A New Madrid Seismic Zone Fault System Model from Relative Event
Locations and Application of Optimal Anisotropic Dynamic Clustering
Abstract
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.