Cause Earthquakes example essay topic

An Earthquake is a sudden tremor or movement of the earth's crust, which originates naturally at or below the surface. The word natural is important here, since it excludes shock waves caused by French nuclear tests, man made explosions and landslides caused by building work. THERE ARE TWO MAIN CAUSES Firstly, they can be linked to explosive volcanic eruptions; they are in fact very common in areas of volcanic activity where they either proceed or accompany eruptions. Secondly, they can be triggered by Tectonic activity associated with plate margins and faults. The majority of earthquakes world wide are of this type. TERMINOLOGY An earthquake can be likened to the effect observed when a stone is thrown into water.

After the stone hits the water a series of concentric waves will move outwards from the center. The same events occur in an earthquake. There is a sudden movement within the crust or mantle, and concentric shock waves move out from that point. Geologists and Geographers call the origin of the earthquake the focus. Since this is often deep below the surface and difficult to map, the location of the earthquake is often referred to as the point on the Earth surface directly above the focus. This point is called the epi centre.

The strength, or magnitude, of the shockwave's determines the extent of the damage caused. Two main scales exist for defining the strength, the Mercalli Scale and the Richter Scale. Earthquakes are three dimensional events, the waves move outwards from the focus, but can travel in both the horizontal and vertical plains. This produces three different types of waves which have their own distinct characteristics and can only move through certain layers within the Earth.

Lets take a look at these three forms of shock waves. TYPES OF SHOCKWAVES P-Waves Primary Waves (P-Waves) are identical in character to sound waves. They are high frequency, short-wavelength, longitudinal waves which can pass through both solids and liquids. The ground is forced to move forwards and backwards as it is compressed and decompressed. This produces relatively small displacements of the ground. P Waves can be reflected and refracted, and under certain circumstances can change into S-Waves.

Particles are compressed and expanded in the wave's direction. 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-wavelength waves, but instead of being longitudinal they are transverse. They move in all directions away from their source, at speeds which depend upon the density of the rocks through which they are moving. They cannot move through liquids. On the surface of the Earth, S-Waves are responsible for the sideways displacement of walls and fences, leaving them 'S's hoped.

S-waves move particles at 90^0 to the wave's direction. L-Waves Surface Waves (L-Waves) are low frequency transverse vibrations with a long wavelength. They are created close to the epi centre and can only travel through the outer part of the crust. They are responsible for the majority of the building damage caused by earthquakes. This is because L Waves have a motion similar to that of waves in the sea. The ground is made to move in a circular motion, causing it to rise and fall as visible waves move across the ground.

Together with secondary effects such as landslides, fires and tsunami these waves account for the loss of approximately 10,000 lives and over $100 million per year. L-waves move particles in a circular path. TECTONIC EARTHQUAKES 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.

The process which explains these earthquakes, known as Elastic Rebound Theory can be demonstrated with a green twig or branch. Holding both ends, the twig can be slowly bent. As it is bent, energy is built up within it. A point will be reached where the twig suddenly snaps. At this moment the energy within the twig has exceeded the Elastic Limit of the twig. As it snaps the energy is released, causing the twig to vibrate and to produce sound waves.

Perhaps the most famous example of plates sliding past each other is the San Andreas Fault in California. Here, two plates, the Pacific Plate and the North American Plate, are both moving in a roughly northwesterly direction, but one is moving faster than the other. The San Francisco area is subjected to hundreds of small earthquakes every year as the two plates grind against each other. Occasionally, as in 1989, a much larger movement occurs, triggering a far more violent 'quake'.

Major earthquakes are sometimes preceded by a period of changed activity. This might take the form of more frequent minor shocks as the rocks begin to move, called fore shocks, or a period of less frequent shocks as the two rock masses temporarily 'stick' and become locked together. Detailed surveys in San Francisco have shown that railway lines, fences and other 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 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. The volcanoes which are most likely to explode violently are those which produce acidic lava.

Acidic lava cools and sets very quickly upon contact with the air. This tends to chock the volcanic vent and block the further escape of pressure. For example, in the case of Mt Pelee, the lava solidified before it could flow down the sides of the volcano. Instead it formed a spine of solid rock within the volcano vent. The only way in which such a blockage can be removed is by the build up of pressure to the point at which the blockage is literally exploded out of the way. In reality, the weakest part of the volcano will be the part which gives way, sometimes leading to a sideways explosion as in the Mt St. Helens eruption.

