Earthquakes may not be the first disaster that comes to mind when developing risk and hazard assessments for workers on a job site, but depending on the part of the country that one works, earthquakes and associated hazards should be included in your job- or task-specific health and safety plan (HASP), and in your Job Hazard Analysis (JHA) or Job Safety Analysis (JSA). Awareness of earthquake hazards could save a worker from serious injury or even death.
The following National Seismic Hazard Map was developed in 2014 by the U.S. Geological Survey (USGS) ranking the level of potential seismic hazards in the various geographic areas of the U.S., including Alaska and Hawaii.
As indicated on the USGS map, the geographic areas in the U.S. with a higher potential for earthquake hazards include the Rocky Mountains west to the Pacific coast, Alaska, Hawaii, areas in the south-central region, and to a lesser extent, New England. Typically, the magnitude of earthquakes is numerically indicated on the Richter magnitude scale, which was developed in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes. The Richter scale is a logarithmic scale used to express the energy released by an earthquake. Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a ten-fold increase in measured amplitude; as an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.
Most earthquakes occur when the frictional stress between Earth’s plates slowly moving along fault lines builds up to a point when that stress is released, sometimes in a sudden movement, the resultant release of energy manifests on the Earth’s surface. In the western U.S., earthquake faults can be hundreds of miles long and be visible on the surface of the earth. A good example is the San Andreas fault that runs somewhat parallel to the coast of California. In the central U.S., faults are buried deep underground and are generally categorized as “seismic zones”, or areas where many smaller faults are clustered together to produce seismic activity. A good example is the New Madrid seismic zone centered near the confluence of Missouri, Arkansas, and Tennessee, and the location of the largest known earthquake east of the Rocky Mountains in 1811-1812.
Earthquakes and seismic activity occur daily at various locations throughout the U.S. and the world. Seismic monitoring uses sensitive seismographs to record the ground motion from seismic waves created by earthquakes or other sources. Seismograms from seismic monitoring stations can be used to determine the location, origin time, and magnitude (as well as other characteristics) of earthquakes. Most of these earthquakes are too small of a magnitude to be felt by humans on the Earth’s surface. The magnitude of these smaller earthquakes on the Richter scale is about 2.0 or less, they are usually called micro-earthquakes, and are generally recorded only on local seismographs. Earthquakes with magnitudes of about 4.5 or greater (there are several thousand such shocks annually) are strong enough to be recorded by sensitive seismographs all over the world.
However, although the occurrence is rare, a higher magnitude earthquake can occur at any time with little to no advanced notice, and result in catastrophic damage to property and human life. Great earthquakes, such as the 1964 Good Friday earthquake in Alaska, have magnitudes of 8.0 or higher. On average, one earthquake of such size occurs somewhere in the world each year. Although the Richter scale has no upper limit, the largest known shocks have had magnitudes in the 8.8 to 8.9 range. Despite some successes and considerable interest and efforts in earthquake prediction, there currently is no consistently reliable method for predicting earthquakes, so significant events occur suddenly and without warning. The type of hazard depends on the strength of seismic activity, along with such factors as local topographic and built features, subsurface geology, and groundwater. A large earthquake will always be followed by a sequence of aftershocks, some of which can cause just as much damage as the initial earthquake.
It is for these types of higher magnitude earthquakes that one must be prepared while working at a job site. The following provides some general information on some of the primary hazards associated with these higher magnitude earthquakes of which workers should be aware if an earthquake strikes at their job site.
Ground Shaking
If the magnitude of an earthquake is large enough, the intensity of ground shaking can be sufficient to severely damage structures like buildings, bridges, and dams. Any worker within a building could be at risk for contact by falling building debris or overhead objects resulting in injury or death. In the largest earthquakes, whole districts can be devastated by the multiple consequences of ground shaking. Ground shaking will vary over an area due to such factors as topography, bedrock type, and the location and orientation of the fault rupture. These all affect the way the seismic waves travel through the ground.
If you are inside a building when an earthquake strikes, officials say you should DROP, COVER, and HOLD ON to shelter until the shaking stops. DROP to your hands and knees where you are, which will protect you from being knocked down, and allows you to stay low and crawl to shelter, if nearby. COVER your head and neck with one arm and hand.
- If a sturdy table or desk is nearby, crawl underneath it for shelter.
- If no shelter is nearby, crawl next to an interior wall (away from windows).
- Stay on your knees; bend over to protect vital organs.
HOLD ON until the shaking stops:
- Under shelter: hold on to it with one hand; be ready to move with your shelter if it shifts.
- No shelter: hold on to your head and neck with both arms and hands.
If you are in a high-rise or multi-story building, follow DROP, COVER, and HOLD ON. In addition:
- Move away from windows and outside walls.
- Stay inside of the building.
- DO NOT use the elevators, if present. The electricity may go out and the sprinkler systems may come on.
- If you are trapped, stay calm. If possible, try to send a text or place a cell phone call. Try to get someone’s attention by banging on hard or metal parts of the structure. Doing so may increase your chances of being rescued. Cover your mouth with your shirt for protection and instead of shouting, use a whistle.
IF YOU ARE INSIDE, STAY INSIDE. DO NOT run outside or to other rooms during an earthquake. You are less likely to be injured if you stay where you are. DO NOT stand in a doorway, as you are safer under a table. Once the shaking stops, please be aware that aftershocks could occur shortly after the initial earthquake, and be prepared to repeat the DROP, COVER, and HOLD ON procedure. Once the earthquake shaking stops, if the building that you are in is damaged, go outside and quickly move away from the building. Do not enter damaged buildings.
