Characteristics of short‐term slow slip events estimated from deep low‐frequency tremors in Shikoku, Japan

Abstract

We have investigated the characteristics of short‐term slow slip events (SSEs), recurrence interval and size distribution, and the slip rate at the transition zone on the plate interface beneath the Shikoku region, Japan, using nonvolcanic deep low frequency (DLF) tremors. On the basis of a proportional relationship between the seismic moment of SSE observed geodetically and the total size of DLF tremors of the corresponding episode, we estimated the seismic moment due to the slip on the plate interface from the DLF tremors and a temporal variation in the cumulative seismic moment. The recurrence interval of major short‐term SSEs is ∼6 months in the western area and 3 months in the central and the eastern areas. The size distribution of short‐term SSEs as well as DLF tremors is approximated by an exponential law rather than by a power law, showing a different scaling for regular earthquakes. The average slip rate at the transition zone estimated from the cumulative seismic moment with time of SSEs is 4.2 cm/yr, 3.3 cm/yr, and 4.9 cm/yr in the western, central, and eastern areas, respectively. These values compensate for the difference between the convergence rate at the trench and the slip deficit rate at the transition zone of the subducting Philippine Sea plate. In other words, the slip rate estimated from the DLF tremors provides a constraint of the slip deficit rate at the transition zone on the plate interface.