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Late Miocene to Recent Evolution of Growth Faults in Greater Breton Sound, Louisiana, USA


Using industry-grade 3D reflection seismic data covering 1400 km2 of greater Breton Sound in southern Louisiana, USA, and coupling it with paleontological and well log data, we are able to characterize the latest Miocene-to-Recent behavior of 6 synsedimentary normal faults down to the 10-meter scale, in both the strike and dip direction. These faults range from 11 to 5.7 km in length and have fault-plane dips between 83 and 88 degrees. Ideal normal-fault models place the maximum displacement (dmax) at the center of the strike-length (L) of the fault, with zero displacement at the fault tips. By mapping greater than 8 displaced horizons across each growth fault, we find that the position of dmax occurs within 16-35% of L from a fault tip. Concordantly, vertical displacement across the faults is not symmetrically distributed along the length of a fault. Instead, these displacements are noticeably skewed toward one fault tip or the other. Fault length is found to increase with both fault displacement and overall burial depth. The highest observed, long-term rate of fault-tip propagation is 0.52 mm/yr. This rate corresponds to 2.6 m of tip propagation per 1 m of vertical fault displacement. The lowest observed rate of fault-tip propagation is very close to 0 mm/yr. Geologic rates for maximum vertical displacement on the faults ranged from 3 – 8 % of the regional burial or subsidence rate of 0.23 mm/yr. These displacement rates have remained roughly constant over the past 7 million years.