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Submitted To: Sir Fahad HameedSubmitted By: Ahmed Younhais Tariq 5th Semester Evening “B”
An earthquake is the resultof a sudden release ofenergy in the Earths crustthat creates seismic waves.The seismic activity of anarea refers to thefrequency, type and size ofearthquakes experiencedover a period of time.
For Example:If you throw stone in a pond of stillwater, series of waves are produced on thesurface of water, these waves spread out in alldirections from the point where the stonestrikes the water similarly, any suddendisturbances in the earth’s crust may producevibrations in the crust which travel in alldirections from point of disturbances.
Focus is the point on the faultwhere rupture occurs and thelocation from which seismicwaves are released.The epicenter is the point onthe Earths surface that is directlyabove the focus, the point wherean earthquakes or undergroundexplosion originates.
A fault line is the surfacetrace of a fault, the line ofintersection between thefault plane and the Earthssurface.A fault scarp isthe topographic expressionof faulting attributed to thedisplacement of the landsurface by movement alongfaults.
The primary cause of an earthquake is faultson the crust of the earth. The cracks or suddenslips of the land are known as faults or faultplanes. Some major causes of earthquakes onbasic of its causes are: Surface causes. Volcanic causes. Tectonic causes.
Great explosions, landslides, slips on steep coasts, dashing of sea waves, avalanches, railway trains, heavy trucks, some large engineering projects cause minor tremors. Some of them are man made, others are natural.
Volcanic eruptions produce earthquakes. Earthquakes may precede, accompany and frequently follow volcanic eruptions. They are caused by sudden violent displacements of lava within or beneath the earth crust.
Structural disturbances resulting in the relative displacements of the parts of the lithosphere is the main cause of this type of earthquake. Most of the disastrous earthquakes belong to this category and occur in areas of great faults and fractures. Sudden yielding to strain produced on the rocks of accumulating stress causes displacements especially along old fault zones known as great transform faults.
Stresses accumulate on the two sides of the fault plane and produce strain. The rock deforms bends and when the stress crosses the elastic limit, sudden displacement of the two sides of the fault plane takes place. This results in a strong blow to the rocks Elastic rebound and produces tremors.
Seismic waves produceddue to earthquake arebasically divided intotwo major types: Body Waves. Surface Waves.
Body waves travels through the interior (body) of earth asthey leave the focus. Body waves are further divided intofollowing types: Primary (P) Waves. Secondary (S) Waves.
Primary waves are high frequency, short-wavelength, longitudinal waves which can pass throughboth solids and liquids which forced to move forwardsand backwards as it is compressed and decompressed.This produces relatively small displacements of theground.P Waves can be reflected and refracted, and undercertain circumstances can change into S-Waves.
Secondary Waves (S-Waves) travel more slowly than P-Waves and arrive at any given point after the P-Waves.Like P-Waves they are high frequency, short-wavelengthwaves, but instead of being longitudinal they aretransverse. They move in all directions away from theirsource, at speeds which depend upon the density of therocks through which they are moving. They cannot movethrough liquids.
Surface waves travels parallel to the earth’s surface andthese waves are slowest and most damaging. Surfacewaves are divided intofollowing types:• Love waves.• Rayleigh waves.
Love waves cause horizontal shifting of the earth duringan earthquake. These waves travel with a slower velocitythan P- or S- waves, but faster than Rayleigh waves .These waves are observed only when there is a lowvelocity layer overlying a high velocity layer.
Rayleigh waves travel near the surface of solids as theycreated close to the epicenter and can only travel throughthe outer part of the crust. Due to these waves the groundis made to move in a circular motion, causing it to rise andfall as visible waves move across the ground.
Earthquakes are basicallydivided into two types on the basicof difference in causes which arefollowing: Tectonic Earthquake. Volcanic Earthquake.
Tectonic earthquakes are triggered when the crust becomes subjected to strain, and eventually moves. The theory of plate tectonics explains how the crust of the Earth is made of several plates, large areas of crust which float on the Mantle. Since these plates are free to slowly move, they can either drift towards each other, away from each other or slide past each other. Many of the earthquakes which we feel are located in the areas where plates collide or try to slide past each other.
Major earthquakes are sometimes occur by a period of changed activity. This might take the form of more frequent minor shocks as the rocks begin to move , called foreshocks , or a period of less frequent shocks as the two rock masses temporarily stick and become locked together. Detailed surveys longitudinal features very slowly become deformed as the pressure builds up in the rocks, then become noticeably offset when a movement occurs along the fault. Following the main shock, there may be further movements, called aftershocks, which occur as the rock masses settle down in their new positions. Such aftershocks cause problems for rescue services, bringing down buildings already weakened by the main earthquake.
