Variety and spatial heterogeneity of tectonic tremor worldwide

Deep tectonic tremor occurs at various sites worldwide, and the source characteristics are heterogeneous, even at small scales. In this study, tremor sources were determined using data sets of seismic waveforms from various locations, some of which are not well recognized as being a site of tremor activity. The regions of interest are subduction zones at Nankai and Kyushu, Japan, Cascadia in western North America, Mexico, southern Chile, and New Zealand. Tremor locations are consistent with the geometry of subducting plates, and tremor depth tends to be shallower where younger plate is subducting. Tremor duration shows a negative correlation with tidal sensitivity, as reported previously in western Shikoku in the Nankai subduction zone. The duration is also related to the width of the tremor zone in the dip direction of the subducting plate. Linear structures, resembling striations, are observed in hypocenter distributions in western Shikoku and in the probability of short-term migration direction. These spatial heterogeneities in tremor activity may be controlled by the heterogeneous frictional properties of the downgoing slab due to long-term plate subduction, thereby providing information on the maturity of the plate interface.