TESTING THE GAUSS METHOD ON HETEROGENEOUS FAULT POPULATIONS IN THE HARTFORD-DEERFIELD BASIN

Paleostress inversion is a commonly used technique to analyze fault-slip data and interpret the tectonic history of a region. Fault-slip datasets are commonly heterogeneous, which has made the technique challenging. However, a number of approaches have been developed over the years to address this issue. The Hartford-Deerfield basin provides an opportunity to evaluate techniques for the separation of heterogeneous fault-slip data into homogeneous subsets because past states of stress can be inferred using other types of data.

We are evaluating the success of the Gauss method for separating a heterogeneous dataset of over 700 faults from the Hartford-Deerfield basin into homogeneous subsets by comparing the results of different runs of the Gauss method with known states of stress for the region. The method requires the user to input values for five parameters, two (s and d) that define the misfit between the theoretical and observed slip along a fault and three (q₁, q₂, and the stress parameter) that constrain the mechanical compatibility. Each run is expected to yield five phases: one normal faulting phase and four strike-slip faulting phases. Use of low values for the misfit parameters results in a large number of misfit faults and incomplete identification of known states of stress. Separation of the strike-slip faults into different phases is generally successful because the orientation of the maximum compressive stress differs by about 40°-50° between the phases. Successful separation of these faults, however, requires that the values of q₁, q₂, and the stress parameter be larger than empirical threshold values. Use of low values of the mechanical compatibility parameters results in a large number of misfit faults, mixing of phases, and fault populations that do not resemble those commonly observed in nature. This work indicates that the Gauss method is an effective tool for separating heterogeneous fault-slip data in the Hartford-Deerfield basin.