When extraordinary levels of pressure develop, the resultant explosion can be devastating, producing an earthquake of considerable magnitude. When Krakatoa (Indonesia, between Java and Sumatra) exploded in 1883, the explosion was heard over 5000 km away in Australia. The shockwave's produced a series of tsunami (large sea waves), one of which was over 36 m high; that's the same as four, two story houses stacked on top of each other. These swept over the coastal areas of Java and Sumatra killing over 36,000 people. 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 doesn't build up, violent explosions do not occur. GROUND SHAKING Ground shaking is a term used to describe the vibration of the ground during an earthquake. Ground shaking is caused by body and surface seismic waves. As a generalization, the severity of ground shaking increases as magnitude increases and decreases as distance from the causative fault increases. Although the physics of seismic waves is complex, ground shaking can be explained in terms of body waves, compressional, or P, and shear, or S, and surface waves, Rayleigh and Love. P waves propagate through the Earth with a speed of about 15,000 miles per hour and are the first waves to cause vibration of a building.

S waves arrive next and cause a structure to vibrate from side to side. They are the most damaging waves, because buildings are more easily damaged from horizontal motion than from vertical motion. The P and S waves mainly cause high-frequency vibrations; whereas, Rayleigh and Love waves, which arrive last, mainly cause low-frequency vibrations. Body and surface waves cause the ground, and consequently a building, to vibrate in a complex manner. The objective of earthquake-resistant design is to construct a building so that it can withstand the ground shaking caused by body and surface waves. In land-use zoning and earthquake-resistant design, knowledge of the amplitude, frequency composition, and the time duration of ground shaking is needed.

These quantities can be determined from empirical data correlating them with the magnitude and the distribution of Modified Mercalli intensity of the earthquake, distance of the building from the causative fault, and the physical properties of the soil and rock underlying the building. The subjective numerical value of the Modified Mercalli Intensity Scale indicates the effects of ground shaking on man, buildings, and the surface of the Earth. When a fault ruptures, seismic waves are propagated in all directions, causing the ground to vibrate at frequencies ranging from about 0.1 to 30 Hertz. Buildings vibrate as a consequence of the ground shaking; damage takes place if the building cannot withstand these vibrations. Compressional and shear waves mainly cause high-frequency (greater than 1 Hertz) vibrations which are more efficient than low-frequency waves in causing low buildings to vibrate.

Rayleigh and Love waves mainly cause low-frequency vibrations which are more efficient than high-frequency waves in causing tall buildings to vibrate. Because amplitudes of low-frequency vibrations decay less rapidly than high-frequency vibrations as distance from the fault increases, tall buildings located at relatively great distances (60 miles) from a fault are sometimes damaged. SURFACE FAULTING Surface faulting -- the differential movement of the two sides of a fracture at the Earth's surface -- is of three general types: strike-slip, normal, and reverse. Combinations of the strike-slip type and the other two types of faulting can be found. Although displacements of these kinds can result from landslides and other shallow processes, surface faulting, as the term is used here, applies to differential movements caused by deep-seated forces in the Earth, the slow movement of sedimentary deposits toward the Gulf of Mexico, and faulting associated with salt domes.

Death and injuries from surface faulting are very unlikely, but casualties can occur indirectly through fault damage to structures. Surface faulting, in the case of a strike-slip fault, generally affects a long narrow zone whose total area is small compared with the total area affected by ground shaking. Nevertheless, the damage to structures located in the fault zone can be very high, especially where the land use is intensive. A variety of structures have been damaged by surface faulting, including houses, apartments, commercial buildings, nursing homes, railroads, highways, tunnels, bridges, canals, storm drains, water wells, and water, gas, and sewer lines.

Damage to these types of structures has ranged from minor to very severe. An example of severe damage occurred in 1952 when three railroad tunnels were so badly damaged by faulting that traffic on a major rail linking northern and southern California was stopped for 25 days despite an around-the-clock repair schedule. The displacements, lengths, and widths of surface fault ruptures show a wide range. Fault displacements in the United States have ranged from a fraction of an inch to more than 20 feet of differential movement. As expected, the severity of potential damage increases as the size of the displacement increases. The lengths of the surface fault ruptures on land have ranged from less than 1 mile to more than 200 miles.

