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

Fig. 6 therefore shows the progressively increasing impact of the Santa Ana indenter on the uplift rate of the Puente Hills at ~200-250 ka, and increasing as the collision intensifies. Fluvial and Strath Terraces: Four fluvial fill terraces, three erosional strath surfaces and the Santa Ana River channel thalweg are identified in the eastern Puente Hills (Fig. 7). The ages of the fill terraces are constrained using soil stratigraphy on the mid-level terraces and OSL dating of the lower deposits. Higher strath surfaces are correlated to the glacial-interglacial sea level curve. These terraces are then used to bracket the age of river systems that are right-laterally deformed by the Whittier fault. The channel thalweg is assumed to be graded to the last glacial sea level. Fluvial and Strath Terraces: Four fluvial fill terraces, three erosional strath surfaces and the Santa Ana River channel thalweg are identified in the eastern Puente Hills (Fig. 7). The ages of the fill terraces are constrained using soil stratigraphy on the mid-level terraces and OSL dating of the lower deposits. Higher strath surfaces are correlated to the glacial-interglacial sea level curve. These terraces are then used to bracket the age of river systems that are right-laterally deformed by the Whittier fault. The channel thalweg is assumed to be graded to the last glacial sea level. Fig. 7: Terrace map through the Santa Ana River canyon (Fig. 1) showing age estimates for the strath and fill terraces (Table 2). Whittier fault shown as thin dashed and dotted red lines, possible 3 km Santa Ana River offset shown as red arrows. Photos of the 120 ka fill terrace (left) with the Whittier fault offsetting Qt3 to surface (note lack of vertical surface offset) and highest (600 ka) strath surface (right). 600 ka