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stress inversion

Stress inversion

Paper on Acoustic Emission activity during hydraulic fracturing experiment in Äspö, Sweden

We published a new paper in the Journal of Geophysical Research: Solid Earth related to the hydraulic fracture experiments performed in 2015 in  Äspö Hard Rock Laboratory, Sweden. Here are the highlights:

  • We analyze source characteristics of picoseismicity (moment magnitudes smaller than -3.5!) related to hydraulic stimulations in Äspö Hard Rock Laboratory, Sweden.
  • We show that spatio-temporal seismicity migration is controlled by changes in hydraulic (pressure times volume) energy.
  • We present that total radiated seismic energy is very low with respect to injected volume, and increases with hydraulic energy rate.

The reference:

Kwiatek, G., Martínez-Garzón, P., Plenkers, K., Leonhardt, M., Zang, A., Specht, S., et al. (2018). Insights Into Complex Subdecimeter Fracturing Processes Occurring During a Water Injection Experiment at Depth in Äspö Hard Rock Laboratory, Sweden. Journal of Geophysical Research: Solid Earth, DOI: 10.1029/2017JB014715. [ Article Page ]

Paper in JGR on improved stress tensor inversion from focal mechanism

Another article related to stress tensor inversion has been published in JGR! This one discusses the improved methodology for stress tensor inversion.

Reference:

Martínez-Garzón, P., Y. Ben-Zion, N. Abofalthian, G. Kwiatek, and M. Bohnhoff (2016). A refined methodology for stress inversions of earthquake focal mechanisms. J. Geophys. Res., 121, 8666-8687, DOI: 10.1002/2016JB013493. [ Article Page ]

Abstract:

We develop an improved methodology for reliable high-resolution inversions of focal mechanisms to background stress field orientation and stress ratio R in two or three dimensions. The earthquake catalog is declustered to remove events likely affected strongly by local stress interactions rather than reflecting the large-scale background stress field. The declustered data are discretized with the k-means algorithm into groups containing a number of focal mechanisms between a minimum number Nmin and 2Nmin. Synthetic tests indicate that Nmin ≈ 30 provides stable inversion results under different stress regimes and noise conditions when R ≈ 0.5, while Nmin ≈ 45 is needed for R near 0 or 1. Additional synthetic tests compare the performance of selecting the fault plane of each focal mechanism using (a) the plane with lowest misfit angle between the slip vector from the focal mechanism and shear traction from the stress tensor and (b) the plane with highest instability coefficient representing proximity to the optimally oriented fault for given stress field and friction coefficient. The instability criterion is found to provide more accurate inversion results under all tested stress regimes, stress ratios, and noise conditions. The refined inversion methodology combines selecting fault planes using the instability criterion iteratively with a damped simultaneous inversion of different focal mechanism groups. Results characterizing neighborhoods of discretized domains merged during the damped inversion provide high-resolution information independent of the discretization. Some aspects of the methodology are illustrated with focal mechanism data from the San Jacinto Fault Zone in Southern California.

New paper on fault instability at The Geysers

We published a new paper in Journal of Geophysical Research: Solid Earth that discusses the influence of long-term fluid injection on fault reactivation potential at The Geysers geothermal field, California.

References:

Martínez-Garzón, P., Kwiatek, G., Bohnhoff, M., and G. Dresen (2016). Impact of fluid injection on fracture reactivation at The Geysers geothermal field. J. Geophys. Res. 121, DOI: 10.1002/2016JB013137. [ Article Page ]

Paper on the influence of pore pressure changes on stress tensor inversion parameters

Another paper! This time we discuss the influence of temporal changes in pore pressure on the results of stress tensor inversion from focal mechanisms, with the special focus on stress shape ratio coefficient. There is also a neat presentation of the effects using the data from The Geysers geothermal field. The paper has been published in Geophysical Research Letters. Have fun!

Reference:

Martínez-Garzón, P., Vavryčuk, V., Kwiatek, G., and M. Bohnhoff. Sensitivity of stress inversion of focal mechanisms to pore pressure changes (2016). Geophys. Res. Lett., 43, 8441-8450, DOI: 10.1002/2016GL070145. [ Article Page ]

Paper in GJI on stress field on North Anatolian fault

We published a paper entitled “Detailed analysis of spatiotemporal variations of the stress field orientation along the Izmit-Düzce rupture in NW Turkey from inversion of first-motion polarity data” in Geophysical Journal International.

The reference:

Ickrath, M., Bohnhoff, M., Dresen, G., Bulut, F., Martínez-Garzón, P., Kwiatek, G. and O. Germer (2015). Detailed analysis of spatiotemporal variations of the stress field orientation along the Izmit-Düzce rupture in NW Turkey from inversion of first-motion polarity data. Geophys J. Int. 202, 2120-2132, DOI: 10.1093/gji/ggv273 [ Article Page ]