SCG63-01

Room:102A

Time:May 25 11:00-11:15

Recent topics on ”Cryoseismology”
KANAO, Masaki1∗ ; TSUBOI, Seiji2 ; TOYOKUNI, Genti3 ; FURUMOTO, Muneyoshi4
1NIPR, 2 JAMSTEC, 3 Tohoku University, 4 Nagoya University

Several kinds of environmental signals associated with ocean - cryosphere - solid earth system have been recently detected inbi-polar regions. Ice-related seismic motions for small magnitude events are generally named ice-quakes (ice-shocks) and canbe generated by glacially related dynamics. Such kinds of cryoseismic sources are classified into the movements of ice sheets,sea-ice, oceanic tide-cracks, icebergs and the calving fronts of ice caps. Cryoseismic waves are likely to be influenced by thevariations in environmental conditions, and the continuous study of their time-space variability provides indirect evidence ofclimate change. As glacial earthquakes are the most prominent phenomena found recently in polar regions, in particular on theGreenland in this 21st century, the new innovative studies from seismology are expected by long-term monitoring under extreme
conditions in the Earth’s environment. Taking these issues into account, the recent topics on ”Cryoseismology” are introduced,
including major achievements on glacial related seismic events involving characteristic phenomenon in polar regions. It isparticularly focused on seismic signals associated with dynamics of ice sheets, sea-ice, icebergs and glaciers.
Keywords: cryosphere dynamics, glacial earthquakes, ice-quakes, global warming, polar surface environment

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SCG63-02

Room:102A

Time:May 25 11:15-11:30

Glaciation and material cycling within the overriding plate wedge: Climate-tectonics interaction in the southern Alaska
KIOKA, Arata1∗ ; ASAHI, Hirofumi2 ; WORTHINGTON, Lindsay L.3 ; DAVIES-WALCZAK, Maureen4 ;OJIMA, Takanori1 ; JAEGER, John M.5 ; GULICK, Sean S.6 ; LEVAY, Leah7 ; NAKAMURA, Atsunori8 ;SUTO, Itsuki9 ; ASHI, Juichiro1
1

Dept. Ocean Floor Geosci., Atmos. Ocean Res. Inst., UTokyo, Japan, 2 Korea Polar Res. Inst., S. Korea, 3 Dept. Earth Planet.
Sci., UNM, USA, 4 Coll. Earth Ocean Atmos. Sci., Oregon State Univ., USA, 5 Dept. Geol. Sci., UFL, USA, 6 Inst. Geophys.,
Jackson Sch. Geosci., UT Austin, USA, 7 IODP, TAMU, USA, 8 Analy. Center Envir. Study, Atmos. Ocean Res. Inst., UTokyo,Japan, 9 Dept. Earth Envir. Sci., Nagoya U., Japan
Recent studies have revealed that climatic changes had driven tectonic perturbations. Plate subduction zones in the subpolar regions, including the southern Alaska and the southern Chile margins, have experienced proximal ice-sheet advances several times
during the Late Cenozoic. Glaciers are highly efficient erosive agents and their presence and extent are known to control underlying topography. However, there is little understanding of the dynamic interplay between tectonics and glaciation-deglaciationin these settings. Moreover, the relationship between plate convergence rates and taper angles in the outer wedges of these
glaciated accretionary margins deviates from the strong correlation observed in other non-glaciated accretionary margins. Herein
we present mechanical variations of the tapered-wedge overriding the North American plate on the southern Alaska subduction margin coupled with glacial erosion associated with the maximum extent of the adjacent Cordilleran ice-sheet around theMid-Pleistocene Transition. Changes in the taper-wedge geometry influence material cycling and fluid distribution as well as
deformation, thermal regime, and seismicity in the wedge. We estimate the geometry of the Cordilleran ice-sheet during its
maximum extent using the modified 2-D Shallow-Shelf Approximation to reconstruct approximate rates of glacial erosion. The
calculated glacial erosion rates are constrained by offshore sedimentary records from recent IODP Expedition 341 as well as
seismic images. We find evidence that the extent of glaciation is considered to definitely affect long-term mechanics of the outertaper-wedge. The large glaciations post-MPT promote an extensionally critical state and enhances fluid and gas escape fromthe wedge to the seafloor. This is likely responsible for the absence of offshore mud volcanoes and bottom-simulating reflectors
indicative of marine methane hydrates in the southern Alaska margin.
Keywords: Climate-tectonics interaction, Cordilleran ice-sheet, glacial erosion, taper wedge, material cycling, Gulf of Alaska

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SCG63-03

Room:102A

Time:May 25 11:30-11:45

Passive seismology of ice: an overview of main seismic sources and their characteristics
PODOLSKIY, Evgeny A.1∗ ; WALTER, Fabian2
1

