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# AAPG Bulletin

AAPG Bulletin, Preliminary version published online Ahead of Print 1 October 2022.

DOI:10.1306/09232220096

## Estimation of detachment depths and displacements from the area-depth markers of contractional growth structures; testing the ‘inverse line’ concept

1 CEPSA, Paseo de la Castellana, 256A, 28046, Madrid, Spain
2 Departamento de Geodinámica, Estratigrafía y Paleontología, Universidad Complutense de Madrid, C/ Jose Antonio Novais, 12, 28040, Madrid, Spain

In a contractional syn-tectonic structure, an inverse line to the area-depth markers of the growth section is a good first approximation to the best fine line defined by the area-depth markers of the pregrowth section, and thus to the true detachment depth and displacement of a structure. The validity of this concept was tested through a series of case studies and fault-propagation fold models. Case studies suggest: 1) that the inverse line tends to underestimate the detachment depth, and 2) that there is a direct relationship between the proxy displacement (D2) given by the inverse line, and the true displacement of the structure (D1) through the power-law function D1 = 0.76·D20.61. Additionally, models indicate that the inverse line gives good predictions of detachment and displacement at high sediment-to-uplift ratios (S/U) for models with low displacements, and vice versa. Thus, two possible solutions are proposed to estimate detachments and displacements directly from the growth section: 1) to use the function derived from the case studies to obtain D1 from D2, or 2) to use the D2 value given by the inverse line and an estimate of S/U to obtain a possible D1/D2 ratio, from which to approximate D1. These workflows could help structural and exploration geologists working in areas where syn-tectonic sequences are observed, but in which seismic data is of poor quality or incomplete at depth.

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