Induced seismicity in pressurised single fractures: a numerical approach

The exploration and exploitation of deep geothermal reservoirs has significantly increased during the last years. These reservoirs use heat exchange to produce heat or electricity. The so-called Enhanced Geothermal Systems (EGS) are characterized by a stimulation phase that aims to increase fluid flow and heat transfer between wells by increasing the permeability and transitivity of the reservoir. This is achieved by injecting high-pressure fluids (normally water) in order to increase the apertures of existing fractures, enhancing their sliding and/or generating new ones. However, this technique induces low-magnitude seismicity that occasionally results in damage at the Earth's surface. Numerical simulations able to reproduce the hydro-thermo-mechanical behaviour of geological reservoirs are an essential tool for the evaluation and forecasting of induced seismicity in such systems. In this study, the numerical code CFRAC is used to systematically evaluate how the orientation of faults with respect to the stress field influences seismicity, the injection rate and the fracture sliding behaviour

Earthquake static stress transfer in the 2013 Gulf of Valencia (Spain) seismic sequence

On 24 September 2013, an Ml 3.6 earthquake struck in the Gulf of Valencia (Spain) near the Mediterranean coast of Castelló, roughly 1 week after gas injections conducted in the area to develop underground gas storage had been halted. The event, felt by the nearby population, led to a sequence build-up of felt events which reached a maximum of Ml 4.3 on 2 October. Here, we study the role of static stress transfer as an earthquake-triggering mechanism during the main phase of the sequence, as expressed by the eight felt events. By means of the Coulomb failure function, cumulative static stress changes are quantified on fault planes derived from focal mechanism solutions (which act as both source and receiver faults) and on the previously mapped structures in the area (acting only as stress receivers in our modeling). Results suggest that static stress transfer played a destabilizing role and point towards an SE-dipping structure underlying the reservoir (or various with analogous geometry) that was most likely activated during the sequence. One of the previously mapped faults could be geometrically compatible, yet our study supports deeper sources. Based on this approach, the influence of the main events in the occurrence of future and potentially damaging earthquakes in the area would not be significant.Peer ReviewedPostprint (published version

DInSAR coseismic deformation of the May 2011 Mw 5.1 Lorca earthquake, (Southern Spain)

The coseismic superficial deformation at the region of Lorca (Murcia, southeastern Spain) due to the Mw 5.1 earthquake on 11 May 2011 was characterized by a multidisciplinary team, integrating information from DInSAR, GPS and numerical modelling techniques. Despite the moderate magnitude of the event, quantitative information was obtained from the interferometric study of a pair of TerraSAR-X images. The DinSAR results defined the trace of the fault plane and evidenced uplift of the hanging wall block in agreement with the estimated deformation obtained through an elastic rupture dislocation numerical model. Meanwhile for the footwall block, interferometric results showed that tectonic deformation is masked by an important subsidence related to groundwater extraction previously identified at the area of study. Horizontal crustal deformation rates and velocity vectors,obtained from GPS stations existent at the area, were also coherent with the tectonic setting of the southern margin of the Iberian Peninsula and with the focal mechanism calculated or the Lorca event. The analysis of a continuous GPS site in Lorca showed good agreement with the horizontal NS direction component relative to the numerical model and tectonics of the region. This is the first time at this seismic active area that a multitechnique analysis has been performed immediately after the occurrence of a seismic event, comparing the existing deformation data with a theoretical numerical model based on estimated seismic rupture dislocation

Present-day deformation of the Pyrenees revealed by GPS surveying and earthquake focal mechanisms until 2011

The Pyrenean mountain range is a slowly deforming belt with continuous and moderate seismic activity. To quantify its deformation field, we present the velocity field estimated from a GPS survey of the Pyrenees spanning 18 yr. The PotSis and ResPyr networks, including a total of 85 GPS sites, were installed and first measured in 1992 and 1995 1997, respectively, and remeasured in 2008 and 2010. We obtain a deformation field with velocities less than 1 mm yr−1 across the range. The estimated velocities for individual stations do not differ significantly from zero with 95 per cent confidence. Even so, we estimate a maximum extensional horizontal strain rate of 2.0 ± 1.7 nanostrain per year in a N S direction in the western part of the range. We do not interpret the vertical displacements due to their large uncertainties. In order to compare the horizontal strain rates with the seismic activity, we analyse a set of 194 focal mechanisms using three methods: (i) the 'r' factor relating their P and T axes, (ii) the stress tensors obtained by fault slip inversion and (iii) the strain-rate tensors. Stress and strain-rate tensors are estimated for: (i) the whole data set, (ii) the eastern and western parts of the range separately, and (iii) eight zones, which are defined based on the seismicity and the tectonic patterns of the Pyrenees. Each of these analyses reveals a lateral variation of the deformation style from compression and extension in the east to extension and strike-slip in the west of the range. Although the horizontal components of the strain-rate tensors estimated from the seismic data are slightly smaller in magnitude than those computed from the GPS velocity field, they are consistent within the 2σ uncertainties. Furthermore, the orientations of their principal axes agree with the mapped active faults

