EFFECTS OF EARTHQUAKE IN THE COMMUNITY

 EFFECTS OF EARTHQUAKE IN COMMUNITY 

MARCH 21,2022

    An earthquake is an intense shaking of Earth’s surface. The shaking is caused by movements in Earth’s outermost layer. Earthquake, any sudden shaking of the ground caused by the passage of seismic waves through Earth’s rocks. Seismic waves are produced when some form of energy stored in Earth’s crust is suddenly released, usually when masses of rock straining against one another suddenly fracture and “slip.” Earthquakes occur most often along geologic faults, narrow zones where rock masses move in relation to one another. The major fault lines of the world are located at the fringes of the huge tectonic plates that make up Earth’s crust. (See the table of major earthquakes.) Earthquakes are caused by sudden tectonic movements in the Earth's crust. The main cause is that when tectonic plates, one rides over the other, causing orogeny collide (mountain building), earthquakes. The largest fault surfaces on Earth are formed due to boundaries between moving plates.

                          Why Do Earthquakes Happen? 

    Although the Earth looks like a pretty solid place from the surface, it’s actually extremely active just below the surface. The Earth is made of four basic layers: a solid crust, a hot, nearly solid mantle, a liquid outer core and a solid inner core.

    A diagram of Earth's layers. Earthquakes are caused by shifts in the outer layers of Earth—a region called the lithosphere.

    The solid crust and top, stiff layer of the mantle make up a region called the lithosphere. The lithosphere isn’t a continuous piece that wraps around the whole Earth like an eggshell. It’s actually made up of giant puzzle pieces called tectonic plates. Tectonic plates are constantly shifting as they drift around on the viscous, or slowly flowing, mantle layer below.

                        

                                  WHAT ARE THE EFFECTS OF AN EARTHQUAKE 

Ground Shaking

    Ground shaking is a term used to describe the vibration of the ground during an earthquake. Ground shaking is caused by body waves and surface 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 waves 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 (observed) 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 waves 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.

    Taken from: Hays, W.W., ed., 1981, Facing Geologic and Hydrologic Hazards -- Earth Science Considerations: U.S. Geological Survey Professional Paper 1240B, 108 p. 

Surface Faulting

    Surface faulting is the differential movement of the two sides of a fracture at the Earth's surface and can be strike-slip, normal, and reverse (or thrust). 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.

    Taken from: Hays, W.W., ed., 1981, Facing Geologic and Hydrologic Hazards --Earth Science Considerations: U.S. Geological Survey Professional Paper 1240B, 108 p.

Ground Failure

Liquefaction Induced

    Liquefaction 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, cohesionless soil (sand or silt) extending from near the ground surface to a depth of about the width of the building.

Taken from: Hays, W.W., ed., 1981, Facing Geologic and Hydrologic Hazards -- Earth Science Considerations: U.S. Geological Survey Professional Paper 1240B, 108 p.

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 Hebgen 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.

Taken from: Hays, W.W., ed., 1981, Facing Geologic and Hydrologic Hazards -- Earth Science Considerations: U.S. Geological Survey Professional Paper 1240B, 108 p.

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.

HOW TO MITIGATE EARTHQUAKE DAMAGE

    The shaking from a major earthquake can shake and shift almost everything inside your home. According to a UCLA study, the majority of the injuries from the damaging 1994 Northridge earthquake were from heavy furniture and household objects falling on people.

    To prepare for next earthquake, evaluate the safety of your home. Your home safety review ranks high on your earthquake preparation checklist, after preparing your earthquake safety kit and gathering essential supplies. Keep your family safe and prevent the injury of your loved ones by being prepared.

Personal Preparedness Guidelines

    Earthquakes produce sudden, rapid shaking of the earth caused by the shifting of rock beneath the earth’s surface. Earthquakes strike without warning, at any time of year, day or night. Avoid earthquake damage and injury.

    Prepare now for your family’s safety and recovery from a devastating earthquake. Create an earthquake safety plan. Practice Drop, Cover, and Hold On.

    

Stay Safe During an Earthquake

     

      Drop. Cover. Hold on.

