Masaki Kanao

By Masaki Kanao, Alessia Maggi, Yoshiaki Ishihara, Masa-yuki Yamamoto, Kazunari Nawa, Akira Yamada, Terry Wilson, Tetsuto Himeno, Genchi Toyokuni, Seiji Tsuboi, Yoko Tono and Kent Anderson

Part of the book: Seismic Waves

By Genti Toyokuni, Hiroshi Takenaka and Masaki Kanao

Part of the book: Seismic Waves

By Masaki Kanao and Takuo Shibutani

Part of the book: Seismic Waves

By Masaki Kanao

Several kinds of seismic signals involving physical interactions within the shallow atmosphere—ocean—cryosphere—solid earth system have been detected in continental margins of Antarctica and surrounding Southern Ocean. In this study, characteristic features of seismic tremors with harmonic overtones recorded at Syowa Station, the Lützow-Holm Bay (LHB), East Antarctica, are demonstrated for the period from October 2014 to March 2015. A few tens of tremors (N = 81) are identified in both the short-period and broadband seismographs. The characteristic tremors with harmonic overtones can be explained by a repetitive source, suggesting the existence of several interglacial asperities. It implies that the tremors might be involved in local origins, presumably be the dynamics of cryosphere, including discharge of sea-ices from bay, collision of icebergs and fast-ices, calving of glaciers, and the other origins. The strong harmonic tremors with frequency overtones found in LHB are mostly generated by collisions between icebergs and the edge of fast sea-ice by comparison with satellite data. Seismic tremors in terms of cryosphere dynamics, therefore, are likely to be associated with variation of surface environment in the Antarctic, and continuous monitoring of their time-space variability provides indirect evidence of climate change.

Part of the book: Earthquakes

By Masaki Kanao and Vladimir D. Suvorov

Passive source studies using teleseismic events demonstrated heterogeneous structure in the Lützow-Holm Bay (LHB) region, East Antarctica. Depth variations of upper mantle discontinuities (410 and 660 km) were derived from long-period receiver functions by local array stations. Shallow depths in topography of upper mantle discontinuity were cleared beneath the continental ice sheet back azimuth. These results reflect a paleo-upwelling of the mantle plume associated with Gondwana breakup. Lithospheric mantle anisotropy derived by shear waves’ (SKS) splitting anticipated a relationship between “fossil” anisotropy and the past tectonics in NE-SW orientation. Origin of mantle anisotropy was assumed to be caused by supercontinent assembly rather than present asthenospheric flow parallel with absolute plate motion. The deep seismic surveys by active sources, moreover, were carried out over continental ice sheet and provided clear information on crust-mantle boundary, together with inner lithospheric mantle reflections. The extracted lithospheric cross-sectional images by seismic reflection analyses implied tectonic influence of compressive stress during Pan-African age.

Part of the book: Tectonics

By Masaki Kanao

Seismological studies on the deep interiors of the Earth (depth range from the mantle to the inner core) viewed from the polar region have an advantage to promote global geosciences, such as for revealing the heterogeneous structural variations along the latitude from the poles to the equators. In this chapter, major seismological investigations, which had been held during the IPY, particularly newly identified founding of deep interiors of the Earth, will be introduced.

Part of the book: Polar Seismology

By Masaki Kanao

Several kinds of seismological investigations have been conducted in the polar region, which include the areas of both the Arctic and the Antarctic regions, in various depth ranges from the surface layers to the deep interiors of the Earth. The polar region has an advantage in order to seek inside the physical condition of the Earth as a “window” viewed from high latitudes. In this chapter, historical issues and progress of seismic research and its observations in the polar region are demonstrated during the last half-century from the era of the International Geophysical Year (IGY 1957–1958).

Part of the book: Polar Seismology

By Masaki Kanao

Among the various kinds of seismological features observed in the polar region, the characteristics of the wavelets and involved seismicity related to cryosphere dynamics are introduced to mark a decade of advances in “cryoseismology.” Classifying the seismic waves originating from the cryosphere dynamics and understanding the generating mechanism as well as the temporal-spatial distributions in seismicity should be important in order to realize surface environmental variations associated with global warming in the polar region.

Part of the book: Polar Seismology

By Masaki Kanao

Among the environmental variations in the surface layers of the Earth, global warming and those involving multisphere interactions in the polar region are reviewed with scientific research funding. By focusing on the wavelet phenomena with various generating sources within the Earth’s system, interdisciplinary research studies are conducted on the influences and responses to climate change in the polar region.

Part of the book: Polar Seismology

By Masaki Kanao

“Polar Seismology” has been developed since the International Geophysical Year (IGY 1957–1958) and contributed significantly to global seismology in particular through the big project of the International Polar Year (IPY 2007–2008). At present, in the first stage of the twenty-first century, “polar regions” play an important role to monitor and understand the drastic variations in the Earth’s system as well as to advance the inter-disciplinary studies of the interactions among multispheres within the system.

Part of the book: Polar Seismology