Reservoir analysis of the Denver earthquakes: A case of induced seismicity

Journal Article · Tue Feb 10 04:00:00 UTC 1981 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB086iB02p00903· OSTI ID:6495005

Hsieh, P A; Bredehoeft, J D

Injection of fluid wastes into the fractured Precambrian crystalline bedrock beneath the Rocky Mountain Arsenal near Denver triggered earthquakes in the 1960's. An analysis, based on the assumption that fluid flow in the fractured reservoir can be approximated by flow in a porous medium, is presented. The configuration and hydrologic properties of the reservoir are determined from two lines of evidence: (1) locations of earthquake hypocenters determined by seismic arrays installed at the Arsenal and (2) observed long-term decline in fluid levels in the injection well. Together these two sets of data indicate that a long, narrow reservoir, aligned in the direction N 60/sup 0/W, exists. The reservoir is 3.35 km in width, extends 30.5 km to the northwest and infinitely to the southeast, and spans a depth interval from 3.7 to 7.0 km below land surface. It has a transmissivity of 1.08 x 10/sup -5/ m/sup 2//s and a storage coefficient of 1.0 x 10/sup -5/. Computed pressure buildup along the length of the reservoir is compared with the spatial distribution of earthquake epicenters. The comparison shows that earthquakes are confined to that part of the reservoir where the pressure buildup exceeds 32 bars. This critical value is interpreted as the pressure buildup above which earthquakes occur. The migration of earthquake epicenters away from the injection well, a phenomenon noted by previous investigators, can be accounted for by the outward propagation of the critical pressure buildup. The analysis is extended to examining the effects of rapid flow in fractures opened by high injection pressure. The results show that the effect is confined to a small region within 1 km of the injection well. The existence of a critical pressure buildup above which earthquakes occur is completely consistent with the theory on the role of fluid pressure in fault movement as presented by Hubbert and Rubey.

• Research Organization: U.S. Geological Survey, Reston, Virginia 22092
• OSTI ID: 6495005
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 86:B2; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580201* -- Geophysics-- Seismology & Tectonics-- (1980-1989)
COLORADO
EARTHQUAKES
FLUIDS
GEOLOGIC AGES
NORTH AMERICA
PRECAMBRIAN ERA
PRECURSOR
RESERVOIR FLUIDS
RESERVOIR ROCK
ROCKY MOUNTAIN REGION
SEISMIC EVENTS
SEISMICITY
USA