--> Abstract: New Insights to the Structural History of Otway Basin Using Automated Techniques, by Laura Evins; #90078 (2008)

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New Insights to the Structural History of Otway Basin Using Automated Techniques

Laura Evins
Paradigm, Houston, TX

Automatic Fault Extraction(AFE) enables us to extract a large number of faults from 3D seismic data from Otway Basin. Statistical analysis using Rose diagrams yields several principle fault orientations for different periods during the Cretaceous. The changes reflect tectonic events during the separation of Antarctica and Australia.

An area of the Otway Basin was evaluated using automated and manual techniques to better understand the complex structural history and to validate a proposed new workflow for carrying out the structural analysis. We constructed a structural framework using AFE and borehole-validated horizon tracking on 2D and 3D data. Lineaments associated with the faulting generated as part of AFE were examined for variations in azimuth, strength, length, and frequency over different parts of the study area and over different geologic periods. Primary, secondary, and tertiary fault orientations were noted on Rose diagrams. We analyzed fault continuity vertically by co-rendering the extracted lineaments with the seismic amplitude data-a valuable tool for llustrating the changes of fault strike over geologic time.

Faulting orientation changed from primarily E-W or NE-SW for the lower Cretaceous to predominantly NW-SE for the upper Cretaceous. The high frequency of the NW-SE faulting of the upper Cretaceous and many apparent fault relays is consistent with slow subsidence during deposition. The co-rendering of seismic amplitude and lineament-azimuth on vertical sections showed that vertical fault cuts which appeared to be continuous over depth had substantial azimuth variations between unconformities indicating rotation of the stress field over time. The lower Cretaceous also contained NW-SE lineaments but they were far less frequent spatially, much shorter in length and with fewer relays, indicating that this episode of faulting was post-deposition.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas