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| Titel |
Induced seismicity at Berlín geothermal field, El Salvador: Spatiotemporal characteristics of microearthquakes down to MW - 0.5 |
| VerfasserIn |
Grzegorz Kwiatek, Fatih Bulut |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250055202
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| Zusammenfassung |
| As presented by a number of field observations in geothermal sites, larger magnitude events
(LMEs hereafter) might be triggered by the shut-in of the wells. It is strongly believed that
fluid injection decreases effective normal stress within the pre-existing fractures resulting in
LMEs depending on injection rate. The GEISER (Geothermal Engineering Integrating
Mitigation of Induced Seismicity in Reservoirs) project has been developed to investigate the
induced seismicity in various geothermal sites focusing on generation process of the
LMEs. In this context, we investigate microseismic activity monitored at Berlín
geothermal field, El Salvador, during a hydraulic stimulation. We used data from a
local seismic network deployed in direct vicinity of simulated area. The network
consists of 12 3-component geophones located in 6 boreholes. Here we analyze
approx. 600 seismic events ranging from MW - 0.5 to MW3.8. Daily rate of the
seismicity indicates remarkable rise in the number of seismic events for particular
time spots compared to the background seismicity and correlates to injection rate.
The largest event considered to be LME (MW3.8) occurred after the shut-in of
injection well. We investigate physical process behind temporal clustering of the
earthquakes using refined hypocenter catalogue. We improve the hypocenter distribution
using Double-Difference relocation technique based on cross-correlation-derived
differential travel times. This provides insight into 3-D view of fault-network and
spatiotemporal behavior of the seismicity, and therefore allows better understanding the
interaction of neighboring sources along the target area. Our preliminary analysis shows
that temporal clusters are characterized by co-located earthquakes representing
progressive failure of adjacent sources within several hours. The source parameters
of co-located events are precisely calculated using spectral ratio technique that
eliminates unknown path effects commonly introduced to the seismic data. The applied
methodology allows characterizing the spatiotemporal distribution of various source
parameters, such as static stress drop and apparent stress, in a well-resolved scale. |
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