Prof. Mark Anders
Earth Institute Contact: Prof. Mark Anders
Locations: United States of America
Western United States
Basin & Range Province
Over the last 30 years geologists and geophysicists have reported finding innumerable examples of crustal penetrating normal faults with dips less than 20°. These reports fall into two general classes of low-angle normal faults: 1) those that form at high angles and then are subsequently rotated to low angles, and 2) those that initiate at low angles and either continue to move at low angles or are rotated to even lower angles. It is the second class of faults that presents the greatest problem for fundamental mechanics. Unless some special conditions exist, fundamental mechanics predicts such faults are unstable and that steeper faults will form to accommodate extension. Moreover, no undisputed seismological data of earthquakes occurring on such low-angle surfaces currently exists. Despite these apparent contradictions, geologists have introduced models of extension where low-angle normal faults have accommodated large displacements (i.e., >20 km) at low-angles. Again, theoretical, experimental and observational data on fault growth suggest that such large displacements, where not truncated along strike by transcurrent faults, should span most of the continents they are formed in. A question to be addressed here is whether some of these extremedisplacement faults might be something other than low-angle crustal-penetrating faults.
The proposed work involves a detailed study of the fault zones of detachment faults which are thought to have accommodated some of the largest displacements known. The results will be compared to other fault zones based on field observations and previously published studies. Preliminary work on some of these extreme-displacement faults in the Basin and Range Province suggests they are surficial slide blocks misidentified as crustal penetrating faults. The obvious questions that follows are: If these presumed mega-displacement detachments are actually surficial block slides, are there other similarly misidentified structures? Also, what are reasonable criteria for distinguishing between the two very different modes of emplacement?
Cross Cutting Themes:
Hazards and Risk
American Chemical Society (ACS)