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The interest in IIS has been prompted by the recent occurrence of a number of important earthquakes, which have been associated with fluid injection in the frame of hydraulic fracturing 17, 18, 19, wastewater disposal 4, 20, conventional hydrocarbon extraction 7, 14, and geothermal exploitation operations 5, 6, 21. While induced seismicity accompanied the exploitation of different natural resources over the past century 7, 10, 11, 12, 13, 14, so-called injection-induced seismicity (IIS) has gained scientific attention in the past few decades 1, 15, 16. For these reasons, anthropogenic seismicity has become a matter of great societal concern and represents a new focus for seismic hazard analysis 1, 7, 8, 9. Due to its shallow depth, induced seismicity poses an important seismic hazard, as even moderate magnitude earthquakes can produce strong shaking and localized damages 3, 4, 5, 6. As a matter of fact, almost all major cases of injection-related induced seismicity with an accurate hypocentral location occurred at ~4вЂ“8вЂ‰km depth (Supplementary Table 1). Since these human actions only affect the uppermost several kilometers of crust, induced earthquakes are expected to occur at similar depths. Seismicity occurred almost exclusively on a secondary fault, located below the reservoir, dipping opposite from the reservoir bounding fault.ДЄnthropogenic seismicity is stimulated by stress perturbations, fracturing processes, or pore pressure changes in the subsurface accompanying fluid and mass movements driven by industrial activities 1, 2. The sequence occurred by progressive fault failure and unlocking, with seismicity initially migrating away from the injection points, triggered by pore pressure diffusion, and then back again, breaking larger asperities loaded to higher stress and producing the largest earthquakes. Here we use advanced seismological techniques applied to an enhanced waveform dataset, to resolve the geometry of the faults, develop a greatly enlarged seismicity catalog and record details of the rupture kinematics. The Castor sequence is one of the most important cases of induced seismicity in Europe and a rare example of seismicity induced by gas injection into a depleted oil field. The 2013 seismic sequence at the Castor injection platform offshore Spain, including three earthquakes of magnitude 4.1, occurred during the initial filling of a planned Underground Gas Storage facility.

Showing waveform in timeline 3d max 2016