Fluids are pumped into the wellbore by pulsing the fluids at a variable, positive pressure relative to the geologic formation until a first pressure threshold in the first fracture zone is satisfied. The pumping results in a first pressure profile in the first fracture zone representing pressures in the first fracture zone over time responsive to the pumping, and a second pressure profile in the second zone representing pressures in the second zone over time responsive to the pumping. In response to determining that the first pressure threshold is satisfied, the fluids are ceased to pump into the wellbore for a duration of time. After the duration of time, the fluids are re-pumped into the wellbore by pulsing the fluids at the variable, positive pressure relative to the geologic formation until a second pressure threshold in the first fracture zone in the first fracture zone is satisfied.