Earthquake

What is an earthquake and what causes them to happen?

An earthquake is caused by a sudden slip on a fault. Stresses in the earth's outer layer push the sides of the fault together. Stress builds up and the rocks slips suddenly, releasing energy in waves that travel through the earth's crust and cause the shaking that we feel during an earthquake. An EQ occurs when plates grind and scrape against each other. In California there are two plates the Pacific Plate and the North American Plate. The Pacific Plate consists of most of the Pacific Ocean floor and the California Coast line. The North American Plate comprises most the North American Continent and parts of the Atlantic Ocean floor. These primary boundary between these two plates is the San Andreas Fault. The San Andreas Fault is more than 650 miles long and extends to depths of at least 10 miles. Many other smaller faults like the Hayward (Northern California) and the San Jacinto (Southern California) branch from and join the San Andreas Fault Zone. The Pacific Plate grinds northwestward past the North American Plate at a rate of about two inches per year. Parts of the San Andreas Fault system adapt to this movement by constant "creep" resulting in many tiny shocks and a few moderate earth tremors. In other areas where creep is NOT constant, strain can build up for hundreds of years, producing great EQs when it finally releases.

Earthquake Facts & Statistics

Fact Sheet 01: Frequency of Occurrence of Earthquakes

Descriptor	Magnitude	Average Annually
Great	8 and higher	1 Â¹
Major	7 - 7.9	17 Â²
Strong	6 - 6.9	134 Â²
Moderate	5 - 5.9	1319 Â²
Light	4 - 4.9	13,000 (estimated)
Minor	3 - 3.9	130,000 (estimated)
Very Minor	2 - 2.9	1,300,000 (estimated)
Â¹ Based on observations since 1900. Â² Based on observations since 1990.

Fact Sheet 02: Year-wise description of Earth Quakes

Number of Earthquakes Worldwide for 2000 - 2005. Located by the US Geological Survey National Earthquake Information Center
Magnitude	2000	2001	2002	2003	2004	2005
8.0 to 9.9	1	1	0	1	2	1
7.0 to 7.9	14	15	13	14	14	9
6.0 to 6.9	158	126	130	140	140	116
5.0 to 5.9	1345	1243	1218	1203	1509	1307
4.0 to 4.9	8045	8084	8584	8462	10894	10264
3.0 to 3.9	4784	6151	7005	7624	7937	5782
2.0 to 2.9	3758	4162	6419	7727	6317	3249
1.0 to 1.9	1026	944	1137	2506	1344	20
0.1 to 0.9	5	1	10	134	103	0
No Magnitude	3120	2938	2937	3608	2939	642

Total	22256	23534	27454	31419	* 31199	* 21390

Estimated Deaths	231	21357	1685	33819	284010	1957

Fact Sheet 03: Largest Earthquakes in the World Since 1900

Location	Date UTC	Magnitude	Coordinates		Reference
1.	Chile	1960 05 22	9.5	-38.24	-73.05
2.	Prince William Sound, Alaska	1964 03 28	9.2	61.02	-147.65
3.	Off the West Coast of Northern Sumatra	2004 12 26	9.0	3.30	95.78
4.	Kamchatka	1952 11 04	9.0	52.76	160.06
5.	Off the Coast of Ecuador	1906 01 31	8.8	1.0	-81.5
6.	Northern Sumatra, Indonesia	2005 03 28	8.7	2.08	97.01
7.	Rat Islands, Alaska	1965 02 04	8.7	51.21	178.50
8.	Andrean of Islands, Alaska	1957 03 09	8.6	51.56	-175.39
9.	Assam - Tibet	1950 08 15	8.6	28.5	96.5
10.	Kuril Islands	1963 10 13	8.5	44.9	149.6
11.	Banda Sea, Indonesia	1938 02 01	8.5	-5.05	131.62
12.	Chile-Argentina Border	1922 11 11	8.5	-28.55	-70.50

