Subsurface velocity structure and site amplification characteristics in Mashiki Town, Kumamoto Prefecture, Japan, inferred from microtremor and aftershock recordings of the 2016 Kumamoto earthquakes

In order to investigate the seismic velocity structure in the region of concentrated severe damage during the 2016 Kumamoto earthquake sequence, we conducted continuous seismic observations in the central area of Mashiki Town, Kumamoto Prefecture. During 4 days of observations at eight temporary sites, 2 months after the mainshock, recordings from 30 aftershocks (1.7 ≤ Mj ≤ 4.3, 1.9 km ≤ depth ≤ 13.5 km) were obtained. The aftershock data showed that site amplifications at approximately 1 Hz are dominant in a zone where almost no buildings were damaged along the Akitsu riverside, whereas site amplifications at higher than 3 Hz are observed in the heavily damaged zones. Our data also showed that the peak acceleration and velocity amplitudes, as well as seismic intensities for the small events in the less damaged zone, are clearly larger than those in the damaged zones, implying that the damage distribution is inconsistent with site response based on linear site amplifications. The estimated phase velocities of Rayleigh waves using the aftershock and microtremor data show dispersive characteristics in the lower frequency range (0.26 ≤ f ≤ 1.27 Hz), but the values are substantially smaller than those derived from the P–S logging model at the nearest KiK-net strong-motion observation station KMMH16. The derived microtremor horizontal-to-vertical spectral ratios and earthquake radial-to-vertical (R/V) spectral ratios show common distinct peaks at around 0.4 Hz, which are possibly related to the response of deep sedimentary layers beneath the area. The refined velocity structure model that better accounts for both the phase velocity and common dominant peak indicates that the values of S wave velocity (Vs) above the bedrock layer (Vs = 2700 m/s) are smaller than those inferred from the logging model and the depth to the bedrock layer could be much deeper (about 600 m) in comparison with the logging model (234 m). The derived R/V spectral ratio at station KMMH16 also shows a distinct peak at 0.4 Hz, suggesting that there is no large difference of deep sedimentary structure between the observation area and station KMMH16

MOESM1 of Subsurface velocity structure and site amplification characteristics in Mashiki Town, Kumamoto Prefecture, Japan, inferred from microtremor and aftershock recordings of the 2016 Kumamoto earthquakes

Additional file 1. Fig.S1: Observed accelerograms and Fourier amplitude spectra at KiK-net KMMH16 and Hi-net N.MSIH stations. a Comparisons of the observed three-component acceleration records, b Fourier amplitude spectra at KiK-net borehole station KMMH16 (black traces) and Hi-net station N.MSIH (red traces) for event EQ18. Note that the original velocity seismograms observed at N.MSIH have been differentiated after the removal of instrumental responses. Fig. S2: Four-day long power spectral density of the recorded seismic noise at site S6. Here the power is expressed as decibel (dB), which corresponds to 10log10(m2/s4/Hz) of spectral acceleration

The Potential Contribution of Phytoestrogens and Organochlorine Pesticides in an Experimental Fish Diet to Estrogenic Activity

Phytoestrogens and organochlorine pesticides in the diet of laboratory animals are a possible source of interference in bioassays that assess estrogenic activity. In the present study, we investigated the levels of dietary phytoestrogens, organochlorine pesticides and the estrogenic activity of various diets for an experimental fish and discuss the potential contribution of these substances to estrogenic activity, in comparison with those used in previous studies. After hydrolysis with β-glucuronidase, genistein and daidzein were detected in all of the diets, and there were no significant differences in the contents of these substances among present and previous investigations. In addition, organochlorine pesticides, such as hexachlorobenzene (HCB), β-benzene hexachloride (β-BHC), γ-BHC, trans-nonachlor, and/or endrin, were detected in most fish diets. All of these diets exhibited higher levels of activation of β estrogen receptors than with α estrogen receptors in an in vitro yeast-based bioassay. These results indicate that phytoestrogens, such as genistein and daidzein, were the main substances contributing to the estrogenic activity of the diet. Moreover, some diets may exert estrogenic activity in in vivo tests, indicating the necessity for more careful selection of the feeding diet and measurement of estrogenic substances when performing routine screening assays for endocrine-disrupting chemicals