Accelerations in seismicity are important precursors to eruptions at volcanoes reawakening after extended repose intervals. These have previously been quantified for subduction-zone settings in terms of the linkage of crustal faults by shearing. Introducing a damage-mechanics criterion for the weakening of rock between major fractures, the model is here modified for failure in tension, consistent with conditions in crust surrounding a pressurized magma reservoir. The results indicate that final accelerations develop over ~2--3 weeks at tensile strains of (4.5 ¿ 3.2) ¿ 10-3. Since a week or more is required to identify an accelerating trend, seismic forecasts of eruptions after long repose are unlikely to be reliable more than days in advance. Improvements will require the integration of additional precursors or extension of the model to earlier stages of fracture growth in stressed crust.