Fact Sheet 04: Largest and Deadliest Earthquakes by Year 1990 - 2005

	Largest Earthquakes				Deadliest Earthquake
Year	Date	Magnitude	Fatalities	Region	Date	Magnitude	Fatalities	Region
2005	03/28	8.7	1,313	Northern Sumatra, Indonesia	03/28	8.7	1,313	Northern Sumatra, Indonesia
2004	12/26	9.0	283,106	Off West Coast of Northern Sumatra	12/26	9.0	283,106	Off West Coast of Northern Sumatra
2003	09/25	8.3	0	Hokkaido, Japan Region	12/26	6.6	31,000	Southeastern Iran
2002	11/03	7.9	0	Central Alaska	03/25	6.1	1,000	Hindu Kush Region, Afghanistan
2001	06/23	8.4	138	Near Coast of Peru	01/26	7.7	20,023	India
2000	11/16	8.0	2	New Ireland Region, P.N.G.	06/04	7.9	103	Southern Sumatera, Indonesia
1999	09/20	7.7	2,297	Taiwan	08/17	7.6	17,118	Turkey
1998	03/25	8.1	0	Balleny Islands Region	05/30	6.6	4,000	Afghanistan-Tajikistan Border Region
1997	10/14	7.8	0	South of Fiji Islands	05/10	7.3	1,572	Northern Iran
	12/05	7.8	0	Near East Coast of Kamchatka
1996	02/17	8.2	166	Irian Jaya Region Indonesia	02/03	6.6	322	Yunnan, China
1995	07/30	8.0	3	Near Coast of Northern Chile	01/16	6.9	5,530	Kobe, Japan
	10/09	8.0	49	Near Coast of Jalisco Mexico
1994	10/04	8.3	11	Kuril Islands	06/20	6.8	795	Colombia
1993	08/08	7.8	0	South of Mariana Islands	09129	6.2	9,748	India
1992	12/12	7.8	2,519	Flores Region, Indonesia	12/12	7.8	2,519	Flores Region, Indonesia
1991	04/22	7.6	75	Costa Rica	10/19	6.8	2,000	Northern India
	12/22	7.6	0	Kuril Islands
1990	07/16	7.7	1,621	Luzon, Philippine Islands	06/20	7.4	50,000	Iran

Fact Sheet 05: List of Some Significant Earthquakes in India

Date	Epicenter		Location	Magnitude
	Lat( Deg N )	Long( Deg E )
1819 Jun 16	23.6	68.6	Kutch,Gujarat	8.0
1869 Jan 10	25	93	Near Cachar, Assam	7.5
1885 May 30	34.1	74.6	Sopor, J&K	7.0
1897 Jun 12	26	91	Shillongplateau	8.7
1905 Apr 04	32.3	76.3	Kangra, H.P	8.0
1918 Jul 08	24.5	91.0	Srimangal, Assam	7.6
1930 Jul 02	25.8	90.2	Dhubri, Assam	7.1
1934jan 15	26.6	86.8	Bihar-Nepalborder	8.3
1941 Jun 26	12.4	92.5	Andaman Islands	8.1
1943 Oct 23	26.8	94.0	Assam	7.2
1950 Aug 15	28.5	96.7	Arunachal Pradesh-China Border	8.5
1956 Jul 21	23.3	7.0	Anjar, Gujarat	7.0
1967 Dec 10	17.37	73.75	Koyna, Maharashtra	6.5
1975 Jan 19	32.38	78.49	Kinnaur, Hp	6.2
1988 Aug 06	25.13	95.15	Manipur-Myanmar Border	6.6
1988 Aug 21	26.72	86.63	Bihar-Nepal Border	6.4
1991 Oct 20	30.75	78.86	Uttarkashi, Up Hills	6.6
1993 Sep 30	18.07	76.62	Latur - Osmanabad, Maharashtra	6.3
1997 May 22	23.08	80.06	Jabalpur, MP	6.0
1999 Mar 29	30.41	79.42	Champoli, UP	6.8
2001 Jan 26	23.40	70.28	Bhuj, Gujarat	6.9

Fact Sheet 06: Seismic Zonation Map of India

Seismic Zonation map of a country is a guide to the seismic status of a region and its susceptibility to earthquakes. India has been divided into five zones with respect to severity of earthquakes. Of these, zone v is seismically the most active where earthquakes of magnitude 8 or more could occur recent strong motion observations around the world have revolutionized thinking on the design of engineering structures, placing emphasis also on the characteristics of the structures themselves it should be realized that in the case of shield type earthquakes, historic data are insufficient to define zones because recurrence intervals are much longer than the recorded human history this may often give a false sense of security. Occurrence of the damaging earthquake at Latur, falling in zone I is a typical example of this situation.

Source: http://earthquake.usgs.gov/hazards/

Earthquake Preparedness

Q: During an Earth Quake (EQ), should you head for the doorway?

Ans: Yes, only if you live in an old, unreinforced adobe. In modern homes, doorways are no stronger than any other parts of the house and usually have doors that will swing and can injure you. You are safer practicing the duck, cover, and hold under a sturdy piece of furniture.

Q: What emergency supplies do I need?

