Scaled Energy Estimation for Shallow Slow Earthquakes.

Deep and shallow slow earthquakes occur at the edge of the seismogenic zone in the Nankai subduction zone. Deep slow earthquakes occur under high‐temperature and high‐pressure conditions, whereas shallow slow earthquakes occur at lower temperatures and pressures. Although these two types of slow earthquake show qualitatively similar behaviors, such as slow deformation and depleted high‐frequency seismic signals, their similarities have not yet been evaluated in quantitative ways. In this work, we analyze shallow tectonic tremors accompanied by very low frequency earthquakes off Kii Peninsula, Japan. We estimate the seismic energy of the shallow tectonic tremors by correcting for the site amplifications of ocean bottom seismic stations and seismic attenuation in the shallow accretionary prism. The estimated seismic energy rates of these tectonic tremors are compared with seismic moment rates of accompanying very low frequency earthquakes, revealing that the scaled energy of shallow slow earthquakes is roughly constant, ~10−9 to 10−8, which is 0 to 1 order of magnitude larger than the typical scaled energy of deep slow earthquakes. Key Points: Seismic energy of shallow tectonic tremor is quantified correcting for site amplification and seismic attenuationSeismic energy rates and seismic moment rates of shallow tremors show along‐dip variations, which are similar to deep tremorsThe scaled energy of shallow slow earthquake is 0 to 1 order of magnitude larger than deep slow earthquake [ABSTRACT FROM AUTHOR]