In contrast to the lower part of the model, the structure in the middle
and upper crust appears to be strongly variable in time. In 2001 to
2004 we observe two anomalies of high Vp/Vs ratio in the mid-crust
and just below Kluchevskoy. In 2005, we detect an abrupt change in
seismic parameters coinciding with the almost simultaneous eruptions
of Kluchevskoy and Bezymianny volcanoes. In 2006 to 2007, generally
low Vp/Vs ratio without any considerable heterogeneity is observed in
the crust. In 2008, an anomaly of high Vp/Vs ratio appears again in the
mid-crust
Dobretsov and Kirdyashkin (1997) based on results of modeling, petrological,
geochemical and geophysical data.