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グリーンランド氷床は地球規模の気候変動に伴って融解が進行している.近年,氷床融解の過程で末端部の氷河が移動する際に,「氷河地震」と呼ばれる地震動が発生することが知られるようになり,地震観測による氷床モニタリングに関心が集まっている.2009 年に発足した「グリーンランド氷床の地震モニタリング観測網(GLISN)」は,氷床モニタリングを目的として国際共同でグリーンランドや周辺の島々に広帯域地震計を展開するプロジェクトである.日本はGLISN 発足時からの参加国として,2011 年から観測隊を派遣しており,米国と共同で氷床上に観測点1 点を新設したほか,他の観測点のメンテナンスにも従事している.これらの観測点から得られた長周期地震波形データは,全球地震波伝播モデリングによる理論波形との比較でチェックを行い,設置場所によるノイズの影響が少ない,良質なデータであることを確認した., Global climate change is currently causing melting of the Greenland ice sheet. Recently, a new type of seismic event, referred to as a "glacial earthquake", has been recognized. Such earthquakes are generated by the movements of large masses of ice within the terminal regions of glacier, and represent a new approach for monitoring ice sheet dynamics. In 2009, the multinational GreenLand Ice Sheet monitoring Network (GLISN), a large broadband seismological network in and around Greenland, was initiated to monitor these events. Japan, a partner country of the GLISN project, has been sending a field team to Greenland each year since 2011, when a joint USA and Japanese team first established a dual seismic-GPS station (station code: ICESG-GLS2) on the Greenland ice sheet. In 2012, the same team contributed to the maintenance of ICESG-GLS2, as well as two other stations (NUUK and DY2G-GLS1). The quality of the long-period seismic waveform data obtained by these stations has been checked by comparing the data with global synthetic seismograms. Results indicate that the data from the three stations have not been substantially affected by noise, and that the quality is well controlled.

第4回極域科学シンポジウム横断セッション：[IP] 極域における多圏融合物理現象11月13日（水）統計数理研究所 ３階セミナー室２（D304）

International audience; This study provides new constraints on the upper-mantle structure from western Greece to central Anatolia using seismic data of permanent broad-band networks recently installed in Greece and Turkey and from a two-year temporary array (SIMBAAD experiment). We used ∼200 seismic events recorded at 146 broad-band stations with a typical interstation distance of 60–100 km across the study area. The high-resolution 3-D shear wave velocity model of the mantle is obtained by inversion of fundamental-mode Rayleigh wave phase velocity maps for periods between 20 and 195 s. The tomography is based on ray tracing in heterogeneous media taking into account external propagation effects. The horizontal resolution is approximately 100 km, however small heterogeneities may suffer from some horizontal smearing and damp- ing. The vertical resolution is approximately 100 km. The vertical smoothing is necessary to avoid unresolved spurious shear wave velocity oscillations in the upper mantle. The errors on shear wave velocities in our 3-D model (0.02–0.1km s−1) are significantly smaller than the amplitude of Vs variations (0.3–0.5 km s−1). In spite of the vertical and horizontal smoothing, our model shows details in the upper-mantle structure never reached at regional scale in the area. The overall structure is characterized by a low-velocity zone (80–200km depth) re- flecting a slow and warm asthenosphere underlying a thin lithosphere. The southwesternmost termination of the low-velocity anomaly corresponds to the northward dipping Hellenic slab. The detailed shear velocity structure of the upper mantle beneath Anatolia appears to be far more geometrically complex than revealed in previous tomographic studies of the area. At depths larger than or equal to 160 km, velocities are overall high beneath Anatolia, partly due to the presence of dipping high-velocity anomalies which we tentatively interpret as remnant slabs. The southernmost high-velocity anomaly beneath Anatolia is separated from the eastern edge of the Hellenic slab by a major low-velocity anomaly which we interpret as the trace of asthenospheric mantle material rising inside a vertical slab tear beneath southwestern Anatolia.

The Kandilli Observatory Real-Time Automated Seismic Data Processing System (KORTASDPS) has been one of the most important infrastructure developments in the last 5 years at Kandilli Observatory and Earthquake Research Institute (KOERI), Boğaziçi University. KORTASDPS uses the Earthworm (EW) software suite for its real-time processing of seismic data. Primary functions of EW are to serve as real-time data server and auto-detect and locate earthquakes. Performance evaluation of EW was done by comparing its hypocenter catalogs from years 2004 and 2005 with catalogs produced by the National Earthquake Monitoring Center (NEMC) at KOERI which relies on manual detection and location techniques. In general EW performance is highest in northwest Turkey where station density and relative station sensitivity are high. Catalog correlations reveal that this area has an estimated 3.1 low magnitude threshold for a 90% earthquake auto-detection and location reliability. For the rest of the country this low magnitude threshold estimate ranges between 4.4 and 4.6. Three initiatives have been proposed to improve EW auto-detection and location accuracy. These are more accurate timing of emergent phases, use of reliable S phases and an increase in the effective seismic network density with more sensitive and reliable stations. Already expansion and modernization of KOERI’s seismic network in 2004 and 2005 have resulted in clear improvements in EW’s auto-detection and location performance. A one month pilot analysis was undertaken to understand the nature of the consistent large numbers of EW cataloged seismic events that do not correlate with NEMC. Results show that after careful manual relocation of these events that the majority are not found in either NEMC’s preliminary or final catalog and that these events represent almost one third of all events found in the combined EW and NEMC catalogs. Since 2003 the KOERI re-designed digital broadband network has increased from 4 to 33 stations and international shared broadband stations from 2 to 10. The past and planned increases of more sensitive and higher quality seismic stations has and will continue to improve the performance of EW’s auto-detection and location reliability and provide a source of information rich data to be used for ongoing and future seismological research activities.

Three main shocks M-1, M-2 and M-3 (17 October 2005 at 05:45 UTC, M-w 5.4; 17 October at 09:46 UTC, M-w 5.8 and 20 October at 21:40 UTC, M-w 5.9) and their associated aftershocks within the Gulf of Sigacik, 50 km southwest of Izmir, Turkey were studied in detail. A temporary seismic network deployed during the activity allowed the hypocentre of M-3 and subsequent aftershocks to be determined with high accuracy. A relative relocation technique was used to improve the epicentres of M-1 and M-2. All three main shocks have strike-slip mechanisms which agree with the linear trends of the aftershock locations. Two distinct zones were illuminated by the aftershock locations. The zones contain clear echelon patterns with slightly different orientations from the trend of the aftershock distribution. M-2 and M-3 ruptured along of the eastern rupture zone which aligns N45 degrees E. However the strike direction of M-1 is not clearly identified. The alignment of the two rupture zones intersect at their southern terminus at an angle of 90 degrees. The fault zones form conjugate pair system and static triggering is considered as a probable mechanism for the sequential west to east occurrence of M-1, M-2 and M-3. This earthquake sequence provides seismological evidence for conjugate strike-slip faulting co-existing within a region dominated by north-south extension and well-developed east-west trending normal faults.