2010年メラピ火山およびシナブン火山噴火から学ぶ

2010年には特筆すべき噴火がインドネシアのシナブン火山とメラピ火山において発生した。これらの噴火活動とその対応から我々は, 次のことを教訓として得た。1)長期の休止後の噴火活動の評価は依然として難しく, 長期の休止期の空白を埋めるための緊急観測が必要である。2)火道最上部が開放した火山での噴火活動の予測はやはり困難を伴う。このような状況では地盤変動観測の高精度化と物質化学的分析が重要となる。3)我が国の火山では火口から20kmにおよぶ警戒区域の設定と38万人にも達する避難者への対応の経験がない。被害区域が拡大した場合の対応を早急に策定する必要があろう。In 2010, noteworthy eruptions occurred at Sinabung, North Sumatra and Merapi in Central Java, Indonesia. Sinabung volcano erupted on August 27 after dormancy more than 400 years and repeated 7 eruptions till September 7. At Merapi volcano, explosive eruption occurred at the summit on October 26 accompanying resultant blast and pyroclastic flow. The eruptive activity reached at the peak on November 3-5, generating continuous pyroclastic flow which ran southward 17 km in distance. We obtain important lessons from these eruptions for evaluation of volcanic activity and prediction of volcanic eruption. Evaluation of volcanic activity is still difficult at volcanoes after long-term dormant period. Quick response to obtain data is important to compensate the gap from the last eruption. It is difficult to predict activity of volcanoes under the condition of open-conduit system, too. Associated with extension of flow length of pyroclastic flow, restricted zone was extended up to 20 km and 380, 000 people evacuated from Merapi volcano. Japan has not been experienced by risk management for such a large number of evacuees from volcanoes. Countermeasure planning against volcanic eruptions with disaster in wider area should be established.2010年には特筆すべき噴火がインドネシアのシナブン火山とメラピ火山において発生した。これらの噴火活動とその対応から我々は, 次のことを教訓として得た。1)長期の休止後の噴火活動の評価は依然として難しく, 長期の休止期の空白を埋めるための緊急観測が必要である。2)火道最上部が開放した火山での噴火活動の予測はやはり困難を伴う。このような状況では地盤変動観測の高精度化と物質化学的分析が重要となる。3)我が国の火山では火口から20kmにおよぶ警戒区域の設定と38万人にも達する避難者への対応の経験がない。被害区域が拡大した場合の対応を早急に策定する必要があろう。In 2010, noteworthy eruptions occurred at Sinabung, North Sumatra and Merapi in Central Java, Indonesia. Sinabung volcano erupted on August 27 after dormancy more than 400 years and repeated 7 eruptions till September 7. At Merapi volcano, explosive eruption occurred at the summit on October 26 accompanying resultant blast and pyroclastic flow. The eruptive activity reached at the peak on November 3-5, generating continuous pyroclastic flow which ran southward 17 km in distance. We obtain important lessons from these eruptions for evaluation of volcanic activity and prediction of volcanic eruption. Evaluation of volcanic activity is still difficult at volcanoes after long-term dormant period. Quick response to obtain data is important to compensate the gap from the last eruption. It is difficult to predict activity of volcanoes under the condition of open-conduit system, too. Associated with extension of flow length of pyroclastic flow, restricted zone was extended up to 20 km and 380,000 people evacuated from Merapi volcano. Japan has not been experienced by risk management for such a large number of evacuees from volcanoes. Countermeasure planning against volcanic eruptions with disaster in wider area should be established

