Unraveling Fault Geometry and Slip Characteristics of the 2022 MW 6.0 Khöst, Afghanistan Earthquake: Shedding Light on the Phenomenon of Shallow Slip Deficit

On 21 June 2022, a shallow MW 6.0 earthquake occurred 55 km southwest of the province of Khöst, Afghanistan. Our analysis of the USGS and GCMT focal mechanisms, mapped active faults within the epicentral area from Ruleman et al., 2007, and surface displacements measured with Sentinel-1 and ALOS-2 satellite Interferometric Synthetic Aperture Radar observations reveal compelling evidence that this earthquake ruptured a NE-SW trending, NW dipping left-lateral fault associated with one of the segments of the North Waziristan-Bannu thrust fault system. In addition, a more detailed analysis involving coseismic slip inversion indicates a concentration of slip from 2 to 8 km at depth with a maximum slip of 2.5 m at a depth of 4 km. The coseismic slip inversion also shows a sudden decrease in slip above 2 km which is a pronounced feature of the shallow slip deficit. Two months of Sentinel-1 postseismic observation were also processed to check if the shallow slip deficit is balanced by an afterslip. However, the post-seismic observation shows a conspicuous absence of afterslip. The presence of the shallow slip deficit and the absence of afterslip introduce intriguing complexities into earthquake dynamics such as how the slip deficit is balanced in the uppermost crust. This observation raises important questions about whether the shallow slip deficit is regulated by the presence of a compliant zone and/or diffused deformation. Additionally, we contemplate whether the shallow slip deficit is a characteristic feature common in moderate to strong magnitude earthquakes (M<7), and its implications for assessment of strong ground motion.