Earthquakes can be measured in several ways, two of which are intensity and magnitude. Intensity measures damage to the surface and the effects on humans. The scale used to measure intensity is called the Modified Mercalli Intensity Scale. Magnitude does not depend on population and effects to ground structures, but rather on wave amplitude and distance from the epicentre. This measure uses formulas and seismograph information to determine the magnitude.
The scale used to measure magnitude is the Richter scale. Although each earthquake has a unique magnitude, its effects will vary greatly according to distance, ground conditions, standards, and other factors. Depending on the size, nature, and location of an earthquake, seismologists use several different methods to estimate magnitude. The uncertainty in an estimate of the magnitude is about plus or minus 0.3 units, and seismologists often revise magnitude estimates as they obtain and analyze additional data.
Richter magnitudes and earthquake effects:
Less than 3.5
Generally not felt, but recorded.
3.5 - 5.4
often felt, but rarely causes damage.
Fewer than 6.0
At most slight damage to well-designed buildings.
Can cause major damage to poorly constructed buildings.
6.1 - 6.9
Can be destructive in areas up to about 100 kilometres across where people live.
7.0 - 7.9
Major earthquake. Can cause serious damage over large areas.
8 or greater
Great earthquake. Can cause serious damage in areas several hundred kilometres across.
Are you ready for the next big one?
Earthquakes in California are common occurrences as the state is located on the , which cuts across and forms the boundary between the and the American Plate. There are many thousands of small per year; most of them are so small that they are not felt. California's complex and interesting landscape can be attributed to the network of faulting that runs underneath the state. The earliest reported earthquake in California was felt in 1769 by the about 30 miles southeast of , probably near the San Andreas Fault. Here is a fault line map-
The town of Park field in central California is located on a section of the San Andreas Fault that produces an earthquake of about magnitude 6 every 20-30 years on average in 1857, 1881, 1901, 1922, 1934, 1966 and 2004.
The largest recorded earthquake in California was the , with an estimated magnitude of 8.0. This earthquake ruptured the San Andreas Fault from Park field to Wrightwood, a distance of 225 miles (350 km). The most destructive earthquake to date was the 7.9 magnitude , in which over 3000 people perished in the earthquake and the fires that followed. The 1906 quake ruptured the northern segment of the San Andreas Fault for 296 miles (477 km), from to near in the north. More recently, the , which affected the , and the which hit the Greater Los Angeles area, caused widespread damage and deaths in their respective regions.
It is claimed again that in San Francisco in California could experience a very strong earthquake of 6.7 or higher on the Richter scale within the next 30 years. It’s also claimed that it’s likely to strike highly populated part of the area.
How earthquakes can change people like
Earthquakes can affect the lives of humans all across the world. This type of natural disaster can upset everything from small towns to huge metropolises.
- Earthquakes affect people by making them stressed out and worried. It can cause them to have trust issues and live in fear. If they've been in a major earthquake and lost their home or their possessions they may always be afraid when there is a slight tremor.
- Some earthquakes will result in a fire that exceeds simple damage to the foundation of a building or home, but can reduce establishments to ash. If one doesn't have insurance, a fire as a result of an earthquake would leave them without a home or possessions.
- During an earthquake at sea, tsunamis are created come into contact with the land with devastating results. The tsunami in the Indian Ocean in 2004 which claimed an estimated 230,000 lives in seven countries is a prime example. For years after the incident, people still had no homes or anything in their name. Moreover, the stagnant flood waters provided the means for disease and infection.
- A sudden earthquake can destabilize slopes causing a landslide. Everyone can be buried alive, and houses are immediately surrounded. Rebuilding on an environment after a sizable landslide can be impossible.
- It will also cause casualties when unfortunate people did not have enough time to evacuate from their homes or did not know there was an earthquake. They could be killed by collapsing houses, which will also cost the people a lot of money to rebuild their homes.
- However, there might be hygiene problems as many people are crammed into a small space, which may in turn cause viruses to spread.
- Many properties and infrastructure might be lost and the government will have to fork out a huge sum of money to assist in rebuilding, which may in turn cause a cripple economy.
Reducing an earthquake damage
Seismic retrofitting is the modification of existing to make them more resistant to , ground motion, or failure due to . With better understanding of seismic demand on structures and with our recent experiences with large earthquakes near urban centres, the need of seismic retrofitting is well acknowledged.
