[SSS15-P16] Receiver Function Analysis of Laboratory Frictional Experiments
Keywords:Receiver function, Laboratory frictional experiment, Fault slip, Antigorite
Sliding and SHS tests with the slip velocity of 1.5 μm/s are conducted using the biaxial slip apparatus at Hiroshima University. We select antigorite serpentinite and Ca-Montmorillonite as simulated gouge layers. We simulate the interface with two sheets of sample powder layers (up to 1.5 mm thickness) by loading 20 kN (~10 MPa) of the normal force in Figure 1. Compressional waves with one cycle of 1 MHz sinusoidal wave are transmitted diagonally to the P and S receivers through the sample layers. The receiver function method is applied by regarding the P-wave receiver as the vertical component and the S-wave receiver as the radial component. The receiver functions are calculated with the Extended-Time Multitaper method (Helffrich, 2006; Shibutani et al., 2008). Frequency dependence is examined by setting Gaussian low-pass parameters; 500 kHz for low-frequency and 800 kHz for high-frequency receiver function.
Some continuous phases around 0.5 to 2 µs and 4 µs are detected in simulated high-frequency receiver functions in Figure 2. These phases are stable in the steady-state frictional condition. Synthetic receiver functions calculated under the velocity model with 1 mm thickness of a low-velocity layer duplicate continuous positive and negative phases around 0.5 to 2 µs and 4 µs, suggesting that the low-velocity sample layer closer to the receivers are detectable by the method. Monitoring of receiver function phases provides a clue to assess faulting processes or the generation of a slow slip on natural faults and plate interfaces, although the input acoustic wave with center frequency of 1 MHz, whose wavelength is around 5 mm in stainless brock, may be relatively low for receiver functions to find out internal structures with 1 mm thickness of the layer.