Long-term Forecasting of Volcanic Eruption in Case of Kekud Volcano, Indonesia

インドネシアのケルート火山では, 約2ヶ月の前駆地震活動を経て2007年11月に, 17年ぶりの噴火が発生した。その活動は山頂火口内に溶岩ドームを形成するという意外な結果で終わった。過去の噴火記録, 地震活動等の研究調査資料を分析し, 今後の噴火の可能性・切迫性を評価するとともに, 今後の観測のあり方や予想される噴火形態等を検討した。今回の噴火による噴出物量は過去の噴火活動から予想されるマグマの蓄積量の約半分程度にとどまり, 潜在的に噴出する能力を有するマグマが地下に残存している可能性が高い。また, 地震の発生頻度は2010年から増加に転じていて, 新たなマグマの供給・蓄積が既に始まっていると推察される。これらのことから, 10年以内に火山活動が活発化し噴火発生に至る可能性が高い。In November, 2007, Kelud volcano, which had repeated plinian eruptions, unexpectedly extruded lava and formed lava dome in the crater lake. The eruption potential at present are evaluated using geological and seismic data. (1) Magma extruded by the 2007 eruption is estimated approximately a half of magma accumulated after the 1990 eruption. (2) Volcanic earthquakes turned to increase in 2010, which suggests magma accumulation is in progress under the volcano. The volcano has already prepared the next eruption, which will occur probably in 10 years. Eruption scenarios and a method of quantitative evaluation of eruption potential were proposed.インドネシアのケルート火山では, 約2ヶ月の前駆地震活動を経て2007年11月に, 17年ぶりの噴火が発生した。その活動は山頂火口内に溶岩ドームを形成するという意外な結果で終わった。過去の噴火記録, 地震活動等の研究調査資料を分析し, 今後の噴火の可能性・切迫性を評価するとともに, 今後の観測のあり方や予想される噴火形態等を検討した。今回の噴火による噴出物量は過去の噴火活動から予想されるマグマの蓄積量の約半分程度にとどまり, 潜在的に噴出する能力を有するマグマが地下に残存している可能性が高い。また, 地震の発生頻度は2010年から増加に転じていて, 新たなマグマの供給・蓄積が既に始まっていると推察される。これらのことから, 10年以内に火山活動が活発化し噴火発生に至る可能性が高い。In November, 2007, Kelud volcano, which had repeated plinian eruptions, unexpectedly extruded lava and formed lava dome in the crater lake. The eruption potential at present are evaluated using geological and seismic data. (1) Magma extruded by the 2007 eruption is estimated approximately a half of magma accumulated after the 1990 eruption. (2) Volcanic earthquakes turned to increase in 2010, which suggests magma accumulation is in progress under the volcano. The volcano has already prepared the next eruption, which will occur probably in 10 years. Eruption scenarios and a method of quantitative evaluation of eruption potential were proposed

Magma intrusion and effusion at Sinabung volcano, Indonesia, from 2013 to 2016, as revealed by continuous GPS observation

We analyzed continuous Global Positioning System (GPS) data from Sinabung to capture and model the migration of magma from the pre-eruptive and syn-eruptive time period between June 2013 and January 2016. We divided this time into four periods of significant deformation: two extensional stages followed by two contractional stages. Using a grid search method, we determined the location and volume change of a Mogi source for each deformation stage. Cumulative volume changes during the contraction periods were approximated by an exponentially decaying function with time. Period 1 began in June 2013 with slight extension, for which an inflation source was modeled at a depth of 3–8 km below sea level (bsl) and a volume change of 0.3–1.8 Mm3. Seismicity in period 1 was marked by a notable increase in deep high frequency volcano tectonic earthquakes (VTs) beginning in July 2013 and shallow VTs in September 2013. Period 2 began in late October 2013 with accelerated extension, with at least 1 cm extension in the baseline length. During period 2 the modeled inflation source ascended to a shallower depth of 0.9 (0.4–2.1) km below sea level (bsl) beneath Sinabung with a change in volume of + 0.39 (+ 0.18–+0.60) Mm3, and with accelerated rates of volume increase during the time period when the magma migrated to the surface. Seismicity during period 2 was marked first by an increase in the incidence of shallow volcano-tectonic (VT) earthquakes and later by repetitive self-similar hybrid events as the magma migrated to the surface. Period 3 began in January 2014, after the appearance of the lava dome, and was marked by rapid steady contraction of ~ 3 cm through March 2014. The modeled source located at 8.4 (7.4–9.9) km bsl beneath the eastern flank of Sinabung with a volume change of − 20.51 (− 26.89 to − 14.12) Mm3. Period 4 began in April 2014 with decelerating contraction, and the modeled deformation center shifted to the northeast, reaching a depth of 12.2 (10.1–14.8) km bsl between Sinabung and Sibayak volcanoes and a change in volume of − 88.26 (− 123.87 to − 52.66) Mm3. Approximately 2/3 of the total volume change related to contraction occurred between January 2014 and May 2016, and the current activity of Sinabung is expected to decrease gradually and almost terminate in the early 2020s, assuming no new intrusion or deformation rate changes. Both of the eruptions at Sinabung in 2010 and Unzen in 1991–1995 show characteristics of ground inflation and subsequent deflation, indicating magma migration and effusion processes similar to the current Sinabung activity. The inflation before the 2010 Sinabung eruptions likely started before 2007 and is an indication of magma intrusion before the 2010 and 2013 eruptions

