Geologic studies indicate there are about 100 potentially active faults in Colorado and more than 400 earthquake tremors of magnitude 2.5 or higher have occurred in Colorado since 1870.
Movement on active faults is responsible for large earthquakes. Colorado experienced a magnitude 6.5 earthquake on November 7, 1882. The location of this earthquake appears to be in the northern Front Range west of Fort Collins. Damages included the power plant in Denver and cracked buildings in Boulder. By way of comparison, the magnitude 6.9 1989 San Francisco, California earthquake resulted in 62 deaths, 3,000 injuries, and $7 billion in property damage.
Seismologists predict that Colorado will again experience a magnitude 6.5 earthquake at some unknown point in the future.
Sudden movement on faults is responsible for large earthquakes. By studying the geologic characteristics of faults, geoscientists can often determine when the fault last moved and estimate the magnitude of the earthquake that produced the last movement.
The Sangre de Cristo Fault, which lies at the base of the Sangre de Cristo Mountains along the eastern edge of the San Luis Valley, and the Sawatch Fault, which runs along the eastern margin of the Sawatch Range, are two of the most prominent potentially active faults in Colorado. In addition, the Cheraw Fault, located in southeast Colorado, appears to have had movement during the recent geologic past.
The most economically damaging earthquake in Colorado's history occurred on August 9, 1967 in the northeast Denver metropolitan area. This magnitude 5.3 earthquake, which was centered near Commerce City, caused more than a million dollars damage in Denver and the northern suburbs. This earthquake is believed to have been induced by the deep injection of liquid waste into a bore hole at Rocky Mountain Arsenal. It was followed by an earthquake of magnitude 5.2 three months later in November 1967. Although these events cannot be classified as major earthquakes, they should not be discounted as insignificant. They occurred within Colorado's Front Range Urban Corridor, an area where nearly 75% of Colorado residents and many critical facilities are located. Since March 1971, 15 earthquakes of approximate magnitude 2.5 or larger have occurred in the vicinity of the northern Denver suburbs.
Be Prepared Before and Earthquake
Earthquakes strike suddenly, violently and without warning. Identifying potential hazards ahead of time and advance planning can reduce the dangers of serious injury or loss of life from an earthquake.
- Fasten shelves securely to walls. Place large or heavy objects on lower shelves.
- Store breakable items such as bottled foods, glass, and china in low, closed cabinets with latches.
- Hang heavy items such as pictures and mirrors away from beds, couches, and anywhere people sit.
- Brace overhead light fixtures.
- Repair defective electrical wiring and leaky gas connections. These are potential fire risks.
- Secure a water heater by strapping it to the wall studs and bolting it to the floor.
- Repair any deep cracks in ceilings or foundations. Get expert advice if there are signs of structural defects.
- Store weed killers, pesticides, and flammable products securely in closed cabinets with latches and on bottom shelves.
- Identify safe places in each room: under sturdy furniture such as a heavy desk or table, against an inside wall, and away from where glass could shatter or heavy bookcases or other furniture could fall over.
- Locate safe places outdoors: In the open, away from buildings, trees, telephone and electrical lines, overpasses, or elevated expressways.
- Make sure all family members know how to respond after an earthquake. Teach them how and when to turn off gas, electricity, and water.
- Contact your local emergency management office or American Red Cross chapter for more information on earthquakes.
- Have disaster supplies on hand.
- Develop an emergency communication plan in case family members are separated from one another during an earthquake and develop a plan for reuniting after the disaster.
- Ask an out-of-state relative or friend to serve as the "family contact." After a disaster, it's often easier to call long distance. Make sure everyone in the family knows the name, address, and phone number of the contact person.
During an Earthquake--Indoors
- Take cover under a piece of heavy furniture or against an inside wall and hold on.
- Stay inside. The most dangerous thing to do during an earthquake is to try to leave the building because objects can fall on you.
During an Earthquake--Outdoors
- Move into the open, away from buildings, street lights, and utility wires.
- Once in the open, stay there until the shaking stops.
- If in a moving vehicle:
- Stop quickly and stay in the vehicle.
- Move to a clear area away from buildings, trees, overpasses, or utility wires.
- Once the shaking has stopped, proceed with caution. Avoid bridges or ramps that might have been damaged by the quake.
After an Earthquake
- Be prepared for aftershocks. Although smaller than the main shock, aftershocks cause additional damage and may bring weakened structures down. Aftershocks can occur in the first hours, days, weeks, or even months after the quake.
- Help injured or trapped persons. Give first aid where appropriate. Do not move seriously injured persons unless they are in immediate danger of further injury. Call for help.
- Listen to a battery-operated radio or television for the latest emergency information.
- Remember to help your neighbors who may require special assistance--infants, the elderly, and people with disabilities.
- Stay out of damaged buildings. Return home only when authorities say it is safe.
- Use phones only for emergency calls.
- Clean up spilled medicines, bleaches or gasoline or other flammable liquids immediately. Leave the area if you smell gas or fumes from other chemicals.
- Open closet and cupboard doors cautiously.
- Inspect the entire length of chimneys carefully for damage. Unnoticed damage could lead to a fire.
Inspecting Utilities After an Earthquake
Check for gas leaks--If you smell gas or hear blowing or hissing noise, open a window and quickly leave the building. Turn off the gas at the outside main valve if you can and call the gas company from a neighbor's home. If you turn off the gas for any reason, it must be turned back on by a professional.
Look for electrical system damage--If you see sparks or broken or frayed wires, or if you smell hot insulation, turn off the electricity at the main fuse box or circuit breaker. If you have to step in water to get to the fuse box or circuit breaker, call an electrician first for advice.
Check for sewage and water lines damage--If you suspect sewage lines are damaged, avoid using the toilets and call a plumber. If water pipes are damaged, contact the water company and avoid using water from the tap.