TY  - JOUR
A1  - Kwiatek, Grzegorz
A1  - Martinez-Garzon, Patricia
A1  - Plenkers, K.
A1  - Leonhardt, Maria
A1  - Zang, Arno
A1  - von Specht, Sebastian
A1  - Dresen, Georg
A1  - Bohnhoff, Marco
T1  - Insights into complex subdecimeter fracturing processes occurring during a water injection experiment at depth in Aspo Hard Rock Laboratory, Sweden
JF  - Journal of geophysical research : Solid earth
N2  - We investigate the source characteristics of picoseismicity (M-w < -2) recorded during a hydraulic fracturing in situ experiment performed in the underground Aspo Hard Rock Laboratory, Sweden. The experiment consisted of six stimulations driven by three different water injection schemes and was performed inside a 28-m-long, horizontal borehole located at 410-m depth. The fracturing processes were monitored with a variety of seismic networks including broadband seismometers, geophones, high-frequency accelerometers, and acoustic emission sensors thereby covering a wide frequency band between 0.01 and 100,000Hz. Here we study the high-frequency signals with dominant frequencies exceeding 1000 Hz. The combined seismic network allowed for detection and detailed analysis of 196 small-scale seismic events with moment magnitudes M-W < -3.5 (source sizes of decimeter scale) that occurred solely during the stimulations and shortly after. The double-difference relocated hypocenter catalog as well as source parameters were used to study the physical characteristics of the induced seismicity and then compared to the stimulation parameters. We observe a spatiotemporal migration of the picoseismic events away and toward the injection intervals in direct correlation with changes in the hydraulic energy (product of fluid injection pressure and injection rate). We find that the total radiated seismic energy is extremely low with respect to the product of injected fluid volume and pressure (hydraulic energy). The radiated seismic energy correlates well with the hydraulic energy rate. The obtained fault plane solutions for particularly well-characterized events signify the reactivation of preexisting rock defects under influence of increased pore fluid pressure on fault plane orientations in good correspondence with the local stress field orientation.
KW  - induced seismicity
KW  - fracking
KW  - picoseismicity
KW  - seismomechanics
KW  - source parameters
KW  - maximum magnitude
Y1  - 2018
U6  - https://doi.org/10.1029/2017JB014715
SN  - 2169-9313
SN  - 2169-9356
VL  - 123
IS  - 8
SP  - 6616
EP  - 6635
PB  - American Geophysical Union
CY  - Washington
ER  -