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

312 PATA Days 2024 This raises questions regarding the earthquake history of the West Caspian Fault, the mechanics of faulting in over-pressured sedimentary basins and at this young triple junction. In this study, we focus on a section of the West Caspian Fault from Salyan and Shirvan (Fig. 1). We present the first paleoseismic trench investigations and aHolocene geologic slip-rate of theWestCaspian Fault. We build the first record of surface rupturing earthquakes over the past 3000 years. We then discuss the significance of these findings in the context of rheologic and tectonic conditions. M E T H O D S Faults were mapped remotely using Google Earth and Digital Elevation Models (DEMs) derived from Pleiades stereo satellite imagery (e.g., Marshall et al., 2024), prior to field mapping in 2021 to 2023. Field mapping consisted of walking portions of the faults identified in Fig. 2. The key study site at Salyan (Fig. 2) was then surveyed with photogrammetry using images captured with a Teokit-equipped DJI Phantom 4 Pro v2 drone (e.g. Pierce et al., 2024). The Teokit is a dGPS used for acquiring precise photo locations that a later PPK corrected to an Emlid Reach RS2 dGPS base station (Zhang et al., 2019). The photographs were then processed using Agisoft Metashape software into DEMs and Orthomosaics with 10 cm/pixel resolution. Two paleoseismic trenches across mapped fault traces were excavated, cleaned, gridded, and logged at the Salyan site. As a base for logging, 3D Structure-from- Motion (SfM) models of the trenches were constructed using Agisoft Metashape software with photographs captured with a Samsung Galaxy S20 Ultra (2022) and a Pixel 7 Pro (2023). The SfM models were accurately rectified, oriented, and scaled in real world units using reference points extracted from iPad-lidar scans of the trench walls, prior to construction and export of the 2D orthohoto-mosaic images (Pierce & Koehler, 2023). The results of this process are 2D images of the trench wall with cm-scale geometric errors (Pierce, 2022, 2023). Logging was then conducted on these 2D images using an iPad. Units and faults were divided and described following standard paleoseismic methods (McCalpin, 2009), including sedimentary facies, cross- cutting relations, and development of soils. Radiocarbon marine shells were logged, sampled and then analysed at the Beta Analytic laboratory in Miami, Florida and calibrated using the OxCal v4.4 (Bronk Ramsey, 1995) with the Marine calibration curve. Sediment was logged and sampled in light- resistant metal tubes. These samples were sent for Infrared Stimulated Luminescence analysis at the luminescence laboratory, University of Sheffield (Rhodes, 2015). R E S U LT S A N D D I S C U S S I O N We show evidence geomorphic evidence of active faulting at three sections on the West Caspian Fault. Each of these sections is associated to larger scale topography, created by fault bends, pressure ridges, and mud volcanism. We speculate that these sections are linked in areas of low topography and the fault trace is buried by sedimentation and agriculture.