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

I N T R O D U C T I O N There is a linkage between the rate of fault slip and the rate of landscape evolution in a process-response relationship. This relationship can be exploited through quantitative geomorphic methods to develop middle to late Quaternary landscape evolution rates. Streams in particular have a predictable and measurable response to the tilting, folding, and faulting of the ground surface. In large areas of the southeastern Los Angeles basin the high stream density permits a high degree of spatial resolution for this exercise. The magnitude of the interglacial-glacial base level changes in a near-coastal fluvial system overwhelms typical tectonic processes, and such base level change is the likely origin of major synchronous terrace surfaces (Personius, 1993). In the absence of other supporting age control, such a conclusion is speculative. However, in the Los Angeles basin there are sufficient data to show that eustatic fluctuations are the dominant terrace-forming events because of their close association to the marine terraces in the uplifted areas (Grant et al., 1999). At 450-meter elevation, the Puente Hills (Fig. 1) are an actively uplifting, antiformal structure trending about N65°W through the eastern Los Angeles Basin in southern California (Gath, 1997). The uplift is facilitated by the blind PuenteHills thrust (Shaw et al., 2002). The strike-slip Whittier fault cuts across the southern flank of the Puente Hills parallel with their trend and right-laterally deforms all fault-crossing streams (Gath, 1997). Two different approaches were used to determine the 2.5-3.0 mm/yr slip rate for the Whittier fault; paleoseismic 3D trenching (Gath et al., 1992; 2017) and terrace dating of incised stream channels (Rockwell, et al., 1988; Gath, 1997). Both approaches yielded similar results, with that slip rate used herein to calculate the uplift rate of the Puente Hills. Fig. 1: DEM of the Puente Hills north of the Santa Ana Mountains, separated by the antecedent Santa Ana River. Red arrows and right- deflected streams denote the trace of the Whittier fault. Areas of Figs. 3 & 7 are shown. Fig. 3 Fig. 7