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.
For comparison, the magnitude 6.9 1989 San Francisco, California earthquake resulted in the deaths of 62 people, 3000 injured and $7 billion in property damage. The US Geological Survey has undertaking more intensive study of earthquake activity in the Trinidad area. Within an approximate two-week period of time, eleven quakes measuring greater than 3.0 on the Richter Scale, the largest being measured at 4.5, occurred in an area about ten miles southwest of Trinidad in the fall of 2001. Additionally, dozens of smaller magnitude quakes have also been detected.
Because the occurrence of earthquakes is relatively infrequent in Colorado and the historical earthquake record is short (only about 130 years), it is not possible to accurately estimate the timing or location of future dangerous earthquakes in Colorado.
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.
Not all of Colorado's potentially active faults are in the mountains and some can not be seen at the earth's surface. For example, the Cheraw Fault, which is in the Great Plains in southeast Colorado, appears to have had movement during the recent geologic past.
Relative to other western states, Colorado's earthquake hazard is higher than Kansas or Oklahoma, but lower than Utah, and certainly much lower than Nevada and California.
Although many of Colorado's earthquakes occurred in mountainous regions of the state, some have been located in the western valley and plateau region or east of the mountains. 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 borehole 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, well after the initial flurry of seismic activity, 15 earthquakes of approximate magnitude 2Â½ or larger have occurred in the vicinity of the northern Denver suburbs.
Summary & Conclusions: Earthquake Subcommittee - Colorado Natural Hazards Mitigation Council
Based on the historical earthquake record and geologic studies in Colorado, an event of magnitude 6Â½ to 7Â¼ could occur somewhere in the state. Scientists are unable to accurately predict when the next major earthquake will occur in Colorado, only that one will occur. The major factor preventing the precise identification of the time or location of the next damaging earthquake is the limited knowledge of potentially active faults. Given Colorado's continuing active economic growth and the accompanying expansion of population and infrastructure, it is prudent to continue the study and analysis of earthquake hazards. Existing knowledge should be used to incorporate appropriate levels of seismic safety in building codes and practices. The continued and expanded use of seismic safety provisions in critical and vulnerable structures and in emergency planning statewide is also recommended. Concurrently, we should expand earthquake monitoring, geological and geophysical research, and mitigation planning.
The Colorado Geological Survey has several publications on Colorado earthquakes and potentially active faults, and maintains a reference collection on Colorado seismicity that includes reports by consultants or agencies. A listing of the reports can be viewed at the Colorado Geological Survey web site from the "related links list."
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.
BEFORE Check for hazards in the home.
Â· Fasten shelves securely to walls.
Â· Place large or heavy objects on lower shelves.
Â· Store breakable items such as bottled foods, glass, and china in low, closed cabinets with latches.
Â· Hang heavy items such as pictures and mirrors away from beds, couches, and anywhere people sit.
Â· Brace overhead light fixtures.
Â· Repair defective electrical wiring and leaky gas connections. These are potential fire risks.
Â· Secure a water heater by strapping it to the wall studs and bolting it to the floor.
Â· Repair any deep cracks in ceilings or foundations. Get expert advice if there are signs of structural defects.
Â· Store weed killers, pesticides, and flammable products securely in closed cabinets with latches and on bottom shelves.
Â· Identify safe places in each room.
o Under sturdy furniture such as a heavy desk or table.
o Against an inside wall.
o Away from where glass could shatter around windows, mirrors, pictures, or where heavy bookcases or other heavy furniture could fall over.
Â· Locate safe places outdoors.
Â· In the open, away from buildings, trees, telephone and electrical lines, overpasses, or elevated expressways.
Â· Make sure all family members know how to respond after an earthquake. Teach all family members how and when to turn off gas, electricity, and water.
Â· Teach children how and when to call 9-1-1, police, or fire department and which radio station to tune to for emergency information.
Â· Contact your local emergency management office or American Red Cross chapter for more information on earthquakes.
Â· Have disaster supplies on hand.
o Flashlight and extra batteries
o Portable battery-operated radio and extra batteries.
o First aid kit and manual
o Emergency food and water
o Non-electric can opener
o Essential medicines
o Cash and credit cards
o Sturdy shoes
Â· Develop an emergency communication plan in case family members are separated from one another during an earthquake (a real possibility during the day when adults are at work and children are at school), develop a plan for reuniting after the disaster.
Â· 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 If indoors:
Â· Take cover under a piece of heavy furniture or against an inside wall and hold on.
Â· Stay inside.
Â· The most dangerous thing to do during the shaking of an earthquake is to try to leave the building because objects can fall on you.
Â· Move into the open, away from buildings, street lights, and utility wires.
Â· Once in the open, stay there until the shaking stops.
If in a moving vehicle:
Â· Stop quickly and stay in the vehicle.
Â· Move to a clear area away from buildings, trees, overpasses, or utility wires.
Â· Once the shaking has stopped, proceed with caution. Avoid bridges or ramps that might have been damaged by the quake.
Pets after an Earthquake
The behavior of pets may change dramatically after an earthquake. Normally quiet and friendly cats and dogs may become aggressive or defensive. Watch animals closely. Leash dogs and place them in a fenced yard.
Pets may not be allowed into shelters for health and space reasons.
Prepare an emergency pen for pets in the home that includes a 3-day supply of dry food and a large container of water.
AFTER 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.
Â· 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.
Â· Listen to a battery-operated radio or television for the latest emergency information.
Â· Remember to help your neighbors who may require special assistance--infants, the elderly, and people with disabilities.
Â· Stay out of damaged buildings. Return home only when authorities say it is safe.
Â· Use the telephone only for emergency calls.
Â· Clean up spilled medicines, bleaches or gasoline or other flammable liquids immediately. Leave the area if you smell gas or fumes from other chemicals.
Â· Open closet and cupboard doors cautiously.
Â· Inspect the entire length of chimneys carefully for damage. Unnoticed damage could lead to a fire.
INSPECTING UTILITIES IN A DAMAGED HOME 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.
You can obtain safe water by melting ice cubes.