Takuto Maeda

Bio: Takuto Maeda is an academic researcher from Hirosaki University. The author has contributed to research in topics: Seismic wave & Rayleigh wave. The author has an hindex of 25, co-authored 89 publications receiving 2145 citations. Previous affiliations of Takuto Maeda include Tohoku University & University of Tokyo.

Significant tsunami observed at ocean-bottom pressure gauges during the 2011 off the Pacific coast of Tohoku Earthquake

Abstract: The 2011 Tohoku Earthquake caused a devastating tsunami along the shoreline from the Tohoku to Kanto districts. Although many of the tide gauge stations along the Tohoku coast were saturated or damaged due to the tsunami, two cabled ocean-bottom tsunami sensors installed off Kamaishi successfully recorded the tsunami waveform just above the source rupture area. The records indicated a characteristic two-stage tsunami development sequence: a smoothly increasing tsunami amplitude from 0 to 2 m during the first 800 s from the earthquake origin time, and a short-period impulsive tsunami with a peak of more than 5 m in the following 200 s. Such observations strongly suggest the lack of any sea floor upheaval at the stations during the earthquake, and the occurrence of an extremely large slip in the shallow portion of the subducting Pacific Plate near the trench axis. The source model derived from the offshore tsunami records indicates that a very large slip of 57 m occurred off Miyagi near the trench axis, south of the rupture area of the 1896 Meiji Sanriku tsunami earthquake, and was the major source of the highly destructive tsunami that subsequently developed.

Seismic Wave Propagation and Scattering in the Heterogeneous Earth: Second Edition

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Depth‐dependent activity of non‐volcanic tremor in southwest Japan

Abstract: [1] With a new location method, we obtained a high-resolution map of non-volcanic tremor along the subducting Philippine Sea plate in southwest Japan and clarified the depth-dependent behavior of the tremor activity. A bimodal distribution of tremor along-dip is apparent in regions where short-term slow slip events (SSEs) and very-low-frequency earthquakes are frequently detected. The separation of bimodal peaks is 5 to 10 km in depth. The updip tremor activity occurs episodically, coincident with major bursts that often accompany geodetically detectable SSEs. The downdip tremor activity is, however, rather stable with frequent minor bursts. This depth-dependent tremor activity likely reflects variation of interplate slip properties, specifically weakening with increasing depth and temperature. In westernmost Shikoku, anomalous tremor activity was detected in only the updip section in late 2003. This is interpreted as being triggered by a long-term SSE in the shallower edge of the tremor zone.

A revised tsunami source model for the 1707 Hoei earthquake and simulation of tsunami inundation of Ryujin Lake, Kyushu, Japan

Abstract: [1] Based on many recent findings such as those for geodetic data from Japan's GEONET nationwide GPS network and geological investigations of a tsunami-inundated Ryujin Lake in Kyushu, we present a revised source rupture model for the great 1707 Hoei earthquake that occurred in the Nankai Trough off southwestern Japan. The source rupture area of the new Hoei earthquake source model extends further, to the Hyuga-nada, more than 70 km beyond the currently accepted location at the westernmost end of Shikoku. Numerical simulation of the tsunami using a new source rupture model for the Hoei earthquake explains the distribution of the very high tsunami observed along the Pacific coast from western Shikoku to Kyushu more consistently. A simulation of the tsunami runup into Ryujin Lake using the onshore tsunami estimated by the new model demonstrates a tsunami inundation process; inflow and outflow speeds affect transport and deposition of sand in the lake and around the channel connecting it to the sea. Tsunamis from the 684 Tenmu, 1361 Shokei, and 1707 Hoei earthquakes deposited sand in Ryujin Lake and around the channel connecting it to the sea, but lesser tsunamis from other earthquakes were unable to reach Ryujin Lake. This irregular behavior suggests that in addition to the regular Nankai Trough earthquake cycle of 100–150 years, there is a hyperearthquake cycle of 300–500 years. These greater earthquakes produce the largest tsunamis from western Shikoku to Kyushu.

