location of an earthquake epicenter. The epicenter is located using the difference in the arrival times between P and S wave recordings, which are related to distance. About 95 percent of the major earthquakes occur in a few narrow zones. Earthquake Direction Earthquake Zones
Locating an Earthquake
Seismic Vibrations 8.3 Destruction from Earthquakes The damage to buildings and other structures from earthquake waves depends on several factors. These factors include the intensity and duration of the vibrations, the nature of the material on which the structure is built, and the design of the structure.
Seismic Vibrations 8.3 Destruction from Earthquakes Building Design - The design of the structure - Unreinforced stone or brick buildings are the most serious safety threats - Nature of the material upon which the structure rests Factors that determine structural damage - Intensity of the earthquake
Seismic Vibrations 8.3 Destruction from Earthquakes Liquefaction Saturated material turns fluid Underground objects may float to surface
Effects of Subsidence Due to Liquefaction
Tsunamis 8.3 Destruction from Earthquakes Cause of Tsunamis A tsunami triggered by an earthquake occurs where a slab of the ocean floor is displaced vertically along a fault. A tsunami also can occur when the vibration of a quake sets an underwater landslide into motion. Tsunami is the Japanese word for “seismic sea wave.”
Movement of a Tsunami
Tsunamis 8.3 Destruction from Earthquakes Large earthquakes are reported to Hawaii from Pacific seismic stations. Tsunami Warning System Although tsunamis travel quickly, there is sufficient time to evacuate all but the area closest to the epicenter.
Other Dangers 8.3 Destruction from Earthquakes With many earthquakes, the greatest damage to structures is from landslides and ground subsidence, or the sinking of the ground triggered by vibrations. Landslides In the San Francisco earthquake of 1906, most of the destruction was caused by fires that started when gas and electrical lines were cut. Fire
Discovering Earth’s Layers 8.4 Earth’s Layered Structure Velocity of seismic waves increases abruptly below 50 km of depth Separates crust from underlying mantle Shadow Zone Absence of P waves from about 105 degrees to 140 degrees around the globe from an earthquake Can be e xplained if Earth contains a core composed of materials unlike the overlying mantle Moho ˇ ´