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Analysis of Scarp Profiles: Evaluation of Errors in Morphologic Dating

Avouac, Jean-Philippe (1993) Analysis of Scarp Profiles: Evaluation of Errors in Morphologic Dating. Journal of Geophysical Research B, 98 (B4). pp. 6745-6754. ISSN 0148-0227. http://resolver.caltech.edu/CaltechAUTHORS:20120911-102136624

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Abstract

Morphologic analysis of scarp degradation can be used quantitatively to determine relative ages of different scarps formed in cohesionless materials, under the same climatic conditions. Scarps of tectonic origin as well as wavecut or rivercut terraces can be treated as topographic impulses that are attenuated by surface erosional processes. This morphological evolution can be modelled as the convolution of the initial shape with erosion (or degradation) function whose width increases with time. Such modeling applies well to scarps less than 10m high, formed in unconsolidated fanglomerates. To a good approximation, the degradation function is Gaussian with a variance measuring the degree of rounding of the initial shape. This geometric parameter can be called the degradation coefficient. A synthetic experiment shows that the degradation coefficient can be obtained by least squares fitting of profiles levelled perpendicular to the scarp. Gravitational collapse of the free face is accounted for by assuming initial scarp slopes at the angle of repose of the cohesionless materials (30°–35°). Uncertainties in the measured profiles result in an uncertainty in degradation coefficient that can be evaluated graphically. Because the degradation coefficient is sensitive to the regional slope and to three-dimensional processes (gullying, loess accumulation, stream incision, etc.), a reliable and accurate determination of degradation coefficient requires several long profiles across the same scarp. The linear diffusion model of scarp degradation is a Gaussian model in which the degradation coefficient is proportional to numerical age. In that case, absolute dating requires only determination of the propotionality constant, called the mass diffusivity constant. For Holocene scarps a few meters high, in loose alluvium under arid climatic conditions, mass diffusivity constants generally range between 1 and 6 m^2/kyr. Morphologic analysis is a reliable method to compare ages of different scarps in a given area, and it can provide approximate absolute ages of Holocene scarplike landforms.


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http://dx.doi.org/10.1029/92JB01962DOIUNSPECIFIED
http://www.agu.org/pubs/crossref/1993/92JB01962.shtmlPublisherUNSPECIFIED
Additional Information:© 1993 American Geophysical Union. Received October 29, 1991; revised July 29, 1992; accepted August 28, 1992. I am grateful to Paul Tapponnier, Gilles Peltzer, and Yves Gaudemer who critically read the manuscript, and I thank Bertrand Meyer and Rolando Armijo for numerous discussions. Geoff King, Ross Stein and Albert Tarantola also provided helpful comments. This is IPGP contribution 1244.
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IPGP1244
Record Number:CaltechAUTHORS:20120911-102136624
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20120911-102136624
Official Citation: Avouac, J.-P. (1993), Analysis of Scarp Profiles: Evaluation of Errors in Morphologic Dating, J. Geophys. Res., 98(B4), 6745–6754, doi:10.1029/92JB01962.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33988
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:11 Sep 2012 17:53
Last Modified:26 Dec 2012 16:08

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