Mechanics of high displacement gradient faulting prior to lithification

We present maximum displacement–length data from normal faults with strike half-lengths ranging from a few centimetres to 5 m. The data are from faults formed in sand prior to lithification in the Talaat nʹYacoub basin, High Atlas, Morocco. Our data typically have an order of magnitude higher average strike displacement gradients as compared to published data for normal faulting of lithified sedimentary rocks. Results are put in a context of strength and frictional parameters most likely to affect fault tip propagation using previous fault growth models. We show that an increase in shear modulus during lithification of sand into sandstone will outweigh the effect of increasing shear strength, resulting in longer faults for a given maximum displacement in lithified sedimentary rocks.