Detailed P‐ and S‐Wave Velocity Models and Fault Structure for the New Madrid Seismic Zone

Abstract Detailed P‐ and S‐wave velocity (Vp and Vs) models and relocated hypocenters are determined for the active New Madrid seismic zone based on inversion of local earthquake arrival time data in the Cooperative New Madrid seismic network catalog for the period 1 January 1997 through 5 July 2025. The data set consists of 5,609 earthquakes, 93,338 P‐wave phases and 66,333 S‐wave phases recorded at 59 stations. The velocity models provide much greater resolution than previous models and allow a more comprehensive interpretation of crustal velocity features. Crust south of the Reelfoot fault is part of the Missouri batholith. The Bootheel lineament is detected as well as a horst below Ridgely Ridge. The presence of the Reelfoot axial ring dike intrusion influences hypocenter locations in the Reelfoot fault. Most Reelfoot fault earthquakes north of the Axial fault occur within the intrusion, along the border of a negative Vs anomaly suggesting the presence of high pore‐pressure fluids. South of the Axial fault, Reelfoot fault earthquakes occur in a low magnetic intensity portion of the intrusion and this segment is cut by northeast trending faults including the Axial, Cottonwood Grove, and Ridgely Ridge faults. We suggest that both strike‐slip and reverse motion occur on the Reelfoot fault during large earthquakes. The portion of Reelfoot fault associated with the greatest amount of vertical uplift has sparse seismicity. This segment may be locked and pose elevated seismic hazard.