Ans:

Fire extinguisher
Adequate supplies of medications that you or family members are taking.
Crescent and pipe wrenches to turn off gas and water supplies.
First-aid kit and handbook.
Flashlights with extra bulbs and batteries.
Portable radio with extra batteries.
Water for each family member for at least 3 days (allow at least 1 gallon per person per day) and purification tablets or chlorine bleach to purify drinking water from other sources.
Canned and package foods, enough for several days and MECHANICAL can opener. Extra food for pets if necessary.
Camp stove or barbecue to cook on outdoors (store fuel out of the reach of children).
Waterproof, heavy-duty plastic bags for waste disposal.

Q: How can I plan ahead for an Earth Quake?

Ans:

Make sure each member of your family knows what to do no matter where they are when EQs occur:

Establish a meeting place where you can all reunite afterward.
Find out about EQ plans developed by children's school or day care.
Remember transportation may be disrupted, keep some emergency supplies--food, liquids, and comfortable shoes, for example--at work.

Know where you gas, electric and water main shutoffs are and how to turn them off if there is a leak or electrical short. Make sure older members of the family can shut off utilities.
Locate your nearest fire and police stations and emergency medical facility.
Talk to your neighbors--how could they help you, or you them after an EQ.
Take Red Cross First Aid and CPR Training Course.

Q: What should I do during an EQ?

Ans:

If you are indoors--stay there! (Get under a desk or table and hang on to it, or move into a hallway or get against an inside wall. Stay clear of windows, fireplaces, and heavy furniture or appliances. Get out of the kitchen, which is a dangerous place (things can fall on you). Do not run downstairs or rush outside while the building is shaking or while there is danger of falling and hurting yourself or being hit by falling glass or debris.
If you are outside--, get into the open, away from building, power lines, chimneys, and anything else that might fall on you.
If you are driving--stop, but carefully. Move your car as far out of traffic as possible. Do not stop on or under a bridge or overpass or under trees, light posts, power lines, or signs. Stay inside your car until the shaking stops. When you resume driving watch for breaks in the pavement, fallen rocks, and bumps in the road at bridge approaches.
If you are in a mountainous area--watch out for falling rock, landslides, trees, and other debris that could be loosened by quakes.

Q: Things Not to do during an EQ?

Ans:

Do not turn on the gas again if you turned it off; let the gas company do it.
Do not use matches, lighters, camp stoves or barbecues, electrical equipment, appliances until you are sure there are no gas leaks. They may create a spark that could ignite leaking gas and cause an explosion and fire.
Do not use your telephone, except for a medical or fire emergency. You could tie up the lines needed for emergency response. If the phone doesn't work send someone for help.
Do not expect firefighters, police or paramedics to help you. They may not be available.

Q: What can I expect in my house when an EQ occurs? How do I identify it? What can be done?

Ans: The contents of your home may be damaged and can be dangerous:

Shaking can make light fixtures fall, refrigerators and other large items move across the floor, and bookcases and television sets topple over. Identify: Look around your house for things that could fall or move.
Ask yourself if your cupboard doors fly open (allowing dishes to shatter on the floor)

What Can Be Done: You can install door latches, braces and fasteners to fix most of these hazards yourself.

Q: What do I do after an earthquake?

Ans:

Wear sturdy shoes to avoid injury from broken glass and debris. Expect aftershocks.
Check for injuries (if a person is bleeding, put direct pressure on the wound, use clean gauze or cloth if available; If a person is not breathing administer CPR; Do not attempt to move seriously injured persons unless they are in further danger of injury; cover injured persons with blankets to keep warm; seek medical help for serious injuries.
Check for hazards (Fire hazards--put out fires in your home or neighborhood immediately, call for help; Gas leaks--shut off main gas valve only if you suspect a leak because of broken pipes or odor; Damaged electrical wiring--Shut off power at the control box if there is any danger to house wiring; Downed or damaged utility lines--do not touch downed power lines or any objects in contact with them; spills--clean up any spilled medicines, drugs, or other harmful materials such as bleach, lye, gas; downed or damaged chimneys--Approach with caution--don't use damaged chimney (it could start fire or let poisonous gases into your house; fallen items--beware of items tumbling off shelves when you open doors of closets and cupboards; (4) check food and water supplies--Do not eat or drink anything from open containers near shattered glass; If power is off, plan meals to use up foods that will spoil quickly or frozen foods (food in the freezer should be good for at least a couple of days; Don't light your kitchen stove if you suspect a gas leak; Use BBQ or camp stoves, outdoors only for emergency cooking; If your water is off you can drink supplies from water heaters, melted ice cubes or canned vegetables (Avoid drinking water from swimming pools or especially spas--it may have too many chemicals in it to be safe.) .

Q: What are the steps to EQ safety/awareness?

Ans:

Estimate what EQ of what size are likely to occur (geology).
Given the EQ size we then estimate what the shaking will be (seismology).
Given the shaking, we estimate the response of different types of buildings (EQ engineering). Only with all these steps can we take steps as society to enact bldg. codes and retrofitting programs to make our community safer.

