HR: 1330h
AN: T43B-04    [Abstracts]
TI: Testing simple models of brittle normal faulting: slip rate, spacing, and segmentation
AU: * Connolly, J
EM: jwilson7@tulane.edu
AF: Tulane University, Dept of Earth and Environmental Sciences, New Orleans, LA 70118 United States
AU: Dawers, N H
EM: ndawers@tulane.edu
AF: Tulane University, Dept of Earth and Environmental Sciences, New Orleans, LA 70118 United States
AB: Fault growth and evolution is a complex process, however any predictable pattern will yield important information for assessing seismic hazard and clues to what controls fault behavior. Models of slip rate variation along strike, spacing of active faults, and scaling of segment length are investigated using data from faults located within the parabola of seismicity around the Yellowstone hotspot. Based on displacement-length relations and segment size, Cowie and Roberts used fault geometry to estimate along-strike slip rate variation in their 2001 paper (JSG,23,1901-1915). Following their model, along-strike slip rate profiles were calculated for three active normal faults: the Beaverhead, Lemhi, and Lost River faults. Though the method yields estimated slip rates, the results roughly mirror along-strike variation in total displacement, because the three faults are similar in size and age. The profiles indicate that the Beaverhead is underdisplaced, i.e. having a low slip rate relative to its length. This suggests that segment linkage occurred later in the development of the Beaverhead than in the others. Cowie and Roberts also proposed a model for fault spacing based on initial fault length and spacing, and maximum length and spacing of fully developed fault systems. Fault spacing is important in determining incidence and magnitude of fault movement. If the distance between faults is too small, strain becomes localized along one while the other exhibits a decrease in seismicity until no activity occurs. In practice it is impossible to know if the distance between the largest faults represents maximum fault spacing, because the fault population is still active and evolving; thus, it is difficult to test or implement the method. A relationship was found among faults within the study area, where spacing of adjacent active faults is proportional to the sums of their lengths. It was also observed that average segment length increases with increasing total fault length. The implications of segment length scaling with fault length are that larger faults should have larger earthquakes and surface ruptures, assuming segment length represents characteristic rupture size, and that processes controlling fault length also control segment length. No clear relationship between segment size and seismogenic layer thickness is observed.
DE: 8000 STRUCTURAL GEOLOGY (New field, replaces single entry 8165)
DE: 8010 Fractures and faults
SC: Tectonophysics [T]
MN: 2005 Joint Assembly