In previous studies, it was suggested that integrating the vertical component of strong acceleration records in time domain often yields a residual velocity, which is always negative. This study proposes a generation mechanism of this residual velocity V_non; at the moment of the action of a horizontal inertia force, the sensor is tentatively tilted in that direction and the horizontal inertia force multiplied by sinθ is felt by the vertical sensor, where θ is the tilt angle. The tilt can be either due to the shear deformation of the ground or the tilt of the house. The apparent residual velocity generated by this mechanism is always negative. It was shown for the K-NET records for which the effect of the housing is small that the proposed mechanism can readily explain the order of magnitude of the observed V_non values.

In this study, horizontal loading tests were conducted on small-diameter buried pipes to evaluate soil spring characteristics for design and to propose an estimation formula for the subgrade reaction modulus (SRM). In the horizontal loading tests, steel pipes were buried in compacted wet sand in a soil tank. Steel rods were fixed to the ends of the pipes and loaded statically from the outside. The relationship between load and displacement was obtained. The relationship was approximated by the Weibull function, and the dependence of the SRM on the normalized displacement, on the loading width, and on the burial depth were evaluated respectively. In addition, the yielding displacement based on the maximum subgrade reaction and elasto-plastic model, and the relationship between the yielding SRM and the elastic SRM were clarified as the soil spring characteristics considering soil yielding. These results were used to construct a correction equation for the SRM obtained from the plate loading tests, and the validity of the correction equation was verified by multiple regression analysis.

At an occurrence of earthquake train operators suspend trains as soon as possible. Then, if necessary, they inspect railway facilities, such as track and structure, based on seismic ground motion observed alongside the railways. The safety inspection takes a significant amount of time depending on cases. Recently the early resumption of train operations has become a weighty issue after earthquakes. If the seismic ground motion along the railway can be estimated continuously, it may be possible to shorten the inspection section. However, the practical use of estimated result for the decision making of resumption of train operations after earthquakes is in progress in some railway operators, but not sufficiently. This may be because the operational method of estimation errors is not defined expressly. In this study, after presenting the concept of the estimation error handling in practice, we propose a method to estimate spatial seismic ground motions by fusing observed data and estimated data. Furthermore, a case study is presented in which seismic ground motions along a virtual railway were estimated using the proposed method with additional observed data by seismometers installed alongside the railway.

After the 1995 Hyogo-ken Nanbu Earthquake, a strong-motion seismograph network has expanded exponentially in Japan. A strong-motion seismograph, including a seismic intensity meter, has four main parts: the sensor module, the analog-to-digital data conversion module, the computation module, and the communications module, which have all been improved as technology advances. In contrast with the rapid technological development, miniaturization, and price reduction of AD conversion, computation, and communications modules, the sensors have been utilizing servo type accelerometers to convert seismic motion into electric signal, and have not shown significant technological change and particularly price reduction from earlier iterations. Modern acceleration and impact sensor modules, which are often installed on smartphones and cars, are called MEMS (Micro Electro Mechanical Systems). These are devices that integrate mechanical elements and electronic circuits made through the help of microfabrication technology. While MEMS is ultra-small, low-cost and able to measure in a wide range, its resolution is low and could barely be used for seismic observation to measure approx. 1×10^-2 m/s² vibration. However, recently, extremely low-noise MEMS acceleration sensors that can be used for strong-motion seismographs have been developed and sold. We developed a MEMS type seismic intensity meter adapting the MEMS acceleration sensor, and evaluated it with wireless data transfer in EPS rooms and basement floors of high-rise buildings.

To solve the problem of evaluating the area S_SMGA of SMGA data, which was a problem in an examination of the strong motion generation area (SMGA) data in the previous paper (Tohdo et al., 2022), the area S_SMGA was evaluated directly from SMGA data in a mean sense. In this evaluation, S_SMGA was scaled with M₀^2/3, M₀^1/2, M₀¹ for seismic moment M_0, associated with the three-stage model in the “Recipe.” The empirical equation for the M₀-S_SMGA relationship was established by applying the least squares method to the SMGA data, and the stress drop calculated using this equation and the pre-set empirical equation for the short-period level was constant regardless of M₀ for each stage of the three-stage, and it was confirmed that they were consistent with the SMGA data.