Q: What are part of the earthquake Supplies and Equipment Checklist?

Ans: When organizing supplies for an earthquake, remember that you need to get to them after an earthquake has turned your house into mess. Store supplies in an easy to find location that has a minimal chance of being buried under falling objects. If you are short on space, a large trashcan makes an excellent storage container. If you live in an apartment, the container can be hidden under a decorative tablecloth. Earthquakes can happen at any time. Are you prepared right now? Have you rotated your food supplies in the last six months? If not, make time on your calendar. Do it now!

Work Gloves.
Ax / Maul (min. 6 lb.).
Shovel (flat head and pointed).
Broom.
Hammer and Nails.
Screwdrivers.
Crowbar or Claw Tool (36" or Longer).
Plastic Sheeting Rolls (4 Mil. IO' X 25').
Plastic Garbage Bags (Heavy Duty, 30 Gal. or Larger).
Small and Large Plastic Bags.
Coils of Rope 1/4", 1/2", 3/4" (25' - 50').
Coil of Wire.
Tent (Family or Tube Type).
Tarp (PVC or Canvas, Minimum Two, 8' X IO').
Sleeping Bags, Blanket, or Space Blanket.
Cheese Cloth (To Strain Particles From Water).
CASH MONEY (Small Denominations & Coin).
Dry Food.
Water.
Clothing.
Walking Shoes and Socks Local Road Map.
Fire Extinguisher (We recommend a dry chemical type with a minimum size rating of 2A -IOBC, with an earthquake restraining strap, a hose type nozzle, and a metal head).
Compass.
Flashlight With Batteries, Chemical Light Sticks and Matches, In Waterproof Container.
Small Radio (Battery Powered Portable).
Entertainment Pack - Family Photos, Notebooks, Literature, and Games.

Q: What are the sanitation supplies one need to carry during the EQ?

Ans.

Plastic Bags - heavy duty garbage can size and smaller zip-lock types
Powdered Chlorine Lime - (proper storage is required, it is an oxidizer and it is corrosive)
Portable Camp Toilet with Chemicals
Tissue Paper
Handi-wipes, Wet-N-Drys, etc. for water free cleanup
Toilet Supplies - Towelettes, Shampoo, Toothpaste, Deodorant, Sanitary Napkins, Etc.
Insect Sprays

Q: What are the structural precautions one can take while constructing house to avoid the risk of EQ?

Ans:

	Strengthen the connections between ceilings, walls and floors using the appropriate hardware (image at right). Inspect all exposed framing in garages, basements, porches and patio covers. Strengthen this where necessary. Brick and Masonry Facades: Check all brick, masonry and stone facades to make sure they are securely attached to your home. Consult a structural engineer for advice on how to do this.
Chimneys:
	One of the most common types of damage suffered in earthquakes is toppled chimneys. This becomes extremely dangerous when bricks penetrate the roof and fall to the rooms below. Check the chimney for loose mortar, flue or bricks. Reinforce the ceiling surrounding the chimney with 3/4" plywood nailed to the beams. This will provide protection from failing bricks that might break through the roof.

Windows:

Inspect all large plate glass windows to make sure they are safety glass.
Consider adding a safety film to all windows. This does not prevent the window from breaking, but it does keep the glass from falling and injuring loved ones.
Homes that have been framed in wood are generally quite resistant to earthquake damage. Watching tall trees in a strong wind storm demonstrates this resistance. It is unlikely that conventionally-frame houses will collapse. This is the case only if the home remains on its foundations and the roof, ceiling and walls remain connected.

Foundation:

The majority of residential structural damage is caused by homes sliding off their foundations during major earthquakes.

Check your house and garage for foundation bolts. These bolts secure the wood structure to the concrete foundation. They are placed approximately six feet apart along the sill plate and should look like the one illustrated.
Using a hammer drill and a carbide bit, drill a hole through the sill plate into the foundation. Place these holes every six feet. Drop a 1/2" X 8" expansion bolt into the holes and finish by tightening the nut and washer.

Cripple Walls:

Inspect the vertical studs that extend from the foundation to the first floor of your home. These are called cripple walls. If they are exposed on the inside, they could buckle in the severe ground motion that accompanies many large earthquakes.
Strengthen the cripple walls by nailing plywood sheeting to the vertical studs.
Inspect the garage for exposed cripple walls. This is particularly important if the garage is supporting living quarters.

