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A refined model of fault structure in the active New Madrid Seismic Zone (NMSZ) is presented based on relocated hypocenters and application of a statistical clustering method to determine fault planes. Over 200 earthquakes are recorded in the NMSZ every year, but the three‐dimensional (3‐D) fault structure is difficult to determine because the zone is covered by thick, Mississippi Embayment sediment. The distribution of earthquakes in the NMSZ indicates four major arms of seismicity, suggesting the presence of a northeast‐southwest trending strike‐slip fault system with a major northwest trending, contractional stepover fault. Relocation of 4,131 earthquakes using HypoDD resulted in major improvement in the depiction of fault structure in the NMSZ including three‐dimensional structural variations along the along the Reelfoot fault (RF) and a well‐defined intersection of the Axial and RFs. Optimal Anisotropic Dynamic Clustering analysis of the relocated hypocenters produced a fault model consisting of 12, well resolved planes. The RF is continuous along strike from the northern end to the Ridgely fault, located south of the intersection with the Axial fault (AF). The crosscutting Ridgely fault may serve as a barrier to rupture propagation along the entire fault. The strike‐slip arms of seismicity are well resolved and correspond to near vertical planes. Three planes are resolved in the southern part of the AF and are associated with the Osceola igneous complex. Plain Language Summary: A refined fault model is determined for the active New Madrid seismic zone using earthquakes that occurred from 2000 to 2019. The seismic zone is located in the central United States and poses a hazard to critical infrastructure and numerous population centers. The major faults are the Reelfoot thrust fault and the strike‐slip Axial fault (AF). The first step in constructing the improved fault model involved relocation of the earthquakes to decrease location error. The second step involved fitting planes to the relocated earthquakes under the assumption that the earthquakes cluster along fault segments. The resulting model provides a three‐dimensional representation of the fault structure. A major fault disrupts the southern portion of the Reelfoot fault, making it discontinuous. The northern part of the AF is very well defined. Earthquakes are more scattered along the southern part of the AF, but three fault planes are resolved that are located along the side of a major intrusion. The fault model can be used in studies involving possible rupture length and magnitude of large earthquakes. Key Points: New Madrid Seismic Zone hypocenters for the years 2000–2019 are relocated and have a median relative location error of 65 mPlanes are fit to the relocated hypocenters producing a detailed three‐dimensional model of fault structureThe Reelfoot fault is segmented by the Ridgely fault [ABSTRACT FROM AUTHOR]

This article describes an unusually well-behaved, unusually well-documented central and eastern United States (CEUS) earthquake sequence. Detailed analysis of regional and local waveform data from the 6 June 2003 Bardwell, Kentucky, earthquake indicates that the mainshock has the seismic moment of M0 1.3 (± 0.5) x 1015 N m (Mw 4.0) and occurred at a depth of about 2 (± 1) km on a near-vertical fault plane. A temporary seismic network recorded 85 aftershocks that delineate an east-trending fault approximately 1 km in length. The hypocenters illuminate a vertical plane between 2.0 and 2.7 km depth. The centroid of the aftershock distribution is at 36.875° N, 89.010° W and a depth of 2.4 km. The aftershock cluster is interpreted as a circular fault area with a radius of 0.44 (± 0.03) km. This source radius yields a static stress drop, Δσ = 67 (± 14) bars for the mainshock. The focal mechanism for the mainshock has strike = 90°, dip = 89°, and rake = - 165° with a subhorizontal P axis trending 135°. A formal stress inversion based on the focal mechanisms of the mainshock and ten aftershocks indicates the maximum compressive stress trends 104° with a plunge of 5°. The local stress field near Bardwell is therefore rotated about 40° clockwise relative to 65° for eastern North America as a whole. The Bardwell earthquakes have the opposite sense of slip to earthquakes with east-trending nodal planes that occur near New Madrid, Missouri. This requires a significant local rotation of the stress field over a distance of 60 km. [ABSTRACT FROM AUTHOR]