Institute of Low Temperature Science, Hokkaido University, 2 Mountain Hydrology and Mass Movements, Swiss Federal Research Institute WSL
Recent ‘flood’ of papers and passive seismic data about ice covered areas of the planet produced a need for generalized ways todistinguish between different types of seismic sources generating ice-quakes. Basing on analysis of more than 100 publications,
we make a step in this direction and attempt to take a quantitative look at key features of previously reported signals. We findthat the emerging seismic ‘portrait’ of the Cryosphere can be mainly explained in terms of released glacial stress and externalforcings. Our study presents the first sketch of criteria which could be ultimately helpful in detecting and categorizing various
ice-related phenomena.

Keywords: icequake, Cryosphere, Seismology, seismic source, magnitude, stress drop

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SCG63-04

Room:102A

Time:May 25 11:45-12:00

Triggered Glacial earthquake by Ocean tide
ITO, Takeo1∗ ; FURUMOTO, Muneyoshi1
1Graduate School of Environmental Studies, Nagoya University

1. Introduction
Recently, global warming melts make glacier melting in Greenland, and increase the spillage of the glacier. We are concerneda rise in sea-level, and relation between the glacier earthquake and the outflow of the glacier. The glacial earthquake occurred
around the outlet of the glacier, and activity of the glacier earthquake is increasing in recent years. These phenomena may reflect
the climate change. However, it is not completely understood that the relationship between the glacial earthquake and the outflowof the glacier.
2. Changes of frictional force and coefficient due to a glacier earthquake and sea-level change
Tsai and Ekstrom (2007) researched seismic wave generated by a glacial earthquake, and reported that the surface wave
magnitude of almost the glacial earthquake in Greenland was about five. Source time function of the glacial earthquake is almost
50 seconds, which is longer than a typical tectonic earthquake. It means that the glacial earthquake is similar to slow earthquake.
In order to understand the dynamics of the glacial earthquake, we attempt to estimate the change of the frictional coefficient
between the glacier and bedrock. As a result, the change of the frictional coefficient due to the glacier earthquake is around
1.6×10−4 . The glacier earthquake may occur by triggering of a small perturbation.
On the other hand, we attempt to estimate the effect of sea-level change due to ocean tide. The change of sea-level makes thechange of pore pressure between the glacial and bedrock. If we assume that the thickness of glacier and sea-level change are
700m and 1.5m, respectively, the ratio of the change of frictional force due to induced sea water to the effective frictional forceof the steady state became about 2.1×10−3 , which is the same order as the change of the frictional coefficient due to the glacierearthquake.
3. The ocean tide triggers the glacier earthquake
In order to statically evaluate the triggered glacier earthquake by ocean tide, we check the relation between sea-level change
and the occurrence of glacier earthquake. As a result, we find 3% of the whole glacier earthquake is affected by sea-level change.
Our estimated situation of frictional state from sea-level change and the glacial earthquake is consistent with the observed glacialearthquake triggered by the ocean tide.
Keywords: Glacial earthquake, Greenland, Ocean tide

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SCG63-05

Room:102A

Time:May 25 12:00-12:15

Significances of GLISN project in Global Seismology
TSUBOI, Seiji1∗ ; TOYOKUNI, Genti2 ; KANAO, Masaki3 ; TONO, Yoko1 ; HIMENO, Tetsuto4
1

JAMSTEC, 2 Tohoku Univ., 3 NIPR, 4 Seikei Univ.

The Greenland Ice Sheet Monitoring Network (GLISN) project?a collaboration between Canada, Denmark, France, Germany,Italy, Japan, Norway, Poland, South Korea, Switzerland, and the United States?provides real-time broadband seismologicalobservations to help address critical, poorly understood aspects of the Arctic system. Geodetic observations are also included atselected stations. Seismic data from GLISN record changes at high temporal resolution and reflect deformation and structuresinternal to the ice and solid Earth. These data complement existing observations from satellite and airborne remote sensing,
ice-penetrating radar, and GPS geodesy. Launched in 2009, the GLISN project completed installation of all 33 initially planned
seismic stations in August 2013. Most GLISN stations in Greenland are installed on bedrock along the ice-free coast at sparsely
populated settlements to take advantage of existing power and communications infrastructure. Four stations are installed inthe ice. Additional stations surrounding Greenland?in Canada, Iceland, and on several Norwegian islands?allow scientists togain a broad view of Greenland’s structure and changes in the ice. The GLISN project has already provided valuable data for
multiple studies. Data from the network (Figure 1) have been used to improve analysis of glacial earthquakes, which result fromcalving events of about 1 cubic kilometer each. GLISN stations have also been used in automatic detection of calving events bymeasurement of tilt associated with seiches (standing waves) in the fjords where many glaciers terminate.
Keywords: glacier earthquake, Greenland, broadband seismograph

