Robust uncertainty quantification of the volume of tsunami ionospheric holes for the 2011 Tohoku-Oki earthquake: towards low-cost satellite-based tsunami warning systems

We develop a new method to analyze the total electron content (TEC) depression in the ionosphere after a tsunami occurrence. We employ Gaussian process regression to accurately estimate the TEC disturbance every 30 s using satellite observations from the global navigation satellite system (GNSS) network, even over regions without measurements. We face multiple challenges. First, the impact of the acoustic wave generated by a tsunami onto TEC levels is nonlinear and anisotropic. Second, observation points are moving. Third, the measured data are not uniformly distributed in the targeting range. Nevertheless, our method always computes the electron density depression volumes, along with estimated uncertainties, when applied to the 2011 Tohoku-Oki earthquake, even with random selections of only 5 % of the 1000 GPS Earth Observation Network System receivers considered here over Japan. Also, the statistically estimated TEC depression area mostly overlaps the range of the initial tsunami, which indicates that our method can potentially be used to estimate the initial tsunami. The method can warn of a tsunami event within 15 min of the earthquake, at high levels of confidence, even with a sparse receiver network. Hence, it is potentially applicable worldwide using the existing GNSS network

自然電位高密度観測による地震予知可能性の探究とその理論的メカニズムの解明

東海大学海洋学部平成8年度は本研究費の最終年度にあたることより,これまでのデータ解析と当初計画で予定した観測を行った.新規観測点としてつくば(茨城県),日立大宮(茨城県)を設置した.つくば観測点では特にVAN法で問題となる人工ノイズの除去を中心に研究を行い,長さ50-100mクラスの複数短基線と長さ2km程度の長基線観測を行った.この結果,単純な東西2測線では観測開始以来9カ月で1000個を越える異常変化が検知されているものが,複数短基線の設置によりすでに50個程度の異常変化にまで絞り込むことができた.さらに平成8年11月より,長基線観測を開始したことにより,それ以降,異常変化と考えられるものは1個だけとなった.この事実は複数短基線は効果的ではあるが,それだけでは十分ではなく,長基線観測との併用こそが、真の異常を抽出するための最低条件であることを示している.また「日本では人工ノイズが多く,ギリシャで開発されたVAN法は適さない」という批判に対し、観測事実をもって答えることができたと確信する.平成8年3月6日に発生した山梨県東部のM5.8の地震の際には震央から約20kmの山梨県・北富士観測点で明瞭なコサイスミックな地電流変化が観測されたばかりでなく,1月29日にはSESの特徴を満たす異常変化が観測された.この北富士観測点は平成8年1月から稼働しているが,それ以降平成9年3月までこのような異常な一度も観測されていない.残念ながら当時はノイズ除去に有効な長基線観測が行われていなかったため、地震の前兆でる必要条件は満たしているが、これが真の異常であると証明されたわけではない.しかしこの研究自体には勇気を与える観測結果であった。平成8年8月にはこの研究の総括及び今後の発展のため,VAN法が開発されたアテネ大学物理学部を訪問し,有益な議論を行うことができた.Whether the geoelectric potential field exhibits anomalous changes before earthquakes is a matter of long-standing debate. Recently many positive results have been reported for Greek earthquakes by the VAN group. To check their method, similar observations have been carried out in the Central Japan area. We established geoelectric potential monitoring stations at Komatsu, Suzu (Ishikawa Pref.), Toyama (Toyama Pref.), Hamaoka and Shimizu (Shizuoka Pref.), Outaki (Nagano Pref.), Kitafuji (Yamanashi Pref.), and Tsukuba and Hitachi-ohmiya (Ibaragi Pref.) during the Grant period.It is generally claimed that Japan is a electrically noisy country, therefore this type of study is impossible. To overcome this opinion, we intensively installed both short and long dipoles in a same station. For example, at the Tsukuba station, we observed over thousand of anomalies for only one-pair of short dipole during nine months, however, to apply two-pairs of dipoles, the anomalies decreased only 50. Furthermore, to install 2km-long dipole, the anomaly decreased only one. It means appropriate dipole configuration works even in Japan.During our observation period, on March 6,1996, we had an M5.8 earthquake at the eastern margin of the Yamanashi Prefecture. Our Kitafuji Station locates 20km apart from the epicenter. At the Kitafuji station, we observed only one anomalous change on January 29,1996. At that moment we had not yet installed a long dipole, therefore artificial noise rejection was not well. However this observation gives us a lot of useful information.On August 1996, the head investigator visited Athen University to summarize our program and discussed a future research plan.研究課題/領域番号:06452412, 研究期間(年度):1994 – 1996出典：研究課題「自然電位高密度観測による地震予知可能性の探究とその理論的メカニズムの解明」課題番号06452412（KAKEN：科学研究費助成事業データベース（国立情報学研究所）） （https://kaken.nii.ac.jp/ja/report/KAKENHI-PROJECT-06452412/064524121996kenkyu_seika_hokoku_gaiyo/）を加工して作