Mobile Homes:

It is relatively easy for a mobile home to be thrown off its supports during an earthquake, even those that produce relatively minor shaking. Leave the wheels on the coach to limit its fall. Check the undercarriage to make sure that it has been securely tied to the foundation.
Tie double-wide mobile homes together. The two halves generally are of different weights. Because of this, they move differently in an earthquake and can easily pull apart.
Seismic bracing systems are commercially available. Be sure that any system you are interested in has been CSA (Canadian Standards Association) certified and inspected by the appropriate local authorities.

Q: What should one do when people comeback home from the disaster?

Ans: Returning home after a major disaster can be both dangerous and difficult. Do not return home until authorities have indicated that it is safe to do so.

Remember that it takes a long time to recover from a disaster. Take your time and pace yourself. Plan a reasonable amount of activity each day. Include children in clean-up and recovery activities. Watch for signs of stress in yourself and family members. If you can't shake feelings of despair, get professional help. While life will not be the same as before the disaster happened, you can and will recover.

The behavior of your pets may change after an emergency. Normally quiet and friendly pets may become aggressive or defensive. Watch animals closely. If after a disaster you have to leave town, take your pet with you. Pets are unlikely to survive on their own.

Try to stay at home and avoid driving to keep roads clear for emergency workers.

If you have appropriate insurance, call your agent. Take pictures of damages. Keep good records of repair and cleaning costs.

Before entering a damaged building:

Put on a sturdy shoes and work gloves for protection against glass or other debris.
Check exterior, roof and chimney for structural damage.
Stay away from fallen or damaged electrical wires. They could still be alive. Do not carry lanterns or torches that could start a fire.
If you have any doubts about safety, have your home inspected by a professional before entering.
Keep a battery operated radio with you to hear any emergency updates

Upon entering:

Check for injured or trapped persons. Give first aid where appropriate. Do not move seriously injured persons unless they are in immediate danger of further injury. Call for help.
Extinguish all open flames.
Until phone service is fully restored, use the phone only for a life-threatening emergency.
Check utilities and appliances:

Check gas supply:

If you smell, gas or hear a blowing or hissing sound, 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 neighbor's home. If you turn off the gas for any reason, it must be turned back on by a professional.

Check electricity:

If you see sparks, broken or frayed wires, or if you smell hot insulation, turn off the electricity at the main fuse box or circuit breaker; call an electrician first for advice.

Check sewage and water lines:

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.

Checking Electrical Appliances

If any of the electrical appliances are wet, turn off the main power switch in the house. Unplug the appliance, dry it out, then reconnect it and turn off the main power switch back on.

If fuses or circuits blow when the electrical power is restored, turn off the main power switch again and inspect for short circuits in the home wiring or appliances. Call a professional if the problem continues to occur.

Cleaning Up:

Clean up spilled medicines, bleaches, gasoline, or other flammable liquids.
Try to protect your home from further damage. Open windows and doors. Patch holes.
Clean and disinfect everything that got wet. The mud left behind by floodwaters can contain sewage and chemicals.
If your basement is flooded, pump it out gradually (about one-third of the water per day) to avoid damage. The walls may collapse and the floor may buckle if the basement is pumped out while the surrounding ground is still waterlogged.
Throw out food, cosmetics and medicines that have come into contact with flood waters.

Source: http://earthquake.usgs.gov/hazards/

Graphic Resources

Source: http://earthquake.usgs.gov/hazards/

What Causes Earthquakes: Information about Faults, Plate Tectonics and Earth Structure

Q: What is an earthquake and what causes them to happen?

Ans: An earthquake is caused by a sudden slip on a fault. Stresses in the earth's outer layer push the sides of the fault together. Stress builds up and the rocks slips suddenly, releasing energy in waves that travel through the earth's crust and cause the shaking that we feel during an earthquake. An EQ occurs when plates grind and scrape against each other. In California there are two plates the Pacific Plate and the North American Plate. The Pacific Plate consists of most of the Pacific Ocean floor and the California Coast line. The North American Plate comprises most the North American Continent and parts of the Atlantic Ocean floor. These primary boundary between these two plates is the San Andreas Fault. The San Andreas Fault is more than 650 miles long and extends to depths of at least 10 miles. Many other smaller faults like the Hayward (Northern California) and the San Jacinto (Southern California) branch from and join the San Andreas Fault Zone. The Pacific Plate grinds northwestward past the North American Plate at a rate of about two inches per year. Parts of the San Andreas Fault system adapt to this movement by constant "creep" resulting in many tiny shocks and a few moderate earth tremors. In other areas where creep is NOT constant, strain can build up for hundreds of years, producing great EQs when it finally releases.

Q: Can we cause earthquakes? Is there any way to prevent earthquakes?