In most situations, you can protect yourself if you immediately:

• DROP down onto your hands and knees before the earthquake knocks you down. This position protects you from falling but allows you to still move if necessary.
• COVER your head and neck (and your entire body if possible) underneath a sturdy table or desk. If there is no shelter nearby, get down near an interior wall or next to low-lying furniture that won’t fall on you, and cover your head and neck with your arms and hands.
• HOLD ON to your shelter (or to your head and neck) until the shaking stops. Be prepared to move with your shelter if the shaking shifts it around.

    

   If you are inside, stay inside.

DO NOT run outside or to other rooms during an earthquake. You are less likely to be injured if you stay where you are.

To reduce your chances of being hurt, take the following actions:

• If possible, within the few seconds before shaking intensifies, quickly move away from glass, hanging objects, bookcases, china cabinets, or other large furniture that could fall. Watch for falling objects, such as bricks from fireplaces and chimneys, light fixtures, wall hangings, high shelves, and cabinets with doors that could swing open.
• If available nearby, grab something to shield your head and face from falling debris and broken glass.
• If you are in the kitchen, quickly turn off the stove and take cover at the first sign of shaking.
• 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 can cause injuries if you walk or roll onto the floor.

    DO NOT stand in a doorway. You are safer under a table. In modern houses, doorways are no stronger than any other part of the house. Doorways do not protect you from the most likely source of injury − falling or flying objects. Most earthquake-related injuries and deaths are caused by falling or flying objects (such as TVs, lamps, glass, or bookcases), or by being knocked to the ground.

If you are in a high-rise building, drop, cover, and hold on.

• Move away from windows and outside walls.
• Stay in the building.
• DO NOT use the elevators. The electricity may go out, and the sprinkler systems may come on.
• If you are trapped, stay calm. Try to get someone’s attention by tapping on hard or metal parts of the structure. Doing so may increase your chances of being rescued.

If you are inside a crowded place, drop, cover, and hold on.

• Do not rush for the doorways. Others will have the same idea.
• Move away from display shelves containing objects that may fall.
• If you can, take cover and grab something to shield your head and face from falling debris and glass.

If you are outside, stay outside.

Stay inside if you are inside and outside if you are outside.

• Move away from buildings, utility wires, sinkholes, and fuel and gas lines. The greatest danger from falling debris is just outside doorways and close to outer walls of buildings.
• Go to an open area away from trees, telephone poles, and buildings. Once in the open, get down low and stay there until the shaking stops.
• The area near the outside walls of a building is the most dangerous place to be. Windows, facades, and architectural details are often the first parts of the building to collapse. Stay away from this danger zone.

If you are in a moving vehicle, stop as quickly and safely as possible.

• Move your car to the shoulder or curb, away from utility poles, overhead wires, and under- or overpasses.
• Stay in the car and set the parking brake. A car may jiggle violently on its springs, but it is a good place to stay until the shaking stops.
• Turn on the radio for emergency broadcast information.
• If a power line falls on the car, stay inside until a trained person removes the wire.
• When it is safe to begin driving again, watch for hazards created by the earthquake, such as breaks in the pavement, downed utility poles and wires, rising water levels, fallen overpasses, or collapsed bridges.

If you are in a stadium or theater, stay in your seat. Protect your head and neck with your arms or any way possible.

• Do not leave until the shaking is over.
• Walk out carefully watching for anything that could fall during the aftershocks.

If you are near the shore, drop, cover, and hold on until the shaking stops.

• If severe shaking lasts 20 seconds or more, immediately evacuate to high ground as a tsunami might have been generated by the earthquake.
• Move inland 2 miles (3 kilometers) or to land that is at least 100 feet (30 meters) above sea level immediately. Don’t wait for officials to issue a warning.
• Walk quickly, rather than drive, to avoid traffic, debris, and other hazards.

If you cannot drop to the ground, try to sit or remain seated so you are not knocked down.

• If you are in a wheelchair, lock your wheels. Remove any items that are not securely attached to the wheelchair.
• Protect your head and neck with a large book, a pillow, or your arms. The goal is to prevent injuries from falling down or from objects that might fall or be thrown at you.
• If you are able, seek shelter under a sturdy table or desk. Stay away from outer walls, windows, fireplaces, and hanging objects.
• If you are unable to move from a bed or chair, protect yourself from falling objects by covering up with blankets and pillows.
• If you are outside, go to an open area away from trees, telephone poles, and buildings, and stay there.
• For more resources for people with impaired mobility and other access and functional needs,