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Seismicity,structure and tectonics in the Arctic region

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Geoscience Frontiers 2015年第5期6卷 665-677页

作者： masaki kanao Vladimir D.Suvorov Shigeru Toda Seiji Tsuboi National Institute of Polar Research.Research Organization of Information and Systems Trofimuk Institute of Petroleum Geology and Geophysics of Siberian Branch Russian Academy of Sciences Department of Earth Sciences Faculty of EducationAichi University of Education Institute for Research on Earth Evolution Japan Agency for Marine-Earth Science and Technology

The "Arctic" region,where the North Pole occupies the center of the Arctic Ocean,has been affecting the environmental variation of the Earth from geological time to the present.However,the seismic activities in the area are not adequately monitored.Therefore,by conducting long term monitoring of seismic phenomenon as sustainable parameters,our understanding of both the tectonic evolution of the Earth and the dynamic interaction between the cryosphere and geosphere in surface layers of the Earth will increase.In this paper,the association of the seismicity and structure of the Arctic region,particularly focused on Eurasian continent and surrounding oceans,and its relationship with regional evolution during the Earth’s history is studied.The target areas cover representative tectonic provinces in the Eurasian Arctic,such as the wide area of Siberia,Baikal Rift Zone.Far East Russia,Arctic Ocean together with Greenland and Northern Canada.Based on discussion including characteristics of seismicity,heterogeneous structure of the crust and upper mantle,tectonic history and recent dynamic features of the Earth’s surface in the Arctic are summarized.

关键词： Arctic region Seismicity Tectonics Earth’s structu

Infrasound observations at Syowa Station,East Antarctica:Implications for detecting the surface environmental variations in the polar regions

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Geoscience Frontiers 2015年第2期6卷 285-296页

作者： Yoshiaki Ishihara masaki kanao Masa-yuki Yamamoto Shigeru Toda Takeshi Matsushima Takahiko Murayama National Institute of Advanced Industrial Science and Technology National Institute of Polar Research Research Organization of Information and Systems Kochi University of Technology Faculty of Education Aichi Education University Faculty of Sciences Kyushu University Japan Weather Association

Characteristic infrasound waves observed at Antarctic stations demonstrate physical interaction involving environmental changes in the Antarctic continent and the surrounding oceans. A Chaparraltype infrasound sensor was installed at Syowa Station （SYO; 39°E, 69°S）, East Antarctica, as one of the projects of the International Polar Year （IPY2007-2008）. Data continuously recorded during the three seasons in 2008-2010 clearly indicate a contamination of the background oceanic signals （microbaroms） with peaks between 4 and 10 s observed during a whole season. The peak amplitudes of the microbaroms have relatively lower values during austral winters, caused by a larger amount of sea-ice extending around the Lutzow-Holm Bay near SYO, with decreasing ocean wave loading effects. Micro- baroms measurements are useful tool for characterizing ocean wave climate, complementing other oceanographic and geophysical data. A continuous monitoring by infrasound sensors in the Antarctic firmly contributes to the Comprehensive Nuclear-Test-Ban Treaty （CTBT） in the southern high latitude, together with the Pan-Antarctic Observations System （PAntOS） under the Scientific Committee on Antarctic Research （SCAR）. Detailed measurements of the infrasound waves in Antarctica, consequently, could be a new proxy for monitoring regional environmental change as well as the temporal climate variations in the polar regions.

关键词： lnfrasound Antarctica Microbaroms Environment Global network

Cryoseismologic Studies for Polar Environment—Recent Progress of Japanese Contribution

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International Journal of Geosciences 2021年第1期12卷 6-22页

作者： masaki kanao National Institute of Polar Research (NIPR) Organization of Information and Systems (ROIS) Midori-Cho Tachikawa-Shi Tokyo Japan

Majority areas of Antarctica and Greenland are under the thick ice sheet and characterized by evolving cryosphere surroundings. In the polar region, associated with the recent trend on climate change such as global warming, glacier relating earthquakes are increasing during this 21st century. In this paper, a decade of progress in “Cryoseismology” at bi-polar regions is re-viewed by focusing on the contribution from Japanese researchers. In particular, the specific cryoseismic events are treated, which occurred in the coastal area of East Antarctica, around the Lützow-Holm Bay, together with the coast and whole inland area of Greenland. As the major scientific results, frequency-overtone signals in the harmonic cryoseismic tremors were analyzed by assuming constant sources, suggesting inter-glacial asperities that generate characteristic tremors. Infrasound source locations were also determined by using the array deployment at the coastal regions in the Antarctic. In contrast, characteristics of glacial earthquakes and seismic interferometry approach have been conducted so as to achieve the fine structure of the Greenland Ice Sheet (GrIS) in particular the basal condition beneath the ice sheet.

