Striations and tremor duration controlling diverse tremor behavior: from western Shikoku to world tremor zones (Invited)

Deep tremor in subduction zones is thought to be caused by small repeating shear slip events on the plate interface with significant slow components. It occurs at a depth of about 30 km and provides valuable information on deep plate motion and shallow stress accumulation on the fault plane of megathrust earthquakes. Tremor has been suggested to repeat at a regular interval, migrate at various velocities and be modulated by tidal stress. Here I show that some time-invariant interface property controls tremor behavior, using precise location of tremor sources with event duration. The first study area is western Shikoku in Nankai subduction zone, Japan, where tremor activity is high and observation condition is good. In areas where tremor duration is short, tremor is more strongly affected by tidal stress and migration is inhibited. Where tremor lasts longer, diffusive migration occurs. The control property may be the ratio of brittle to ductile areas, perhaps determined by the influence of mantle wedge serpentinization on the plate interface. The spatial variation of the controlling property seems to be characterized by striations in tremor source distribution, which follows either the current or previous plate subduction directions. This suggests that the striations and corresponding interface properties are formed through the subduction of inhomogeneous structure, such as seamounts, for periods as long as ten million years. I apply the same method to tremor activities in several regions worldwide: other regions in the Nankai subduction zone, Cascadia, northern Mexico, and southern Chile. Despite different observation conditions, generally tremor duration correlates well with the sensitivity to tidal stress. Cascadia tremor has anomalously long duration and wide distribution. Along-strike diffusive migration, long recurrence time, and collocation with slow slip events may be the features of such long duration tremor. Acknowledgements: Seismic waveform data are downloaded from Hi-net and IRIS data server.