The intense examination of the northern Gulf of Mexico (GOM) Basin for oil and gas during the 20th Century has spawned the development of several fundamental geologic concepts concerning the development of passive continental margins. One of the most important ideas to emerge has been that of the role played by normal faults in the creation of depositional space to accommodate the greater than 10-kilometer thick section of Jurassic to Holocene sediments and for the development of the architecture of hydrocarbon reservoirs. Unfortunately, geologic data lack the spatial and temporal detail to fully document and understand many of the underlying physical processes.

This presentation will describe the modern behavior of normal faults in the New Orleans area as inferred from late 20th Century geodetic and water-level measurements. The high precision of these data allow for process identification and kinematic analysis that provide key insights into how GOM Basin normal faults behave. For example, analysis of normal faults which mark the historic hingeline of the Gulf basin show that several individual faults are active and move continuously at centimeter per year rates. Such motion, however, does not occur at constant rates at yearly and decadal timescales as implied by geologic relations. Data also do not support the notion that Gulf Coast normal faults are weak and are inherently unable to accumulate and then release significant elastic strain energy. Instead of short-lived slip events marked by large acoustic emissions, GOM Basin faults release their elastic strain energy during “slow earthquakes.” An example will be provided that that shows that, although the accumulation of regional strain was similar in form to modern seismogenic normal faults, strain release was marked by an approximately 40-year-long interval of non-linear, largely aseismic slip that was manifested at the surface by regional subsidence. The implications that these modern observations and insights have for improved understanding of ancient faults will also be explored.

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