**5. Conclusions**

(1) Active volcanoes are injectors of magma and water into adjacent structures, which creates high-temperature production reservoirs.

(2) Seismic data reveal magma hydrofracking and stress conditions around active volcanoes.

(3) Magma fracking reservoirs may reside within production geothermal reservoirs.

(4) Seismogenic faults on the Kamchatka shelf are indicators of geofluid generation and water propagation to 250 km depth.

(5) Geysers result from CO2-gaslift in active silicic volcanic areas. Continuously performed measurements of CO2 partial pressures in hydrothermal features are a possible key to understanding the mechanisms of the relationship between anomalous hydrothermal perturbations [24], volcanic activity, and strong earthquakes.

**Author Contributions:** Conceptualization, methodology, software, validation, data curation, writing—original draft preparation: A.K. Koryaksky and Avachinsky volcanoes MEQ's data curation and analysis: E.C.; Mutnovsky MEQ's data curation and analysis, field works organization: A.P.; EQ mechanisms analysis: A.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by RFBR project # 18-05-00052-19.

**Acknowledgments:** Authors express gratitude to P.A., P.O. Voronin, N.B. Zhuravlev, M.V. Lemzikov, O.O. Usacheva, T.V. Rychkova, M.A. Maguskin, A.I. Kozhurin and Sergeeva A.V. for their help in field survey and data analysis. Special thanks for constructive comments to A.A. Lyubin. Thorough editing of the manuscript performed by J.C. Eichelberger highly appreciated.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
