Yixin Zhang

and 4 more

A new 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. The most seismogenic faults are the strike-slip Axial fault and the Reelfoot thrust fault. Developing an accurate, 3-D fault model is important for dynamic modeling of the fault system and better specification of the seismic hazard. We relocated 4131 hypocenters for earthquakes occurring between 2000 and 2019 using the HypoDD double difference relocation technique. HypoDD is appropriate for the NMSZ because the earthquakes are tightly clustered, and the network stations are dense. The Optimal Anisotropic Dynamic Clustering technique is used to develop the fault structure for the NMSZ using the relocated hypocenters. The Reelfoot fault is continuous along strike from the northern end to the Ridgely fault, located south of the intersection with the Axial fault. The strike-slip arms are well resolved and correspond to near vertical planes. Three planes are resolved in the southern part of the Axial fault and are associated with the Osceola intrusive complex.