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SCG63-06

Room:102A

Time:May 25 12:15-12:30

Seismic waveform modeling for a structural model with the Greenland ice sheet
TOYOKUNI, Genti1∗ ; TAKENAKA, Hiroshi2 ; KANAO, Masaki3 ; TSUBOI, Seiji4 ; TONO, Yoko4
1RCPEV / Tohoku Univ., 2 Okayama Univ., 3 NIPR, 4 JAMSTEC

We calculate regional synthetic seismograms for a realistic structure model beneath Greenland, including both surface topography and ice sheet thickness. In 2009, the multinational GreenLand Ice Sheet monitoring Network (GLISN) was initiated tomonitor seismic events in and around the Greenland. Japan has been sending a field team to Greenland each year since 2011,
to construct and maintain the GLISN stations especially on ice. However, the thick and heterogeneous Greenland ice sheet isconsidered to cause various kinds of distortion on seismic waveforms observed at these ice stations. We have been working
for construction of a numerical technique, which can calculate accurate regional seismic wavefields with small computationalrequirements.
In this work, we calculate elastic wave propagation up to 2 Hz for four structural models of the Greenland ice sheet radiatedfrom a seismic source with various depths and mechanisms. Our computations for a realistic ice sheet model, the near-surface
seismic source produced a very characteristic wave train with the group velocity smaller than the S -wavespeed in the ice, whichis considered as an icesheet guided S wave, developed by a superposition of post-critical reflections between the free surface andthe ice bed. We named this wave ”Le ” on the analogy of the Lg wave, a crustally guided S wave (”e ” comes from the German
word ”Eisdecke”, meaning the ice sheet). Furthermore, computation for a deeper seismic source resulted in reinforcement of thecrustal Sg -coda wave with a group velocity range of ˜3.1-2.6 km/s, which well explains the characteristic waveform observed on
the Greenland ice sheet.
Keywords: Greenland ice sheet, Seismic waveform, Guided wave, Finite-difference method (FDM), GLISN project

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SCG63-P01

Room:Convention Hall

Time:May 25 18:15-19:30

Seismicity, structure and tectonics in the Arctic region
TODA, Shigeru1∗ ; KANAO, Masaki2 ; TOYOKUNI, Genti3 ; TSUBOI, Seiji4
1

Aichi University of Education, 2 National Institute of Polar Research, 3 Research Center for Prediction of Earthquakes andVolcanic Eruptions, Tohoku University, 4 JAMSTEC, Data Research Center for Marine-Earth Sciences
The ’Arctic’ region, where the North Pole occupies the center of the Arctic Ocean, has been affecting the environmentalvariation of the Earth from geological time to the present. However, the seismic activities in the area is not adequately monitored.
Therefore, by conducting long term monitoring of seismic phenomenon as sustainable parameters, our understanding of boththe tectonic evolution of the Earth and the dynamic interaction between the cryosphere and geosphere in surface layers of theEarth will increase. In this presentation, an overview of the structure and tectonics of the Arctic is demonstrated by incorporating
recently deployed seismic approaches and detailed seismicity of the region. In particular, the Eurasian continent is largely
focused in wide areas of Siberian Arctic, Baikal Rift Zone and the Far East. Though the majority areas of the Arctic are occupied
by relatively stable continents, the tectonic history reveals distinct variations during the formation of the present landscapes andcrustal structure. A variety of tectonic settings are present in the Arctic such as the collision zones at the Plate boundary, deformed
areas inside the continents, mantle plumes, rift systems, and so on. On the other hand, in particular for Greenland, a drastic change
in the overlying cryosphere has been identified in terms of global warming which has currently resulted in an increase of glacial
earthquake activities. In addition, micro-seismic and volcanic monitoring has now been carried out including at the bottom of theArctic Ocean. A continuous accumulation of the Arctic data from global networks could definitely contribute to the developmentof high space resolution analysis, the understanding of the deformation and uplift mechanism involving seismicity, the formation
processes of the super-continents, and the bedrock topography and geological structure underneath the ice-sheet, in many partsof the polar region. A complete view of global tectonics could be achieved by advancing inter-disciplinary research in the Arctic,
in particular at the Eurasian continent and Greenland. The Arctic is, without doubt, one of the frontiers that remain at present
to human beings, and also the place which has a crucial role to clarify the tectonic history and current variations on the Earth’ssurface. It is expected by using fully developed seismological approaches the whole understanding of multi-sphere systems in
the Arctic will be enhanced.
Keywords: Arctic region, seismicity, crustal structure, tectonics, glacial earthquakes

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