Magma Transport at Mt. Unzen Associated with the 1990-1995 Activity Inferred from Leveling Data

1990年11月に198年ぶりに噴火活動を開始した雲仙普賢岳は、1991年5月20目からデイサイト質溶岩を噴出し、1995年始めまで、溶岩噴出と火砕流発生を繰り返した。国立大学総合研究班および国土地理院は、雲仙普賢岳の北山麓から山頂へ向かう路線、および島原半島西岸沿いの路線に沿って水準測量を繰り返してきた。また、GPS観測も繰り返された。その結果、島原半島西部の地盤は溶岩流出まで隆起・膨張し、溶岩流出開始後沈降・収縮に転じたことがわかった。これまでの研究によって、普賢岳山頂の直下から西に向かって次第に深さを増す、3つの圧力源、A、BおよびCを仮定すれば雲仙岳周辺の地盤の変動が説明できることが示された。本研究では、水準測量データの測定誤差を考慮した上で、点力源モデルを適用して、3つの圧力源の位置、およびそれぞれの圧力源の強度の時間的変化を再計算した。その上で、溶岩噴出率および地震活動と圧力源の強度の関係、また、地盤の変形体積と溶岩噴出率をもとに地下深部からのマグマ供給率を推定した。[1]普賢岳火口の地下1.4kmに力源A、普賢岳の西方約3km、深さ4.1kmに力源B、および普賢岳西方約5km、深さ6.8kmに力源Cの存在が推定された。各力源は島原半島西方の橘湾から普賢岳に伸びる地震帯の直下に位置する。[2]溶岩噴出開始以降、普賢岳直下の力源Aの強度の変化は、溶岩噴出率と普賢岳の地震活動の増減と対応している。[3]力源Bの強度の変化は溶岩噴出率の2度の増大に対応している。一方、力源Cの強度は溶岩流出開始まで増大し、その後は時間とともに減少している。[4]以上の結果より、マグマが力源Cから、力源Bおよび力源Aを経由して輸送され、普賢岳山頂から噴出したことが推定される。地盤の変動体積の変化が力源でのマグマ蓄積量の増減に等しいと仮定して、地下深部から力源Cへのマグマ供給率を推定した。マグマ供給率は、溶岩噴出開始の約半年前から急増し、1991年終わりにヒ。一クに達し、それ以後減少して、1995年始めには停止した。1990年から1995年までのマグマ供給量は0.17km^3と推定される。The recent activity of Mt. Unzen (Fugendake) was preceded by an earthquake swarm beneath the Tachibana Bay, west of the Shimabara Peninsula, in November 1989 and the subsequent migration of seismic activity toward Mt. Unzen.On November 17, 1990, phreatic eruption started at the summit, then a dacite lava dome appeared at the summit crater on May 20, 1991. Subsequent discharge of lava and intermittent pyroclastic flows have continued until early 1995. The total volume of discharged lava was 0.2 km^3.Universities and the Geographical Survey Institute had repeated leveling survey along the western coast of the peninsula, and the other route from the northern flank to the summit, and found out significant deflation of the ground centered a few kilometer west of the summit, which was also clarified by GPS survey. The magma supply system composed of three chambers, and an inclined magma pathway along seismic zone were proposed by previous studies.Applying the Point-Source Model (Mogi's Model), the location of three pressure sources and their intensity change with time were re-examined including the evaluation of measurement error of leveling data, and the relationship between the intensity changes at pressure sources and volcanic activity.(1) The near surface source A is located at a depth of 1.4 km beneath the summit, and the source B is 4.1 km deep, 3 km west of the summit. And the deepest one C is located 6.8 km deep, west of the summit. These sources are aligned just beneath the inclined seismic zone.(2) The intensity change at A-source seems to be related to the discharge rate of lava and seismic activity at the summit.(3) The intensity change at B-source has two peaks corresponding to the two epochs of discharge of lava and increased prior to the onset of discharge of lava. The intensity of C source increased until the lava dome appeared, and then gradually decreased.(4) These results suggest magma was transported from C-source through B- and A-sources to the summit. Assuming the deformation volume of the ground surface due to pressure sources is equal to the volume change of magma at each source, the supply rate of magma from deeper portion to C-source was estimated using the data on discharge lava. The supply rate of magma increased rapidly after the phreatic eruption in November 1990, and reached its peak in the end of 1991, then decayed. In early 1995, magma supply stopped.The total volume of magma supplied since 1990 is estimated to be 0.17 km^31990年11月に198年ぶりに噴火活動を開始した雲仙普賢岳は、1991年5月20目からデイサイト質溶岩を噴出し、1995年始めまで、溶岩噴出と火砕流発生を繰り返した。国立大学総合研究班および国土地理院は、雲仙普賢岳の北山麓から山頂へ向かう路線、および島原半島西岸沿いの路線に沿って水準測量を繰り返してきた。また、GPS観測も繰り返された。その結果、島原半島西部の地盤は溶岩流出まで隆起・膨張し、溶岩流出開始後沈降・収縮に転じたことがわかった。これまでの研究によって、普賢岳山頂の直下から西に向かって次第に深さを増す、3つの圧力源、A、BおよびCを仮定すれば雲仙岳周辺の地盤の変動が説明できることが示された。本研究では、水準測量データの測定誤差を考慮した上で、点力源モデルを適用して、3つの圧力源の位置、およびそれぞれの圧力源の強度の時間的変化を再計算した。その上で、溶岩噴出率および地震活動と圧力源の強度の関係、また、地盤の変形体積と溶岩噴出率をもとに地下深部からのマグマ供給率を推定した。[1]普賢岳火口の地下1.4kmに力源A、普賢岳の西方約3km、深さ4.1kmに力源B、および普賢岳西方約5km、深さ6.8kmに力源Cの存在が推定された。各力源は島原半島西方の橘湾から普賢岳に伸びる地震帯の直下に位置する。[2]溶岩噴出開始以降、普賢岳直下の力源Aの強度の変化は、溶岩噴出率と普賢岳の地震活動の増減と対応している。[3]力源Bの強度の変化は溶岩噴出率の2度の増大に対応している。一方、力源Cの強度は溶岩流出開始まで増大し、その後は時間とともに減少している。[4]以上の結果より、マグマが力源Cから、力源Bおよび力源Aを経由して輸送され、普賢岳山頂から噴出したことが推定される。地盤の変動体積の変化が力源でのマグマ蓄積量の増減に等しいと仮定して、地下深部から力源Cへのマグマ供給率を推定した。マグマ供給率は、溶岩噴出開始の約半年前から急増し、1991年終わりにヒ。一クに達し、それ以後減少して、1995年始めには停止した。1990年から1995年までのマグマ供給量は0.17km^3と推定される。The recent activity of Mt. Unzen (Fugendake) was preceded by an earthquake swarm beneath the Tachibana Bay, west of the Shimabara Peninsula, in November 1989 and the subsequent migration of seismic activity toward Mt. Unzen.On November 17, 1990, phreatic eruption started at the summit, then a dacite lava dome appeared at the summit crater on May 20, 1991. Subsequent discharge of lava and intermittent pyroclastic flows have continued until early 1995. The total volume of discharged lava was 0.2 km^3.Universities and the Geographical Survey Institute had repeated leveling survey along the western coast of the peninsula, and the other route from the northern flank to the summit, and found out significant deflation of the ground centered a few kilometer west of the summit, which was also clarified by GPS survey. The magma supply system composed of three chambers, and an inclined magma pathway along seismic zone were proposed by previous studies.Applying the Point-Source Model (Mogi's Model), the location of three pressure sources and their intensity change with time were re-examined including the evaluation of measurement error of leveling data, and the relationship between the intensity changes at pressure sources and volcanic activity.(1) The near surface source A is located at a depth of 1.4 km beneath the summit, and the source B is 4.1 km deep, 3 km west of the summit. And the deepest one C is located 6.8 km deep, west of the summit. These sources are aligned just beneath the inclined seismic zone.(2) The intensity change at A-source seems to be related to the discharge rate of lava and seismic activity at the summit.(3) The intensity change at B-source has two peaks corresponding to the two epochs of discharge of lava and increased prior to the onset of discharge of lava. The intensity of C source increased until the lava dome appeared, and then gradually decreased.(4) These results suggest magma was transported from C-source through B- and A-sources to the summit. Assuming the deformation volume of the ground surface due to pressure sources is equal to the volume change of magma at each source, the supply rate of magma from deeper portion to C-source was estimated using the data on discharge lava. The supply rate of magma increased rapidly after the phreatic eruption in November 1990, and reached its peak in the end of 1991, then decayed. In early 1995, magma supply stopped.The total volume of magma supplied since 1990 is estimated to be 0.17 km^

