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

Beneath the surface of the Campiche wetland in Quintero Bay, three sharp contacts between peat and mud layers accompanied by shifts in diatom assemblages reveal sudden environmental changes (Fig. 1). Based on stratigraphic correlations, radiocarbon dating and pine pollen analysis we propose that these changes resulted from 1730, 1822 and 1906 earthquakes. Qualitative and quantitative reconstructions using diatom data show that Campiche was subsided by the 1730 earthquake and subsequently uplifted by the 1822 and 1906 earthquakes. While our findings of coastal uplift for the 1822 and 1906 earthquakes are well supported by written accounts, the subsidence suggested for the 1730 earthquake is reported for the first time. Numerical models indicate that while the uplift observed in 1822 and 1906 is best explained by a deeper than average megathrust rupture, the subsidence in 1730 aligns with a previously proposed shallow megathrust rupture (Carvajal et al., 2017). These findings illustrate the variability in rupture depths during successive earthquakes along the same strike section of a subduction fault. A C K N O W L E D G E M E N T S This research is funded by Fondecyt projects Nº1240681 and N°1231735. Nelson, A. R., Shennan, I., & Long, A. J. (1996). Identifying coseismic subsidence in tidal-wetland stratigraphic sequences at the Cascadia subduction zone of western North America. Journal of Geophysical Research, 101(B3), 6115–6135. Plafker, G., 1969, Tectonics of the March 27, 1964 Alaska earthquake: U.S. Geological Survey Professional Paper 543– I, 74 p., 2 sheets, scales 1:2,000,000 and 1:500,000, https:// pubs.usgs.gov/pp/0543i/ Plafker, G., & Savage, J. C. (1970). Mechanism of the Chilean earthquakes of may 21 and 22, 1960. Geological Society of America Bulletin, 81(4), 1001. Pilarczyk, J. E., Dura, T., Horton, B. P., Engelhart, S. E., Kemp, A. C., & Sawai, Y. (2014). Microfossils from coastal environments as indicators of paleo- earthquakes, tsunamis and storms. Palaeogeography, Palaeoclimatology, Palaeoecology, 413, 144–157. Shennan, I., Bruhn, R., Barlow, N., Good, K., & Hocking, E. (2014). Late Holocene great earthquakes in the eastern part of the Aleutian megathrust. Quaternary Science Reviews, 84, 86–97. Fig. 1: Vertical changes interpreted from shifts in diatom assemblages at Campiche lowland.