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S U M M A R YWe analyse the statistical behaviour of about 1.6 E+6 high-frequency, acoustic emission events recorded in a rock mass in a salt mine over a 3-yr time period. The rock mass is directly located above a cavity that is backfilled during a 6 months time interval within the investigated time period. The rock mass consists mainly of rock salt with large anhydrite blocks in it. Location, event rate and strength of the events are studied in 3 months time intervals before, during, and after the backfilling process. We observe strong temporal and spatial changes of event rate and b-values that correlate with the structural features and the loading of the rock mass: two regions with a b-value maximum above the cavity start developing with the beginning of backfilling. They reach extremely high b-values of up to b = 3.18 and are located at the transition zones between the different materials. The b-value ratio in anhydrite and rock salt anti-correlates during times of equilibrium and fast loading. We conclude that b-value mapping during transient loading is useful to investigate structural heterogeneities in the rock volume, whereas b-values during equilibrium phases better indicate the level of ambient stress and visco-plastic stress relaxation in the salt rock.

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