Mapping the 2010 Merapi pyroclastic deposits using dual-polarization Synthetic Aperture Radar (SAR) data

International audienceL-band ALOS-PALSAR images acquired before, during and after the 2010 Merapi eruption have been used to classify and map the pyroclastic deposits emplaced during this VEI-4 event. We characterize the deposits using direct-polarized and cross-polarized L-band SAR data and by combining the information of amplitude evolution with temporal decorrelation. Changes in amplitude of the radar signal enable us to map the pyroclastic density currents (PDCs) and tephra-fall deposits. Radar amplitudes in direct (HH) and cross (HV) polarizations decrease where the valley-confined and overbank block-and-ash flow (BAF) deposits (D1) are emplaced. Rainfall- and runoff-reworked PDC deposits (D2) are characterized by an increase in ground backscattering for HH polarization and a decrease for HV polarization. Ground backscattering transiently increases in both polarizations after pyroclastic surge (D3) and tephra fall (D4) deposition. We use a supervised classification method based on maximum likelihood to map the deposits D1–D4. The temporal decorrelation of the radar signal and the amplitude evolution improve the quality of classification results. Classification derived from ALOS-PALSAR images using the maximum likelihood classification provides a result with 70% classification accuracy for deposits overall. The estimated areas of valley-confined and overbank PDC deposits (either primary or reworked by rainfall and runoff) are consistent with the areas measured by other studies, while the large discrepancy in area estimated for pyroclastic-surge deposits can be partly explained by the strong erosion due to intense rainfall that removed a large part of these thin deposits

Method for estimating the end of the deflation initiated in 2014 at Sinabung volcano, Indonesia, under the assumption that the magma behaves as a Bingham fluid

We herein estimated the end of the ongoing deflation at Sinabung volcano, Indonesia, which began in 2014 under the assumption that the magma is incompressible and behaves as a Bingham fluid. At first, we estimated the temporal volume change of the deformation sources for deflation periods from the end of 2013 until December 2016. The deflation rate is decreasing gradually, and the deflation is expected to cease in the future. Next, we obtained the absolute pressure in the reservoir as a function of time by modeling the magma as an incompressible fluid inside a spherical reservoir with a cylindrical vent and applying the estimated volume change function to the model. We then estimated the yield stress of the Sinabung magma to be 0.1–3 MPa from a previously derived linear relationship between the silica content and yield stress of lava and the measured silica content of Sinabung ashfall from 2010 to 2014, which was reported to be 58–60%. The absolute pressure in the reservoir is expected to fall below the yield stress between August and September 2018, which means that the magma would stop migrating from the reservoir toward the summit under the assumption that it behaves as a Bingham fluid. As a result, the deflation of Sinabung is estimated to end between August and September 2018. In comparison with the 1991–1995 deflation at Unzendake, the total deflation volume of Sinabung is comparable, whereas the duration of the deflation of Sinabung is approximately 1 year longer

