CodaQ−1was determined from the decay rate of coda waves in the bands of 1.5 to 24 Hz in the Hida region, central Japan. The data consist of routinely made observations for events from 1985 to 1991 (367 events), with magnitudes less than 4.0 and depths shallower than 30 km. We found a systematic temporal variation in codaQ−1. CodaQ−1increased with time in the volcanic area. The interpretation of the systematic temporal change in codaQ−1in the Hida region is that aseismic fractures due to magma accumulation can modify the scattering environment and consequently the codaQ−1
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