Fig. 2

Model calibration approach. Top row shows the usage of combination of displacement boundary conditions at the vertical model boundaries. Lower row shows the associated implementation in the model with stress magnitude data that are used for calibration. Red (\(\text{S}_\text {Hmax}\)) and blue (\(\text{S}_\text {hmin}\)) indicate the horizontal stress magnitudes and the associated possible boundary conditions that fit their respective value. a For a single \(\text{S}_\text {hmin}\) data record the combinations of boundary conditions that satisfy the calibration data record is described by a linear function. One possible set of boundary conditions is indicated here. b An \(\text{S}_\text {hmin}\) and \(\text{S}_\text {Hmax}\) calibration data record can be modelled individually again by boundary conditions on a straight line each. However, if both \(\text{S}_\text {Hmax}\) and \(\text{S}_\text {hmin}\) should be satisfied the intersection of these two lines, indicated by a solid white dot in the top row, is the unique pair of boundary conditions that fits both. c If several \(\text{S}_\text {Hmax}\) and \(\text{S}_\text {hmin}\) data records are available, for each \(\text{S}_\text {Hmax}\) and \(\text{S}_\text {hmin}\) the linear function with the least mean difference between observation and model is derived. Then, the intersection of these two functions is used as the valid set of boundary conditions that minimises the differences between modelled and observed stress state