Study of blind thrust faults underlying Tokyo and Osaka urban areas using a combination of high-resolution seismic reflection profiling and continuous coring

We acquired high-resolution seismic reflection profiles and continuously cored boreholes to evaluate active flexures
produced by major blind thrust fault systems within two densely populated Neogene-Quaternary sedimentary
basins in Japan: the Fukaya Fault System near Tokyo in the Kanto Basin and the Uemachi Fault System in
the Osaka Basin. The high-resolution seismic reflection survey made clear the length, geometry and growth history
of fault-related folds, or flexures formed above the two blind thrusts. Continuously cored boreholes linked
with high-resolution seismic profiles enabled us to estimate the uplift rate as defined by shallow stratigraphic
horizons and constrain the age of the most recent growth of the flexures during earthquakes on the Fukaya and
Uemachi fault systems. Even with the high quality of the data we collected, it is still not possible to exactly constrain
the age of the most recent blind thrust earthquake recorded by flexure of these fault-related folds. Data
presented in this paper form the basis for future efforts aimed at mechanical and kinematic models for fault
growth to evaluate the activity of blind thrusts underlying urban areas.