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Keywords:

  • earthquake scaling;
  • KiK-net;
  • Japan;
  • seismic energy-to-moment ration;
  • scaled energy;
  • apparent stress

[1] We investigate earthquake source characteristics and scaling properties using the results of a spectral inversion of more than 29,000 accelerometric borehole recordings from 1,826 earthquakes (MJMA 2.7–8) throughout Japan. We find that the calculated source spectra can be well characterized by the omega-square model and show on average self-similar scaling over the entire magnitude range, with median stress drops of 1.1 and 9.2 MPa for crustal and subcrustal events, respectively. The seismic energy-to-moment ratio, as theoretically expected if the omega-square model is valid, shows a strong dependency on stress drop only, which, in conjunction with data selection practice in some studies to cope with limited recording bandwidth, can explain the often observed apparent scale-dependence. Our observations suggest that there is no significant deviation from similarity of the energy radiation in the investigated magnitude range and that the observed scatter is mainly related to the scatter in stress drop.