Preliminary luminescence ages of offset and unfaulted alluvium along the Mission Creek strand

Ayush Joshi, Nathan D. Brown, Seulgi Moon, & Marina O. Argueta

Submitted September 11, 2022, SCEC Contribution #12389, 2022 SCEC Annual Meeting Poster #096

Whether or not the Mission Creek strand of the San Andreas fault was active in the late Pleistocene and Holocene is currently debated (Blisniuk et al., 2021; Yule et al., 2021). To investigate this issue, we estimate the depositional ages of unfaulted alluvial terraces north of the Mission Creek Stonehouse (Fig. 4 of Yule et al., 2021) and a tectonically offset channel deposit (Fig. 6 of Blisniuk et al., 2021), all within a ~1-km length of the Mission Creek strand of the San Andreas fault. The apparently unfaulted alluvial deposits overlie the fault zone, so their depositional ages should provide a minimum age for the most recent activity of the Mission Creek strand at these locations. On the basis of regional sediment accumulation rates, soil development, and 10Be surface exposure ages of similar surfaces, Yule et al. (2021) have argued that these deposits constrain the most recent event to be older than >3 - 18 ka. Additionally, we sampled deposits from a fluvial channel in this same region that has been deflected by ~50 m of right-lateral offset by the Mission Creek strand and should therefore pre-date the observed offset (Fosdick and Blisniuk, 2018). Samples were collected in August 2022 and analyzed with post-infrared infrared stimulated luminescence (p-IR IRSL) dating, a technique which estimates how long sand grains have been buried away from sunlight. Given the high-energy depositional context of these grains, we use single grain measurements to examine the between-grain variability in apparent burial age and to estimate the true burial age using the minimum age population.

Key Words
Chronology, Luminescence, IRSL, Mission Creek

Citation
Joshi, A., Brown, N. D., Moon, S., & Argueta, M. O. (2022, 09). Preliminary luminescence ages of offset and unfaulted alluvium along the Mission Creek strand . Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology