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

A real-time tephra fallout rate model by a small-compact X-band Multi-Parameter radar

Real-time monitoring of volcanic tephra fallout rate is an important factor to predict ash plume dispersion and to mitigate risk to air traffic. Ground-based weather radar has been one of the fundamental instruments to detect the plume and derive eruptive source parameters, such as the tephra fallout rate. The current work presents the use of two small and compact X-band Multi-Parameter (X-MP) radars for a new tephra fallout rate model development and the technical aspects of the system in Sinabung and Merapi Volcanoes. The new model estimates the tephra fallout rate using two radar parameters: the specific differential phase shift parameter and the reflectivity intensity factor. Total cumulated mass estimated from the radar-based tephra fallout rate model from the radar is compared with the plume height model and an empirical radar-based model. A volcanic eruptive index (VEI)-2 of Sinabung generated a plume exceeding 15 km, resulting in a maximum tephra fallout rate of 0.58 kg m−2 h−1 and a total tephra mass of 51 × 106 kg. The VEI 1 of Sinabung caused a plume height of 2.5 km, resulting in a maximum tephra fallout rate of 0.3 kg m−2 h−1 and a total cumulated tephra of 9 × 106 kg. In the last case, a VEI 1 eruption of Mt. Merapi produces a 6 km plume, resulting in a maximum tephra fallout rate of 0.28 kg m−2 h−1 and a total cumulated tephra of 35 × 106 kg. The sector range height indicator scan-mode strategy in the VEI 2 eruption of Mt. Sinabung ran at six degrees azimuth angles capturing only a partial volume of the plume. Thus, the total mass was only 22% of the result from the empirical plume height model, even though the plume height was assumed to be equally the same with the maximum height scanned of radar at 7 km. In contrast, the volumetric scan by a plan position indicator strategy gave a total cumulated tephra mass, that matches better to the result of the empirical plume height model at 65–92%. Based on these results and the ability of the X-MP radar to capture the volcanic plume at the same reported onset time, we can confirm the importance of an X-MP radar for real-time tephra fallout monitoring during an eruption