What we can’t see below ground that actually causes an earthquake.

Earthquakes are caused by rocks deep underneath the Earth’s surface moving along faults, which are fractures in the Earth’s crust where the rock has broken.

• The Earth’s crust is like a giant puzzle with several pieces called tectonic plates. These plates constantly move.
• As the plates move, they build friction, getting stuck at their edges. This pressure builds like a rubber band pulling back.
• Then the building pressure from the plates overcomes the friction and suddenly releases. The location below the earth’s surface where the earthquake starts are called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter. The rock breaking along the fault releases a tremendous amount of energy in seismic waves, vibrations or ripples of energy that radiate outward from the epicenter of the disturbance through the crust. 
• The waves shake the ground with varying degrees of severity, depending on the size of the quake. The strength of the waves is measured on the Richter Scale. More destructive earthquakes typically have magnitudes between about 5.5 and 8.9. A difference of one represents a thirtyfold difference in magnitude. The 2023 Türkiye Syria Earthquake was a 7.8.
• The largest earthquake ever instrumentally recorded happened on May 22, 1960, off the coast of southern Chile. This earthquake, known as the Great Chilean Earthquake, measured a staggering 9.5 on the moment magnitude scale. It was incredibly powerful, shaking the ground for around 10 minutes and triggering destructive tsunamis across the Pacific Ocean.

The events that can follow the main quake are more predictable but sometimes more deadly and terrifying.

Tsunamis

Often triggered by major underwater earthquakes where oceanic plates slide beneath continental plates suddenly, displacing a large volume of water. Unlike regular wind-driven waves, tsunamis have much longer wavelengths (the distance between wave crests), often spanning hundreds of kilometers in the open ocean. This means they may appear as only a slight rise in water level initially, making them difficult to detect. Despite their low initial height, tsunamis carry a massive amount of energy due to their immense volume of displaced water. As they approach shallow coastal areas, the energy becomes concentrated, causing the waves to slow down and grow dramatically in height, reaching tens of meters in extreme cases.

One such tsunami in Southeast Asia in 2004 generated waves up to 100 feet high, killing 230,000 people in 14 countries and destroying entire towns and villages. While ancient history has recorded the deadliest earthquakes primarily in China and Syria, the Indian Ocean Earthquake that produced the Southeast Asia Tsunami is often considered the deadliest earthquake and tsunami event in modern history. Read how Americares worked with local partners over a 10-year period of recovery in Southeast Asia.

Aftershocks

The initial quake (mainquake) is followed in the hours and days after by many aftershocks, some of the magnitude nearly equal to the first tremor. Sometimes foreshocks will occur that give authorities an indication that an earthquake might follow. Often there is no such warning.

What is an earthquake aftershock? They are smaller earthquakes that occur after the mainshock, in the same general area, caused by the Earth’s crust readjusting, as rocks around the fault that ruptured during the mainshock try to settle back into a stable position. They add to the continuing terror from the catastrophe.

Landslides

Landslides and other disasters often involve human activity such as damage to a nuclear facility or major fires from combustible sources damaged in the quake. Much structural damage is amplified by poor building construction. Buildings can be strengthened to withstand quakes, but in the case of communities with older buildings, limited resources, or inadequate construction requirements, that may mean greater levels of deadly destruction.

Earthquakes are most likely to happen along the boundaries of Earth’s tectonic plates. There are three main areas where these boundaries are particularly active, making them earthquake hotspots:

• The Pacific “Ring of Fire”: This horseshoe-shaped belt encircles the Pacific Ocean and experiences about 81% of the world’s largest earthquakes. This belt includes countries like Chile, Japan, Indonesia, and the west coast of North America.
• The Alpide Belt: This belt stretches from Indonesia and Sumatra through the Himalayas, the Mediterranean, and out into the Atlantic. It accounts for about 17% of the world’s largest earthquakes, including some devastating ones like the 2023 Türkiye SyriaEarthquake, 2015 Nepal Earthquake, and the 2004 Indian Ocean earthquake and tsunami.
• The Mid-Atlantic Ridge: This underwater mountain range marks where two tectonic plates are spreading apart. Earthquakes here are generally smaller than those in subduction zones, but they can still be significant.

While seismologists (earthquake experts) can make educated guesses about earthquake prone areas, predicting the exact time, location, and intensity of an earthquake remains a challenge. Remember that earthquakes can occur anywhere on Earth, without warning, even in areas considered less active. Stay informed about earthquake risks and preparedness measures in your local area, regardless of its position on the global earthquake map. Examples of major earthquakes that occurred far from the three earthquake zones include the 2020 Puerto Rico Earthquake  and the 2010 Haiti Earthquake (7.0 magnitude that killed more than 230,000 people)  

Don’t Wait. Get Ready Now.

• Earthquake safety depends largely on a good emergency plan
• Be prepared for no electrical or water service for days or weeks.
• Have a combination weather radio, flashlight and hand crank charger for cellphones at the ready.
• Have a cash reserve.
• Know where the shutoff valve and tool are for your natural gas line and the main switch for your electrical service.
• Secure bookshelves to walls or any other heavy objects that could fall and injure.
• Create an earthquake kit (a “Go Bag”) with food, water, gear and other necessities for 72 hours.
• Go Bag should also include copies of your IDs and insurance records.
• Store your important papers (i.e. Insurance, household and personal information) in a fireproof container that can withstand major shocks and falling debris.
• For a more detailed set of preparedness instructions click on these links:
  • Preparing for the Big One in the Bay Area
  • More Specifics to Get Ready

What to do in an Earthquake

• If you are inside, stay. Avoid doorways and do not run outside.
• Drop down and cover your head and neck. If a sturdy table or desk is near, crawl under it. Stay away from exterior walls and windows.
• If you are in bed, turn face down and cover head and neck with a pillow
• If you are outside, stay outside and away from buildings.
• If you are in a car, pull over, stop (not underneath anything) and set the hand brake.

Volcanic Activity

Volcanic eruptions can bury entire communities or inundate whole areas with lava flows and fill the air with deadly toxic gases or ash. In 2020 we responded to the eruption of the Taal Volcano as well as a 7.1 earthquake that occurred on July 26, 2022, in the Philippines. The Nevado del Ruiz volcano, located on the border of the Colombia departments Tolima and Caldas has recently been under an orange alert due to its possible risk of eruption. Our Colombia team is prepared to respond should such an event occur.

Earthquake Response and Recovery

1. Major structural damage to or complete destruction of health facilities
   • Set up temporary structures such as the transitional medical facility after the Earthquake in Ecuador to provide immediate care for the injured, followed by rebuilding stronger, using materials, structural techniques and location based on best practices to better withstand future seismic events as we did after the Nepal Earthquake.
2. Relocation to temporary shelters with loss of housing
   • Supply family emergency kits, water purification, emergency medical care, medicine and supplies for those who lost their homes and who had to flee quickly without their personal belongings or medications.
3. Great impact of disaster on the most vulnerable in a community
   • Identifying and serving the specific health needs of the most vulnerable and least mobile (i.e. the elderly, small children, expectant mothers, people with disabilities)
4. Catastrophe produces trauma and stress in community and in health workers serving them
   • Training health workers to identify trauma and implementing longer-term mental health support programs for those most at risk. Read how the availability of mental health support helped one health worker survive and thrive after an Earthquake in Syria.
5. Loss of access to health care
   • Support Emergency Medical Teams equipped to handle or refer impact or crush injuries and provide primary care for those with ongoing treatment needs (e.g. chronic disease).