Moreover, a prominent long-period near-fault velocity pulse is observed both along the strike-normal and strike-parallel directions.
Fig. 3 a Fault slip velocity (v) and b shear stress on the bilateral symmetry line in the lower crust for model W1E.
Tanaka et al. (2015) assumed an exponential relationship between the Coulomb stress change ( Delta {text{CFS}} ) and the fault slip velocity ( V ): ( V = V_{0} exp left( {frac{{Delta {text{CFS}}}}{A}} right) ), where ( V_{0} ) and ( A ) denote a steady-state velocity under no applied external stress and a constant prescribing slip response to stress, respectively.
This correction is to account for typical differences between the time of the main shock and the generation of the tsunami; this is almost equivalent to assuming an averaged apparent (i.e. projected to the seafloor) fault rupture velocity of 2 km/s.
Red and blue crosses denote the observed P- and S-wave velocities beneath the Atotsugawa fault system (velocities at grid nodes within 10 km of the surface trace of the Atotsugawa fault) and the NKTZ (velocities at grid nodes located below the NKTZ), respectively.
Fig. 4 Fault-parallel velocity and displacement at KMMH16 are plotted for the estimation of the Dc″ value.
As observed in this study, locations away from the footwall of the fault, the velocities are predominantly primary, while behind the footwall of the fault (corresponding to the fault shadow zone), lower-than-normal velocities predominant.
Three possible causes are (i) the magnitude of fault displacement velocities during the late Quaternary, (ii) the accumulation of parent nuclides caused by historical large earthquakes, and (iii) recent seismicity at nearby faults.
By using the fault-parallel velocity and displacement, we estimated a Dc″ of 1 m, which could be considered at least as the upper bound value of the slip-weakening distance on the fault.
Fig. 1 a Topography, faults, GPS velocity field with 95% confidence ellipses relative to the Eurasian Plate, coseismic horizontal GPS deformation and Sentinel-1A SAR image range in the epicenter and the surrounding area of the Jiuzhaigou earthquake.
Accumulated coupling below the land may not lead to the nucleation of earthquake because transition of characteristics on fault friction from velocity weakening to velocity strengthening occurred at about 300 °C and earthquake is not expected to nucleate below a depth of that degree (e.g., Scholz 1998).