非定常熱針法による熱伝導率自動計測システムの開発と熱伝導率測定誤差原因の解明

金沢大学理学部研究課題/領域番号:01740226, 研究期間(年度):1989出典：研究課題「非定常熱針法による熱伝導率自動計測システムの開発と熱伝導率測定誤差原因の解明」課題番号01740226（KAKEN：科学研究費助成事業データベース（国立情報学研究所）） （https://kaken.nii.ac.jp/ja/grant/KAKENHI-PROJECT-01740226/）を加工して作

Ground tilt observations at Syowa Station, Antarctica. Part 2. Water-tube tiltmeter

To observe the secular change of ground tilt in response to deglaciation in Antarctica, a water-tube tiltmeter was installed at Syowa Station, in the snow-free area without a vault. It was the first observation of ground tilt using a water-tube tiltmeter in Antarctica. The tiltmeter adopted is a moving float type using antifreeze as the fluid. The tiltmeter consists of four detectors which measure two tilt components. The detectors were covered with wooden boxes and the water-tubes were covered by airtight polyvinyl chloride tubes. Observations began in April 1981. The records were strongly affected by air temperature and solar radiation. In spite of these problems it was found that the ground tilt observations by means of water-tube tiltmeters was possible in the Antarctic region, even if there was no vault for installing the equipments

Heat flow measurements in Lutzow-Holm Bay, Antarctica

Five heat flow measurements were made during the winter season of the 22nd Japanese Antarctic Research Expedition in the Lutzow-Holm Bay, Antarctica. The apparatus used for the temperature measurements was a 1.2m long Bullard type probe with three thermistors. Temperature gradients were determined at five different sites in shallow waters on the shore fast sea ice in November 1981. The temperature data were corrected following Bullard\u27s method. The temperature gradients ranged from -0.028 to 0.197℃/m. The thermal conductivities were determined on sediment samples recovered by coring before the temperature measurements were made. The thermal conductivities ranged 2.25 to 2.63×(10)^cal/cm・s℃. Corrected heat flow values were -0.74,0.21,4.39,4.53 and 1.19 HFU. Since these measurements were made in shallow water, the effects of the sea floor topography and the water temperature variation were considered. The topographic effect computed by a two-dimensional relaxation method resulted in corrections ranging from 7 to 41%. Annual sinusoidal temperature variation with an assumed amplitude of 0.31℃ at the sea floor gave a correction of up to ±4.2 HFU. Because of the sea floor temperature in November is increasing, the temperature gradient of sediments has a tendency to decrease. Therefore, the high heat flows valued 4.39 and 4.53 HFU can not be denied

Estimation of the ice thickness of cirque glaciers by the gravimetric survey at the Yamato Mountains, East Antarctica

As part of geophysical investigations by the 22nd Japanese Antarctic Research Expedition (JARE-22), the gravity measurements were carried out along the inland traverse route and in the Yamato Mountains region in 1981. In the latter area, the depth of subglacial rock surfaces under two peculiar cirque glaciers and one outlet glacier was estimated by gravity measurements, in addition to the investigation of the gravity field in ice-free areas. The results are as follows : 1) On the west side of Massif B, the bedrock height decreases steeply with a gradient of 300m/1000m from the shallow cirque glacier bottom to the west, 2) the deepest bedrock in the cross profile near the terminal part of the Nizi-no-kubo cirque glacier in Massif D reaches 265m, 3) the relationship among depth of cirque bottom, depth of the neighboring ice sheet, and surface features of cirque glaciers and the ice sheet suggest that the cirques were formed mainly prior to the ice sheet cover, and that the tectonic displacement might have been responsible for the deep subglacial bottom of the surrounding area, 4) the subglacial bedrock topography suggests that the fault line runs along the southern foot of Massif G, and the surface configuration of the outlet glacier between Massifs F and G seems to be influenced not only by snow accumulation controlled by surface topography but also by subglacial rock topography

Estimation of the crustal structure and the bedrock topography by the gravitational method around Syowa Station, East Antarctica

Gravity survey was carried out at 303 stations in Lutzow-Holm Bay and in the Mizuho Plateau during the wintering in 1981. Using the gravity data, the crustal structure in the Lutzow-Holm Bay region and the bedrock topography in the Mizuho Plateau have been revealed in this study. The results are as follows : 1) In Lutzow-Holm Bay, the thickness of the crust increases from northwest to southeast. 2) In the Mizuho Plateau, at least two subglacial valleys exist near Mizuho Station, whose strike is estimated to be consistent with the flow direction of the ice sheet. 3) In the Yamato Mountains region, the crustal thickness is larger than that in the Lutzow-Holm Bay region by about 3.8km estimated from the result of simple Bouguer anomaly difference. And the difference of the crustal thickness between Syowa and Mizuho Stations is less than 2km