LOOKING FOR SEISMOGENIC FAULTS RESPONSIBLE FOR INCREASED SEISMICITY, CENTRAL OKLAHOMA

Since 2008, seismicity in Oklahoma has increased in frequency and magnitude. Most upper crustal earthquakes are related to slip on faults, however most events in Oklahoma have occurred where no known faults lie. Cronin et al. (2008) has developed a new method for identifying and locating seismogenic faults, called the Seismo-Lineament Analysis Method (SLAM). This method incorporates data from earthquake focal locations and mechanism solutions, geomorphology, and geological (and potentially geophysical) fieldwork in a set of procedures to spatially correlate an earthquake with the surface trace of the fault that generated it. Where a nodal plane from a focal mechanism solution intersects the ground is called a seismo-lineament. When the uncertainties associated with hypocenter location and nodal plane geometries are accounted for, the seismo-lineament is a swath at the surface. The fault is likely to be found within the seismo-lineament if 1) the nodal plane is the fault plane solution, 2) the fault is emergent or detectable using geophysical methods, and 3) the fault is approximately planar from the hypocenter to the ground.

Epicenters for 45 events M≥3.5 near Oklahoma City align into two approximately parallel trends. One nodal plane from the events M≥4 (12 events) also align parallel to these trends, indicating a strong likelihood in that nodal plane being the fault plane solution for these events.

A GPS crustal strain analysis might help improve our understanding of the cause of the current increased seismicity in the region by comparing the magnitude of strain with that of areas of similar seismic activity, and by comparing seismicity with areas of similar strain magnitude.