The Earth’s crust and the outer mantle layer beneath it are made up of seven massive plates and many smaller ones that fit together like puzzle pieces and are constantly moving above the molten core. When these tectonic plates slip over, under, or past each other at the fault lines where they meet, energy builds up and is released as an earthquake. Undersea earthquakes sometimes cause ocean waves called tsunamis.
As tectonic plates shift, the Earth’s landscape is reformed — creating mountains and volcanoes and redrawing coastlines.
As many as 500,000 earthquakes occur each year, and about 100,000 are large enough to be felt. Perhaps as many as 100 cause damage. Major earthquakes that measure magnitude 7 or greater happen somewhere on the Earth upwards of once a month.
FAQs: What you need to know about earthquakes and tsunamis
Explore frequently asked questions about earthquakes and tsunamis and find out how to help people affected by natural disasters.
- Fast facts: Earthquakes and tsunamis
- What is an earthquake? What causes an earthquake?
- How are earthquakes measured?
- What hazards are caused by earthquakes?
- How can I help people affected by earthquakes and tsunamis?
- What is a tsunami? What causes a tsunami?
- Where do tsunamis occur?
- Is a tsunami the same as a tidal wave?
- How can I prepare for an earthquake?
- What to do in an earthquake
- How does World Vision help people affected by earthquakes and tsunamis?
- Timeline: History of earthquake and tsunami studies
Fast facts: Earthquakes and tsunamis
- Shifts and collisions of tectonic plates cause earthquakes.
- The epicenter of an earthquake is the surface location directly above the quake’s hypocenter, the below-surface location where the rupture of the fault begins.
- The scientific study of earthquakes is called seismology.
- A magnitude 9.5 earthquake in Chile on May 22, 1960, is the most powerful earthquake in recorded history.
- The largest-known quake in the United States struck Prince William Sound, Alaska, on March 28, 1964, and measured magnitude 9.2.
- Earthquakes below magnitude 7.5 seldom cause tsunamis.
- The 2004 Indian Ocean tsunami, which was created by a magnitude 9.1 earthquake near Sumatra, caused widespread damage in 14 countries.
What is an earthquake? What causes an earthquake?
Earthquakes are disturbances at ground level and below caused by shifts and collisions of tectonic plates, the geologic structures that form the Earth’s outer layer. Friction between plates causes their edges to stick and build up energy even as the plates continue to move. That energy is released as an earthquake when the plates come unstuck and slip past each other. Earthquakes can happen anywhere at any time, but they most commonly occur on known fault lines such as the Pacific Ring of Fire.
How are earthquakes measured?
A worldwide network of seismic stations measures the movement of the ground, from which seismologists can calculate the magnitude of the quake at its source. When a major quake occurs, the first calculations of magnitude are based on only a few seismic readings. Within days or weeks, the magnitude may be adjusted based on more exact measurements.
Intensity is another indicator of an earthquake’s strength. Based on an agreed scale of damage, Roman numerals are assigned to indicate the amount of shaking and damage in different locations.
What hazards are caused by earthquakes?
Strong earthquakes can be extremely dangerous. The earth’s shaking may cause landslides or even rupture the surface of the ground. When saturated loose soils lose their stiffness and form, liquefaction occurs, and the ground collapses like a liquid. In a one-two punch, a tsunami may follow an undersea earthquake, bringing massive destruction to coastal zones.
Most earthquake deaths are due to structural failures of buildings. The 2010 Haiti earthquake, for example, struck hardest in the capital, Port-au-Prince, where poorly constructed buildings collapsed. An estimated 250,000 people died, and 1.5 million people were left homeless.
Secondary effects of earthquakes can include a collapse of infrastructure, fires, and disease outbreaks. After the Haiti quake, a cholera outbreak spread quickly through the camps where people lived for months or even years. The 1906 San Francisco earthquake triggered a secondary hazard: Damaging fires ignited by ruptured gas mains burned for three days and destroyed about 500 blocks of the city. In more recent disasters, fires are also caused by downed power lines.
How can I help people affected by earthquakes and tsunamis?
- Give: Donate to World Vision’s Disaster Relief Fund to bring healing to affected children, families, and communities.
- Pray: Join us in praying for World Vision staff and responders as they help families recover and rebuild after earthquakes and other disasters: Almighty Father, we ask for Your caring mercy on people hard hit by natural disasters, including earthquakes and tsunamis. Amid their struggle to recover, give them patience, peace, and hope that their lives will continue to improve.
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What is a tsunami? What causes a tsunami?
A tsunami is a series of giant waves caused by an earthquake or underwater volcano that suddenly shifts the seafloor. Tsunamis can travel at 500 miles an hour — as fast as a jet plane — across the open ocean.
Tsunami waves slow down and pile up higher as they approach land. Both the 2004 Indian Ocean tsunami and the 2011 Japan tsunami were more than 100 feet tall when they reached the shore.
Where do tsunamis occur?
Tsunamis occur most frequently in the Pacific Ocean’s “Ring of Fire,” a horseshoe-shaped seismically active belt where many volcanic eruptions and earthquakes also happen.
Is a tsunami the same as a tidal wave?
