The Early Evolution of a Young Normal Fault in the Aysén Fjord, Chile

Abstract Seismic reflection data have been used to investigate the evolution of faults in oil and gas basins for decades and typically image deeply buried faults at low resolution, with biostratigraphic age control to date horizons at scales of 10 Myr. This study applies quantitative fault analysis techniques typically utilized in the oil and gas industry to ultra‐high resolution seismic reflection data from the Aysén Fjord in Chile to investigate active faulting. By combining these fault analysis techniques with sedimentological observations of a long marine core with a new time depth relationship derived for the study area, we are able to quantitatively constrain the ages of past surface ruptures of the Río Pescado Fault at 10 3 –10 4 yr timescales. This study presents a palaeoseismic record over ∼13 kyr and constrains the gradual evolution and linkage of a young fault by the hybrid fault growth model. In particular, two palaeoearthquakes, each with maximum backstripped throws of ∼2.80 and ∼1.23 m are identified, which occurred at 1,791 ± 65 cal yrs BP and ∼8,000 ± 60 cal yrs BP respectively. This research provides a proof of concept for the use of ultra‐high resolution seismic reflection data combined with sediment cores as a tool to conduct quantitative well constrained palaeoseismological studies and highlights its importance in constraining the early structural evolution of faults by resolving individual segment growth and linkage over millennial timescales.