Jul 032017
 

Nearly 100 potentially hazardous faults have been identified in Colorado. Generally, these are faults thought to have had movement within about the past 2 million years. There are other faults in the state that may have potential for producing future earthquakes. Because the occurrence of earthquakes is relatively infrequent in Colorado and the historical earthquake record is relatively short (only about 130 years), it is not possible to accurately estimate the timing or location of future dangerous earthquakes in Colorado. Nevertheless, the available seismic hazard information can provide a basis for a reasoned and prudent approach to seismic safety.

Faulting

Sudden movement on long 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. In some cases it is possible to evaluate how frequently large earthquakes occurred on a specific fault during the recent geological past.

Geological studies in Colorado have discovered about 100 faults that moved during the Quaternary Period (past 2 million years) and could be considered potentially active. 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 prominent and potentially active faults in Colorado. However, not all of Colorado’s potentially active faults are in the mountains. For example, the Cheraw fault, which is in the Great Plains Physiographic Province in southeast Colorado, appears to have had multiple movements during the recent geologic past. Some potentially active faults cannot be seen at the earth’s surface. The Derby fault near Commerce City lies thousands of feet below the earth’s surface. It has not been recognized at ground level, and for that reason it is not included on the CGS Earthquake and Late Cenezoic Fault and Fold Map Server [1].

Screen-shot from the Earthquake and Late Cenezoic Fault and Fold Map Server.

Screen-shot from the Earthquake and Late Cenezoic Fault and Fold Map Server.

Several potentially active faults in Colorado are thought to be capable of causing earthquakes as large as magnitude 7.2 based on recent detailed studies. In comparison, California has hundreds of hazardous faults, one or two of which can cause earthquakes of magnitude 8.0 or larger. The time interval between large earthquakes on faults in Colorado is generally much longer than on faults in California.

Past and Possible Future Earthquakes

About 400 earthquake tremors of magnitude 2.5 or higher have been reported in Colorado since 1867. More earthquakes of magnitude 2.5 to 3.0 probably occurred during that time, but were not recorded because of the sparse distribution of population and limited instrumental coverage in much of the state. The largest known historical earthquake in Colorado occurred on November 7, 1882 and had an estimated magnitude of 6.6. The location of this earthquake probably was in the northern Front Range.

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 best known Colorado earthquakes were a series of events in the 1960s that were later shown to be triggered by the injection of liquid waste into a deep borehole at the Rocky Mountain Arsenal. Twelve of the so-called “Arsenal” earthquakes caused damage, including a magnitude 5.3 earthquake on August 9, 1967 that resulted in more than a million dollars in damage in Denver and the northern suburbs. This series of earthquakes continued for about ten years and was followed by about six years of quiescence. Earthquake activity resumed in the northeast Denver area in 1978, including a magnitude 4.3 event on April 2, 1981.

Colorado’s earthquake hazard is similar to other states in the intermountain west region. It is less than in states like California, Nevada, Washington, and Oregon, but greater than many states in the central and eastern United States. It is prudent to expect future earthquakes as large as magnitude 6.6, the largest historical event in Colorado.

Conclusions and Recommendations

Based on Colorado’s historical earthquake record and geologic studies, an event as large as magnitude 6.5 to 7.2 could occur somewhere in the state. Scientists are unable to accurately predict when the next major earthquake will take place in Colorado; only that one will occur. The major factors that prevent the prediction of the timing and location of future damaging earthquakes are the limited knowledge of potentially active faults and short historical record of earthquakes. 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 into building codes and practices. Seismic safety of critical facilities and vulnerable structures is especially important. Emergency response and recovery planning should consider earthquake hazards and risk. Concurrently, we should expand earthquake monitoring, geological and geophysical research, and mitigation planning and activities.

References:

[1] Kirkham, R. M., W. P. Rogers, L. Powell, M. L. Morgan, V. Matthews, and G. R. Pattyn. “Bulletin 52B – Earthquake and Late Cenezoic Fault and Fold Map Server.” Earthquake. Bulletin. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2004.