Volcanic earthquakes are far less common than Tectonic ones. They are triggered by the explosive eruption of a volcano. Given that not all volcanoes are prone to violent eruption, and that most are quiet for the majority of the time, it is not surprising to find that they are comparatively rare. When a volcano explodes, it is likely that the associated earthquake effects will be confined to an area 10 to 20 miles around its base, where as a tectonic earthquake may be felt around the globe.
By contrast, volcanoes producing free flowing basic lava rarely cause earthquakes. The lava flows freely out of the vent and down the sides of the volcano, releasing pressure evenly and constantly. Since pressure doesnt build up, violent explosions do not occur.
The intensity and strength of an earthquake ismeasured on Richter scale, the scale invented byCharles Richter California, USA in 1935, whichcategories earthquake on the basis of energyreleased.
Intensity of earthquake on Richter Energy release (amount of TNT):scale:1.0 170 Grams2.0 6 Kilogram3.0 179 Kilogram4.0 5 Metric Tons5.0 179 Metric Tons6.0 5643 Metric Tons7.0 179100 Metric Tons7.5 1 Mega Tons8.0 564300 Metric Tons
Increase in magnitude significantly increase the time ofshaking and potential damage. Richter Magnitude: Duration of strong ground shaking ( seconds): 8-8.9 30-90 7-7.9 20-50 6-6.9 10-30 5-5.9 2-50 4-4.9 0-5
Landslides:Earthquakes, along withsevere storms, volcanicactivity, coastal waveattack, and wildfires, canproduce slope instabilityleading to landslides, amajor geological hazard.
Shaking and groundrupture:Shaking and ground rupture arethe main effects created byearthquakes, principally resultingin more or less severe damage tobuildings and other rigidstructures. Specific localgeological, geomorphological, and geostructural features caninduce high levels of shaking onthe ground surface even fromlow-intensity earthquakes. Thiseffect is called site or localamplification.
Fires:Earthquakes can cause firesby damaging electricalpower or gas lines, andsometime it may also becomedifficult to stop the spread ofa fire once it has started.For example, more deaths inthe 1906 San Franciscoearthquake were caused byfire than by the earthquakeitself.
Soil liquefaction:Soil liquefaction occurswhen, because of theshaking, water-saturatedgranular material (such assand) temporarily loses itsstrength and transforms froma solid to a liquid. Soilliquefaction may cause rigidstructures, like buildings andbridges, to tilt or sink into theliquefied deposits. This can bea destructive effect ofearthquakes.
Tsunami:Tsunamis are long-wavelengthsea waves produced by thesudden or abrupt movement oflarge volumes of water. In theopen ocean the distance betweenwave crests can surpass 100kilometers and the wave periodscan vary from five minutes toone hour. Such tsunamis travel600-800 kilometers per hour(373–497 miles perhour), depending on waterdepth. Such tsunami cause a hugedestruction to nearby seashores.
Floods:A flood is an overflow ofany amount of water thatreaches land.Floods may be secondaryeffects of earthquakes, ifdams are damaged.Earthquakes may causelandslips to damrivers, which collapseand cause floods.
Human impacts:An earthquake may causeinjury and loss of life, roadand bridge damage, generalproperty damage andcollapse or destabilization(potentially leading to futurecollapse) of buildings. Theaftermath may bringdisease, lack of basicnecessities, and higherinsurance premiums.
Earthquake prediction is usually defined as thespecification of the time, location, and magnitude ofa future earthquake within stated limits. Manymethods have been developed for predicting thetime and place in which earthquakes will occur.Despite considerable research efforts byseismologists, scientifically reproducible predictionscannot yet be made to a specific day or month. Majorearthquakes are often followed by reports that theywere predicted, but no claim of a successfulprediction of a major earthquake has survived closeinquiry.
But some evidence of upcoming Earthquake arefollowing: Animal Behavior: Unusual and anomalous behavior of animals is evidence of coming earthquake. Water Level in Wells: Water level in wells changes also produce possibility of an earthquake. Foreshocks: Minor shocks before major earthquake. Oil Production: Large scale fluctuations of oil from oil wells are also show a chance of possible coming earthquake.
Emission of Radon Gas: Radon gas is inert produced by the decay of uranium . Radon remain within rocks until some event force it out. So emission of radon gas is evidence of earthquake. Uplifting of Earth surface: Uplifting of earth’s surface is also use for prediction of earthquake.
If you are in a house; Don’t use lift for getting down from building. Be prepared to move with your family.If you are in shop, school or office; Don’t run for an exit. Take cover under a desk/table. Move away from window glass. Do not go near electric points and cable. Keep away from weak portion of the building and false ceiling.
If you are outside; Avoid high buildings, walls, power lines and other objects that could fall and create block. Don’t run through streets. If possible, move on to an open area away from hazard including trees.If you are in vehicle; Stop in a safe and open place. Remain inside vehicle. Close windows, doors and vents.