Averaged stress drop equations are important in fault modeling for predicting strong ground motions, because they relate the outer and inner fault parameters describing the asperity model. We examined several equations, including an equation of a buried circular crack by using the seismic moment, the area of the asperities, and the stress drop on the asperities. We compared the relationships between the seismic moment and the seismic fault area calculated by each equation with the existing empirical relationships, and concluded that the equation of a buried circular crack can be applied to small crustal and subduction plate-boundary earthquakes without surface breakings such as the May 1997 Kagoshima-ken Hokuseibu earthquake (MW 6.1) and the 2003 Tokachi-oki earthquake (MW 8.1). Most of the results showed that the equation of a buried circular crack cannot be applied to large crustal or subduction plate-boundary earthquakes with surface breakings such as the 2016 Kumamoto earthquake (MW 7.1) and the 2011 off the Pacific coast of Tohoku earthquake (MW 9.0). This is because the equation of a buried circular crack was derived from the fault model without surface breakings. Our examinations showed that the stress drop equation by Fujii and Matsu'ura (2000) and the dynamic stress drop equation by Irie et al. (2011) for a vertical strike-slip fault can be applied to the Kumamoto earthquake and that the dynamic stress drop equation by Dorjpalam et al. (2015) for a thrust fault can be applied to the Tohoku earthquake.
The aim of this study is to understand the ground hazards of an area by considering its ground-vibration characteristics by means of a relatively simple method based on the horizontal-to-vertical spectral ratio (HVSR) derived using single-point microtremor observations. The applicability of evaluating the ground hazard as the product of the predominant period and peak value from the HVSR is examined. It is confirmed that the ground-hazard distribution map so created is consistent with the average shear-wave velocity in the upper 30 m, which is a seismic-code standard.
Nowadays, the scenario-based strong motion prediction is strongly required quantitatively to show its diversity and uncertainty. We focus on the variation or uncertainty in source parameters such as the size and stress drop of the strong motion generation area (SMGA). Repeating M6-class plate-boundary earthquakes occurring off Kesennuma, northeast Japan, were analyzed. The latest event on May 13, 2015 (MJMA 6.8) had two SMGAs, and each event in 1973, 1986 and 2002 had one SMGA. The SMGA1 of the 2015 event and SMGAs of the other three events were close to each other in space, and their spatial extent was almost same. The variation in the estimated stress drop of SMGA was approximately less than 1.6 times of the smallest event.
This paper presents a new method of generating the time-history waveforms which are compatible with multiple-damping target spectra. To assess the structural integrity of buildings and reactor buildings, time-history response analyses are conducted using simulated earthquake ground motions which are matched with the target spectra. The damping factors of simulated earthquake ground motions are defined as approximately from 0.01 to 0.05. These damping factors differ from damping factors applied to seismic isolated structures because the seismic isolated structures use the damping forces corresponding to the damping factors of approximately 0.2 to 0.4. The time-history waveforms which are matched with the target spectrum with a damping factor of 0.05 can lead to large variations in the seismic responses for the seismic isolated structures. The iteration schemes to suppress the large variations in the seismic responses have been developed by employing the corrective waveforms. However, these iteration schemes which are capable of being applied to structures with high damping factors, such as the seismic isolated structures, have not been developed yet. This is because the frequency intervals of corrective waveforms significantly affect the convergence to the target spectra with the increased damping factor. Therefore, this paper presents a new type of method focused on the frequency intervals of corrective waveforms and demonstrates the effectiveness of this method by generating the time-history waveforms which are compatible with multiple-damping spectra including the high-damping factors.
The Republic of the Union of Myanmar and its surrounding area is one of the earthquake-prone areas of the world. The highly active Sagaing Fault runs down the central part of the country over 1,500 km and is 30 km away on the east of Yangon, the former capital city. Meanwhile, there are many old buildings in Yangon which were built up to the mid-twentieth century during British colonial rule. Moreover, there are no seismic standards for office and commercial buildings that are being built in recent years and extensive damage is expected if an earthquake occurs. To evaluate the ground amplification function during earthquake, the authors conducted micro tremor observations at North Dagon in Yangon with consideration of short period (of around 1 s) and long period microseisms. The short and long period seisms involve with ground properties in the top several tens of meters and several hundred meters to several kilometers deep, respectively. A single-point (three components) micro-tremor observation and an array observation were carried out for determining the H/V spectrum and the dispersion curve of the Rayleigh wave, respectively. Then the findings as well as the estimation of the geological structure are discussed based on both results.
We used a geographic information system to reconsider factors leading to damage of agricultural reservoirs in Aomori Prefecture during the 1983 Middle Japan Sea Earthquake considering damaged reservoirs, topographical and geotechnical conditions, embankment and foundation ground materials, and reservoir ledgers. Results implicated the combined materials of embankments and foundations in damage to the reservoirs. The percentage of damage occurrence being attributable to sandy soil material was particularly high, and it was caused by the influence of liquefaction.