Most fault displacement is confined to a narrow zone ranging from 6 to 1,000 feet in width, but separate subsidiary fault ruptures may occur 2 to 3 miles from the main fault. The area subject to disruption by surface faulting varies with the length and width of the rupture zone. GROUND FAILURE LIQUIFACTIONLiquefaction is not a type of ground failure; it is a physical process that takes place during some earthquakes that may lead to ground failure. As a consequence of liquefaction, clay-free soil deposits, primarily sands and silts, temporarily lose strength and behave as viscous fluids rather than as solids. Liquefaction takes place when seismic shear waves pass through a saturated granular soil layer, distort its granular structure, and cause some of the void spaces to collapse.

Disruptions to the soil generated by these collapses cause transfer of the ground-shaking load from grain-to-grain contacts in the soil layer to the pore water. This transfer of load increases pressure in the pore water, either causing drainage to occur or, if drainage is restricted, a sudden buildup of pore-water pressure. When the pore-water pressure rises to about the pressure caused by the weight of the column of soil, the granular soil layer behaves like a fluid rather than like a solid for a short period. In this condition, deformations can occur easily.

Liquefaction is restricted to certain geologic and hydrologic environments, mainly areas where sands and silts were deposited in the last 10,000 years and where ground water is within 30 feet of the surface. Generally, the younger and looser the sediment and the higher the water table, the more susceptible a soil is to liquefaction. Liquefaction causes three types of ground failure: lateral spreads, flow failures, and loss of bearing strength. In addition, liquefaction enhances ground settlement and sometimes generates sand boils (fountains of water and sediment emanating from the pressurized liquefied zone). Sand boils can cause local flooding and the deposition or accumulation of silt. Lateral Spreads - Lateral spreads involve the lateral movement of large blocks of soil as a result of liquefaction in a subsurface layer.

Movement takes place in response to the ground shaking generated by an earthquake. Lateral spreads generally develop on gentle slopes, most commonly on those between 0.3 and 3 degrees. Horizontal movements on lateral spreads commonly are as much as 10 to 15 feet, but, where slopes are particularly favorable and the duration of ground shaking is long, lateral movement may be as much as 100 to 150 feet. Lateral spreads usually break up internally, forming numerous fissures and scarps.

Damage caused by lateral spreads is seldom catastrophic, but it is usually disruptive. For example, during the 1964 Prince William Sound, Alaska, earthquake, more than 200 bridges were damaged or destroyed by lateral spreading of flood-plain deposits toward river channels. These spreading deposits compressed bridges over the channels, buckled decks, thrust sedimentary beds over abutments, and shifted and tilted abutments and piers. Lateral spreads are destructive particularly to pipelines. In 1906, a number of major pipeline breaks occurred in the city of San Francisco during the earthquake because of lateral spreading.

Breaks of water mains hampered efforts to fight the fire that ignited during the earthquake. Thus, rather inconspicuous ground-failure displacements of less than 7 feet were largely responsible for the devastation to San Francisco in 1906. Flow Failures - Flow failures, consisting of liquefied soil or blocks of intact material riding on a layer of liquefied soil, are the most catastrophic type of ground failure caused by liquefaction. These failures commonly move several tens of feet and, if geometric conditions permit, several tens of miles.

Flows travel at velocities as great as many tens of miles per hour. Flow failures usually form in loose saturated sands or silts on slopes greater than 3 degrees. Flow failures can originate either underwater or on land. Many of the largest and most damaging flow failures have taken place underwater in coastal areas.

For example, submarine flow failures carried away large sections of port facilities at Seward, Whittier, and Valdez, Alaska, during the 1964 Prince William Sound earthquake. These flow failures, in turn, generated large sea waves that overran parts of the coastal area, causing additional damage and casualties. Flow failures on land have been catastrophic, especially in other countries. For example, the 1920 Kansu, China, earthquake induced several flow failures as much as 1 mile in length and breadth, killing an estimated 200,000 people.

