How could the largest earthquake in any underground gas storage be induced at Castor?
The Underground Gas Storage (UGS) project of Castor, Spain, caused the three largest earthquakes (M4.08, M4.01 and M3.97) ever induced by any of the more than 640 UGS facilities all around the world. Injection of cushion gas, which lasted for 15 days, induced hundreds of seismic events, with the largest earthquakes being felt by the local population despite the platform was located some 20 km off the coast. The project was finally cancelled, implying an investment compensation to the operating company that may cost up to 4.73 billion euros to Spanish citizens. The largest magnitude earthquakes at Castor have the following interesting features: 1) they occurred 20 days after the stop of injection, 2) they nucleated between 4 to 10 km, much deeper than the injection depth, i.e., 1.7 km, and 3) they are the largest ever induced in a UGS. We have proposed a plausible combination of triggering mechanisms that explains these features of the induced seismicity (Vilarrasa et al., 2021). First, gas injection reactivated, through pore pressure buildup and buoyancy, the critically stressed Amposta fault, which bounded the storage formation. The Amposta fault crept even after the stop of injection because of the permanent effect of buoyancy caused by the injected gas. The progressive accumulation of aseismic slip of the Amposta fault eventually reactivated a critically stressed unmapped deep fault through shear slip stress transfer. Once this deep fault was reactivated, the sequence of earthquakes was induced by shear slip stress transfer, with transient deformation-induced pore pressure changes likely controlling the delay between earthquakes. The high risk of inducing seismicity at Castor would have been identified prior to gas injection by analyzing fault stability.
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| Format: | comunicación de congreso biblioteca |
| Language: | English |
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2021-06-10
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| Subjects: | Gas storage, Castor Project, |
| Online Access: | http://hdl.handle.net/10261/246857 |
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