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Temporal variation of crustal structure is key to our understanding of Earth processes on human timescales. Often, we expect that the most significant structural variations are caused by strong ground shaking associated with large earthquakes, and recent studies seem to confirm this. Here we test the possibility of using P receiver functions (PRF) to isolate structural variations over time. Synthetic receiver function tests indicate that structural variation could produce PRF changes on the same order of magnitude as random noise or contamination by local earthquakes. Nonetheless, we find significant variability in observed receiver functions over time at several stations located in northeastern Honshu. Immediately following the Tohoku-oki earthquake, we observe high PRF variation clustering spatially, especially in two regions near the beginning and end of the rupture plane. Due to the depth sensitivity of PRF and the timescales over which this variability is observed, we infer this effect is primarily due to fluid migration in volcanic regions and shear stress/strength reorganization. While the noise levels in PRF are high for this type of analysis, by sampling small data sets, the computational cost is lower than other methods, such as ambient noise, thereby making PRF a useful tool for estimating temporal variations in crustal structure.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18801号 / 理博第4059号 / 新制||理||1584(附属図書館) / 31752 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 岩田 知孝, 教授 平原 和朗, 准教授 久家 慶子 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The 2011 March 11 Tohoku-Oki earthquake with moment magnitude of 9.0 east of Honshu, Japan, has been the fourth strongest event in the era of instrumental seismology. This thesis is focussed on a detailed analysis of earthquake distribution in time and space in the broader area of Honshu during the time interval of fifty years (1964 - 2013), and on correlation of seismological data with tectonic structure and surface morphology, including the sea floor. The aim of the thesis is not to predict the earthquake retroactively but to put its occurrence into the context of the long-term development of seismicity, to identity differences in the seismic response to the process of plate tectonics prior, during and after the Tohoku-Oki earthquake and to delimitate the tectonic causes of areal limitation of the extent of the aftershock series. The space-time analysis of the development of earthquake occurrence utilized relocated hypocentral parameters primarily identified by the International Seismological Centre (so called EHB data), focal mechanisms of the Global Centroid Moment Tensor Solution programme, surface morphology and bathymetry data, and eruptive history database of active volcanoes. A series of epicentral maps and vertical sections of focal zones were construced for the analysis of seismic...

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23455号 / 理博第4749号 / 新制||理||1681(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 成瀬 元 助教 松岡 廣繁, 教授 生形 貴男 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

The slip behaviour of subduction faults and the viscoelastic rheology of Earth’s mantle govern crustal deformation throughout the subduction earthquake cycle. This Ph.D. dissertation presents research results on two topics: (1) coseismic and postseismic slip of the shallowest segment of subduction faults and (2) postseismic deformation following great subduction earthquakes controlled by mantle viscoelasticity. Topic 1: Slip behaviour of the shallowest subduction faults. By modelling high-resolution cross-trench bathymetry surveys before and after the 2011 Mw 9.0 Tohoku-oki earthquake, we determine the magnitude and distribution of coseismic slip over the most near-trench 40 km of the Japan Trench megathrust. The inferred > 60 m average slip and a gentle increase by 5 m towards the trench over this distance indicate moderate degree of net coseismic weakening of the shallow fault. Using near-trench seafloor and sub-seafloor fluid pressure variations as strain indicators in conjunction with land-based geodetic measurements, we determine coseismic-slip and afterslip distributions of the 2012 Mw 7.6 Costa Rica earthquake. Here, trench-breaching slip similar to the Tohoku-oki rupture did not occur during the earthquake, but afterslip extended to the trench axis and reached ~0.7 m over 1.3 years after the earthquake, exhibiting a velocity-strengthening behaviour. These two contrasting examples bracket a possibly wide range of slip behaviour of the shallow megathrust. They help us understand why large tsunamis are generated by some but not all subduction earthquakes. Topic 2: Postseismic deformation following great subduction earthquakes. Due to the asymmetry of megathrust rupture, with the upper plate undergoing greater coseismic tension than the incoming plate, viscoelastic stress relaxation causes the trench and land areas to move in opposite, opposing directions immediately after the earthquake. Seafloor geodetic measurements following the 2011 Tohoku-oki earthquake, modelled in this work, provided the first direct observational evidence for this effect. Systematic modelling studies in this work suggest that such viscoelastic opposing motion should be common to all Mw ≥ 8 subduction earthquakes. As the effect of viscoelastic relaxation decays with time and the effect of fault relocking becomes increasingly dominant, the dividing boundary of the opposing motion continues to migrate away from the rupture area. Comparative studies of ten 8 ≤ Mw ≤ 9.5 subduction earthquakes in this dissertation quantifies the primary role of earthquake size in controlling the “speed” of the evolution of this deformation. Larger earthquakes are followed by longer-lived opposing motion that affects a broader region of the upper plate. / Graduate

