Near-Field Effects for Earthquakes of the Klyuchevskoy Group of Volcanoes

The study is based on unique data from the KISS field experiment (2015-2016), during which a dense network of 83 seismic stations was deployed within a 55 km radius around the Klyuchevskoy group of volcanoes in Kamchatka. This made it possible to obtain recordings from distances as short as a few kilometres from the hypocenters and, for the first time, to examine near-field effects in detail for small volcanic earthquakes.

Figure 1. Histogram of distances from which the maximum individual (station) values of seismic moments were obtained.

The authors empirically found that the near-field extent depends on the event type: 10 km for long-period earthquakes and 20 km for high-frequency earthquakes. At such distances, individual station estimates of seismic moment are systematically overestimated, and the difference in moment magnitude estimates obtained with and without accounting for the near-field reaches 0.2-0.3 magnitude units.

Figure 2. Dependence of the obtained moment magnitudes Mw on the local magnitude ML for (a) high-frequency (blue, N = 3328) and (b) long-period (red, N = 1187) earthquakes.

Gray dots represent station magnitude estimates. Bold blue/red dots represent average moment magnitudes obtained from records at hypocentral distances of 20–100 km. The dark gray line shows the previously established relationship for Kamchatka between moment and regional magnitudes, obtained from a dataset of stronger tectonic (subduction) earthquakes in the magnitude range Mw = 3–6 [Abubakirov et al., 2018]. Light blue/pink dots represent average moment magnitudes determined without considering the near-field zone, i.e., for hypocentral distances of 0–100 km. The light blue/pink straight line is an approximation of the average moment magnitudes using the orthogonal regression method. The blue/red straight line is an approximation of the average moment magnitudes using the orthogonal regression method.

Molokova A.P., Bergal-Kuvikas O.V., Skorkina A.A., Smirnov V.B. “Near-Field Effects for Earthquakes of the Klyuchevskoy Group of Volcanoes” in the Journal of Volcanology and Seismology (2026, no. 1, pp. 97-110). DOI: 10.7868/S3034513826010056.