Joint inversion of full-waveform ambient noise and gravity data for simultaneously deriving high-resolution three-dimensional crustal <i>S</i>-wave velocity and density models: application to the Jingpohu volcanic area in Northeast China

SUMMARY Both crustal velocity and density models provide important constraints for understanding crustal tectonics, composition and magmatic system. However, conventional gravity inversion methods for density models are troubled by poor depth-resolution and non-uniqueness. We apply a joint inversion method to full-waveform ambient noise and gravity data for simultaneously deriving high-resolution 3-D crustal S-wave velocity (Vs) and density models. By constraints of seismic and gravity data, our joint inversion could significantly improve the resolution of density models and reduce the uncertainty on the inversion results. Our method is suitable for any areas especially with low seismicity and can be extended to basin-scale. We apply the method on the seismic and gravity data around the Jingpohu (JPH) volcanic area in Northeast China to obtain high-resolution 3-D crustal Vs and density models, which are subsequently used to build the crustal lithological model. Our models demonstrate that the JPH volcanic group is located near the junction of the Mudanjiang–Yilan and Dunhua–Mishan fault zones and was tectonically controlled by them. A steep crustal-scale mafic intrusion with high Vs and density is present beneath the JPH volcanic group, and we interpret it as the same product as the JPH volcanic basaltic rocks outcropped on the surface by the mantle-sourced magmatic upwelling. Furthermore, none significant molten magma reservoirs with low Vs and density are observed currently within the crust of the JPH volcanic group. Thus, our results support that the JPH volcanic group is a single volcanic genesis with a mantle-only magma source.