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foci

foci

Update 3.8.1 to foci software package

New version (3.8.1) of foci software package has been released recent week. This version brings some new features that will be developed in next months:

– Introduction of inelastic attenuation correction in calculation of full seismic moment tensor.
– Multiple corrections to preferences window.
– Introduction of foci package into github version control system
– Code cleanup.

The polish version of foci website has been also rearranged and refurbished. This is the first step to translate this page into english.

Paper in GRL on non-double-couple components at The Geysers geothermal field

Finally we published a paper related to investigation of seismic moment tensors of microseismic events at The Geysers geothermal field.

Reference

Martínez-Garzón, P., Kwiatek, G., Bohnhoff, M., and G. Dresen (2017). Volumetric components in the earthquake source related to fluid injection and stress state. Geophys. Res. Lett. 44, DOI: 10.1002/2016GL071963. [ Article Page ]

Abstract

We investigate source processes of fluid-induced seismicity from The Geysers geothermal
reservoir in California to determine their relation with hydraulic operations and improve the corresponding seismic hazard estimates. Analysis of 869 well-constrained full moment tensors (Mw 0.8–3.5) reveals significant non-double-couple components (>25%) for about 65% of the events. Volumetric deformation is governed by cumulative injection rates with larger non-double-couple components observed near the wells and during high injection periods. Source mechanisms are magnitude dependent and vary significantly between faulting regimes. Normal faulting events (Mw<2) reveal substantial volumetric components indicating dilatancy in contrast to strike-slip events that have a dominant double-couple source. Volumetric components indicating closure of cracks in the source region are mostly found for reverse faulting events with Mw>2.5. Our results imply that source processes and magnitudes of fluid-induced seismic events are strongly affected by the hydraulic operations, the reservoir stress state, and the faulting regime.

Another paper on Acoustic Emission

We published a paper in European Journal of Environmental and Civil Engineering on analysis of acoustic emission data in fracture and fluid-injection experiments in sandstone. Here is the reference:

Kwiatek, G., Charalampidou, E.-M., Dresen, G., and S. Stanchits (2014). An improved method for seismic moment tensor inversion of acoustic emissions through assessment of sensor coupling and sensitivity to incidence angle. Int. J. Rock Mech. Min. Sci. 65, 153-161, DOI: 10.1016/j.ijrmms.2013.11.005 [ Article Page ]

Abstract:

We performed laboratory experiments on sandstone specimens to study brittle failure and the reactivation of an experimentally produced failure plane induced by pore-pressure perturbations using constant force control in high compressive stress states. Here, we focus on the shear failure of a dry sample and the later on induced fracture plane reactivation due to water injection. Acoustic Emission (AE) monitoring has been used during both experiments. We also used ultrasonic wave velocities to monitor pore fluid migration through the initially dry specimen. To characterise AE source mechanisms, we analysed first motion polarities and performed full moment tensor inversion at all stages of the experiments. For the case of water injection on the dry specimen that previously failed in shear, AE activity during formation of new fractures is dominated by tensile and shear sources as opposed to the fracture plane reactivation, when compressive and shear sources are most frequent. Furthermore, during the reactivation of the latter, compressive sources involve higher compressive components compared to the shear failure case. The polarity method and the moment tensor inversion reveal similar source mechanisms but the latter provides more information on the source components.