Feb 172017
 
IS-79 Colorado Mineral and Energy Industry Activities 2015-16 (cover)

The current annual Colorado Mineral and Energy Industry Activities report 2015-16 is now available. Following up on the 2014 report, this report, based on 2015 production data, sketches a comprehensive overview of Colorado’s mineral resource production. Of note is the fact that total value of mineral and energy fuels production in Colorado for 2015 is estimated to be $13.43 billion, a 29% decline from the $18.8 billion production value in 2014. The decline was caused primarily by a precipitous decrease in oil and gas market prices which provide 70% of Colorado mineral resource revenue. Oil and gas production actually registered at all-time highs of 127.6 Mbbl and 1,709 Bcf, respectively.

Nonfuel mineral production — including metals, industrial minerals, and construction materials — posted a modest 3.9% increase in revenue. Increased production of crushed stone, cement, and sand and gravel aggregate accounted for the increase. With a 2015 production of 21,790 metric tons of molybdenum from two mines, Colorado is the largest molybdenum producer in the U.S. Although just one mine in the state publicly reported gold production in 2015, Colorado remains the third largest producer of the metal in the U.S. as it was in 2014.


Citation: Cappa, James A., Michael K. O’Keefe, James R. Guilinger, and Karen A. Berry. “IS-79 Colorado Mineral and Energy Industry Activities 2015-16.” Mineral and Energy Industry. Information Series. Golden, CO: Colorado Geological Survey, 2016.
Jan 312017
 

A collaboration between the CGS and the Denver Museum of Nature & Science (DMNS) has resulted in a new stratigraphic chart for the state of Colorado. This beautifully (offset-)printed 42″ x 39″ color chart was designed from the ground up to illustrate the Proterozoic to Holocene stratigraphy that spans the state’s many sedimentary basins. A collaborative effort led by Robert Raynolds and James Hagadorn, the chart builds upon the work of dozens of colleagues and updates Richard Pearl’s seminal 1974 stratigraphy chart. The chart leverages the community’s stratigraphic work in both the subsurface and outcrop, and depicts new geochronologic constraints for many units. To facilitate comparison of strata to external forcing factors, the chart employs a linear timescale. Each unit’s dominant depositional environment is depicted as are major mountain building events, erosional events, and regional unconformities. Printed on heavy-duty 100# coated cover stock, these rolled posters may be purchased from the CGS online bookstore. They will make a fine gift for geoscientists, rockhounds, or anyone interested in how Colorado’s magnificent landscapes came to be.



From the chart itself:

Colorado’s stratigraphy is dominated by gaps. The distribution of strata reflects the tectonic and climatic evolution of each of the region’s eleven basin areas, depicted in the map below. To foster comparison of these patterns, we have organized the stratigraphy using a linear timescale and illustrated where orogenic uplift has led to removal of strata or nondeposition. Not all orogenic features are illustrated on the chart. For example, some orogenies caused sediment ponding and accumulation in intermontane basins, such as during the Laramide in northwestern Colorado. In the past ~10 Ma, regional uplift has raised Colorado and has allowed the modern landscapes to be created due to erosion. The chart’s color scheme for stratigraphic units gives a sense of dominant lithologies and depositional environments across basins. Updates to this chart, as well as additional stratigraphic resources, such as stratigraphic and structural cross-sections, may be found at http://coloradostratigraphy.org. To learn more about the unit names on this chart, resources are available at the U.S. Geological Survey’s Geolex site. This chart scaffolds on the work of Richard H. Pearl’s 1977 compilation (Rocky Mountain Association of Geologists, Special Publication 2). With the exception of the Carboniferous and Permian periods, this data has been re-cast against the International Commission on Stratigraphy’s chronostratigraphic chart v. 2015/01, updated at http://stratigraphy.org.


Citation: Raynolds, R. G., and James W. Hagadorn. “MS-53 Colorado Stratigraphy Chart.” Stratigraphic. Map Series 53. Denver, CO: Colorado Geological Survey and the Denver Museum of Nature & Science, January 2017.