Continental-scale deep electrical resistivity structure beneath China

Abstract

Electrical resistivity structure in the deep Earth can provide important information and constraints on regional geodynamics, especially in regions with complex tectonics and geodynamical processes. In this study, we image the electrical resistivity structure in the depth range of 350–1200 km beneath China by inverting the frequency-dependent ratios of geomagnetic field components at a relatively dense network of geomagnetic observatories. Very long time series of hourly mean values of the three-component geomagnetic field from 45 geomagnetic observatories are collected and processed to derive robust ratios of the geomagnetic components, which are then converted to the apparent resistivities and impedance phases in the period range of 5.3–113.8 days and used in 1-D Occam inversion with smoothing constraint and the ρ+ method to obtain the electrical resistivity profiles and delta function models at individual observatories. 1-D electrical resistivity models suggest that low electrical resistivity structure exists in the mantle transition zone beneath eastern China. High water content in the mantle minerals due to the subduction of seismically fast Pacific slab is proposed as the main reason for the low electrical resistivity beneath eastern China. Our results provide further evidence that the western front of the subducting Pacific slab in the mantle transition zone roughly coincides with the abrupt change in the surface topography in eastern China.