Propagation history of the Osaka-wan blind thrust, Japan, from trishear modeling

• Published in: Journal of structural geology 2014-01, Vol.58, p.79-94
• Main Authors: Grothe, Pamela R., Cardozo, Nestor, Mueller, Karl, Ishiyama, Tatsuya
• Format: Article
• Language: English
• Subjects: Blinds; Construction; Correlation; Displacement; Fault propagation folding; Faults; Growth strata; High-resolution seismic profiles; Inhibitors; Osaka Bay; Osaka-wan fault; Slip; Thrust; Trishear
• ISSN: 0191-8141; 1873-1201
• DOI: 10.1016/j.jsg.2013.10.014

Mapping the nucleation and 3D fault tip growth of the active Osaka-wan blind thrust provides an opportunity to asses how reactivated thrusts build slip from preexisting faults and the threat they pose as sources of large earthquakes. Analysis of folded growth strata, based on 2D trishear inverse modeling allows a range of best-fit models of the evolution of slip and propagation of the fault to be defined. The depth of the fault tip at 1200 ka varies between ∼1.5–4.5 km, suggesting the fault grew upward from high in the crust, and that it is reactivated. From its onset at ∼1500 ka, the fault grew rapidly along strike in ∼300 ky, and upwards with a P/S ratio of 2.5–3.0, but variable fault slip in space and time. Shallower depths of the fault tip at initiation and thinner basin fill correlates with slower propagation with time, contradicting models that argue for sediments as inhibitors of fault growth. Results also suggest the displacement profile of the currently active thrust is offset from its predecessor, assuming shallower depths to the original fault correlate with greater displacement in its prior history. These results suggest reactivated faults may accrue slip differently than newly developed ones, based on the history of upward fault propagation. •We reconstruct slip and propagation of the Osaka-wan fault with trishear models.•Models of growth strata suggest constant fault propagation to slip ratio of 2.5–3.0.•Trishear models suggest variable trishear angle and zone asymmetry along strike.•Shallow fault tips at 1200 ka suggest that the Osaka-wan fault is a reactivated fault.•Best-fit models show changes in fault slip and propagation through time and space.