A computer-implemented method comprising: receiving mechanical information (714, 1515) of a geologic environment and location information of natural fractures of the geologic environment, wherein the location information of the natural fractures comprises location information of a discrete fracture network (718, 1525); receiving measured microseismicity information associated with the geologic environment; using a model of the geologic environment, calculating values of a plastic strain tensor associated with hydraulic fracturing in the geologic environment; calculating at least microseismicity event locations by evaluating changes in plastic strain in cells of the model as crossed by discrete fractures of the discrete fracture network (718, 1525) at individual points in time, wherein evaluating the changes includes projecting values of the plastic strain tensor on discontinuity planes of the model before hydraulic fracturing to obtain a reference value for cumulated plastic strain during initialization and/or for plastic strain related to history of material of the geologic environment and projecting values of the plastic strain tensor on the discontinuity planes during at least opening of one or more hydraulic fractures of the hydraulic fracturing; calibrating the model of the geologic environment based at least in part on the calculated microseismicity event locations and based at least in part on the measured microseismicity information to provide a calibrated model; and using the calibrated model, determining an increase in reactivated fracture volume associated with hydraulic fracturing in the geologic environment. receiving mechanical information (714, 1515) of a geologic environment and location information of natural fractures of the geologic environment, wherein the location information of the natural fractures comprises location information of a discrete fracture network (718, 1525); receiving measured microseismicity information associated with the geologic environment; using a model of the geologic environment, calculating values of a plastic strain tensor associated with hydraulic fracturing in the geologic environment; calculating at least microseismicity event locations by evaluating changes in plastic strain in cells of the model as crossed by discrete fractures of the discrete fracture network (718, 1525) at individual points in time, wherein evaluating the changes includes projecting values of the plastic strain tensor on discontinuity planes of the model before hydraulic fracturing to obtain a reference value for cumulated plastic strain during initialization and/or for plastic strain related to history of material of the geologic environment and projecting values of the plastic strain tensor on the discontinuity planes during at least opening of one or more hydraulic fractures of the hydraulic fracturing; calibrating the model of the geologic environment based at least in part on the calculated microseismicity event locations and based at least in part on the measured microseismicity information to provide a calibrated model; and using the calibrated model, determining an increase in reactivated fracture volume associated with hydraulic fracturing in the geologic environment.