2001年5月29日第11次《聯合國海洋法公約》締約國會議通過SPLOS/72號決定，於1999年5月13日以前對其生效之公約締約國，如欲依《聯合國海洋法公約》第76條規定主張200海里以外之大陸礁層，必須在1999年5月13日起算10年內向聯合國大陸礁層界限委員會提交與其所主張大陸礁層外部界限相關科學及技術佐證資料。由於《聯合國海洋法公約》所定義之大陸礁層外部界限範圍可能超越專屬經濟海域範圍，而大陸礁層不僅是魚類資源較豐富也是漁業活動重要資源地，同時也是海底油氣與礦場等重要自然資源的集中地區。因此，包括我國相鄰之日本、菲律賓、越南、馬來西亞等公約締約國紛紛進行大陸礁層調查來擴展自己國家的海洋權益。至2009年12月止，已有51個延伸大陸礁層外部界限之提案，及44個初步資訊，聯合國大陸礁層界限委員會並已就部分提案作成決議。 日本於2008年11月12日向聯合國大陸礁層界限委員會提出該國延伸大陸礁層外部界限之申請，卻也因此引起中國大陸及韓國對日本提案中以「沖之鳥礁」為基礎劃定超出200海里延伸大陸礁層之主張提出反對意見，質疑「沖之鳥礁」之法律地位及其所能享有的海域管轄空間。本論文爰由《聯合國海洋法公約》第121條「島嶼制度」形成的過程、相關國家實踐及學者見解，以及《聯合國海洋法公約》中「大陸礁層」之相關規範及聯合國大陸礁層界限委員會之組織與運作情形，探討日本的延伸大陸礁層外部界限提案中以「沖之鳥礁」為基礎主張延伸大陸礁層之適法性問題，並分析以聯合國大陸礁層界限委員會作為「沖之鳥礁」法律地位爭端解決途徑之可能性等。研究結果顯示，日本提案以「沖之鳥礁」為基礎主張延伸大陸礁層外部界限不符合《聯合國海洋法公約》第121條第3項規定，但該項規定並未具備有習慣國際法的效力，亦缺乏客觀的認定標準，聯合國大陸礁層界限委員會的場域無法解決「沖之鳥礁」的法律地位爭端，其他沿海國僅能利用聯合國大陸礁層界限委員會中「第三國意見」之機制凸顯爭端的存在，提醒國際社會注意此類島礁的海域管轄空間主張的合理性問題，並應尊重公約所賦予的權利與義務。 / On 29 May 2001, the 11th Meeting of States Parties to the United Nations Convention on the Law of the Sea (UNCLOS) adopted the SPLOS/72 Decision regarding the date of commencement of the ten-year period for making submissions to the Commission on the Limits of the Continental Shelf set out in Article 4 of Annex II to the UNCLOS. It was decided that, in the case of a State Party for which the Convention entered into force before 13 May 1999, the ten-year time period for it to submit the scientific and technical data supporting the outer limits of its continental shelf beyond 200 nautical miles under Article 76 of the UNCLOS shall be taken to have commenced on 13 May 1999. For quite a few States the outer limits of their continental shelf as defined by the UNCLOS may go beyond the limits of the Exclusive Economic Zone (EEZ). Besides, continental shelf is abundant in fisheries resources, crude oil, natural gas and minerals. Consequently, the neighboring States of Taiwan, including Japan, the Philippines, Viet Nam, and Malaysia, have already begun their surveys on continental shelf in order to expand their interests hidden in the ocean. As of December of 2009, there have been 51 formal submissions and 44 Preliminary Information delivered to the United Nations. The Commission on the Limits of the Continental Shelf (CLCS) has been undertaking the consideration of these submissions and already completed such process for some of them with recommendations. For Japan, the submission to support the outer limits of its extended continental shelf was made on 12 November 2008 to the CLCS. Such submission was challenged by China and Korea whose focus is on the part of extended continental shelf generated by Oki-no-tori Shima. The legal status of Oki-no-tori Shima as being capable of generating EEZ, continental shelf, and extended continental shelf beyond 200 nautical miles, is being disputed by the communications from China and Korea. To provide educated comments on such controversy, this thesis will discuss the legislative process of Article 121 of the UNCLOS, namely, the regime of islands. Related state practices and teachings of the most highly qualified publicists will be studied in this connection. The author will also examine the regime of continental shelf under the UNCLOS and the institution of the CLCS. These will pave the way to scrutinize the legality of using Oki-no-tori Shima as the basis to generate extended continental shelf as having been done by Japan in its submission. The author will also explore the feasibility for the CLCS to settle the dispute over the legality of Japanese submission with respect to Oki-no-tori Shima. As shown by research works, the Japanese submission using Oki-no-tori Shima to generate extended continental shelf is inconsistent with Article 121(3) of the UNCLOS. However, the rule as contained in Article 121(3) has not yet been received into customary international law. Also lacking are the objective criteria to decide whether a given rock meets the conditions as stipulated by Article 121(3) or not. The forum of the CLCS is not suitable to settle the dispute over the legality of using Oki-no-tori Shima by Japan to generate extended continental shelf. Other coastal States can only use the forum of the CLCS to demonstrate the legal controversy over this case through sending third party communications to notify the CLCS the existence of dispute and their unwillingness to support the CLCS to consider the Japanese submission with respect to the part of Oki-no-tori Shima. As submitted by this author, the international community should be reminded of the necessity to respect the integrity of the rights and duties enshrined by the UNCLOS. Also worthy of careful scrutiny is the legitimacy of such kinds of exaggerated maritime claims generated by the rock as defined by Article 121(3) of the UNCLOS.