关键词： Ice-Quakes Glacial Earthquakes Dynamic Cryosphere Cryoseismology Climate Change Polar Regions

Statistics of Seismic Tremors with Harmonic Overtones Recorded at Syowa Station, Antarctica: October 2014-March 2015

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International Journal of Geosciences 2017年第6期8卷 811-820页

作者： masaki kanao National Institute of Polar Research Research Organization of Information and Systems Tokyo Japan

During the period from October 2014 to March 2015, a total number of 82 seismic tremors and 66 ice-quakes were identified in both three-component short-period seismographs (HES) and broadband seismographs (STS-1) at Syowa Station (SYO), Antarctica. Statistics of the number of these tremors indicated that many tremors were likely to occur when large increases in temperature and/or wind speed during the period. This implied that the rapid increase in temperature enhanced a melting speed of cryosphere environment with generating seismic energy;the tremors were also excited by stormy conditions, associated with interactive resonance between sea-ices and oceanic swells. The characteristic tremors of harmonic overtones with strong amplitudes were explained by repetitive sources, suggesting inter-glacial asperities such as the collision of icebergs and fast sea-ice, calving of glaciers/ice-streams at the coastal environment of Antarctica. These high amplitude tremors occurred independently from other majority types of events, characterized by non-linear, small amplitude and weak signals at the stormy condition and rapid increase in temperature.

关键词： Seismic Tremors Harmonic Overtones Statistics Syowa Station Antarctica

Seismicity in the Antarctic Continent and Surrounding Ocean

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Open Journal of Earthquake Research 2014年第1期3卷 5-14页

作者： masaki kanao National Institute of Polar Research Midori-cho Tachikawa-shi Tokyo Japan

Seismicity in the Antarctic and surrounding ocean is evaluated based on the compiling data by the International Seismological Centre (ISC). The Antarctic continent and surrounding ocean have been believed to be one of the aseismic regions of the Earth for many decades. However, according to the development of Global Seismic Networks and local seismic arrays, the number of tectonic earthquakes detected in and around the Antarctic continent has been increased. A total of 13 seismicity areas are classified into the Antarctic continent (3 areas) and oceanic regions within the Antarctic Plate (10 areas). In general, seismic activity in the continental areas is very low in Antarctica. However, a few small earthquakes are identified. Wilkes Land in East Antarctica is the most tectonically active area in the continent, with several small earthquake events having been detected during the last four decades. In the oceanic region, in contrast, seismic activity in the area of 120?-60? W sector is three times higher than that in the other oceanic areas. This may be considered to be involved in a tectonic stress concentration toward the Easter Island Triple Junction between the Antarctic Plate, the Pacific Plate and the Nazu- ca micro-Plate. Three volcanic areas, moreover, the Deception Island, the Mts. Erebus and Melbourn, are also found to be high seismic activities in contrast with surrounding vicinity areas.

关键词： Seismicity Antarctic Plate Antarctic Continent Southern Ocean Tectonic Stress

Passive Seismic Deployments from the Lützow-Holm Bay to Inland Plateau of East Antarctica: The Japanese IPY Contribution to Structure and Seismicity

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International Journal of Geosciences 2013年第5期4卷 837-843页

作者： masaki kanao Akira Yamada Genti Toyokuni Geodynamics Research Center Ehime University Matsuyama Japan National Institute of Polar Research Tokyo Japan Research Center for Prediction of Earthquakes and Volcanic Eruptions Graduate School of Science Tohoku University Sendai Japan

Deployments of seismic stations in Antarctica are an ambitious project to improve the spatial resolution of the Antarctic Plate and surrounding regions. Several international programs had been conducted in wide area of the Antarctic continent during the International Polar Year (IPY 2007-2008). The “Antarctica’s GAmburtsev Province (AGAP)”, the “GAmburtsev Mountain SEISmic experiment (GAMSEIS)” as a part of AGAP, and the “Polar Earth Observing Network (POLENET)” were major contributions to the IPY. The AGAP/GAMSEIS was an internationally coordinated deployments of more than few tens of broadband seismographs over the wide area of East Antarctica. Detailed information on crustal thickness and mantle structure provides key constraints on an origin of the Gamburtsev Mountains;and more broad structure and evolution of the East Antarctic craton and sub-glacial environment. From POLENET data obtained, local and regional signals associated with ice movements were recorded together with a significant number of teleseismic events. Moreover, seismic deployments have been carried out in the Lützow-Holm Bay (LHB), East Antarctica, by Japanese activities. The recorded teleseismic and local events are of sufficient quality to image the structure and dynamics of the crust and mantle, such as the studies by receiver functions suggesting a heterogeneous upper mantle. In addition to studies on the shallow part of the Earth, we place emphasis on these seismic deployments’ ability to image the Earth’s deep interior, as viewed from Antarctica, as a large aperture array in the southern high latitude.

