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The fast sweeping method has been proved very efficient in calculating the first arrivals in isotropic media. In this study, we extend the fast sweeping method to heterogeneous anisotropic medium by adapting the Lax-Friedrichs local scheme. The new fast sweeping method is able to solve the first arrival traveltime field for both qP and qS waves. By comparing the traveltime field to the full-waveform solution, we demonstrate that the iso-surfaces of the time field follow the constant phase of the wave and form a continuous envelope wrapping the wavefront. The iso-surfaces for the shear wave identify two continuous wavefronts one ahead of the other even in the directions where the triplication of qS-wave is developed. The rays for both qP and qS wave can be traced using the slowness vector from the traveltime field and we compared its accuracy with a two-point ray tracing method in a layered model. We show that rays from the traveltime field is nearly identical to the two-point ray tracing results. This new fast sweeping method not only avoids the multipath and shadow zone issues in complex heterogeneous media but also circumvent the multiple shear branch problems due to anisotropy.

Passive monitoring of induced microseismic (MS) events provides a unique means for imaging fracture propagation in response to engineering operations. Particularly during hydraulic treatment of hydrocarbon-bearing reservoirs rock MS monitoring provides feedback to field operators on the effect of the treatment and the changes imposed on the fracture network and fluid conductivity within the rock.

seismic (MS) events from streaming data recorded by surface monitoring survey. The symmetric nature of the semblance with respect to the origin time was used to identify the MS location. In this paper, we form a comprehensive workflow by extending this algorithm to include arrival time refinement using cross-correlation and nonlinear optimization similar to Geiger’s method to update the location and origin time in order to minimize the residual between the observed and the theoretical arrivals. We demonstrate the efficiency of our workflow on seismograms continuously recorded by surface monitoring stations. We show that the automated grid search identified a significant amount of potential signals indicating the level of local seismic activities. The nonlinear optimization is applied to events with clear arrivals, and the vertical uncertainty due to the surface acquisition geometry and the coarse grid effect in the grid search are reduced. This algorithm can be directly applied to both natural earthquakes and reservoir stimulation monitoring.

Currently, only microseismicity is used as a proxy for stress near deep mines. However, most of the physical properties of crystalline rocks are highly stress dependent. As such, the nonlinear and anisotropic variability of the in situ P- and S-wave velocities can potentially be linked directly to changes in the stress field. At an in-mine seismic laboratory, multi-component sensor arrays are deployed in multiple locations (3D) allowing for both controlled source and passive recordings. Previous in-mine seismic observatories have experienced a number of challenges with regards to sensitivity and longevity. Hence, the geothermally cool but highly stressed Sudbury mining camp offers a favourable setting for fundamental research in to time-lapse monitoring of seismicity, stress, and stress dependent physical properties at a deep mine.

The Fast Sweeping Method (FSM) is a finite difference algorithm providing significant computational efficiency and modelling capability in calculating the first arrivals of seismic P- or S-waves. Based on the calculated travel-timetable, we stack waveform amplitude for every possible source location and origin time followed by semblance weighting. With three-component (3-C) data, the stacked image can be further improved by matching the waveform polarization with the modelled ray vector from FSM and thus reduce the azimuth ambiguity in the location of microseismic (MS) events. We apply the algorithm on synthetic surface and borehole data and show that the combination of FSM and enhanced waveform stacking can efficiently locate MS events with high spatial resolution even when realistic noise levels are added. Finally we test the algorithm on a set of field 3-C data from the stimulation of a sandstone reservoir monitored using two borehole arrays. The method allowed the location of twice the number of event compared to locations using each borehole individually, with both sets defining a consistent fracture structure.