Loss of Bearing Strength - When the soil supporting a building or some other structure liquefies and loses strength, large deformations can occur within the soil, allowing the structure to settle and tip. The most spectacular example of bearing-strength failures took place during the 1964 Niigata, Japan, earthquake. During that event, several four-story buildings of the Kwangishicho apartment complex tipped as much as 60 degrees. Most of the buildings were later jacked back into an upright position, underpinned with piles, and reused. Soils that liquefied at Niigata typify the general subsurface geometry required for liquefaction-caused bearing failures: a layer of saturated, cohesion less soil (sand or silt) extending from near the ground surface to a depth of about the width of the building. LANDSLIDES Past experience has shown that several types of landslides take place in conjunction with earthquakes.

The most abundant types of earthquake induced landslides are rock falls and slides of rock fragments that form on steep slopes. Shallow debris slides forming on steep slopes and soil and rock slumps and block slides forming on moderate to steep slopes also take place, but they are less abundant. Reactivation of dormant slumps or block slides by earthquakes is rare. Large earthquake-induced rock avalanches, soil avalanches, and underwater landslides can be very destructive.

Rock avalanches originate on over-steepened slopes in weak rocks. One of the most spectacular examples occurred during the 1970 Peruvian earthquake when a single rock avalanche killed more than 18,000 people; a similar, but less spectacular, failure in the 1959 Hebben Lake, Montana, earthquake resulted in 26 deaths. Soil avalanches occur in some weakly cemented fine-grained materials, such as loess, that form steep stable slopes under non seismic conditions. Many loess slopes failed during the New Madrid, Missouri, earthquakes of 1811-12.

Underwater landslides commonly involve the margins of deltas where many port facilities are located. The failures at Seward, Alaska, during the 1964 earthquake are an example. The size of the area affected by earthquake-induced landslides depends on the magnitude of the earthquake, its focal depth, the topography and geologic conditions near the causative fault, and the amplitude, frequency composition, and duration of ground shaking. In past earthquakes, landslides have been abundant in some areas having intensities of ground shaking as low as VI on the Modified Mercalli Intensity Scale. TSUNAMIS Tsunamis are water waves that are caused by sudden vertical movement of a large area of the sea floor during an undersea earthquake.

Tsunamis are often called tidal waves, but this term is a misnomer. Unlike regular ocean tides, tsunamis are not caused by the tidal action of the Moon and Sun. The height of a tsunami in the deep ocean is typically about 1 foot, but the distance between wave crests can be very long, more than 60 miles. The speed at which the tsunami travels decreases as water depth decreases. In the mid-Pacific, where the water depths reach 3 miles, tsunami speeds can be more than 430 miles per hour. As tsunamis reach shallow water around islands or on a continental shelf; the height of the waves increases many times, sometimes reaching as much as 80 feet.

The great distance between wave crests prevents tsunamis from dissipating energy as a breaking surf; instead, tsunamis cause water levels to rise rapidly along coast lines. Tsunamis and earthquake ground shaking differ in their destructive characteristics. Ground shaking causes destruction mainly in the vicinity of the causative fault, but tsunamis cause destruction both locally and at very distant locations from the area of tsunami generation. Earthquakes release the pressure building up in the earths mantle and core. A small earthquake has the advantage of avoiding a larger one in certain instances. The threat of earthquakes has forced mankind to mitigate the effect of earthquakes since they cannot control them.

Improved building construction practices, improvements in emergency disaster relief measures examples of good that can come out of earthquakes. By: Anu pama K. V 'B'PRECAUTIONS TO BE TAKEN DURING AN EARTHQUAKE. If you are indoors during an earthquake, drop, cover, and hold on. Get under a desk, table or bench.

Hold on to one of the legs and cover your eyes. If there's no table or desk nearby, sit down against an interior wall. An interior wall is less likely to collapse than a wall on the outside shell of the building... Pick a safe place where things will not fall on you, away from windows, bookcases, or tall, heavy furniture... It is dangerous to run outside when an earthquake happens because bricks, roofing, and other materials may fall from buildings during and immediately following earthquakes, injuring persons near the building... Wait in your safe place until the shaking stops, then check to see if you are hurt.

You will be better able to help others if you take care of yourself first, then check the people around you... Move carefully and watch out for things that have fallen or broken, creating hazards. Be ready for additional earthquakes called 'aftershocks. '. Be on the lookout for fires. Fire is the most common earthquake related hazard, due to broken gas lines, damaged electrical lines or appliances, and previously contained fires or sparks being released...

