SIMULATION ANALYSIS OF LONG PERIOD GROUND MOTIONS IN COASTAL AREA OF ISE BAY DURING THE 2011 TOHOKU EARTHQUAKE AND AMPLIFICATION CHARACTERISTICS DEPENDING ON AZIMUTHAL ANGLES OF S-WAVE INCIDENCE

In this study, empirical fragility curves expressed in terms of relationship between damage ratio indices of buildings and ground motion indices were developed in northern Miyagi prefecture located in near-field areas during the 2011 off the Pacific coast of Tohoku Earthquake. The ground motion indices were evaluated from observed ground motions at strong-motion stations and estimated at sites at which no strong-motion accelerometers were deployed during the mainshock. The ground motions at the non-instrumental sites were estimated using the empirical Green’s function method based on bedrock motions inverted from observed records on surfaces from small events that occurred inside the source fault, transfer functions due to underground velocity structures identified from microtremor H/V spectral ratios, and a short-period source model of the mainshock. The findings indicated that the empirical fragility curves as functions of Japan Meteorological Agency (JMA) instrumental seismic intensity during the 2011 Tohoku Earthquake almost corresponded to those during the 1995 Kobe Earthquake and the seven disastrous earthquakes that occurred between 2003 and 2008. However, the empirical fragility curves as functions of peak ground velocity were the lowest. A possible reason for this is that the response spectra of the ground motions in the period ranging from 1.0 s to 1.5 s were small during the 2011 Tohoku Earthquake. Another reason could be the seismic resistant capacities of buildings in the studied districts involved during the 2011 Tohoku Earthquake exceeded those in the cities affected during the 1995 Kobe Earthquake.

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Tsunami Characteristics in Tokai Coastal Area Due to the 2011 Tohoku Earthquake

Journal of Japan Society of Civil Engineers Ser B2 (Coastal Engineering) ◽

10.2208/kaigan.69.i_186 ◽

2013 ◽

Vol 69 (2) ◽

pp. I_186-I_190

Author(s):

Koji KAWASAKI ◽

Kazuki SUZUKI ◽

Yuki TAKASUGI ◽

Yoshitaka TAKASUGI

Keyword(s):

Coastal Area ◽

Tohoku Earthquake ◽

2011 Tohoku Earthquake ◽

The 2011 Tohoku Earthquake

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Long-Period Ground Motions Observed in the Northern Part of Kanto Basin, During the 2011 off the Pacific Coast of Tohoku Earthquake, Japan

Journal of Disaster Research ◽

10.20965/jdr.2013.p0781 ◽

2013 ◽

Vol 8 (sp) ◽

pp. 781-791 ◽

Cited By ~ 2

Author(s):

Seiji Tsuno ◽

◽

Andi Muhamad Pramatadie ◽

Yadab P. Dhakal ◽

Kosuke Chimoto ◽

...

Keyword(s):

Wave Velocity ◽

Love Wave ◽

Pacific Coast ◽

Velocity Structure ◽

Ground Motions ◽

Tohoku Earthquake ◽

S Wave ◽

Long Period ◽

The Pacific ◽

Kanto Basin

During the 2011 off the Pacific coast of Tohoku earthquake (Mw 9.0), strong ground motions were observed at many seismic stations in the Tokyo Metropolitan Area located about 200 km away from the southern edge of the earthquake source fault. Large earthquake responses in high-rise buildings having long natural periods of several seconds were also observed. The largest ground responses for a period of 4 to 5 seconds were observed locally in Oyama (K-NET TCG012) and Koga (K-NET IBR009) on the border between Tochigi and Ibaraki Prefectures in the northern part of Kanto basin. Geophysical information in these areas was not accurate enough, however, to evaluate these ground motions. To understand S-wave velocity structures, we performed array microtremors observations at TCG012 seismic station in Oyama. We applied the Spatial Autocorrelation (SPAC) method to array microtremors data for vertical components. Rayleigh wave phase velocity from 0.3 to 1.6 km/s was obtained for a period of 0.25 to 3 seconds. We inverted phase velocity to a S-wave velocity structure reaching to bedrock at a depth of 1.6 km, using a Genetic Algorithm. The estimated structure explained the first peak of the H/V spectral ratio of microtremors well by the ellipticity of fundamentalmode Rayleigh wave. To evaluate long-period ground motions observed around Oyama during the main shock, we estimated earthquake ground motions by 1-D analysis, showing agreements with and the differences from those observed. As a result, velocity calculated at IBR008 located midway between the Tsukuba Mountains and Oyama, explained that observed for main phases and later phases. However, velocity calculated at TCG012 did not explain that observed for later phases. According to the emphasis of airy phases for group velocity of Love wave using the estimated S-wave velocity structure and the principal axis for later phases obtained by PCA corresponding to the vibration direction of Love wave propagating from the earthquake source fault and through the Tsukuba Mountains, long-period ground motions of a period of 3 to 5 seconds observed at TCG012 lasting for 200 seconds after the arrival of main phases, consist of Love wave.

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Damage Related to the 2011 Tohoku Earthquake in and Around Kamaishi City – Beyond the Tsunami Disaster –

Journal of Disaster Research ◽

10.20965/jdr.2019.p1185 ◽

2019 ◽

Vol 14 (9) ◽

pp. 1185-1200

Author(s):

Tsuneo Ohsumi ◽

Yuji Dohi ◽

Hemanta Hazarika ◽

◽

Keyword(s):

Coastal Area ◽

Tohoku Earthquake ◽

2011 Tohoku Earthquake ◽

The South ◽

The 2011 Tohoku Earthquake ◽

Tsunami Disaster ◽

South Central ◽

The Pacific ◽

Iwate Prefecture ◽

Eastern Japan

Widespread damage was caused in eastern Japan as a result of the earthquake and tsunami which occurred in 2011 off the Pacific coast of Tohoku (hereinafter, the 2011 Tohoku Earthquake). A large tsunami struck the coastal area of eastern Japan and caused damage to buildings, breakwaters, tide embankments and river levees. The joint reconnaissance team of the Tohoku and Kyushu branches of the Japanese Geotechnical Society investigated the geotechnical damage in the south-central coastal area of Iwate Prefecture from the beginning of April to September 2011. This report summarizes the geotechnical hazards and the damage to port structures, roads, railways, river levees, and buildings caused by the earthquake motion and tsunami in the 2011 Tohoku Earthquake in the south-central coastal area of Iwate Prefecture. Major investigation areas are Kamaishi City (Koshirahama Port, Touni-Chou), the coastal area of Ofunato City (Sanriku-Chou Yoshihama, Sanriku-Chou Okirai), and Rikuzentakata City. In the 2011 Tohoku Earthquake, many people could not or did not evacuate from the tsunami. However, students at junior high and elementary schools started tsunami evacuation quickly, resulting in what is known as the “Kamaishi Miracle.” This study focused on the tsunami evacuation of children in Unosumai district, Kamaishi City.

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