Improving the knowledge of the 2013 Castor UGS (Spain) seismic sequence from a seismological and geomechanical standpoint
The injection of fluids into the crust can modify the governing stress state and therefore generate seismic activity. The 2013 seismic sequence which took place in the area around the Castor offshore underground gas storage facility in northeastern Spain is studied here; the project aims to assess t...
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| Tipo de recurso: | tesis de maestría |
| Fecha de publicación: | 2016 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/105984 |
| Acceso en línea: | https://hdl.handle.net/2117/105984 |
| Access Level: | acceso abierto |
| Palabra clave: | Seismology Sismologia Àrees temàtiques de la UPC::Enginyeria civil::Geotècnia::Sismologia |
| Sumario: | The injection of fluids into the crust can modify the governing stress state and therefore generate seismic activity. The 2013 seismic sequence which took place in the area around the Castor offshore underground gas storage facility in northeastern Spain is studied here; the project aims to assess the anthropogenic seismicity problem. Location of a dataset of 50 earthquakes which are interpreted jointly with the largest 45, and a focal mechanism computation of the 8 strongest events were performed; seismological aspects were completed by studying the frequency-magnitude relationship. The final part of the study focused on earthquake static stress transfer as a trigger, which was quantified through Coulomb stress changes. Results show that relating earthquakes and faults from earthquake location is difficult, but focal mechanism solutions indicate that both NE-SW to NNE-SSW and NW-SE oriented planes could have hosted the earthquakes. Seismicity could have taken place at greater depths than the reservoir bottom. Frequency-magnitude distribution points towards a first phase of the sequence exhibiting a b value of around 1.5, higher than expected for tectonic earthquakes, but lower than the usually reported values for induced seismicity; afterwards, the b parameter drops towards likely values for slip in active fault systems (near to 1.0), although the linearity of the distribution should be argued. Computed static stress transfer due to the 8 largest earthquakes is consistent with the activation of an eastdipping, NE-SW-striking fault, and it should not have significantly altered return periods of characteristic tremors in the area. The question regarding the origin of seismicity cannot be rigorously addressed unless a quantitative model which considers gas injections and fluid diffusion throughout the fracture network, as well as other earthquake-triggering mechanisms, is made. |
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