Geology

__Geology__ >> Earth's surface directly above the focus is the epicenter. >> The frame of a seismometer is anchored to the ground. when an earthquake occurs, the frame moves but the hanging mass and attached pen do not. the mass and pen record the relative movement as the recording device move under them. >> the record produced by a seismometer that can provide individual tracking of each type of seismic wave is a seismogram >> the separation of seismic waves on seismograms can be used to determine the distance from the epicenter of an earthquake to the seismic facility that recorded the seismogram Tagging pages is now done in a new place. Once you have saved your changes, click on the "Page" tab and select "Details and Tags". Help  · About  · Blog  · Terms  · Privacy  · [|**Support**]  · [|**Upgrade**] Contributions to http://treversnotes.wikispaces.com are licensed under a [|Creative Commons Attribution Share-Alike 3.0 License] <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">. >> <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">Portions not contributed
 * Along the boundaries between two tectonic plates, rocks in the crust often resist movement. Over time stress builds up.
 * Stress- the<span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;"> total force acting on crustal rocks per unit of area.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">Thewre are three kinds of stress that act on Earth's rocks:
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">Compression, tension, and shear
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">Compression causes a material to shorten. Tension causes a material to lengthen. Shear causes distortion of a material. The deformation of materials in response in response to stress is called **Strain.**
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">Even though rocks can be twisted, squeezed and stretched. They fracture when stress and strain reach a critical point. At these breaks, rocks can move, releasing the energy built up as a result of stress. Earthquakes are the result of this movement and release of energy.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">**Elastic Deformation** is caused under conditions of low stress when a material is compressed. When the stress is removed, material reurns to its original shape.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">When stress builds up past a certain point, called the elastic limit, rocks undergo **plastic deformation.** this type of train produces permanent deformation. This type of strain produces permanent deformation. most materials exhibit both elastic and plastic behavior. as pressure increases, rocks require greater stress to reach the elastic limit. at high enough temperatures, solid rock can also deform, causing it to flow in a fluid like manner. this flow reduces stress.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">**Faults**
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">crustal rocks fail when stresses exceed the strength of the rocks. the resulting movement occurs along a weak region in the crystal rock called a fault, which is any fracture or system of fractures along which Earth moves.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">**Reverse** **Fault**
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">Reverse faults from as a result of horizontal and vertical compression that squeezes rock and creates s shortening of the crust. this causes rock on one side of a reverse fault to be pushed up relative to the other side.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">**Normal Fault**
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">Movement along a normal fault is partly horizontal and partly vertical. the horizontal movement pulls rock apart and stretches the crust. vertical movement occurs as the stretching causes rock on one side of the fault to move down relative to the other side.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">**Strike-slip fault**
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">strike-slip faults are caused by horizontal shear. the movement at a strike-slip fault is mainly horizontal and in opposite directions, similar to the way cars move in opposite directions on either side of a freeway.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">**Earthquake Waves**
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">irregular surfaces in rocks can snag and lock along faults when movement occurs. as stress continues to build in these rocks, they undergo elastic deformation. before the elastic limit, they bend or stretch. beyond the limit, an earthquake occurs when they slip or crumble.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">**Types of seismic waves**
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">The vibrations of the ground produced during an earthquake are called seismic waves. every earthquake generates three types of seismic waves: primary waves, secondary waves, and surface waves
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">**Primary waves**
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">squeeze and push rocks in the direction along which the waves are traveling.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">**Secondary waves**, called s- waves, are named with respect their arrival times. they are slower then P- waves, so they are the second set f waves to be felt. S- waves have a motion that causes rocks to move at right angles in relation to the direction of the waves.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">the third and slowest type of waves are **surface waves**, which travel only along Earth's surface. surface waves can cause the ground to move sideways and up and down like ocean waves.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">The **focus** of an earthquake is the point of initial fault rupture, which is usually several kilometers below Earth's surface. the point on
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">**Seismometers and seismograms**
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">most of the vibrations caused by seismic waves cannot be felt as great distances from an earthquakes epicenter, but they can be detected by sensitive instruments called seismometers, which measure horizontal or vertical motion during an earthquake.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">__**Travel-time curves**__
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">provide the average time it takes for p- and s- waves to reach seismic stations located at different distances from an earthquake's epicenter
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">**__Distance from epicenter__**
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">waves recorded on seismograms from more distant facilities are farther apart than waves recorded on seismographs at stations closer to the epicenter
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">__**Earth's internal structure**__
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">Seismic waves change speed and direction when at the boundaries between different materials. as P- waves and S- waves initially travel through the mantle, they follow fairly direct paths. when P- waves strike the core, they are refracted, which manes they bend.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">__**Earth's internal structure**__
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">to find out what happens to S-waves generated by an earthquake, seismologists first determined that the back - and - forth motion of S-Waves do not travel through Earth's center
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">__**Earth's composition**__
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">Seismic waves change their speed as they encounter boundaries between zones of different materials
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">__**Visualizing seismic Waves**__
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">the travel times and behavior of seismic waves provide a detailed picture of Earth's internal structure. <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">these waves also provide clues about the composition of the various parts of Earth
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">__**Imaging Earth's interior**__
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">Because the speed of seismic waves depends on temperature and composition. it is possible to use seismic waves to create images of structures such <span style="font-family: 'Courier New',Courier,monospace; font-size: 10px;">as slabs and plumes. in general, the speed of seismic waves decreases as temperature increases noneunderstanding that earth has an outer core that is liquid and an inner core that is solid. Seismic waves change their speed as they encounter boundaries between zones of different materials.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">**<span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">Visualizing seismic waves- ** <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;"> the travel times and behavior of seismic waves provide a detailed picture of earths internal structure. There waves also provide clues about the composition of the various parts of earth.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">**__ Earthquake magnitude and intensity- __** the Richter scale, devised by a geologist named Charles Richter, is a numerical rating system that measures magnitude of an earthquake.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">**Magnitude-** is the measure of the energy released during an earthquake. The numbers in the Richter scale are determined by the height, called the amplitude, of the largest seismic wave.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">**Moment magnitude scale-** it is a rating scale of the energy released by an earthquake, taking into account the size of the fault rupture, the amount of movement along the fault, and the rocks stiffness.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">**Modified mercalli scale-** it is used to measure earthquake intensity on a scale from I to XII. The higher the number, the greater the damage the earthquake has caused. The intensity of an earthquake depends primarily on the amplitude of the surface waves generated. Maximum intensity values are observed in the region near the epicenter; Mercalli values decrease to I at distances far from the epicenter.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">**Depth of focus-** earthquakes are classified as shallow, intermediate, or deep, depending on the location of the focus. Shallow-focus earthquakes are the most damaging.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">** Locating an earthquake- ** the location of an earthquakes epicenter and the time of the earthquakes occurrence are usually not known at first. However, the epicenters location, as well as the time of occurrence, can be determined using seismograms and travel-time curves.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">** Distance to an earthquake- ** seismologists determine the distance to an earthquakes epicenter by measuring the separation on any seismogram and identifying that same separation tine on the travel-time graph. To locate the epicenter of an earthquake, scientists identify the seismic stations on a map, and draw a circle with the radius of distance to the epicenter from each station. The point where all the circles intersect is the epicenter.
 * <span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt;">**<span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;">Time of an earthquake- **<span style="font-family: 'Courier New',Courier,monospace; font-size: 10pt; line-height: 115%;"> seismologists can use a seismogram to gain information about the exact time that an earthquake occurred at the focus. The time can be determined by using a table similar to a travel-time graph.
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