Crustal Structures and Seismogenic Setting of the West Henan Region, North China, as Revealed by Magnetotelluric Imaging

The west Henan region, China, has experienced four historical moderate-to-strong earthquakes. Many micro-earthquakes continue to occur in this area. However, due to inaccurate positioning of the micro-earthquake epicenters and lacking geophysical data, the initial mechanism of seismogenesis for this region is still indefinable. Here, we investigated the electrical resistivity structures of the crust using magnetotelluric (MT) data collected in the west Henan region. The electrical resistivity model obtained by 3D inversion of MT data shows moderately resistive features in the lower crust and a conductive body in the upper crust (10–25 km). Furthermore, we combined the accurately relocated hypocenter locations for micro-earthquakes using the double-difference earthquake relocation algorithm (hypoDD) to further understand the seismogenic setting, revealing that earthquakes occur either near the surroundings of the conductor or around faults, but do not happen in the zones where both conductor and faults are distributed. The possible cause of earthquakes occurring around the conductor and the moderate historical earthquake happening in the study area is the change in crustal viscosity. The concentration of micro-earthquake hypocenters in the vicinity of faults may result from both the uneven stress in the crust and fluid flow in and out of the fault fracture zones along with fault movement. The origin of a few events distributed in the zones with both the conductor and fault distribution may be the release of stress in time through faults.