Where to build
Earth scientists try to identify areas that would likely suffer great damage during an earthquake. They develop maps that show fault zones, flood plains (areas that get flooded), areas subject to landslides or to soil liquefaction, and the sites of past earthquakes. From these maps, land-use planners develop zoning restrictions that can help prevent construction of unsafe structures in earthquake-prone areas.
How to build
Engineers have developed a number of ways to build earthquake-resistant structures. Their techniques range from extremely simple to fairly complex. For small- to medium-sized buildings, the simpler reinforcement techniques include bolting buildings to their foundations and providing support walls called shear walls. Shear walls, made of reinforced concrete (concrete with steel rods or bars embedded in it), help strengthen the structure and help resist rocking forces. Shear walls in the centre of a building, often around an elevator shaft or stairwell, form what is called a shear core. Walls may also be reinforced with diagonal steel beams in a technique called cross-bracing.
Builders also protect medium-sized buildings with devices that act like shock absorbers between the building and its foundation. These devices, called base isolators, are usually bearings made of alternate layers of steel and an elastic material, such as synthetic rubber. Base isolators absorb some of the sideways motion that would otherwise damage a building.
Skyscrapers need special construction to make them earthquake-resistant. They must be anchored deeply and securely into the ground. They need a reinforced framework with stronger joints than an ordinary skyscraper has. Such a framework makes the skyscraper strong enough and yet flexible enough to withstand an earthquake.
Earthquake-resistant homes, schools, and workplaces have heavy appliances, furniture, and other structures fastened down to prevent them from toppling when the building shakes. Gas and water lines must be specially reinforced with flexible joints to prevent breaking.
Self preparedness
What to do before and earthquake?
Earthquakes strike suddenly, violently and without warning. Identifying potential hazards ahead of time and advance planning can reduce the dangers of serious injury or loss of life from an earthquake. Repairing deep plaster cracks in ceilings and foundations, anchoring overhead lighting fixtures to the ceiling, and following local seismic building standards, will help reduce the impact of earthquakes.
Six Ways to Plan Ahead
- Check for Hazards in the Home
- Fasten shelves securely to walls.
- Place large or heavy objects on lower shelves.
- Store breakable items such as bottled foods, glass, and china in low, closed cabinets with latches.
- Hang heavy items such as pictures and mirrors away from beds, couches, and anywhere people sit.
- Brace overhead light fixtures.
- Repair defective electrical wiring and leaky gas connections. These are potential fire risks.
- Secure a water heater by strapping it to the wall studs and bolting it to the floor.
- Repair any deep cracks in ceilings or foundations. Get expert advice if there are signs of structural defects.
- Store weed killers, pesticides, and flammable products securely in closed cabinets with latches and on bottom shelves.
- Identify Safe Places Indoors and Outdoors
- Under sturdy furniture such as a heavy desk or table.
- Against an inside wall.
- Away from where glass could shatter around windows, mirrors, pictures, or where heavy bookcases or other heavy furniture could fall over.
- In the open, away from buildings, trees, telephone and electrical lines, overpasses, or elevated expressways.
- Educate Yourself and Family Members
- Contact your local emergency management office or American Red Cross chapter for more information on earthquakes. Also read the "How-To Series" for information on how to protect your property from earthquakes.
- Teach children how and when to call 9-1-1, police, or fire department and which radio station to tune to for emergency information.
- Teach all family members how and when to turn off gas, electricity, and water.
- Have Disaster Supplies on Hand
- Flashlight and extra batteries.
- Portable battery-operated radio and extra batteries.
- First aid kit and manual.
- Emergency food and water.
- Nonelectric can opener.
- Essential medicines.
- Cash and credit cards.
- Sturdy shoes.
- Develop an Emergency Communication Plan
- In case family members are separated from one another during an earthquake (a real possibility during the day when adults are at work and children are at school), develop a plan for reuniting after the disaster.
- Ask an out-of-state relative or friend to serve as the "family contact." After a disaster, it's often easier to call long distance. Make sure everyone in the family knows the name, address, and phone number of the contact person.
- Help Your Community Get Ready
- Publish a special section in your local newspaper with emergency information on earthquakes. Localize the information by printing the phone numbers of local emergency services offices, the American Red Cross, and hospitals.