If you must leave a building after the shaking stops, use the stairs, not the elevator. Earthquakes can cause fire alarms and fire sprinklers to go off. You will not be certain whether there is a real threat of fire. As a precaution, use the stairs...

If you are outside in an earthquake, stay outside. Move away from buildings, trees, streetlights, and power lines. Crouch down and cover your head. Many injuries occur within 10 feet of the entrance to buildings. Bricks, roofing, and other materials can fall from buildings, injuring persons nearby.

Trees, streetlights, and power lines may also fall, causing damage or injury... Assemble a Disaster Supplies Kit. Earthquake-specific supplies should include the following: A flashlight and sturdy shoes by each person's bedside; Disaster Supplies Kit; and an Evacuation Supply Kit. HOW TO PROTECT YOUR PROPERTY. Bolt bookcases, china cabinets, and other tall furniture to wall studs. Brace or anchor high or top-heavy objects.

During an earthquake, these items can fall over, causing damage or injury... Secure items that might fall (televisions, books, computers, etc. ). Falling items can cause damage or injury... Install strong latches or bolts on cabinets. The contents of cabinets can shift during the shaking of an earthquake.

Latches will prevent cabinets from flying open and contents from falling out... Move large or heavy objects and fragile items (glass or china) to lower shelves. There will be less damage and less chance of injury if these items are on lower shelves... Store breakable items such as bottled foods, glass, and china in low, closed cabinets with latches.

Latches will help keep contents of cabinets inside... Store weed killers, pesticides, and flammable products securely in closed cabinets with latches, on bottom shelves. Chemical products will be less likely to create hazardous situations from lower, confined locations... Hang heavy items, such as pictures and mirrors, away from beds, couches, and anywhere people sit.

Earthquakes can knock things off walls, causing damage or injury... Brace overhead light fixtures. During earthquakes, overhead light fixtures are the most common items to fall, causing damage or injury... Strap the water heater to wall studs. The water heater may be your best source of drinkable water following an earthquake.

Protect it from damage and leaks... Bolt down any gas appliances. After an earthquake, broken gas lines frequently create fire hazards... Install flexible pipe fittings to avoid gas or water leaks.

Flexible fittings will be less likely to break... Repair any deep cracks in ceilings or foundations. Get expert advice if there are signs of structural defects. Earthquakes can turn cracks into ruptures and make smaller problems bigger... Check to see if your house is bolted to its foundation. Homes bolted to their foundations are less likely to be severely damaged during earthquakes.

Homes that are not bolted have been known to slide off their foundations, and many have been destroyed because they are uninhabitable... Consider having your building evaluated by a professional structural design engineer. Ask about home repair and strengthening tips for exterior features, such as porches, front and back decks, sliding glass doors, canopies, carports, and garage doors. Learn about additional ways you can protect your home. A professional can give you advice on how to reduce potential damage. IMMEDIATE THINGS TO DO DURING AN EARTHQUAKE.

Drop, cover, and hold on! Move only a few steps to a nearby safe place. Most injured persons in earthquakes move more than five feet during the shaking. It is very dangerous to try to leave a building during an earthquake because objects can fall on you.

Many fatalities occur when people run outside of buildings, only to be killed by falling debris from collapsing walls. If you are in bed, hold on and stay there, protecting your head with a pillow. You are less likely to be injured staying where you are. Broken glass on the floor has caused injury to those who have rolled to the floor or tried to get to doorways...

If you are outdoors, find a clear spot away from buildings, trees, streetlights, and power lines. Drop to the ground and stay there until the shaking stops. Injuries can occur from falling trees, street-lights and power lines, or building debris... If you are in a vehicle, pull over to a clear location, stop and stay there with your seatbelt fastened until the shaking has stopped. Trees, power lines, poles, street signs, and other overhead items may fall during earthquakes. Stopping will help reduce your risk, and a hard-topped vehicle will help protect you from flying or falling objects.

Once the shaking has stopped, proceed with caution. Avoid bridges or ramps that might have been damaged by the quake... Stay indoors until the shaking stops and you are sure it is safe to exit. More injuries happen when people move during the shaking of an earthquake.

After the shaking has stopped, if you go outside, move quickly away from the building to prevent injury from falling debris... Stay away from windows. Windows can shatter with such force that you can be injured several feet away... In a high-rise building, expect the fire alarms and sprinklers to go off during a quake. Earthquakes frequently cause fire alarm and fire sprinkler systems to go off even if there is no fire. Check for and extinguish small fires, and, if exiting, use the stairs...

