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Cues Pages 162-181in your textbook. Earthquake Notes Stress in Earth's Crust Name the 3 types of force and what kind of fault they produce. Faults in Earth's crust are caused by these same tectonic forces: 1) tension – stretches a body and pulls it apart, located at divergent plate boundaries, and creates a Normal fault. Ex. rift valley (The Basin-and-Range province of Nevada, Utah, and eastern Oregon is a region of strong extension that has many normal faults cutting the crust, making fault-bounded mountains and basins.) 2) compression - squeezes material inward and causes shortening, located at convergent plate boundaries, and creates a reverse or thrust fault and anticline/ syncline, fault-block and folded mountains. Large mountain ranges such as the Himalayas (active) and the Appalachians (ancient), Sierra Nevada and Tetons were formed by strong compression, which produced thrust and reverse faults and many large folds. What are seismic waves? What are the two categories and two types within each? What kind of motion and damage is made by each type? 3) shearing - forces that push two sides of a body in opposite directions (like the sliding deformation of a deck of cards). Located at transform plate boundaries, creates a strike-slip fault. ex. The San Andreas fault is a large active strike-slip fault that poses significant earthquake hazards in California. seismic waves - waves of energy generated by an earthquake 2 categories of seismic waves: A. Body Waves: (1) primary waves - the first waves that move through Earth causing particles to move back & forth in the same direction. (ex. slinky) (P= push wave) (longitudinal wave) (travels through solids and liquids) (2) secondary waves - the second set of waves which move through Earth causing particles to move at right angles to the direction of the wave. (S wave) (ex. rope) (transversal wave) (travel through solids only) B. Surface Waves: Waves that travel on Earth's surface causing the most damage of all waves. (L = last waves) (1) Love waves - named after A.E.H. Love, a British mathematician who worked out the mathematical model for this kind of wave in 1911. It's the fastest surface wave and moves the ground from side-to-side. (2) Rayleigh Waves - named for John William Strutt, Lord Rayleigh, who mathematically predicted the existence of this kind of wave in 1885. A Rayleigh wave rolls along the ground What is the difference between the focus and the epicenter? just like a wave rolls across a lake or an ocean. Because it rolls, it moves the ground up and down, and side-to-side in the same direction that the wave is moving. Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves. - focus - the point in the Earth’s interior where the earthquake originates Define seismologist, seismograph, and magnitude. Name and describe 3 scales used to describe earthquakes. - epicenter - the point on the Earth’s surface above the focus. - seismologists - scientists who study earthquakes and seismic waves. - seismograph - an instrument which measures the three types of earthquake (seismic) waves. - magnitude - a measure of the amount of energy released Earthquake Scales: 1) the Mercalli scale - invented by Giuseppe Mercalli in 1902, this scale uses the observations of the people who experienced the earthquake to estimate its intensity. The amount of damage caused by the earthquake may not accurately record how strong it was. 2) the Richter magnitude scale - developed in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes. The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs. Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; as an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value. 3) the Moment Magnitude scale is the measure of total energy released by an earthquake. Moment magnitude is the measurement and term generally preferred by scientists and seismologists to the Richter scale because moment magnitude is more precise. Moment Magnitude is not based on instrumental recordings of a quake, but on the area of the fault that ruptured in the quake. This means that the moment magnitude describes something physical about an earthquake. Moment Magnitude is calculated in part by multiplying the area of the fault's rupture surface by the distance the earth moves along the fault. Name and describe 4 types of earthquake hazards. Earthquake Hazards 1) Soil Conditions and Liquifaction - The first main earthquake hazard is the effect of ground shaking. Buildings can be damaged by the shaking itself or by the ground beneath them settling to a different level than it was before the earthquake (subsidence). Loose soil shakes more than solid rock. Liquefaction is the mixing of sand or soil and groundwater (water underground) during the shaking of a moderate or strong earthquake. When the water and soil are mixed, the ground becomes very soft and acts similar to quicksand. If liquefaction occurs under a building, it may start to lean, tip over, or sink several feet. The ground firms up again after the earthquake has past and the water has settled back down to its usual place deeper in the ground. Liquefaction is a hazard in areas that have groundwater near the surface and sandy soil. This is the main hazard to the Coastal Plain and Coastal Zone of South Carolina. 2) Ground Displacement - is ground movement along a fault. If a structure (a building, road, etc.) is built across a fault, the ground displacement during an earthquake could seriously damage or rip apart that structure. Aftershocks are earthquakes which occur from hours to months after a larger earthquake. Aftershocks often topple already weakened buildings. 