Fault
Scaling in an Incipient Rift: Example From the Afar Triple Junction, Ethiopia and Djibouti
Abstract
Rift basins and passive margins continue to be significant targets for hydrocarbon exploration. Modern, active rift basins allow us to closely examine the evolution of structural traps in such settings. The Afar region of east Africa is the only sub-aerial exposure of a rift-rift-rift triple junction, and thus provides a rare view of the final stages of continental break-up. In the Afar, the East African rift meets the Red Sea and Gulf of Aden mid-ocean ridge rift propagators. Here, the ridges do not link discretely; rather diffuse normal faulting with some minor components of strike slip faulting accommodates extension between the overlapping rift propagators. All Quaternary deformation dissects extensive flood basalts of the 1 – 4 Ma Afar Stratoid Basalt series, such that minimum estimates of fault
displacement can be easily determined by examining vertical offsets of the relict stratoid surface. One question that we seek to address in the Afar rift is the contribution of small faults to the overall extensional budget of the region. The contribution of large faults has been studied in past decades, but as faulting is very diffuse in this region, the contribution of small faults cannot be ignored.
Fault
displacement and length scaling relations provide a means of assessing the bulk strain and
fault
density in a rift basin. To examine
fault
growth and
fault
scaling relationships, we analyzed a set of stereographic panchromatic and orthorectified multispectral images. The stereographic images were processed into a 5 m DEM, which was used with the panchromatic and multispectral images were used as basis for mapping in ArcGIS. Once mapped, the
fault
traces were analyzed using a script in ArcGIS, with
fault
throws being calculated along the length of each
fault
. This analysis shows that
fault
maximum throw in Dobe graben scales proportionally to
fault
length following a power law. Additionally,
fault
length appears to follow a power law distribution. Previous work has shown that
fault
length follows an exponential distribution in regions experiencing high amounts of strain (e.g. mid ocean ridges; ɛ > 8%), while following a power law distribution in regions of lesser strain. Further mapping and statistical analysis should help pinpoint the transition between largely exponentially distributed
fault
length in the hyperextended Asal rift with power law
fault
scaling in the central Afar rift and Main Ethiopian Rift.
AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015