Ans: Earthquakes induced by human activity have been documented in a few locations in the United States, Japan, and Canada. The cause was injection of fluids into deep wells for waste disposal and secondary recovery of oil, and the use of reservoirs for water supplies. Most of these earthquakes were minor. The largest and most widely known resulted from fluid injection at the Rocky Mountain Arsenal near Denver, Colorado. In 1967, an earthquake of magnitude 5.5 followed a series of smaller earthquakes. Injection had been discontinued at the site in the previous year once the link between the fluid injection and the earlier series of earthquakes was established. (Nicholson, Craig and Wesson, R.L., 1990, Earthquake Hazard Associated with Deep Well Injection--A Report to the U.S. Environmental Protection Agency: U.S. Geological Survey Bulletin 1951, 74 p.) Other human activities, even nuclear detonations, have not been linked to earthquake activity. Energy from nuclear blasts dissipates quickly along the Earth's surface. Earthquakes are part of a global tectonic process that generally occurs well beyond the influence or control of humans. The focus (point of origin) of earthquakes is typically tens to hundreds of miles underground. The scale and force necessary to produce earthquakes are well beyond our daily lives. We cannot prevent earthquakes; however, we can significantly mitigate their effects by identifying hazards, building safer structures, and providing education on earthquake safety.

Q: What do we know about the interior of the Earth?

Ans:

Five billion years ago the Earth was formed by a massive conglomeration of space materials. The heat energy released by this event melted the entire planet, and it is still cooling off today. Denser materials like iron (Fe) sank into the core of the Earth, while lighter silicates (Si), other oxygen (O) compounds, and water rose near the surface. The earth is divided into four main layers: the inner core, outer core, mantle, and crust. The core is composed mostly of iron (Fe) and is so hot that the outer core is molten, with about 10% sulfur (S). The inner core is under such extreme pressure that it remains solid. Most of the Earth's mass is in the mantle, which is composed of iron (Fe), magnesium (Mg), aluminum (Al), silicon (Si), and oxygen (O) silicate compounds. At over 1000 degrees C, the mantle is solid but can deform slowly in a plastic manner. The crust is much thinner than any of the other layers, and is composed of the least dense calcium (Ca) and sodium (Na) aluminum-silicate minerals. Being relatively cold, the crust is rocky and brittle, so it can fracture in earthquakes. (Univ. of Nevada).

Q: What are plate tectonics?

Ans: Plate tectonics is the continual slow movement of the tectonic plates, the outermost part of the earth. This motion is what causes earthquakes and volcanoes and has created most of the spectacular scenery around the world.

Q: What is a fault and what are the different types?

Ans: A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep. Faults may range in length from a few millimeters to thousands of kilometers. Most faults produce repeated displacements over geologic time. During an earthquake, the rock on one side of the fault suddenly slips with respect to the other. The fault surface can be horizontal or vertical or some arbitrary angle in between.

Earth scientists use the angle of the fault with respect to the surface (known as the dip) and the direction of slip along the fault to classify faults. Faults which move along the direction of the dip plane are dip-slip faults and described as either normal or reverse, depending on their motion. Faults that move horizontally are known as strike-slip faults and are classified as either right-lateral or left-lateral. Faults, which show both dip-slip and strike-slip motion are known as oblique-slip faults.

The following definitions are adapted from The Earth by Press and Siever.

Normal fault- a dip-slip fault in which the block above the fault has moved downward relative to the block below. This type of faulting occurs in response to extension and is often observed in the Western United States Basin and Range Province and along oceanic ridge systems.

Thrust fault- a dip-slip fault in which the upper block, above the fault plane, moves up and over the lower block. This type of faulting is common in areas of compression, such as regions where one plate is being sub ducted under another as in Japan. When the dip angle is shallow, a reverse fault is often described as a thrust fault.

Strike-slip fault - a fault on which the two blocks slide past one another. The San Andreas Fault is an example of a right lateral fault.

A left-lateral strike-slip fault is one on which the displacement of the far block is to the left when viewed from either side.

A right-lateral strike-slip fault is one on which the displacement of the far block is to the right when viewed from either side.

Q: At what depth do earthquakes occur?

Ans: Earthquakes occur in the crust or upper mantle, which ranges from the earth's surface to about 800 kilometers deep (about 500 miles).

Q: What is "surface rupture" in an earthquake?

Ans: Surface rupture occurs when movement on a fault deep within the earth breaks through to the surface. NOT ALL earthquakes result in surface rupture.

Q: What is the relationship between faults and earthquakes? What happens to a fault when an earthquake occurs?

Ans: Earthquakes occur on faults - strike-slip earthquakes occur on strike-slip faults, normal earthquakes occur on normal faults, and thrust earthquakes occur on thrust or reverse faults. When an earthquake occurs on one of these faults, the rock on one side of the fault slips with respect to the other. The fault surface can be vertical, horizontal, or at some angle to the surface of the earth. The slip direction can also be at any angle.

Q: How do we know a fault exists?

Ans:

if the EQ left surface evidence, such as surface ruptures or fault scarps (cliffs made by EQs).
if a large EQ has broken the fault since we began instrumental recordings in 1932.
if the faults produces small EQs that we can record with the denser seismographic network established in the 1970s.

Q: Where can I go to see the/a fault?

Ans: The closest fault depends on where you live. Some earthquakes produce spectacular fault scarps, and others are completely buried beneath the surface. Sometimes you may not even know that you are looking at a fault scarp.

Q: What does an earthquake feel like?

Ans: Generally, during an earthquake you first will feel a swaying or small jerking motion, then a slight pause, followed by a more intense rolling or jerking motion. The duration of the shaking you feel depends on the earthquake's magnitude, your distance from the epicenter, and the geology of the ground under your feet. Shaking at a site with soft sediments, for example, can last 3 times as long as shaking at a stable bedrock site such as one composed of granite. If the site is in a building, then the height of the building and type of material it is constructed from are also factors. For minor earthquakes, ground shaking usually lasts only a few seconds. Strong shaking from a major earthquake usually lasts less than one minute. For example, shaking in the 1989 magnitude 7.1 Loma Prieta (San Francisco) earthquake lasted 15 seconds; for the 1906 magnitude 8.3 San Francisco earthquake it lasted about 40 seconds. Shaking for the 1964 magnitude 9.2 Alaska earthquakes, however, lasted three minutes.

Q: Foreshocks, aftershocks - what is the difference?

Ans: "Foreshock" and "aftershock" are relative terms. Foreshocks are earthquakes, which precede larger earthquakes in the same location. Aftershocks are smaller earthquakes, which occur in the same general area during the days to years following a larger event or "mainshock", defined as within 1-2 fault lengths away and during the period of time before the background seismicity level has resumed. As a general rule, aftershocks represent minor readjustments along the portion of a fault that slipped at the time of the main shock. The frequency of these aftershocks decreases with time. Historically, deep earthquakes (>30km) are much less likely to be followed by aftershocks than shallow earthquakes. (Univ. of Washington).

Q: Two earthquakes occurred on the same day. Are they related?

Ans: Often, people wonder if an earthquake in Alaska may have triggered an earthquake in California; or if an earthquake in Chile is related to an earthquake that occurred a week later in Mexico. Over these distances, the answer is no. Even the Earth's rocky crust is not rigid enough to transfer stress fields efficiently over thousands of miles.

Source:http://earthquake.usgs.gov/hazards/

Frequently Asked Questions

Q:Can you predict earthquakes?

Ans:No. Neither the USGS nor Caltech nor any other scientists have ever predicted a major earthquake. They do not know how, and they do not expect to know how any time in the near future. However based on scientific data, probabilities can be calculated for potential future earthquakes. For example, scientists estimate that over the next 30 years the probability of a major EQ occurring in the San Francisco Bay area is 67% and 60% in Southern California.

Q: Can animals predict earthquakes?

Ans:Changes in animal behavior can not be used to predict earthquakes. Even though there have been documented cases of unusual animal behavior prior to earthquakes, a reproducible connection between a specific behavior and the occurrence of an earthquake has not been made. Animals change their behavior for many reasons and given that an earthquake can shake millions of people, it is likely that a few of their pets will, by chance, be acting strangely before an earthquake.

Q: Can you prevent large earthquakes by making lots of small ones, or by "lubricating" the fault with water?

Ans: Seismologists have observed that for every magnitude 6 earthquake there are 10 of magnitude 5, 100 of magnitude 4, 1,000 of magnitude 3, and so forth as the events get smaller and smaller. This sounds like a lot of small earthquakes, but there are never enough small ones to eliminate the occasional large event. It would take 32 magnitudes 5's, 1000 magnitude 4's, 32,000 magnitude 3's to equal the energy of one magnitude 6 event. So, even though we always record many more small events than large ones, there are never enough to eliminate the need for the occasional large earthquake.

As for "lubricating" faults with water or some other substance, injecting high pressure fluids deep into the ground is known to be able to trigger earthquakes to occur sooner than would have been the case without the injection. However, this would be a dangerous pursuit in any populated area, as one might trigger a damaging earthquake.

Q: Can some people sense that an earthquake is about to happen? (Earthquake sensitive)?

Ans: There is no scientific explanation for the symptoms some people claim to have preceding an earthquake, and more often than not there is no earthquake following the symptoms.

Q: Is there earthquake weather?

