Definitions

earthquake    a vibration or movement of a part of the earth's surface, due to the faulting of rocks, to volcanic forces, etc.     

Introduction

Colorado is generally considered to be an area which has little earthquake activity. In fact, Eastern Colorado has almost no seismic activity at all. Most of the earthquakes which have been observed in Colorado have occurred west of the Front Range of the Rocky Mountains.

The first known reference to an earthquake here in Colorado was on December 4, 1870. The report consists of an account of bottles on a shelf, one inch apart which were knocked together violently. This took place at Fort Reynolds, about 20 miles east of Pueblo.

Between this early quake, and the availability of seismographs of sufficient quality and quantity to make accurate records of tremors, a period of over 80 years passed. During this time, newspaper articles were the primary source of information in published form regarding earthquake activity.

You may well ask, if Colorado has such infrequent earthquake activity, then why should we here in Fort Collins be concerned? Interestingly enough, the largest earthquake in all of Colorado's history took place on November 7, 1882 and the epicenter was described as "west of Fort Collins!" This was also the first recorded earthquake to cause damage in Denver. It was estimated to be a magnitude 6.6 on the Richter Scale and caused moderate damage in Boulder where plaster fell from the walls at the University of Colorado. This quake was felt as far away as Salina, Kansas and Salt Lake City, Utah. The magnitude of this earthquake has been extrapolated by USGS seismologists from information about the distances from which it was felt. Fortunately, in those days Fort Collins was not heavily populated and urbanized.

If we had a magnitude 6.6 earthquake in Fort Collins tomorrow, what do you think the result would be? By comparison, the devastating Northridge earthquake in Southern California at 4:31 a.m. on January 17, 1994 was also a magnitude 6.6 earthquake. Here are some photographs of the results...

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Severe structural damage to an apartment complex. This earthquake was the largest and most costly disaster to which FEMA has ever responded. Click photo for larger version.

PLANNING

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Severe structural damage to concrete and steel freeway overpass. The damage area from this event covered 2,192 square miles in Los Angeles, Ventura, and Orange counties. Click photo for larger version.

EDUCATION

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A flattened freeway structure. Assessed damage costs from this earthquake are estimated at $25 billion. Click photo for larger version.

MITIGATION

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A collapsed parking structure. The earthquake epicenter was one mile south of Northridge at a depth of 11 miles. Click photo for larger version.

TRAINING

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Here an apartment complex suspended above a parking garage collapsed onto the vehicles below. There have been at least 14,000 recorded aftershocks from this event including 11 of magnitude 5.0 or greater. Click photo for larger version.

NOTIFICATION

The most damaging earthquake ever recorded in Colorado took place on August 9, 1967 near the Rocky Mountain Arsenal. This quake was measured at 5.3 on the Richter Scale, and rated intensity VI or VII on the Modified Mercalli Intensity Scale. It caused damage in Northglenn, Commerce City, Denver, and other nearby cities.

Since the 1960's, Colorado has had a few moderate earthquakes, but none in excess of 4.0 on the Richter Scale.

Definitions and Introduction | The Modified Mercalli Intensity Scale | The Richter Magnitude Scale | Colorado's Seismic Risk | Secondary Hazard Events | Survival Tips