If the Earth moves beneath our feet, is it because Atlas shrugged? In Greek mythology, there were twelve Titans, immortal beings of incredible strength, who ruled the world. Atlas was one of them and his role was to hold up the celestial sphere. Thankfully we’re way beyond Greek mythology.
But if you do like myths as I do, here is another one suggested by the California Department of Conservation: There’s nothing I can do about earthquakes, so why worry about them?
Well, some folks are worrying about them. The USGS Earthquake Hazards Program is responsible for monitoring, reporting, and researching earthquakes and earthquake hazards. The USGS reported that, as of September 18, there were 12, 754,003 participants registered for the upcoming Great ShakeOut Earthquake Drills.
Causes of Earthquake Shake
As W.G. Moore points out, “the damage done by the shaking (waves in the crust) provides the only lasting visible effect,” of an earthquake. But what causes this shaking?
The short answer is that the crust of the earth, when it is subject to both natural tectonic forces and human activity, bends slightly.
This bending movement can occur at a plate boundary (along or under, which is a subduction zone) or at a fault or weak point in the crust (termed mid-plate or intra-plate earthquakes and poorly understood) sometimes far away from the edges of plates. The action creates at least three distinct sets of seismic waves and as they pass a place, the ground may be felt to rock and buildings sway.
In California, for instance, we find the San Andreas Fault System, the dividing line between the Pacific tectonic plate and the North American tectonic plate. If you live in California, as my sister did for many years, you’ve heard of the myth that California could fall into the sea because of an earthquake. Why is it a myth? As the California Department of Conservation explains, “The movement is horizontal, so while Los Angeles is moving toward San Francisco, California won’t sink. However, earthquakes can cause landslides, slightly changing the shape of the coastline.”
Monitoring and Reporting Earthquakes
Monitoring all starts with earth motions that are sensed by seismometers and a permanent record produced by seismographs. Scientists then use these records to calculate the energy released by earthquakes and from that, the position on magnitude scales.
There are two main magnitude scales used for public reports, namely:
- Richter Scale– describes the amplitude of seismic waves.
- Modified Mercalli Intensity Scale- describes different earthquake effects e.g. I (not felt) to XII (total destruction).
Earthquakes under magnitude 5.0 rarely cause significant damage. As a result, the USGS only locates and produces timely reports (30 minutes or less) of earthquakes worldwide of magnitude 5.0 and larger, and in the U S, of earthquakes magnitude 4.0 and larger. At some point, however, all are displayed on the USGS’s real-time map and classified by earthquake age.
The USGS also provides a free e-mail service (ENS) that personally sends subscribers automated notifications when earthquakes happen in their area.
Prediction and Forecast of Earthquakes
Each year there are several million earthquakes throughout the world and efforts are being made to predict them in a timely fashion.
Although earthquake foreshocks have been used in some cases, the problem is there is still no way to accurately and consistently predict an earthquake by assigning a specific date, location, and magnitude.
In an effort to safeguard lives and property from the future quakes that are certain to strike, however, U.S. scientists, as part of the Natural Earthquake Hazard Reduction Program, evaluate earthquake probabilities based on seismic records. The 1989 Bay Area World Series earthquake, for instance, fell within the magnitude range, time span, and region forecast by U.S. Geological Survey staff.
I Can’t Do Anything About Earthquakes, So Why Worry?
Although we can’t prevent earthquakes, we can greatly reduce the damage done through prudent planning and preparedness.
The California Department of Conservation stresses preparation with 4 reminders:
- Put together an earthquake kit (food, water, flashlight, etc.);
- Practice “drop, cover and hold on” drills at home with your family and at work e.g register for the great October 17 ShakeOut earthquake drills;
- Develop an earthquake plan (where would you meet family members if you weren’t together when an earthquake hit?); and
- Remember that standard homeowners insurance doesn’t cover damage from earthquakes.
Like other natural disasters, the more you prepare in advance, the better off you will be. Be aware of local threats in your area, and make sure you’re ready for anything that might happen.
CA.Gov. Earthquake Mythology or… Don’t Believe Everything You Hear! Department of Conservation. Accessed September 19, 2013.
CERI. Public Awareness. Accessed September 19, 2013.
Dekel, Jon. 5.2 magnitude earthquake hits Southern Ontario and Quebec. (2013). Canada.com. Accessed September 19, 2013.
EMSC. Worldwide earthquakes with M4.0+. (2010). Accessed September 19, 2013.
Moore, W.G. A Dictionary of Geography. (1963). Penguin Reference Books.
SCEC. Uniform California Earthquake Rupture Forecast (UCERF). (2007). Accessed September 19, 2013.
USGS. Shake Map. Accessed September 19, 2013.
USGS. Modified Mercalli Intensity Scale. (2013). Accessed September 19, 2013.
USGS. California Earthquake Information. Accessed September 19, 2013.
USGS. Quaternary Fault and Fold Database of the United States Accessed September 19, 2013.
USGS. Man-Made Earthquakes. (2013). Accessed September 19, 2013.
Weinberg, Rick. World Series Halted by Bay Area Earthquake. ESPN. Accessed September 19, 2013.