Scaling Relationships of Source Parameters of Inland Crustal Earthquakes in Tectonically Active Regions

We examined the scaling relationships of inland crustal earthquakes occurring in tectonically active regions such as the Japanese Islands. Two important points related to reliable scaling relationships are discussed empirically: the objective estimation of source parameters such as the seismic moment and rupture area, and the regionality of the scaling. Rupture areas are objectively estimated by trimming heterogeneous slip distributions obtained from waveform inversion. Two trimming procedures have been proposed to determine effective rupture areas, by Somerville et al. (Seismol Res Lett 70:59-80, 1999) and Thingbaijam and Mai (Bull Seismol Soc Am 106:1802-1816, 2016). We confirmed that both trimmed rupture areas agree well with each other when applied to the same dataset. The source scaling characteristics are known to depend on the seismotectonic regime. We investigate the source scaling relationships of inland crustal earthquakes in Japan using source parameters obtained from 36 slip models for 22 recent events (M-w 5.4-7.1) by waveform inversion analysis. We confirmed that the source scaling relationships consisting of two stages were almost the same as those obtained for crustal earthquakes on the US West Coast by Hanks and Bakun (Bull Seismol Soc Am 92:1841-1846, 2002). For larger earthquakes (M-w > 7.4) in seismically active regions, Tajima et al. (ZISIN2; J Seismol Soc Jpn 66:31-45, 2013) found saturation of fault displacements showing the third stage. Combining the earthquake data of M-w 5.4-7.1 in this study with those of M-w 7.0-8.0 compiled by Murotani et al. (Pure Appl Geophys 172:1371-1381, 2015), we conclude that the scaling relationship for rupture area versus seismic moment coincides with the three-stage source scaling relationship using source parameters extracted from waveform inversions.