Strong ground motions from the 2011 off-the Pacific-Coast-of-Tohoku, Japan (Mw = 9.0) earthquake obtained from a dense nationwide seismic network

Abstract

Takashi Furumura I Shunsuke Takemura I Shinako Noguchi I Teito Takemoto I Takuto Maeda I Kazuhisa Iwai I Simanchal Padhy Strong ground motions from the 2011 off-the Pacific-Coast-of-Tohoku, Japan (Mw=9.0) earthquake obtained from a dense nationwide seismic network Abstract The dense recordings of the K-NET and KiK-net nationwide strong motion network of 1,189 accelerometers show clearly the radiation and propagation properties of the strong ground motions associated with the 2011 off-the-Pacific Coast-ofTohoku, Japan (Mw=9.0) earthquake. The snapshots of seismic wave propagation reveal strong ground motions from this earthquake that originate from three large slips; the first two slips occurred over the plate interface of off-Miyagi at the southwest and the east of the hypocenter, and the third one just beneath the northern end of Ibaraki over the plate interface or in the crust. Such multiple shocks of this event caused large accelerations (maximum 1-2G) and prolonged ground shaking lasting several minutes with dominant high-frequency (T<1s) signals over the entire area of northern Japan. On the other hand, ground motions of relatively longer-period band (T=1-2s), which caused significant damage to wooden-frame houses, were about 1/2-1/3 of those observed near the source area of the destructive 1995 Kobe, Japan (M=7.3) earthquake. Also, the long-period (T=6-8s) ground motion in the Kanto (Tokyo) sedimentary basin was at an almost comparable level of those observed during the recent Mw=7 inland earthquakes, but not as large as that from the former M=8 earthquakes. Therefore, the impact of the strong ground motion from the present M=9 earthquake was not as large as expected from the previously M=7-8 earthquakes and caused strong motion damage only to short-scale construction and according to instruments inside the buildings, both have a shorter (T<1s) natural period.

Dynamic process of turbidity generation triggered by the 2011 Tohoku‐Oki earthquake

“…This observation suggests development of a sliding surface deeper than 0.5 m below the seafloor, which would further favor unstable sliding under such a large ground acceleration. The prolonged shaking and large ground accelerations at interval of about 50 s [ Furumura et al , 2011] also confirms our results.…”

Long-period ground motions in a laterally inhomogeneous large sedimentary basin: observations and model simulations of long-period surface waves in the northern Kanto Basin, Japan

“…The dominant period of the long-period ground motions observed in the Kanto Basin tends to be approximately 7 s for shallow moderate-to-large earthquakes (e.g., Miyake and Koketsu 2005;Furumura and Hayakawa 2007;Furumura et al 2011), which is strongly controlled by the velocity structure at depths of less than 2 km (e.g., Yoshimoto and Takemura 2014b). Using seismic data from dense strong motion networks in the Kanto Basin (Kinoshita 1998;Okada et al 2004), previous studies have revealed that the long-period ground motions are generated by surface waves propagating over the thick sediments in the Kanto Basin (e.g., Koketsu and Kikuchi 2000;Miura and Midorikawa 2001;Furumura and Hayakawa 2007;Hayakawa 2009).…”

Ground uplift related to permeability enhancement following the 2011 Tohoku earthquake in the Kanto Plain, Japan

“…Their observations suggest changes in fluid conditions such as a permeability of near-surface cracks in the upper few hundred meters beneath the surface Snieder 2011, 2012). Because the sediment layer beneath the local uplift area is thicker than in other areas (>2000-3000 m thick), which also appear as a negative Bouguer anomaly (e.g., Tada 1982), Furumura et al (2011) andFurumura (2014) have reported that the velocity response spectrum shows that the earthquake caused long seismic shear waves (~1-30 s). The geological characteristics would alter the permeability of the aquifer structure and induce pore fluid migration in the area significantly.…”