Re-examination of scaling relationships of source parameters of the inland crustal earthquakes in Japan based on the waveform inversion of strong motion data

Abstract

Using the waveform inversion results of recent eighteen crustal earthquakes (M w 5.4-6.9) in Japan, which happened after the 1995 Hyogo-ken Nanbu earthquake, we extracted the source parameters (entire rupture area (S) and asperity area (Sa)) from the inverted heterogeneous slip distributions following the criterion of Somerville et al.(1999). We recognized that the scaling relationship of entire rupture area S versus seismic moment M 0 obtained in this study coincides with that of Somerville et al.(1999) for earthquakes with M w <6.5 and does with that of Irikura and Miyake (2001) for earthquakes with M w >6.5, respectively. The combined area of asperities over the entire rupture area (Sa/S) is about 0.16 in average for eighteen earthquakes, which is smaller than previous result (0.22) by Somerville et al.(1999). We examined the relationship between source fault length L estimated from the waveform inversion results and seismic moment M 0. The scaling relationship of L versus M 0 for earthquakes smaller than M w 6.5 is consistent with that of Takemura (1998), whereas those larger than M w 6.5 is consistent with the scaling relation of HERP (Headquarters for Earthquake Research Promotion). We further reexamined the source fault lengths estimated from the waveform inversion results of damaging earthquakes (M w >6.5), which happened before the 1995 Hyogo-ken Nanbu earthquake. We find that reexamined relationship between source fault length L and seismic moment M 0 for earthquakes with M w >6.5 before the 1995 Hyogo-ken Nanbu earthquake also coincide with that of HERP.

Applicability of source scaling relations for crustal earthquakes to estimation of the ground motions of the 2016 Kumamoto earthquake

“…It has been confirmed by Irikura and Miyake (2001) and Miyakoshi et al (2015) that an asperity area with a large slip increases proportionally in area with the entire rupture area. The asperity area was determined following the procedure of Somerville et al (1999) based on the inverted heterogeneous slip distributions.…”

“…The seismic moment was also determined using a long-period full-wave inversion analysis of broadband F-net data (Fukuyama et al 1998). In past evaluation of the scaling relationships of crustal earthquakes (Miyakoshi et al 2015), seismic moments obtained from the long-period, full-wave data from the F-net were found to be more stable than those from the inversion of strong-motion data. Therefore, to be consistent with the previous study, we adopted the F-net seismic moment and a logarithmic average of the rupture areas of the three models for the scaling relationship of seismic moment versus rupture area.…”

“…The relationship between the rupture area S and the seismic moment M 0 for the 2016 Kumamoto earthquake with M w 7.0 was added to the scaling relationships confirmed by Miyakoshi et al (2015) shown in Fig. 2.…”

“…The seismic moment from F-net was adopted. Then, the relationship of D versus M 0 for the 2016 Kumamoto earthquake was plotted with the corresponding scaling relationship of Miyakoshi et al (2015) , that is, D versus M 0 for this event nearly coincides with the second-stage scaling. The relationships between D and M 0 for individual models are also plotted in Fig.…”

“…Miyakoshi et al (2015) examined the effectiveness of these scaling relationships using the waveform inversion results of 18 crustal earthquakes (M w 5.4-6.9) that occurred in Japan between the 1995 Hyogo-ken Nanbu earthquake and 2015. The maximum M w of the crustal earthquakes whose slip distributions were determined by these workers from waveform inversion was 6.9, i.e., the 1995 Hyogo-ken Nanbu earthquake itself.…”