Особенности профессионального выгорания субъектов образовательного процесса

Мушкевич Мирослава Іванівна - канд. псих. наук, доцент, зав. кафедрою медичної психології та психодіагностики Східноєвропейського національного університету ім. Лесі Українк

El método del espectro de capacidad aplicado a la evaluación de daños sísmicos

El método del espectro de capacidad constituye una herramienta nueva que se puede utilizar para el análisis de daños estructurales y no estructurales debidos a una acción sísmica tanto para la generación de escenarios de daños como para la rehabilitación de edificios. Basándose en parámetros espectrales como desplazamiento o aceleración, el método del espectro de capacidad es un procedimiento de análisis estructural no lineal simplificado. Una aplicación preliminar del método en la estimación del riesgo sísmico se ha hecho para un espectro de demanda adaptado a las condiciones locales de la ciudad de Barcelona. Los resultados se han comparado con otros estudios anteriores.The Capacity Spectrum Method is a recent tool which could be very useful far the analysis of structural and non-structural seismic damages far producing damage scenarios and far buildings retrofitting. Based on spectral parameters like displacement or acceleration, the Capacity Spectrum Method is a simplified han linear structural analysis procedure. A preliminary application of this method has been carried out in arder to estímate the seismic risk corresponding to the local site conditions far the city of Barcelona. The results are compared with previous studies.Peer ReviewedPostprint (published version

Recent vertical movements from precise leveling data in Catalonia

To determine recent vertical movements (R.V.M.) from precise leveling data we have compared the original height differences recorded in the field by the Instituto Geografico Nacional in two different campaigns. The accuracy, number of releveled bench marks and leveling paths of the two campaigns are adecuated to measure R.V.M.. The two studied profiles show significatives R.V.M.. Two steps of about 150 mm ± 30 mm, in 37 and 38 years (4 mm/year of relative velocity), which have, partially, tectonic origin has been obtaine

Integration of a permanent OBS offshore NE Iberian Peninsula to the CAtalan Seismic Network

We summarize the results of more than 3 years of operation of a permanent Ocean Bottom Seismometer (OBS)deployed 40 km offshore Catalonia in terms of the site ambient noise conditions and quality of the data acquired. As observed on most of the ocean-floor observatories, the noise level at the OBS site is quite large on all components. However, the integration of the OBS station into the Catalan seismic network has allowed to improve hypocenter locations

Induced seismicity in enhanced geothermal systems: a numerical investigation on the influence of the friction model

Hydraulic stimulation in Enhanced Geothermal Systems (EGS) produces low-magnitude induced seismicity that sometimes can result in damage at the Earth's surface. Numerical simulations taking into account the hydrothermo- mechanic behaviour of geological reservoirs are an essential tool in order to evaluate and forecast induced seismicity in such systems. In this study, the numerical code CFRAC is used to evaluate the seismicity of an isolated fault during fluid injection using two different frictional models: (i) rate-and-state and (ii) velocity weakening. The results show that both models predict similar microseismicity, although there are differences in the number of events and their magnitudes between both models

Earthquake static stress transfer in the 2013 Gulf of Valencia (Spain) seismic sequence

On 24 September 2013, an Ml 3.6 earthquake struck in the Gulf of Valencia (Spain) near the Mediterranean coast of Castelló, roughly 1 week after gas injections conducted in the area to develop underground gas storage had been halted. The event, felt by the nearby population, led to a sequence build-up of felt events which reached a maximum of Ml 4.3 on 2 October. Here, we study the role of static stress transfer as an earthquake-triggering mechanism during the main phase of the sequence, as expressed by the eight felt events. By means of the Coulomb failure function, cumulative static stress changes are quantified on fault planes derived from focal mechanism solutions (which act as both source and receiver faults) and on the previously mapped structures in the area (acting only as stress receivers in our modeling). Results suggest that static stress transfer played a destabilizing role and point towards an SE-dipping structure underlying the reservoir (or various with analogous geometry) that was most likely activated during the sequence. One of the previously mapped faults could be geometrically compatible, yet our study supports deeper sources. Based on this approach, the influence of the main events in the occurrence of future and potentially damaging earthquakes in the area would not be significant.Peer Reviewe