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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Late 20th Century Subsidence of South Louisiana:
Insights into the Nature of Passive Margin Normal
Faults
Fruehan Professor of Engineering
Department of Civil & Environmental
Engineering and Center of GeoInformatics
Louisiana State University
Baton Rouge, LA
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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