Ans: In the 4th Century B.C., Aristotle proposed that earthquakes were caused by winds trapped in subterranean caves. Small tremors were thought to have been caused by air pushing on the cavern roofs, and large ones by the air breaking the surface. This theory lead to a belief in earthquake weather, that because a large amount of air was trapped underground, the weather would be hot and calm before an earthquake. A later theory stated that earthquakes occurred in calm, cloudy conditions, and were usually preceded by strong winds, fireballs, and meteors.

However, there is no connection between weather and earthquakes. They are the result of geologic processes within the earth and can happen in any weather and at any time during the year. Earthquakes originate miles underground. Wind, precipitation, temperature, and barometric pressure changes affect only the surface and shallow subsurface of the Earth. Earthquakes are focused at depths well out of the reach of weather, and the forces that cause earthquakes are much larger than the weather forces. Earthquakes occur in all types of weather, in all climate zones, in all seasons of the year, and at any time of day. Sometimes, we are asked: "Do earthquakes change the weather in any way? Earthquakes themselves do not cause weather to change. Earthquakes, however, are a part of global tectonics, a process that often changes the elevation of the land and its morphology. Tectonics can cause inland areas to become coastal or vice versa. Changes significant to alter the climate occur over millions of years, however, and after many earthquakes.

Q: Are there more earthquakes in the morning/in the evening/at a certain time of the month?

Ans: Earthquakes are equally as likely to occur at any time of the day or month or year. The factors that vary between the time of the day, month, or year do not affect the forces in the earth that cause earthquakes.

Q: Can the position of the moon or the planets affect seismicity?

Ans: The moon, sun, and other planets have an influence on the earth in the form of perturbations to the gravitational field. The relative amount of influence is proportional to the objects mass, and inversely proportional to the square of its distance from the earth. No significant correlations have been identified between the rate of earthquake occurrence and the semi-diurnal tides when using large earthquake catalogs. There have, however, been some small but significant correlations reported between the semi-diurnal tides and the rate of occurrence of aftershocks in some volcanic regions, such as Mammoth Lakes.

Q: Can the ground open up during an earthquake?

Ans: Shallow crevasses can form during earthquake induced landslides, lateral spreads, or other types of ground failures. Faults, however, do not open up during an earthquake. Movement occurs along the plane of a fault, not perpendicular to it. If faults opened up, no earthquake would occur because there would be no friction to lock them together.

Q: Why are we having so many earthquakes? Has earthquake activity been increasing? Does this mean a big one is going to hit? We haven't had any earthquakes in a long time; does this mean that the pressure is building up and there will be a big one?

Ans: Although it may seem that we are having more earthquakes, earthquakes of magnitude 7.0 or greater have remained fairly constant throughout this century and, according to our records; have actually seemed to decrease in recent years. A partial explanation may lie in the fact that in the last twenty years, we have definitely had an increase in the number of earthquakes we have been able to locate each year. This is because of the tremendous increase in the number of seismograph stations in the world and the many improvements in global communications. In 1931, there were about 350 stations operating in the world; today, there are more that 4,000 stations and the data now comes in rapidly from these stations by telex, computer and satellite. This increase in the number of stations and the more timely receipt of data has allowed us and other seismological centers to locate many small earthquakes which were undetected in earlier years, and we are able to locate earthquakes more rapidly. The NEIC now locates about 12,000 to 14,000 earthquakes each year or approximately 35 per day. Also, because of the improvements in communications and the increased interest in natural disasters, the public now learns about more earthquakes. According to long-term records (since about 1900), we expect about 18 major earthquakes (7.0 - 7.9) and one great earthquake (8.0 or above) in any given year. However, let us take a look at what has happened in the past 32 years, from 1969 through 2001, so far. Our records show that 1992, and 1995-1997 were the only years that we have reached or exceeded the long-term average number of major earthquakes since 1971. In 1970 and in 1971 we had 20 and 19 major earthquakes, respectively, but in other years, the total was in many cases well below the 18 per year, which we may expect based on the long-term average.

A temporal increase in earthquake activity does not mean that a large earthquake is about to happen. Similarly, quiescence, or the lack of seismicity, does not mean a large earthquake is going to happen.

Q: Do earthquakes cause volcanoes?

Ans: No, there are different earth processes responsible for volcanoes. Earthquakes may occur in an area before, during, and after a volcanic eruption, but they are the result of the active forces connected with the eruption, and not the cause of volcanic activity.

Source: http://earthquake.usgs.gov/hazards/

News Updates

For detailed news update on the earthquake in the subcontinent, check out the following links. The links cover the information pertaining to death toll, rescue and relief operations, impact of political relations of India and Pakistan on the rescue and relief operation etc.