A GEOFORENSIC APPROACH FOR IDENTIFICATION AND DATING OF FAULT AND EARTHQUAKE EVENTS: NORTHERN GULF OF MEXICO

The realization that neotectonic processes are primary shapers of late Quaternary landforms changes forever our perception of the landscape of the northern Gulf of Mexico region. Apparently passive lowlands and terraces of south Louisiana and southeast Texas are actually in almost continuous motion in response to stress and movement within the linked tectonic systems that underlie the region. The region overlies a 50,000 ft deep sediment filled trough. Most tectonic processes and features are deep seated and related to infill and post-depositional movement of sediment within this trough, yet the tectonic processes affect landforms and surface features. Examples of influences of subsurface faults, fractures and salt domes on alignments and geometry of streams, lakes, bays, shorelines, and barrier islands are ubiquitous. Subsidence and tilting of fault bound blocks results in submergence, hydrological change, ecological change, and adverse impacts to infrastructure. Not all fault movement is slow and imperceptible. Earthquakes are known to have occurred along regional faults and tremors probably caused localized liquefaction of sand and silt deposits as well as breakup of floating marsh mats.

Surface signatures of fault and earthquake movement have been identified, classified, described and measured. Tectonic signature types are defined on the basis of form, but are grouped in reference to: salt domes, fault traces and scarps (cuspate, en echelon, horse tail, grabens, “D-shaped” depressions), river patterns (along or across structural strike), fractures, fissures, lakes and bays, shore zone features (barrier island, beach complexes, headlands, submerged lands), and eruption features (gas-mud vents, pimple mounds). A geoforensic approach, including geomorphological, and geoarchaeological methods has been used in dating surface signatures of tectonic events.

As a result of study findings, revisions to some traditional interactive process-response models are proposed. Affected models include the: growth fault-sediment pod, deltaic barrier island cycle, delta cycle, delta switching, and Late Quaternary sea level rise models.

Tectonic signature types and process-response models, are cross-referenced to the regional tectonic framework, which is made up of linked systems and subsystems.