インドネシア・グントール火山以南の地震活動

グントールはインドネシア・西ジャワのバンドン市の南東35kmにある火山群である。19世紀まで半ばまで頻繁に山頂のグントール火口において爆発的噴火を繰り返してきたが，1943年の噴火を最後に160年以上噴火が発生していない。一方，火山性地震及び周辺の地震活動は活発であり，今後の火山活動を予測する上で地震活動は重要な指標となる．火山地質災害軽減センターが火山監視用に設置した観測点に加え，グントール火山周辺の8点に地震計を設置した。2009年1～3月まではグントール火山の南にあるチクライ山の東山麓で地震活動が活発であった。5月以降12月まではダラジャット地熱地帯における地震活動が活発となり，地震の震源は北西?南東方向の深さ2-9kmに配列することが分かった。Guntur is a volcano complex located 35 km SE of Bandung, West Java, Indonesia. Explosive eruptions frequently occurred at Guntur crater during the period from 1690 to the middle of 19th century, however, no eruption has occurred for 167 years after the 1843 eruption. In spite of dormancy of eruptivity, seismicity of the Guntur volcano is high and earthquake swam sometimes occurred. In order to locate the earthquakes in wider area around the volcano, we installed 8 temporary stations around the volcano in addition to the permanent seismic stations operated by CVGHM at volcanoes around Guntur. Hypocenters were aligned from north to south at eastern flank of the Cikuray volcano, south of Guntur, at depths around 6 km from January to April, 2009. After May, earthquake origins were distributed around Darajat geothermal area at depths 2-9 km, showing alignment from NW to SE.グントールはインドネシア・西ジャワのバンドン市の南東35kmにある火山群である。19世紀まで半ばまで頻繁に山頂のグントール火口において爆発的噴火を繰り返してきたが，1943年の噴火を最後に160年以上噴火が発生していない。一方，火山性地震及び周辺の地震活動は活発であり，今後の火山活動を予測する上で地震活動は重要な指標となる．火山地質災害軽減センターが火山監視用に設置した観測点に加え，グントール火山周辺の8点に地震計を設置した。2009年1～3月まではグントール火山の南にあるチクライ山の東山麓で地震活動が活発であった。5月以降12月まではダラジャット地熱地帯における地震活動が活発となり，地震の震源は北西?南東方向の深さ2-9kmに配列することが分かった。Guntur is a volcano complex located 35 km SE of Bandung, West Java, Indonesia. Explosive eruptions frequently occurred at Guntur crater during the period from 1690 to the middle of 19th century, however, no eruption has occurred for 167 years after the 1843 eruption. In spite of dormancy of eruptivity, seismicity of the Guntur volcano is high and earthquake swam sometimes occurred. In order to locate the earthquakes in wider area around the volcano, we installed 8 temporary stations around the volcano in addition to the permanent seismic stations operated by CVGHM at volcanoes around Guntur. Hypocenters were aligned from north to south at eastern flank of the Cikuray volcano, south of Guntur, at depths around 6 km from January to April, 2009. After May, earthquake origins were distributed around Darajat geothermal area at depths 2-9 km, showing alignment from NW to SE

噴火に伴う空気振動の長周期成分の解析 -阿蘇山の例-

研究課題「阿蘇山の噴火活動・マグマ水蒸気爆発を理解する」 2017年2月27日(月)-28(火), 於: 熊本大学教育学部(本館3-A講義室), 研究代表者: 横尾 亮

Tilt observation with half-filled type watertube tiltmeter at Oosumi observatory

日向灘地殻活動総合観測線大隅観測室に設置した傾斜計は, 液体の自由表面が両端の水槽から水管全体にわたるハーフ・フィルド型の水管傾斜計で, さらに水管内の液体に, 水に比べ粘性の大きいシリコンオイルを使ったという点で従来の水管傾斜計と大きく違っている。この傾斜計により従来の計器とは異なる特異な記録が得られ, これまでに得られた観測記録とハーフ・フィルド型傾斜計の特徴について考察した。A half-filled type watertube tiltmeter, whose liquid surface is continuous between two measurement pots, was installed at Oosunii observatory in the observation network of crustal activities in the Hynganada region, Kyushu, Japan. Silicon oil is used as liquid of the instrument. An instrument of this type has a long characteristic period and silicon oil is very viscous, therefore the response to forced tilt is negligible for the shorter period than that of semi-diurnal earth tides. Some other characters of this instrument are also recognized from the records in a brief observation.日向灘地殻活動総合観測線大隅観測室に設置した傾斜計は,液体の自由表面が両端の水槽から水管全体にわたるハーフ・フィルド型の水管傾斜計で,さらに水管内の液体に,水に比べ粘性の大きいシリコンオイルを使ったという点で従来の水管傾斜計と大きく違っている。この傾斜計により従来の計器とは異なる特異な記録が得られ,これまでに得られた観測記録とハーフ・フィルド型傾斜計の特徴について考察した。A half-filled type watertube tiltmeter, whose liquid surface is continuous between two measurement pots, was installed at Oosunii observatory in the observation network of crustal activities in the Hynganada region, Kyushu, Japan. Silicon oil is used as liquid of the instrument. An instrument of this type has a long characteristic period and silicon oil is very viscous, therefore the response to forced tilt is negligible for the shorter period than that of semi-diurnal earth tides. Some other characters of this instrument are also recognized from the records in a brief observation