12 research outputs found
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Correlation Between Precision Gravity and Subsidence Measurements at Cerro Prieto
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Correlation Between Precision Gravity and Subsidence Measurements at Cerro Prieto
Precision gravity measurements were made in the region of the Cerro Prieto geothermal field at yearly intervals from 1977 to 1981 to assess the feasibility of using gravity to determine subsurface reservoir changes with time. The extent of mass recharge in response to the continued production of fluids from this field was studied. Changes in gravity and ground elevation were observed throughout the region for the period of observation. Results indicate that the largest changes observed were the result of the Magnitude 6.1 (Caltech) Victoria earthquake of 8 June 1980. The epicenter of this earthquake was located 25 km southeast of the field on the Cerro Prieto Fault, which bounds the field on the southwest. Subsidence of up to 55 cm was measured east of the power plant, in the region between the northern end of the Cerro Prieto Fault and the southern end of the Imperial Fault. This area has been postulated to be the site of an active spreading center or pull-apart basin, and has been characterized by a high level of seismic activity during the last 10 years. Minor subsidence and small related gravity changes for the period preceeding the Victoria earthquake suggest that in spite of large fluid production rates, the reservoir is being almost completely recharged and that a measurable increase in subsurface density may be taking place. The results of measurements of horizontal ground motions made in this area are discussed in relation to the gravity and subsidence observations
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Correlation Between Precision Gravity and Subsidence Measurements at Cerro Prieto
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An Assessment of Precise Surface Gravity Measurements for Monitoring the Response of a Geothermal Reservoir to Exploitation
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An Assessment of Precise Surface Gravity Measurements for Monitoring the Response of a Geothermal Reservoir to Exploitation
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Assessment of Precise Surface-Gravity Measurements for Monitoring the Response of a Geothermal Reservoir to Exploitation
Recommendations for carrying out surveys which achieve 15, 10 and 5 microgal precisions are presented. Achieving the smaller standard deviations will require more field effort and will be more costly. For a 60 station survey, at commercial rates in 1981, typical costs are estimated to be 26,000 and $35,000 respectively, for data collection, reduction and interpretation. These figures exclude instrument purchase or rental. Twenty geothermal areas in the western United States which might be suitable for precise repetitive gravity monitoring were evaluated. The evaluation criteria included capability for subsidence on a geological basis, estimated electrical production, environmental impact, and anticipation of production in the near future. It is felt that the most promising areas in order of priority are: (1) the Salton Sea field, California; (2) Valles Caldera, New Mexico; (3) The Geysers-Clear Lake; and (4) Westmorland, California; (5) Roosevelt Hot Springs, Utah; and (6) Heber; (7) Brawley; and (8) Long Valley, California