3) Flooding - An earthquake can rupture (break) dams or levees along a river. The water from the river or the reservoir would then flood the area, damaging buildings and maybe sweeping away or drowning people. Tsunamis and seiches can also cause a great deal of damage. A tsunami is what most people call a tidal wave, but it has nothing to do with the tides on the ocean. It is a huge wave caused by an earthquake under the ocean. Tsunamis can be tens of feet high when they hit the shore and can do enormous damage to the coastline. Seiches are like small tsunamis. They occur on lakes that are shaken by the earthquake and are usually only a few feet high, but they can still flood or knock down houses, and tip over trees. 4) Fire - Fires can be started by broken gas lines and power lines, or tipped over wood or coal stoves. They can be a serious problem, especially if the water lines that feed the fire hydrants are broken, too. For example, after the Great San Francisco Earthquake in 1906, the city burned for three days. Most of the city was destroyed and 250,000 people were left homeless. What are some safety measures to take before, during and after an earthquake? Earthquake safety: During an Earthquake If indoors: Take cover under a piece of heavy furniture or against an inside wall and hold on. Stay inside. The most dangerous thing to do during the shaking of an earthquake is to try to leave the building because objects can fall on you. If outdoors: Move into the open, away from buildings, street lights, and utility wires. Once in the open, stay there until the shaking stops. If in a moving vehicle: Stop quickly and stay in the vehicle. Move to a clear area away from buildings, trees, overpasses, or utility wires. Once the shaking has stopped, proceed with caution. Avoid bridges or ramps that might have been damaged by the quake. After an Earthquake Be prepared for aftershocks. Although smaller than the main shock, aftershocks cause additional damage and may bring weakened structures down. Aftershocks can occur in the first hours, days, weeks, or even months after the quake. Help injured or trapped persons. Do not move seriously injured persons unless they are in immediate danger of further injury. Remember to help your neighbors who may require special assistance -- infants, the elderly, and people with disabilities. Listen to a battery-operated radio or television for the latest emergency information. Stay out of damaged buildings. Return home only when authorities say it is safe. Use the telephone only for emergency calls. Clean up spilled medicines, bleaches or gasoline or other flammable liquids immediately. Leave the area if you smell gas or fumes from other chemicals. Open closet and cupboard doors cautiously. Inspect the entire length of chimneys carefully for damage. Unnoticed damage could lead to a fire. Check for gas leaks--If you smell gas or hear blowing or hissing noise, open a window and quickly leave the building. Turn off the gas at the outside main valve if you can. Gas should only be turned on by a professional. Look for electrical system damage--If you see sparks or broken or frayed wires, or if you smell hot insulation, How are most people injured during an earthquake? turn off the electricity at the main fuse box or circuit breaker. Check for sewage and water lines damage--If you suspect sewage lines are damaged, avoid using the toilets and call a plumber. If water pipes are damaged, contact the water company and avoid using water from the tap. Most of the hazards to people come from things falling on people. Name 4 devices used in buildings to make them earthquake resistant. How Buildings are Made Earthquake Resistant Seismic devices: 1) shear walls - Triangular steel or concrete components may be added to an existing building or designed into a new one. These components are free to move in an earthquake, so the wall may bend and crack, but won't break. 2) braced framing - Sometimes referred to as trussed framing, bracing stretches diagonally within a bay to create a triangulated vertical frame. As in roof trusses, the triangles are able to handle stresses better than a conventional rectangular frame. They also add stiffness. 3) shock-absorbing devices or dampers - There are four basic types of dampers: visco-elastic, friction, metallic, and viscous. Each employs some type of pumping component or piston that operates against a friction device-pads or fluid-filled chambers-to release energy in the form of friction or heat. 4) base isolation - the structure is build on a series of blocks made of alternating layers of rubber and steel, enabling them to move and absorb the energy from the earthquake. This allows the structure to move independently of the shifting ground below. These may be used alone or, for tall buildings, in combination. Why do we need at least 3 seismic stations to find the epicenter of an earthquake? How Earthquakes are located: We observe earthquakes with a network of at least 3 seismometers on the earth's surface. When an earthquake occurs, we observe the times at which the wave-front passes each station. The seismograms are a recording of the time (arrival & duration) and amplitude (intensity) of all three types of seismic waves. We must find the unknown earthquake source knowing these wave arrival times. The distance between the beginning of the first P wave and the first S wave tells you how many seconds the waves are apart. This number will be used to tell you how far your seismograph is from the epicenter of the earthquake. To know exactly where the earthquake occurred, you'll need a drawing compass and a map (with a scale of 1cm=1km). Calculate the distance on the map using the scale. Using your compass, draw a circle with a radius equal to the number you came up with for each seismograph station. All of the circles should overlap. The point where all of the circles overlap is the approximate epicenter of the earthquake. Can Earthquakes be predicted? Many earthquakes give some kind of signal that precedes the slip. There are a variety of precursors that have been noted: ground deformation foreshocks hydrologic changes low frequency radio waves seismic wave velocity changes electromagnetic changes poorly understood observations such as strange animal behavior. Summaries