Spatio-temporal evolution of frequency-magnitude distribution and seismogenic index during initiation of induced seismicity at Guy-Greenbrier, Arkansas

In this study, we carry out detailed analyses of the spatio-temporal variations of seismic b-value during the onset of the potentially induced-earthquake sequence between Guy and Greenbrier, Arkansas, to investigate correlations with pore-pressure change. The range of b-values suggests that the seismicity in the Guy-Greenbrier area is mostly a result of the activation of pre-existing faults. The spatial distribution of b-value correlates with modeled pore-pressure changes. In the northern segment of the fault, b-value increases with depth due to large pore-pressure changes and opening of new fractures in the deeper part and stress relaxation in the shallower parts. Whereas, in the southern segment, the shallower part shows higher b-values due to higher pore-pressure fluctuations but the deeper part in the crystalline basement has low b-value due to higher confining stress. The correlation between the temporal variation of b-value and hypocentral depth explains a previously observed temporal drop of b-value. This suggests that temporal variations should be interpreted along with the spatial variations. Estimation of the seismogenic indices for the Guy-Greenbrier fault is provided. Our analysis suggests that monitoring changes in b-value and seismogenic indices during an injection period might be used to avoid the occurrence of significant events if injection volume is reduced at critical times.