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| Titel |
Characterisation of the Seismotectonic State of Reservoir Locations Using the Magnitude Distribution of Earthquakes |
| VerfasserIn |
C. Dinske, F. Wenzel, S. A. Shapiro |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250069008
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| Zusammenfassung |
| Fluid injections in geothermal reservoirs usually induce small-magnitude earthquakes
(M < 2). Sometimes, however, earthquakes with larger magnitudes (M ~ 4) occur. A key
point for evaluating a potential seismic hazard due to a fluid injection is to identify the
parameters which define the earthquake magnitude and its frequency. Recently, we have
shown that under rather general conditions the probability of a seismic event having a
magnitude larger than a given one increases proportionally to the injected fluid
mass. The number of earthquakes larger than a given magnitude also depends on the
seismotectonic state of the injection site. To characterise this state, we introduced the
seismogenic index Σ. It combines four, generally unknown, site-specific seismotectonic
quantities. Here we continue to comparatively analyse the seismotectonic state of several
geothermal as well as non-geothermal reservoir locations using observations from
fluid injection experiments. From our analysis it is obvious that the seismogenic
index has a characteristic range of values for geothermal reservoirs on the one hand,
[-4 < Σ < 0.5], and hydrocarbon reservoirs on the other hand, [-10 < Σ < -4]
(the higher is the seismogenic index, the higher is the probability of an earthquake
having a significant magnitude). We show that knowledge of the seismogenic index
allows for estimating the level of seismic activity. It means that we can compute the
expected number of induced earthquakes exceeding a given magnitude. Application
of the seismogenic index in combination with the homogeneous Poisson model
describing the earthquake occurrence permits to estimate the occurrence probability of a
given magnitude earthquake. Furthermore, we analyse correlations between the
seismogenic index and other injection-, reservoir- and seismicity-related parameters. We
also address the question whether natural tectonic seismic activity within an area
where a fluid injection is planned can be used to evaluate the seismotectonic state.
For this purpose, we expand and reformulate the conceptual framework valid for
fluid-induced seismicity to natural seismicity and derive an equivalent tectonic seismogenic
index. We apply this model to reservoir locations with known seismogenic index
determined from fluid-induced seismicity. We conclude from the obtained results that our
formalism contributes to evaluate a possible seismic hazard by fluid injections. |
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