It is important to grasp ground motion distributions right after a major earthquake. Ground motion is very sensitive to subsurface structure, but because seismic stations are sparsely distributed, it is necessary to estimate ground motion distributions at sites with no stations from subsurface structure data at those sites and ground motions data recorded only at surrounding stations. In this study, we investigated relationship between ground motion and subsurface structure to estimate ground motion distribution applying corrections according to the subsurface structure differences. Maximum velocity responses with a period of 3 s or longer were correlated with the first natural period of the deep subsurface structure, but maximum velocity responses with a shorter period correlated more strongly with the average S-wave velocity in the upper 30 m (AVS30) than with the first natural period. However, the ratios of maximum velocity responses at one station to those at a nearby station often differed for different earthquakes, indicating that there is limitation in estimating the ratios of maximum velocity responses only from the subsurface structures. Moreover, we did not detect any notable correlations between the subsurface structures and the durations of the velocity responses. Although these results were obtained by using relative velocity responses, similar results were obtained when pseudo-velocity responses were used.
We examined the standard gas scales and the stability of methane (CH4) standard gases that have been used for atmospheric measurements at the Japan Meteorological Agency (JMA) since 2000. Calibration of the JMA standards at the National Oceanic and Atmospheric Administration (NOAA) using the NOAA04 gravimetric scale, which is the accepted World Meteorological Organization (WMO) CH4 mole fraction scale, showed that CH4 mole fractions in the NOAA04 scale differ by +1.3 to −4.5 nmol mol−1 from those in the gravimetric scale in use at JMA. We established a linear relationship between the differences, which can be used for conversion between the two scales. Stability tests showed significant drift of −1 nmol mol−1 yr−1 for the mole fractions of two of the standard gases tested; all other standards were shown to be stable. Experiments comparing the results obtained for standards used at JMA and the Meteorological Research Institute (MRI) between 2000 and 2014 verified the conversion to the WMO scale and the drift correction used. The Inter-Comparison Experiments for Greenhouse Gases Observation (iceGGO) program in Japan can provide a useful means of validating the MRI/JMA CH4 scale and comparing it with other gravimetric scales used in Japan.
Electrical charges related to cloud-to-ground (CG) lightning discharge were investigated using ground electric fields measured around the Shonai area in the Tohoku district, Japan. First, the requirement for preciseness for least-squares fitting of the electric fields derived theoretically assuming a point electrical charge to the measured electric fields is discussed. The horizontal resolution needed to obtain appropriate solutions is proposed using a set of theoretical electric fields made by electrical charges at heights with intervals of 0.1 km. A numerical fitting with the proposed spatial resolution was applied to the measured ground electric fields, and the locations and amounts of charges were estimated for 19 negative CG lightning discharges that occurred around Shonai during the warm and cold seasons in 2012. The estimated locations of the charges were compared to the atmospheric temperature, Doppler radar measurements, and the distribution of very-high-frequency (VHF) radiation sources detected by a VHF-based lightning detection system for two events. In one of the analyzed events, the estimated electrical charge revealed the characteristics of a negative charge that could have caused the discharge. In the other event, the charge was estimated to have been located at low altitude, and the event could not be interpreted by the usual negative CG lightning discharge model. The discussion concerning the numerical fitting presented in this study may be useful for future investigations of the electrical charge related to lightning discharges based on a small number of ground electric field measurements.