Magma system beneath Tengchong volcanic zone inferred from local earthquake seismic tomography

Abstract

The Tengchong volcanic zone (TCVZ) located in the southeastern part of the India-Eurasia collision zone is characterized by large-scale volcano groups, significant thermal activities and active seismicity. To reveal the magma system, we present new 3-D models of Vp, Vs and Vp/Vs ratio to 10 km depth beneath the TCVZ based on the tomographic inversion of P- and S-wave arrival times from local earthquakes recorded by 10 broadband seismic stations. We use arrival times to construct a reference velocity model. Checkerboard and jackknife tests are carried out to assess the reliability of the inversion results. At shallow depths, we suggest that the complex distribution of high Vp/Vs ratio is the result of a combination of water and magmatic activity. At depth of 10 km, only three areas show obvious high Vp/Vs ratio corresponding to areas of high relative geothermal value observed through hot springs at the surface. We suggest that the three high Vp/Vs ratio areas are magma chambers. The upwelling volatiles heat the water in the shallow layer, inducing the corresponding high relative geothermal value at the surface. Meanwhile, the magma chamber beneath Rehai spring, which corresponds to high He3/He4 ratio, may be fed by mantle magma. We suggest that the Heikongshan volcano and Dayingshan volcano are fed by the magma chambers and that Maanshan volcano is separated from the magma. We also infer that the significant geothermal activity and active seismicity beneath Rehai spring are the result of interaction between the magma and hot-water reservoir.