If you are in a coastal area, move to higher ground. Tsunamis are often created by earthquakes... If you are in a mountainous area or near unstable slopes or cliffs, be alert for falling rocks and other debris that could be loosened by the earthquake. Landslides commonly happen after earthquakes. WHAT TO DO AFTER AN EARTHQUAKE. Check yourself for injuries.

Often people tend to others without checking their own injuries. You will be better able to care for others if you are not injured or if you have received first aid for your injuries... Protect yourself from further danger by putting on long pants, a long-sleeved shirt, sturdy shoes, and work gloves. This will protect you from further injury by broken objects...

After you have taken care of yourself, help injured or trapped persons. If you have it in your area, base emergency, then give first aid when appropriate. Don't try to move seriously injured people unless they are in immediate danger of further injury... Look for and extinguish small fires. Eliminate fire hazards. Putting out small fires quickly, using available resources, will prevent them from spreading.

Fire is the most common hazard following earthquakes. Fires followed the San Francisco earthquake of 1906 for three days, creating more damage than the earthquake... Leave the gas on at the main valve, unless you smell gas or think it's leaking. It may be weeks or months before professionals can turn gas back on using the correct procedures.

Explosions have caused injury and death when homeowners have improperly turned their gas back on by themselves... Clean up spilled medicines, bleaches, gasoline, or other flammable liquids immediately. Avoid the hazard of a chemical emergency... Open closet and cabinet doors cautiously. Contents may have shifted during the shaking of an earthquake and could fall, creating further damage or injury...

Inspect your home for damage. Get everyone out if your home is unsafe. Aftershocks following earthquakes can cause further damage to unstable buildings. If your home has experienced damage, get out before aftershocks happen... Help neighbors who may require special assistance. Elderly people and people with disabilities may require additional assistance.

People who care for them or who have large families may need additional assistance in emergency situations... Listen to a portable, battery-operated radio (or television) for updated emergency information and instructions. If the electricity is out, this may be your main source of information. Local radio and local officials provide the most appropriate advice for your particular situation...

Expect aftershocks. Each time you feel one, drop, cover, and hold on! Aftershocks frequently occur minutes, days, weeks, and even months following an earthquake... Watch out for fallen power lines or broken gas lines, and stay out of damaged areas. Hazards caused by earthquakes are often difficult to see, and you could be easily injured... Stay out of damaged buildings.

If you are away from home, return only when authorities say it is safe. Damaged buildings may be destroyed by aftershocks following the main quake... Use battery-powered lanterns or flashlights to inspect your home. Kerosene lanterns, torches, candles, and matches may tip over or ignite flammables inside... Inspect the entire length of chimneys carefully for damage. Unnoticed damage could lead to fire or injury from falling debris during an aftershock.

Cracks in chimneys can be the cause of a fire years later... Take pictures of the damage, both to the house and its contents, for insurance claims... Avoid smoking inside buildings. Smoking in confined areas can cause fires... When entering buildings, use extreme caution. Building damage may have occurred where you least expect it.

Carefully watch every step you take... Examine walls, floor, doors, staircases, and windows to make sure that the building is not in danger of collapsing... Check for gas leaks. If you smell gas or hear a blowing or hissing noise, open a window and quickly leave the building.

Turn off the gas, using the outside main valve if you can, and call the gas company from a neighbor's home. If you turn off the gas for any reason, it must be turned back on by a professional... Look for electrical system damage. If you see sparks or broken or frayed wires, or if you smell burning insulation, turn off the electricity at the main fuse box or circuit breaker. If you have to step in water to get to the fuse box or circuit breaker, call an electrician first for advice... Check for sewage and water line 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. You can obtain safe water from undamaged water heaters or by melting ice cubes... Watch for loose plaster, dry wall, and ceilings that could fall... Use the telephone only to report life-threatening emergencies.

Telephone lines are frequently overwhelmed in disaster situations. They need to be clear for emergency calls to get through... Watch animals closely. Leash dogs and place them in a fenced yard. The behavior of pets may change dramatically after an earthquake. Normally quiet and friendly cats and dogs may become aggressive or defensive.