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| Title: |
Seismic monitoring of EGS tests at the Coso Geothermal area, California, using accurate MEQ locations and full moment tensors |
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| Creator/Author: |
Foulger, G.R.
;
B.R. Julian, B.R.
;
F. Monastero
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| Publication Date: | 2008 Apr 01 |
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| OSTI Identifier: | OSTI 926252 |
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| Report Number(s): | Final Report supplement 2 |
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| DOE Contract Number: | FG36-06GO16058 |
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| Document Type: | Conference |
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| Specific Type: | |
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| Coverage: | |
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| Resource Relation: | Journal Volume: SGP-TR-185; Conference: Thirty-Third Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, California, January 28-30, 2008. |
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| Other Number(s): | |
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| Research Org: | Gillian R. Foulger (Foulger Consulting) |
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| Sponsoring Org: | USDOE - Office of Geothermal Technologies(EE-12) |
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| Subject: | 15 GEOTHERMAL ENERGY |
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| Keywords: | geothermal, earthquakes, hydrofracturing |
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| Description/Abstract: | We studied high-resolution relative locations and full
moment tensors of microearthquakes (MEQs)
occurring before, during and following Enhanced
Geothermal Systems (EGS) experiments in two wells
at the Coso geothermal area, California. The
objective was to map new fractures, determine the
mode and sense of failure, and characterize the stress
cycle associated with injection. New software
developed for this work combines waveform crosscorrelation
measurement of arrival times with relative
relocation methods, and assesses confidence regions
for moment tensors derived using linearprogramming
methods. For moment tensor
determination we also developed a convenient
Graphical User Interface (GUI), to streamline the
work.
We used data from the U.S. Navy?s permanent
network of three-component digital borehole
seismometers and from 14 portable three-component
digital instruments. The latter supplemented the
permanent network during injection experiments in
well 34A-9 in 2004 and well 34-9RD2 in 2005. In the
experiment in well 34A-9, the co-injection
earthquakes were more numerous, smaller, more
explosive and had more horizontal motion, compared
with the pre-injection earthquakes. In the experiment
in well 34-9RD2 the relocated hypocenters reveal a
well-defined planar structure, 700 m long and 600 m
high in the depth range 0.8 to 1.4 km below sea level,
striking N 20° E and dipping at 75° to the WNW. The
moment tensors show that it corresponds to a mode I
(opening) crack. For both wells, the perturbed stress
state near the bottom of the well persisted for at least
two months following the injection. |
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| Publisher: | |
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| Country of Publication: | US |
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| Language: | English |
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| Size/Format: | Medium: ED; Size: 261-268, |
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| Rights: | |
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| Availability: | http://www.dur.ac.uk/g.r.foulger/Offprints/MTStanford2008Paper.pdf |
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| System Entry Date: | 2008 Aug 25 |
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