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| Titel |
Linking an injection fracture model to seismicity: Application to the Krafla 1975-1984 Caldera unrest episode (Iceland) to estimate overpressure, acting stress gradients and variations of dike opening. |
| VerfasserIn |
Torsten Dahm, Bryndís Brandsdóttir, Páll Einarsson |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250038365
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| Zusammenfassung |
| Recently, a 2D injection model has been developed to explain the asymmetric growth of
hydro-fracture induced seismicity in a gas formation (Fischer et al., 2009, GJI, 179,
634-639; Dahm et al., 2010, JGR, in review). The theory explains nonlinear and
asymmetric bi- and unilateral growth of the seismicity with respect to the injection
center and variations of the event-rate as well as the occurrence of a seismicity
backfront.
The Krafla 1975-1984, North Iceland, caldera unrest and rifting episode is an exemplary case
of subsequent, alternating, bi- and unilateral dike intrusions over a length of more than 70
km, fed by a central shallow magma chamber beneath the Krafla caldera. Altogether, 16 or
more crustal dike events occurred over the period of 9 years. Each dike emplacement was
accompanied by rapid caldera deflation, and each dike induced a trace of migrating weak
earthquakes which were observed on local seismic stations. The Krafla unrest is
one of the best studied rifting events until today. However, dynamic parameters of
the intrusions and the controlling pressures and stress distributions are still poorly
known.
We apply the new intrusion-seismicity model to the Krafla events in order to estimate
pre-intrusion magma pressure, stress gradients and the time-dependent dike opening for the
largest of the intrusions. Although the model is 2D only, it gives interesting insights in the
mechanics of lateral rifting events and first order estimates of internal pressures and stress
gradients. |
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