Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

Fig. 3: Trishear models using the current morphology of the Q4 (a) and Q3 (b) surfaces. Red line represents the maximum values and the green the minimum ones. Parameters used for forward modeling are displayed in the upper square, whereas the resulting shortening values are located at the bottom square. The near field scarp amplitude (S.A) of each profile is shown. See Fig. 2 for each location. The trishear model applied in the Q4 unit was created using the easternmost branch, in order to compare the shortening value obtained here with the one calculated for the same thrust in a younger surface (Q3; Fig. 2, 3). The trishear parameters are shown in Fig. 3a, and the models (Fig. 3a) produce shortening values ranging from a minimum of 8.56 m to a maximum of 10.33 m. Considering the 12.6 ± 0.2 ka age and accounting for the methodological error of the dating (Schmidt et al., 2011a; Fig.3 a), the rate ranges from 0.66 mm/a to 0.94 mm/a. At the Q3 unit we modeled the easternmost splay, which corresponds to the same branch that involves the older Quaternary level (Q4; Figs. 2, 3). Trishear parameters are displayed in Fig. 3b and the models (Fig. 3 b) yield minimum and At the Q3 unit we modeled the easternmost splay, which corresponds to the same branch that involves the older Quaternary level (Q4; Figs. 2, 3). Trishear parameters are displayed in Fig. 3b and the models (Fig. 3 b) yield minimum and maximum shortening values of 2.90 and 5.06 m, respectively. Considering the 3.3 ± 1.3 ka age and accounting dating errors (Schmidt et al., 2011a; Fig. 3 b), the shortening rates calculated ranges from 0.63 mm/a to 2.53 mm/a. We also modeled the Q5 unit (Fig. 2), which, despite having less significance than the previous two surfaces due to the absence of a visible fault plane and lack of specific dating, still provides an approximate value for characterizing the shortening rate at the southern margin of La Escondida creek. In the trishear model we incorporate the maximum and minimum ramp angle values measured at the Q3 fault exposure (Alvarellos et al., 2022), along with the oldest age obtained in Q4 (13 ka) and the youngest age of Q6 (16 ka; Schmidt et al., 2011a), to generate maximum and minimum shortening scenarios, respectively. This approach yielded maximum and minimum shortening rates of 0.09 and 0.14 mm/yr, respectively. D I S C U S S I O N This study examines the shortening of LPTS that propagate as footwall splays. The youngest deformation is attributed to the branches located further east, affecting the youngest Quaternary levels (Q3, Q4, Q5). Trishear models of alluvial surfaces were chosen to match the warping of the hanging