The relative amplitude levels of backscattered shear waves (coda) of local earthquakes as expressed in coda magnitude residuals were studied for nine Kamchatka seismograph stations. Coda magnitudes were determined from coda amplitudes measured on three-component photograph records of 1.2-s period displacement-recording (between 1 and 10 Hz) instruments. A coda magnitude scale was specially designed for this study. It is rather precise, with a standard deviation of about 0.15 for log amplitudes measured at any single station. At each station, for each event we compute the station magnitude residual, i.e., station magnitude (averaged over three components) minus network average magnitude. Station corrections for each station and component were determined and included in the procedure. Time series of coda magnitude residuals including 500--1000 events for each station for the 24-year period of observations (1967--1990) show moderate but statistically significant oscillations around a constant level. Superposed on this background, two prominent anomalies are revealed. One, at station KGB, of 3 years duration, preceded two M≈8 shallow earthquakes within 100 km from the station. Another, at station APH, of 1.5 years duration, preceded a major (volume of 2.5 km3) fissure volcanic eruption within a 70-km distance from the station. No other comparable shallow earthquakes or eruptions took place on Kamchatka during this period. The sign and the amplitude of the anomalies indicate a possible 30% increase of S -wave attenuation in the lithosphere under the stations. ¿ American Geophysical Union 1995