Height of faceted spurs, a proxy for determining long‐term throw rates on normal faults: Evidence from the North Baikal Rift System, Siberia

Abstract

[1] We present new results on the long-term throw rates of active normal faults in the North Baikal Rift (NBR), eastern Siberia, based on a statistical analysis of triangular faceted scarps. Fault-bounded ridges in the NBR display typical morphologies with several contiguous facets separated by fault-perpendicular catchments. Over a range of 20 fault segments analyzed, triangular facet heights vary from $200 to >900 m. As fault scarps have been developing under similar long-term climatic conditions, we infer that the scatter in mean facet height arises from long-term differences in fault throw rate. We compare the morphology of NBR facets with results obtained in a previously published numerical model of facet growth. Using facet height as an input, model results provide estimates of the long-term fault throw rate. NBR throw rates vary between 0.2 and 1.2 mm yr À1 . The throw rates are then compared with the cumulated throw, which has been constrained by geophysical and stratigraphic data in the basins. This provides an estimate of the age of fault and basin initiation. We show that the modern stage of basin development started circa 3 Myr ago, except for the North Baikal basin ($8 Ma). Our results also suggest that a proportion of the observed throw is inherited from an earlier tectonic stage. Citation: Petit, C., B. Meyer, Y. Gunnell, M. Jolivet, V. San'kov, V. Strak, and N. Gonga-Saholiariliva (2009), Height of faceted spurs, a proxy for determining long-term throw rates on normal faults:

The unusual temporal and spatial slip history of the Wassuk Range normal fault, western Nevada (USA): Implications for seismic hazard and Walker Lane deformation

“…Surprisingly, their sensitivity tests suggest that a fault scarp will only bear faceted spurs when diffusion and incision processes balance, with the formation of these features not strongly controlled by climatic conditions (Petit et al, 2009a). In addition, the fault dip angle does not significantly control facet height or slope angle; these values are instead primarily controlled by the vertical displacement rate (Petit et al, 2009a;2009b), an idea supported by the development of triangular facets on the spurs of the hanging walls of reverse faults (e.g., Bull, 2007). Petit et al (2009a) point out that facet shape (including facet height) reaches a steady state by ∼0.7 -1.0 Ma regardless of the duration of the experiment or variations in model erosion parameters, a finding that we can apply to facet development along the Wassuk Range fault.…”

“…We also use the faceted-spur analysis method developed by Petit et al (2009a;2009b) to provide another estimate of the long-term (>1 Ma) vertical displacement rate for the range-front fault system. These two new slip rate estimates fill in important temporal gaps for the Wassuk Range fault system and permit us to better evaluate strain release over time.…”

“…To provide an estimate of vertical displacement rate along the Wassuk Range normal fault system at the >1 Ma time scale, we applied the results of numerical modeling by Petit et al (2009a;2009b) to faceted spurs along the Wassuk Range normal fault system. Petit et al (2009a) tested the sensitivity of climatic (diffusion coefficient, effective precipitation rate, and characteristic length scale) and tectonic (fault dip angle and slip rate) parameters upon the development of faceted spurs associated with major active normal faults.…”

“…Using normal fault systems along the Wasatch range (Utah, U.S.A.) and the Northern Baikal Rift (Russia), Petit et al (2009a;2009b) demonstrated that that the height of triangular faceted spurs along the footwalls of normal fault systems could be used as a proxy to determine the long-term (> 1Ma) throw rates on these fault systems (Petit et al, 2009a;2009b). Importantly, Petit et al (2009a;2009b) quantified strong linear correlations between mean facet height and mean facet slope as well as between mean facet height and throw rate.…”

“…In this study, we use new geologic data, terrestrial cosmogenic nuclide (TCN) age data, shallow seismic data, gravity data, and large-scale fault scarp analysis (using the numerical modeling results of Petit et al, 2009a;2009b) to construct a more complete record of vertical displacement rate over 6 temporal windows ranging from 10 6 yr to 10 1 yr.…”