Increment of Macroseismic Intensity at Seismic Stations of the Kamchatka Region Relative to the Petropavlovsk Seismic Station

The paper presents the method and results of calculating the increment of macroseismic intensity at seismic stations of Kamchatka. Calculation is based on measurement of the relative level of maximum accelerations of intense earth vibrations in the phase of S-waves of comparatively strong regional earthquakes and the root-mean-square deviation of acceleration in the phase of P-waves of a strong distant earthquake. In the latter case, records of an earthquake with a magnitude of 9.1, which occurred in Japan on March 11, 2011, were used. The Petropavlovsk seismic station was used as the reference station. At the foundation of this station rests on rocky soil composed of siliceous shales. An estimate of the increment for the majority of digital stations is presented. Anomalously high intensity values were noted at a number of stations. The data obtained are used to assess the properties of soils in the investigated area. At several stations, the intensity of the horizontal component of soil vibrations above the intensity of the vertical component is much greater than the corresponding design value, which is probably due to the presence of resonant soil layers under these stations. The discrepancy in the incremental intensity estimates from records of intense oscillations from regional earthquakes and from records of a very strong remote earthquake obtained from sensors located in basements of heavy-frame concrete structures is revealed. To avoid distortion in recording ground vibrations, it is desirable to place seismic instruments far from such structures. The results obtained in the study can be used for seismic microzoning of construction sites in the investigated territory.