Detailed 3D Seismic Velocity Structure of the Prague, Oklahoma Fault Zone and the Implications for Induced Seismicity

The 2011 Mw 5.7 Prague earthquake is the second largest induced earthquake in Oklahoma, and occurred after decades of wastewater disposal. The local geological structure that led to the triggering of this large earthquake is not well understood. In this study, tomographic inversion of seismic data recorded by a dense local seismic network resulted in a high-resolution 3D velocity model with three major layers. The model clearly illuminates the geometry and characteristics of the Meeker-Prague Fault that hosted the 2011 Prague sequence. A conceptual model is proposed to link the tomographic structure to the triggering process of the sequence. The low-permeability second layer at similar to 1.5-3.5 km may be the key that delays the occurrence of the first sizeable earthquake after decades of wastewater injection. However, a low-shear-velocity zone within this layer at the intersection of two major faults could have provided a fluid pathway to facilitate downward fluid propagation.