Spatiotemporal distribution of seismic energy radiation from low-frequency tremor in western Shikoku, Japan

Abstract: [1] The spatiotemporal patterns of the radiated seismic energy from low-frequency tremor associated with slow slip events in western Shikoku, Japan, have been estimated. A spatially decaying mean square amplitude and differential traveltime measurement from envelope correlations observed at Hi-net stations were used to locate tremors and to estimate their seismic energies. Tremor amplitude was corrected for the site amplification factors estimated using the coda normalization method. The location of the tremor is estimated as the position where both the decay of the observed energy and the differential travel times are well explained. The temporal pattern of the total energy released agrees very well with the observed tilt records. Although the spatial patterns of the energy radiation vary strongly among the six slow slip events (SSEs) in western Shikoku, the region where they overlap always radiates relatively high levels of energy. The estimated band-limited energy rate of the tremor for a 2 to 10 Hz bandwidth was typically between 105 and 106 J/min, though there is temporal variation of the radiation energy. The released total energy associated with the SSEs whose magnitude is 5.9–6.1 is on the order of 108 J within the duration of SSEs of 8–13 days. This is quite small energy radiation compared to the moment release of accompanying SSE. The scaled energy, which is the ratio of the seismic moment and the seismic energy, for the slow slip and a very low frequency earthquake was estimated to be 5 orders of magnitude smaller than that of a regular earthquake.

Seismic Wave Propagation and Scattering in the Heterogeneous Earth

Abstract: Introduction- Heterogeneity in the Lithosphere- Phenomenological Approaches to Seismogram Envelopes in short-periods- Born approximation for Wave Scattering in Random Media- Attenuation of High-Frequency Seismic Waves- Synthesis of Three-Component Seismogram Envelopes for Earthquakes Using Scattering Amplitudes from the Born Approximation- Envelope Synthesis Based on the Radiative Transfer Theory: Multiple Scattering Models- Parabolic approximation and Envelope Synthesis based on the Markov Approximation Summary and Epilogue

An integrated perspective of the continuum between earthquakes and slow-slip phenomena

Abstract: Slow slip, a mechanism by which faults can relieve stress, was thought to be distinct from earthquakes. However, a global review of slow-slip phenomena suggests that instead there is a continuum between the two types of event.

「Earth,Planets and Space」のオープンアクセス出版

Abstract: ▶ Gathers original articles on topics in earth and planetary sciences ▶ Coverage includes geomagnetism, aeronomy, space science, seismology, volcanology, geodesy and planetary science ▶ Official journal of the Society of Geomagnetism and Earth, Planetary and Space Sciences, The Seismological Society of Japan, The Volcanological Society of Japan, The Geodetic Society of Japan, and The Japanese Society for Planetary Sciences

Depth‐varying rupture properties of subduction zone megathrust faults

Abstract: Subduction zone plate boundary megathrust faults accommodate relative plate motions with spatially varying sliding behavior. The 2004 Sumatra-Andaman (M_w 9.2), 2010 Chile (Mw 8.8), and 2011 Tohoku (M_w 9.0) great earthquakes had similar depth variations in seismic wave radiation across their wide rupture zones – coherent teleseismic short-period radiation preferentially emanated from the deeper portion of the megathrusts whereas the largest fault displacements occurred at shallower depths but produced relatively little coherent short-period radiation. We represent these and other depth-varying seismic characteristics with four distinct failure domains extending along the megathrust from the trench to the downdip edge of the seismogenic zone. We designate the portion of the megathrust less than 15 km below the ocean surface as domain A, the region of tsunami earthquakes. From 15 to ∼35 km deep, large earthquake displacements occur over large-scale regions with only modest coherent short-period radiation, in what we designate as domain B. Rupture of smaller isolated megathrust patches dominate in domain C, which extends from ∼35 to 55 km deep. These isolated patches produce bursts of coherent short-period energy both in great ruptures and in smaller, sometimes repeating, moderate-size events. For the 2011 Tohoku earthquake, the sites of coherent teleseismic short-period radiation are close to areas where local strong ground motions originated. Domain D, found at depths of 30–45 km in subduction zones where relatively young oceanic lithosphere is being underthrust with shallow plate dip, is represented by the occurrence of low-frequency earthquakes, seismic tremor, and slow slip events in a transition zone to stable sliding or ductile flow below the seismogenic zone.

Connecting slow earthquakes to huge earthquakes

Abstract: Slow earthquakes are characterized by a wide spectrum of fault slip behaviors and seismic radiation patterns that differ from those of traditional earthquakes. However, slow earthquakes and huge megathrust earthquakes can have common slip mechanisms and are located in neighboring regions of the seismogenic zone. The frequent occurrence of slow earthquakes may help to reveal the physics underlying megathrust events as useful analogs. Slow earthquakes may function as stress meters because of their high sensitivity to stress changes in the seismogenic zone. Episodic stress transfer to megathrust source faults leads to an increased probability of triggering huge earthquakes if the adjacent locked region is critically loaded. Careful and precise monitoring of slow earthquakes may provide new information on the likelihood of impending huge earthquakes.