ABSTRACT
We carried out laboratory monitoring of spatiotemporal variations in the extent of contact between rock surfaces using transmitted P-wave. We constructed contacting surface by putting a granite block on a plate of the same granite. A piezoelectric transducer (PZT) was installed on the top surface of the block as a wave source, and 16 receiver-PZT’s were installed on the bottom surface of the plate. Normal load was applied by the weight of the granite block itself, while no shear load was applied. We added steel blocks to see transient response to an increase in load. Significant variations in transmitted P-wave amplitude were observed in time and two-dimensional space. A correlation between initial amplitude and rate of logarithmic increase in the amplitude was seen. We also tested the normal load dependence of the amplitudes of transmitted P-wave. It was confirmed that our newly developed method detected subtle, spatiotemporal variation of contact. So, if we monitor contact during a slip experiment, we expect that we can reveal how spatiotemporal variation affects faulting process, e.g. when and where rupture initiates and how rupture expands in the case of sufficient shear stress.
