Earthquake Information
Introduction: What is an Earthquake?
An earthquake is a shift in the upper layers of the Earth caused by the movement of tectonic plates; natural divisions within the planet’s surface. Though the specifics of plate tectonics are relatively complex, it should be understood that there are three major kinds of tectonic boundaries, categorized by their activities: these are divergent, convergent, and transform boundaries. When friction occurs along the edges of the plates due to their natural shifting, an earthquake occurs. The earthquake begins deep within the Earth at a place called the focus. The area of the Earth’s surface directly above this point is known as the epicenter and is the “central” point of the earthquake as experienced by people above ground. Earthquakes are measured by devices called seismographs, which record the seismic waves of energy released by earthquakes as they happen. Seismographs are mainly used in early detection of earthquakes, but they are also helpful for measuring the duration and intensity of a quake. The strength of a quake is measured according to the Richter Intensity Scale, which links earthquake strength to seismological readings. The Mercalli Intensity Scale is a related measure that depicts shaking intensity and damage.
Where Do the Majority of Earthquakes Occur and Why?
Over 90% of earthquakes occur along the boundaries of the continental and oceanic tectonic plates. The plates tend to have their borders at the edges of major land masses. Earthquakes take place when there is motion in these plates, brought on by conditions deep inside the Earth. There are three types of motion: plates moving away from each other (at divergent boundaries); moving toward each other (at convergent boundaries) or they sliding past one another (at transform boundaries). Any of these activities can result in rock breaking, which leads to major tectonic disturbances. Earthquakes can also occur along faults, fractures in the Earth further from the edges of plates, where sections of a plate or pair of plates are in motion. The vast majority of earthquakes are associated with plate boundaries and happen in California, Alaska, Japan, South America, and the Philippines. Only about 5% of earthquakes that take place are far from the boundaries at faults.
Plate Boundaries: Illustrated guide to the various kinds of plate movement, their location and effects.
FAQs on Earthquakes: Extensive question-and-answer format information on earthquakes, their causes, the measurement of quakes, precautions to take, and a huge variety of related topics compiled by the U.S. Geological Survey.
What is an Earthquake?: Accessible, illustrated introductions to earthquakes, geology, plate tectonics, causes of earthquakes, famous seismic events, and more.
Danger
The Richter Scale is a common means of measurement on the magnitude of the impact of an earthquake by referencing the level of seismic disturbance it causes over a given time. Earthquakes with a Richter magnitude of under 3.5 are rarely felt by people in the earthquake zone except for those who are at rest, placed on higher floors, or otherwise in favorable conditions. At 4.0 and above, there is minor shaking of grounded objects and swinging of hanging objects. From 5.0, severe damage to poorly constructed buildings is possible, though damage to well-constructed shelters will still be minimal to moderate. At 6.0, serious damage is possible over an area of 100 miles surrounding the epicenter in populated areas, and this figure increases. A 10.0 earthquake has never been recorded by humans, and earthquakes in the 8.0 to 9.9 range are very rare. By contrast, earthquakes beneath the threshold of human perception occur on a daily basis.
Richter Magnitude: Basic overview of the Richter Magnitude Scale.
Modified Mercalli Intensity Scale: Overview of the Mercalli Scale, which is used to depict damage from vibrations during earthquakes.
Japan Meteorological Society Seismic Intensity Scale (English): Description of the different levels of the seismic intensity scale used by Japanese authorities.
Preventative Measures
When possible, the most obvious way to avoid earthquake danger is to avoid common places where earthquakes occur. Earthquakes are extremely uncommon in inland areas far from tectonic plates. In the United States, the most dangerous area for earthquake activity is California; most other areas of the country are relatively safe. Earthquakes occur most frequently in an area of the Pacific known as the “ring of fire” where movement of the edges of the Pacific plate prompts earthquake and volcano activity. If you must be in an area where earthquakes are possible, there are important steps to take before and during the event. Fasten shelves securely, placing heavy objects on lower shelves and breakable items inside latched cabinets. Brace overhead light fixtures and check wiring, gas lines, and walls for faults and cracks that might contribute to fire. Stock up on supplies like flashlights, batteries, first aid kits, food and water, and medicines. During an earthquake, drop to the ground and take cover under a heavy piece of furniture. An inside corner is the safest place to wait for shaking to stop. Stay away from windows, light fixtures and fans that might fall, and avoid outside doors or walls. Remember that ground movement is relatively rare as a cause of death or injury from an earthquake; most earthquake fatalities take place due to collapsing walls, shattered glass, and impacts from falling items.
Earthquake Information from FEMA: Variety of earthquake safety topics from the Federal Emergency Management Agency.
Seven Step to Earthquake Safety: Seven-step checklist for earthquake safety before, during, and after a quake. From the Earthquake Country Alliance in the state of California.
What is Seismology?: Basic introduction to the science of seismology, which is used to measure the duration and intensity of earthquakes.
Conclusion
Earthquakes are dangerous natural disasters, and can strike suddenly, but they are confined to very specific areas. As in any crisis, it is vital to become informed and take the right precautions in order to minimize danger. Earthquakes can be particularly challenging for victims because severe seismic events may impair movement and cause panic. However, even in the most severe earthquakes, the basic rules of safety remain the same and can save lives.