- Conduct a week-long series on locating hazards in the home.
- Work with local emergency services and American Red Cross officials to prepare special reports for people with mobility impairments on what to do during an earthquake.
- Provide tips on conducting earthquake drills in the home.
- Interview representatives of the gas, electric, and water companies about shutting off utilities.
- Work together in your community to apply your knowledge to building codes, retrofitting programs, hazard hunts, and neighbourhood and family emergency plans.
What to do during and earthquake?
Stay as safe as possible during an earthquake. Be aware that some earthquakes are actually foreshocks and a larger earthquake might occur. Minimize your movements to a few steps to a nearby safe place and if you are indoors, stay there until the shaking has stopped and you are sure exiting is safe.
If indoors
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DROP to the ground; take COVER by getting under a sturdy table or other piece of furniture; and HOLD ON until the shaking stops. If there isn’t a table or desk near you, cover your face and head with your arms and crouch in an inside corner of the building.
- Stay away from glass, windows, outside doors and walls, and anything that could fall, such as lighting fixtures or furniture.
- Stay in bed if you are there when the earthquake strikes. Hold on and protect your head with a pillow, unless you are under a heavy light fixture that could fall. In that case, move to the nearest safe place.
- Use a doorway for shelter only if it is in close proximity to you and if you know it is a strongly supported, load bearing doorway.
- Stay inside until the shaking stops and it is safe to go outside. Research has shown that most injuries occur when people inside buildings attempt to move to a different location inside the building or try to leave.
- Be aware that the electricity may go out or the sprinkler systems or fire alarms may turn on.
- DO NOT use the elevators.
If outdoors
- Stay there.
- Move away from buildings, streetlights, and utility wires.
- Once in the open, stay there until the shaking stops. The greatest danger exists directly outside buildings, at exits and alongside exterior walls. Many of the 120 fatalities from the 1933 Long Beach earthquake occurred when people ran outside of buildings only to be killed by falling debris from collapsing walls. Ground movement during an earthquake is seldom the direct cause of death or injury. Most earthquake-related casualties result from collapsing walls, flying glass, and falling objects.
If in a moving vehicle
- Stop as quickly as safety permits and stay in the vehicle. Avoid stopping near or under buildings, trees, overpasses, and utility wires.
- Proceed cautiously once the earthquake has stopped. Avoid roads, bridges, or ramps that might have been damaged by the earthquake.
If trapped under trash
- Do not light a match.
- Do not move about or kick off dust.
- Cover your mouth with a handkerchief or clothing.
- Tap on a pipe or wall so rescuers can locate you. Use a whistle if one is available. Shout only as a last resort. Shouting can cause you to inhale dangerous amounts of dust.
What to Do After an Earthquake
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Expect aftershocks. These secondary shockwaves are usually less violent than the main quake but can be strong enough to do additional damage to weakened structures and can occur in the first hours, days, weeks, or even months after the quake.
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Listen to a battery-operated radio or television. Listen for the latest emergency information.
- Use the telephone only for emergency calls.
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Open cabinets cautiously. Beware of objects that can fall off shelves.
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Stay away from damaged areas. Stay away unless your assistance has been specifically requested by police, fire, or relief organizations. Return home only when authorities say it is safe.
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Be aware of possible tsunamis if you live in coastal areas. These are also known as seismic sea waves (mistakenly called "tidal waves"). When local authorities issue a tsunami warning, assume that a series of dangerous waves is on the way. Stay away from the beach.
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Help injured or trapped persons. Remember to help your neighbours who may require special assistance such as infants, the elderly, and people with disabilities. Give first aid where appropriate. Do not move seriously injured persons unless they are in immediate danger of further injury. Call for help.
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Clean up spilled medicines, bleaches, gasoline or other flammable liquids immediately. Leave the area if you smell gas or fumes from other chemicals.
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Inspect the entire length of chimneys for damage. Unnoticed damage could lead to a fire.
- Inspect utilities.
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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 and call the gas company from a neighbour’s home. If you turn off the gas for any reason, it must be turned back on by a professional.
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Look for electrical system damage. If you see sparks or broken or frayed wires, or if you smell hot 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.
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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. You can obtain safe water by melting ice cubes.
Last Advice-always prepare for an earthquake!