Tsunamis and tidal waves are both sea waves, but they have different causes and characteristics. A tidal wave is a shallow water wave caused by the gravitational effects of the sun and moon on the Earth. A tsunami is not influenced by the tides and may reach great heights as it comes thundering onto shore.
How can I prepare for an earthquake?
The U.S. Geological Service cautions people to prepare their households to be self-sufficient for a week or more in case of an earthquake.
Items to stockpile include:
- Fire extinguisher
- Dried and packaged food for several days
- A gallon of water a day for each family member; bleach or purification tablets to treat water
- First-aid kit and medications
- Tools to turn off gas and water lines
- Camp stove or barbecue and fuel for cooking
- Flashlight, along with extra bulbs and batteries
- Heavy plastic bags for waste disposal
To practice what to do when the ground underneath starts to rumble and shake, join in the International ShakeOut Day. The annual event is always on the third Thursday of October.
What to do in an earthquake
When an earthquake strikes, federal, state, and local officials all agree that the best way to stay safe is to drop onto your hands and knees, cover your head and neck, and hold on until the shaking stops! They do not recommend standing in a doorway or running outside, but if you are close enough to a sturdy table or desk, crawl underneath it for shelter.
If you or a loved one is affected by a disability that prevents you from dropping to the ground, check out these resources from the Earthquake Country Alliance.
How does World Vision help people affected by earthquakes and tsunamis?
World Vision pre-positions relief supplies and trains staff for emergency work in areas including child protection, relief supply chain management, and clean water provision. In disaster-prone communities, we organize programs to reduce risks from disasters and train local first responders.
World Vision’s 37,000 staff in nearly 100 countries around the world work to improve the lives of children and families and to help them prepare for and recover from disasters.
World Vision provided aid to survivors of these recent earthquakes and tsunamis:
- 2001 Bhuj, Gujarat, India earthquake — magnitude 7.9, 20,000 people died
- 2004 Indian Ocean earthquake and tsunami — magnitude 9.1; 220,000 people died
- 2005 Kashmir earthquake — magnitude 7.6, 73,000 people died
- 2010 Haiti earthquake — magnitude 7.0, 220,000 people died
- 2011 Japan earthquake and tsunami — magnitude 9.0, 20,000 people died
- 2014 Iquique earthquake and tsunami, Chile — magnitude 8.2; 5 people died, four from heart attacks
- 2015 Nepal earthquake — magnitude 7.8, 9,000 people died
- 2017 Ecuador earthquake — magnitude 7.8, 700 people died
- 2017 Mexico earthquakes — magnitudes 8.1 and 7.1, 315 people died
- 2018 Indonesia earthquakes and tsunami — magnitudes 6.9 and 7.5, more than 2,000 people died
Timeline: History of earthquake and tsunami studies
132 — The first seismic measuring device is invented in China.
1566 — An earthquake in Shaanxi, China, kills 830,000 people.
1811 to 1812 — A series of three major earthquakes and numerous aftershocks near New Madrid, Missouri, are felt as far away as Boston and Denver.
1883 — In the Indonesian islands, the Krakatoa volcano explodes. Its lengthy effects include ash clouds that cover the globe and a massive tsunami.
1906 — About 700 people were killed in San Francisco, California, when an earthquake was followed by about 30 fires that raged for three days.
1933 — In Japan, the Sanriku earthquake and tsunami occur in a location that saw damaging quakes in 1896.
1935 — Charles Richter develops the Richter scale, which rates earthquakes based on the size of their seismic waves.
1960 — At magnitude 9.5, the 1960 Valdivia earthquake in Chile is the most powerful quake ever recorded.
1964 — The Alaska earthquake, at magnitude 9.2, is the second-most powerful to date. The tsunami it generated caused damage as far away as Hawaii.
1965 — Plate tectonics is recognized as the theory that unifies current knowledge of earthquake science.
1977 — The National Earthquake Hazard Reduction Program is established by the U.S. Congress to reduce future risks to life and property from earthquakes.
1986 — The Global Seismographic Network was established to measure quakes and combine data using modern technology.
1989 — The Northridge quake in California causes $64 billion in losses.
1994 — For earthquakes over magnitude 3.5, the moment magnitude scale (MMS), developed in the 1970s, replaces the Richter scale. MMS rates earthquakes based on the total amount of energy released.
2004 — A magnitude 9.1 earthquake off the coast of Sumatra created a massive tsunami, now known as the Indian Ocean tsunami, that caused damage in 14 countries. A global effort accelerates the development of a tsunami early warning system.
2011 — A magnitude 9.0 earthquake hits off the northeast coast of Japan’s Honshu island, generating a massive tsunami.
2012 — The city of Sendai, Japan, is recognized as a model for urban resilience for its recovery from the earthquake of 2011.
2018 — Indonesia is hit with nine significant earthquakes, six measuring magnitude 6.0 or greater. Aftershocks rumble in Central Sulawesi months later, with a magnitude 5 quake on November 3. More than 2 million people are affected by the quakes and aftershocks. On the evening of December 22, more than 400 people are reported dead after a tsunami strikes western Java and southern Sumatra islands.