2D Broadband Magnetotelluric Study of the Axial Fault Region of the New Madrid Seismic Zone

Abstract This study investigates whether seismicity in the New Madrid Seismic Zone (NMSZ), specifically the Axial Fault, is predominantly influenced by fluids or fault locking. Previous resistivity studies in the region were restricted by their focus, MT station spacing, and equipment bandwidth, which limited the resolution of resistivity structures near fault zones. We conducted a comprehensive investigation using broadband magnetotelluric (MT) soundings from December 2021 to March 2023. Data were collected along five profiles spanning frequencies from 0.00005 to 10,000 Hz. Four shallow‐focus profiles were located near Steele and Caruthersville in the Missouri Bootheel region, while a deeper cross‐section extended from Obion, TN to Wardell, MO, reaching a depth of 80 km and crossing the Reelfoot Rift's Axial Fault. Our findings indicate that earthquakes cluster within a highly resistive zone (1,000–10,000 Ω‐m), suggesting a fault‐locking mechanism in the brittle zone because they coincide with low velocity anomalies from previous studies. The profiles usually have a conductive anomaly on the SE side of the fault at a depth of 2–30 km. That conductive anomaly may be interpreted as a weaker, more ductile zone adjacent to the stronger brittle zone associated with the fault. These results suggest that both fault locking and fluid presence significantly influence NMSZ seismicity, with their effects varying by depth and location.