Photo: Snowbrains.com
Image: USGS
When the earth begins to move, it’s scary. Caused by the breaking and shifting of subterranean rock as it releases accumulated strain, earthquakes can start out mildly and then strengthen to extremely violent quickly. This movement passes the stress energy on to other items attached to the earth, like buildings, streets, railroad tracks, tunnels and bridges. Any object can become a flying projectile, houses can be moved off their foundations or collapse, utilities, roads and their structures are all subject to damage. Earthquakes have also triggered landslides, avalanches and tsunamis. [1]
All 50 states and 5 U.S. Territories are at some risk of earthquakes. The risk is higher in seismic identified zones, where frequent movements have been recorded. Earthquakes happen when two blocks of the earth slip past one another. The surface where the slip occurs is called a fault plane. Earthquakes can be made up of small movements (foreshocks) before a big one (mainshock) and small quakes that occur afterward (aftershocks).
The crust and top of the mantle (parts of the four major layers of the earth) are made up of many pieces, like a puzzle covering the earth’s surface. These pieces (tectonic plates) keep slowly moving around, sliding past one another and bumping into others. The plate boundaries (edges) have many faults. Most of the earth’s earthquakes occur along theses faults. When these edges move far enough they get unstuck, releasing energy and resulting in an earthquake. This energy radiates out in all directions as seismic waves. The seismic waves shake the earth as they move. They shake the ground and everything on it, including us. [2]
Scientists measure the size of earthquakes by recording these movements on a seismograph, creating a seismograph, a series of wiggly lines that vary in height. The taller the wiggly line the greater the quakes magnitude. Scientists have seismographs located at many different places throughout the country. When a quake occurs all the seismographs record the movement. The epicenter of where it occurs is determined by a method called triangulation. There are two types of waves associated with earthquakes, P waves and S waves. P waves, compressional wave, are the fastest and the first to arrive at a given location. It alternately compresses and expands material in the same direction it is traveling, results in a small jolt or light shaking. An S wave, or shear wave, is a seismic body wave that shakes the ground back and forth perpendicular to the direction the wave is moving. S waves create a larger jolt or strong shaking. [2]
Scientist can’t actually predict when an earthquake will occur. Strong seismic shaking from an earthquake travels at about 2 miles per second, so it is possible to detect a large earthquake near its source and broadcast a warning of imminent strong shaking to more distant areas before the shaking arrives. Earthquake Early Warning Systems are operational in several countries around the world, including Mexico, Japan, Turkey, Romain, China Italy, and Taiwan. All of these systems rapidly detect earthquakes and track their evolution to provide warnings of pending ground shaking. Systems can vary depending on the local faults and the specific ground motion data available. Mexico City’s system has been operational since 1991. Japan has the world’s most sophisticated warning system.
Seven Steps to Earthquake Safety
Before the next earthquake four steps are recommended that will make you, your family, or your workplace better prepared to survive and cover quickly. [4]
- Secure your space by identifying hazards and securing moveable items. This includes placing bookshelves or heavy wall mounted items away from places where people sit, sleep or spend a lot of time. Put the heaviest shelved objects on the lowest shelf. It also means securing heavy furniture and appliances to wall studs.
- Plan to be safe by creating a disaster plan on what each person in your family should do during an earthquake to remain safe. These plans should include practicing “drop, cover, and hold on”(also Step 5), identifying safe spots in every room, and how to protect yourself no matter where you are when an earthquake strikes. Also make plans on how you will communicate and where you will meet after the initial event is over.
- Organize disaster supplies in convenient locations. Everyone should have personal disaster supplies. Store some at home, at work and in your vehicle. Emergency supplies will reduce the impact on you or your family.
- Minimize financial hardship by organizing important documents, strengthening your property, and considering insurance. Keep copies of identification, insurance cards, lists of emergency numbers and photos of your belongings in your home all organized in a “grab-and-go” bag.
- During the next big earthquake, and immediately after, is when your level of preparedness will make a difference in how you and others survive and can respond to emergencies. Be prepared to “drop, cover, and hold on” when the earth shakes. This action can save lives and reduce the risk of injury.
- Improve safety after earthquakes by evacuating if necessary, helping the injured, and preventing further injuries or damage. Be prepared to move to higher ground if a tsunami is possible. If you are not in a tsunami zone, evacuate only if there is damage to the building or the surrounding area is unsafe. If you are trapped by falling items or a collapse, protect your mouth, nose, and eyes from dust. If you are bleeding, put pressure in the wound and elevate the injured part. Signal for help. The signal rescue personnel will be listening for are sounds in a group of three. Once you are safe, help others and check for damage. Wear sturdy shoes and work gloves to avoid injury from broken glass or debris. Dust mask and eye protection can also help. Be prepared for aftershocks and stay away from anything that looks like it may fall. Register on the Red Cross “Safe and Well” website so family members will know you are okay.
- Reconnect and restore – restore daily life by reconnecting with others, repair damage and rebuild the community. There is a process to go through to handle the time after an earthquake.
Once you have recovered from the earthquake, go back to step one and do the things you did not do before, or do them more thoroughly. Learn what happened during the earthquake so you will be safer and recover more quickly next time.
References
1. https://www.ready.gov/earthquakes
2. https://earthquake.usgs.gov/learn/kids/eqscience.php
3. https://earthquake.usgs.gov/research/earlywarning/background.php
4. https://www.earthquakecountry.org/sevensteps/
Billie Nicholson, Editor
March 2018