关键词： Passive Seismic Deployments Lützow-Holm Bay East Antarctica Mantle Structure Earth’s Deep Interiors

Evaluation of Long-Period Detectability of Teleseismic Events at Syowa Station, Antarctica

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International Journal of Geosciences 2012年第4期3卷 809-821页

作者： masaki kanao Dmitry Storchak Ben Dando International Seismological Centre Research Organization of Information and Systems

Phase identification procedures for teleseismic events at Syowa Station (69.0°S, 39.6°E;SYO), East Antarctica have been carried out since 1967 after the International Geophysical Year (IGY;1957-1958). Since the development of INTELSAT telecommunication link, digital waveform data have been transmitted to the National Institute of Polar Research (NIPR) for the utilization of phase identification. Arrival times of teleseismic phases, P, PKP, PP, S, SKS have been detected manually and reported to the International Seismological Centre (ISC), and published by “JARE Data Reports” from NIPR. In this paper, hypocentral distribution and time variations for detected earthquakes are demonstrated over the last four decades in 1967-2010. Characteristics of detected events, magnitude dependency, spatial distributions, seasonal variations, together with classification by focal depth are investigated. Besides the natural increase in the occurrence of teleseismic events on the globe, a technical advance in the observing system and station infrastructure, as well as the improvement of procedures for reading seismic phases, could all combine to produce the increase in detection of events in last few decades. Variations in teleseismic detectability for longer terms may be possible by association with the meteorological environment and seaice spreading area around the Antarctic continent. Recorded teleseismic and local seismic signals have sufficient quality for many analyses on dynamics and structure of the Earth as viewed from Antarctica. The continuously recorded data are applied not only to lithospheric studies but also to the Earth’s deep interiors, as a significant contribution to the Federation of Digital Seismological Networks (FDSN) from high southern latitude.

关键词： Teleseismic Events Detectability Syowa Station Antarctica Global Network

Infrasonic Waves in Antarctica: A New Proxy for Monitoring Polar Environment

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International Journal of Geosciences 2013年第4期4卷 797-802页

作者： Masa-Yuki Yamamoto Yoshiaki Ishihara masaki kanao Kochi University of Technology Kami-shi Japan National Institute of Advanced Industrial Science and Technology Tsukuba Japan National Institute of Polar Research Tokyo Japan

Characteristic infrasound waves are clearly recorded at Syowa Station (SYO), East Antarctica, involving physical interaction in surrounding environments at the continent and SouthernOcean. A Chaparral microphone type infrasound sensor is deployed at SYO during the International Polar Year (IPY2007-2008), the most diverse international science program held recently. Continuous recorded data in 2008-2010 indicate a contamination of background oceanic signals (microbaroms). The characteristic signals are identified as the “microbaroms” with peaks between 4 and 10 s in the records. The peak amplitudes of microbaroms may be enhanced by the extratropical cyclonic storms and wind noises in Southern Ocean. The microbaroms has relatively lower amplitudes during austral winters, which may be caused by the larger amount of the sea-ice extent around theLützow-HolmBaynear SYO, with decreasing the ocean wave loading effects. In addition, the large energy with intrinsic periods between 12 and 30 s are observable under excellent storm conditions, particularly in local winter. The oceanic effects appearing on infrasound data are modulated by the presence of sea-ice and explained by a relationship between the atmosphere-ocean-cryosphere systems. Microbaroms measurements could be a useful tool for characterizing ocean wave climate, as well as a new proxy for monitoring a regional environmental variation inAntarctica.

关键词： Infrasound Antarctica Microbaroms Environmental Monitoring Global Network

Seismic Tremors and Their Relation to Cryosphere Dynamics in April 2015 around the Lützow-Holm Bay, East Antarctica

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International Journal of Geosciences 2017年第8期8卷 1025-1047页

作者： masaki kanao Takahiko Murayama Masa-Yuki Yamamoto Yoshiaki Ishihara National Institute of Polar Research Research Organization of Information and Systems Tokyo Japan Japan Weather Association Tokyo Japan Kochi University of Technology Kochi Japan Japan Aerospace Exploration Agency Kanagawa Japan

Characteristics and statistics of seismic tremors occurring during April 2015 were investigated by using short-period and broadband seismographs deployed at Syowa Station (SYO), in the Lützow-Holm Bay (LHB), East Antarctica. In order to examine a relationship between surface environments in particular cryosphere variation, the MODIS satellite images were utilized for comparison with the detected tremor events. Since a large volume of sea-ice was discharged during the April, together with several large icebergs passed through from the west to the east at northern edge of the fast sea-ice of LHB, it was expected to detect seismic tremors involving cryospehre dynamics. During the month, a total number of 49 tremor events including short duration ice shocks were identified. Majority of the events (N = 39) had their duration times more than 15 minutes, which were divided into both tremors and ice shocks on the basis of experienced definition at SYO. Cryospheric sources recorded by seismic tremors were classified into several origins (collision, calving, crevassing, crashing, etc.): “crevassing events” along the large cracks inside the fast sea-ice in LHB (04 April), “discharge events” of fast sea-ice from the Bay (07 April), “collision events” between iceberg and the edge of fast sea-ice (14 April), “crashing movement” between fragmentation of fast sea-ice and packed sea-ice (18 April), and other origins. In particular, strong amplitude tremors with harmonic overtones were assumed to be occurred independently from whether condition, because these overtone tremors were identified at less stormy days by comparison with infrasound data at SYO.

关键词： Seismic Tremors Ice Shocks Cryosphere Dynamics Sea-Ice Icebergs Lützow-Holm Bay Antarctica