IF YOU ARE OUTSIDE, STAY OUTSIDE.
- Move away from buildings, utility wires, sinkholes, and fuel and gas lines. The greatest danger from falling debris is just outside doorways and close to outer walls of buildings.
- Go to an open area away from trees, telephone poles, and buildings. Once in the open, get down low and stay there until the shaking stops.
- The area near the outside walls of a building is the most dangerous place to be. Windows, facades, and architectural details are often the first parts of the building to collapse. Stay away from this danger zone.
If you are in a moving vehicle, stop as quickly and safely as possible.
- Move your vehicle to the shoulder or curb, away from utility poles, overhead wires, and under- or overpasses.
- Stay in the vehicle and set the parking brake. A vehicle may jiggle violently on its springs, but it is a good place to stay until the shaking stops.
- Turn on the radio for emergency broadcast information.
- If a power line falls on the vehicle, stay inside until a trained person removes the wire.
- When it is safe to begin driving again, watch for hazards created by the earthquake, such as breaks in the pavement, downed utility poles and wires, rising water levels, fallen overpasses, or collapsed bridges.
As part of the Job Safety Analysis (JSA) or Job Hazard Analysis (JHA), the area of the job site should be evaluated to identify whether any dams are located upgradient or upstream of the job site. Catastrophic dam failure is unlikely, but if your job site is downstream from a dam, you should know flood-zone information and have prepared an evacuation plan for getting to high ground as quickly and safely as possible.
Underground natural gas lines and other fuel lines can rupture during an earthquake. If ruptured lines are encountered during or after an earthquake as indicated by a hissing sound, odors, or fire, the area should be immediately evacuated as quickly and safely as possible to avoid fire and explosion hazards from the ruptured lines.
Live downed power lines may be present after an earthquake. Avoid contact with any downed power lines or electrical conduit (metal pipes and sheeting, pools of water, etc.) that unknowingly may be in contact with live power lines.
Tsunami
A tsunami is a series of enormous, long wavelength ocean waves generated by the sudden displacement of seawater by a shallow earthquake, volcanic eruption, or submarine landslide. Tsunamis can travel 20 to 30 miles per hour with waves 10 to 100 feet high. Several waves may be produced which can travel long distances at high speeds to flood far-off shores. The height of a tsunami varies and may be affected by the sea floor depth and underwater topography, and other factors. Near-source tsunamis will allow for very little warning. In the U.S., the greatest risk for tsunamis is along coasts that border the Pacific Ocean or the Caribbean Sea. Signs of an impending tsunami include a sudden rise or draining of ocean waters.
Large earthquakes also may generate tsunami waves in enclosed water bodies such as large lakes. In the U.S., tsunamis can occur and have occurred on the Great Lakes . As another example, evidence of tsunamis has been documented at Lake Tahoe .
If you are in a tsunami area and there is an earthquake, first protect yourself from the earthquake by following DROP, COVER, and HOLD ON. When the shaking stops, if there are natural signs or official warnings of a tsunami, then move immediately to a safe place as high and as far inland as possible. Listen to the authorities, but do not wait for tsunami warnings and evacuation orders. If you are outside of the tsunami hazard zone and receive a warning, then stay where you are unless officials tell you otherwise.
If a job site is located near the ocean or a large, enclosed body of water, the job site should be evaluated for the potential of tsunamis as part of the Job Safety Analysis (JSA) or Job Hazard Analysis (JHA). Also, an evacuation plan should be included for getting to high ground as quickly and safely as possible.
Landslides, Rockfalls, and Avalanches
If your job site is located on a relatively steeper slope such as the side of a mountain or larger hill, some other potential hazards to evaluate as part of the Job Safety Analysis (JSA) or Job Hazard Analysis (JHA) are landslides, rockfalls, and avalanches. Ground shaking during earthquakes can destabilize cliffs and steep slopes, causing landslides and rockfalls as a significant side-effect. Heavy rain and unconsolidated or fractured rock are exacerbating factors.
In areas of accumulated significant snowfall, avalanches also are a potential hazard at a job site because of ground shaking during an earthquake. Avalanches occur when four ingredients are present: a slab, a weak layer, a trigger, and a slope angle steep enough to slide, generally between 25 to 45 degrees. Ground shaking from an earthquake can provide the trigger needed for an avalanche to occur. Not all slopes are steep enough to avalanche and some are too steep to regularly form slabs of accumulated snow.
Once triggered, landslides, rockfalls, and/or avalanches have the potential to engulf, seriously injure, or bury workers located downslope from the triggered release. Also, buildings and other structures can be heavily damaged or destroyed resulting in additional hazards to site workers. Depending on the location of your job site, the potential for landslides, rockfalls, and avalanches should be evaluated as part of the Job Safety Analysis (JSA) or Job Hazard Analysis (JHA).
Be Prepared
If your job site is in an area of higher risk for an earthquake, a disaster kit could be compiled for potential use during the emergency. Disaster kits are recommended to include:
- First aid kit
- Enough supplies of food and water to last three days
- Battery-operated radio
- Satellite phone (if no cell phone service in the area)
- Flashlights and batteries
- Blankets
- Extra clothing and more
In addition to these items, a personal or work cell phone that you carry with you is important to have, if in an area where there is cell service. The best time to prepare for hazards associated with earthquakes is before one occurs. Once potential hazards associated with earthquakes are identified for your job site and a plan is developed to address those potential hazards, then training employees on the components of that plan by conducting periodic earthquake drills is the best next step.
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