Aso Volcano Research Articles

A38 阿蘇火山中岳火口湖(湯だまり)における水温・溶存成分濃度の変動解析(火山の物質科学(3),日本火山学会2008年秋季大会)

A38 阿蘇火山中岳火口湖(湯だまり)における水温・溶存成分濃度の変動解析(火山の物質科学(3),日本火山学会2008年秋季大会)

A47 阿蘇火山における約 2 万～1 万年前の降下テフラ噴出量の時間的変化

A47 阿蘇火山における約 2 万～1 万年前の降下テフラ噴出量の時間的変化

E31-01 阿蘇火山中岳の最近 1.5 万年の活動史

E31-01 阿蘇火山中岳の最近 1.5 万年の活動史

B3-08 阿蘇火山Aso-3大規模噴火サイクルのマグマ供給系 : 層状マグマ溜まり形成に関する岩石学的制約(溶岩流・マグマ供給系,口頭発表)

B3-08 阿蘇火山Aso-3大規模噴火サイクルのマグマ供給系 : 層状マグマ溜まり形成に関する岩石学的制約(溶岩流・マグマ供給系,口頭発表)

A1-19 ACTIVE観測による阿蘇火山中岳周辺の浅部比抵抗の時間変化(火山の電磁気学,口頭発表)

A1-19 ACTIVE観測による阿蘇火山中岳周辺の浅部比抵抗の時間変化(火山の電磁気学,口頭発表)

P55 阿蘇火山における火口径と噴出物量との関係(ポスターセッション)

P55 阿蘇火山における火口径と噴出物量との関係(ポスターセッション)

B3-09 古地磁気方位からみた阿蘇火山中央火口丘群北西部の活動(噴火プロセス,口頭発表)

B3-09 古地磁気方位からみた阿蘇火山中央火口丘群北西部の活動(噴火プロセス,口頭発表)

PA02 阿蘇火山西部におけるカルデラ形成後の火山活動 : 微量元素化学組成と温度推定

PA02 阿蘇火山西部におけるカルデラ形成後の火山活動 : 微量元素化学組成と温度推定

A24 阿蘇火山における約6万〜3万年前のテフラ層序概報

A24 阿蘇火山における約6万〜3万年前のテフラ層序概報

H32-13 阿蘇火山の過去 7 万年の噴火史と 1989 年噴火

H32-13 阿蘇火山の過去 7 万年の噴火史と 1989 年噴火

P16 航空機搭載型放射伝達スペクトルスキャナ(ARTS)による阿蘇中岳第一火口付近の輝度温度等の観測(ポスターセッション)

P16 航空機搭載型放射伝達スペクトルスキャナ(ARTS)による阿蘇中岳第一火口付近の輝度温度等の観測(ポスターセッション)

A21-09 阿蘇火山観測坑道の傾斜・伸縮計観測

A21-09 阿蘇火山観測坑道の傾斜・伸縮計観測

P54 阿蘇山一の宮及び白水火山観測施設の観測井岩石コア試料のK-Ar年代(ポスターセッション)

P54 阿蘇山一の宮及び白水火山観測施設の観測井岩石コア試料のK-Ar年代(ポスターセッション)

Slip history of the 2016 Mw 7.0 Kumamoto earthquake: Intraplate rupture in complex tectonic environment

AbstractRupture history of the 2016 Mw 7.0 Kumamoto earthquake is constrained by using the waveforms of strong motion observations, teleseismic broadband body waves, and long‐period surface waves. Its fault geometry is modeled with Hinagu (orienting 205° and dipping 73°) and Futagawa (orienting 235° and dipping 60°), two segments. The result reconciles the difference between moment tensor solutions and the surface fault trace. It reveals a complex rupture process that initiated on the Hinagu segment in dextral motion, propagated northeastward unilaterally, and after 15 s ceased near Aso volcano with normal fault motion. The average slip, rise time, and slip rate are 1.8 m, 2.0 s, and 1.2 m/s, respectively. The rupture broke through an ~30° fault intersection without notable delay, which can be a result of dynamic “unclamping.” The northeast boundary of the largest asperity might mark the bottom of the seismogenic zone, which becomes shallower gradually near Aso volcano.

阿蘇火山中岳第1火口の2014～2015年活動でみられた灰噴火

阿蘇火山中岳第1火口の2014～2015年活動でみられた灰噴火

Volcanic magma reservoir imaged as a low-density body beneath Aso volcano that terminated the 2016 Kumamoto earthquake rupture

We resolve the density structure of a possible magma reservoir beneath Aso, an active volcano on Kyushu Island, Japan, by inverting gravity data. In the context of the resolved structure, we discuss the relationship between the fault rupture of the 2016 Kumamoto earthquake and Aso volcano. Low-density bodies were resolved beneath central Aso volcano using a three-dimensional inversion with an assumed density contrast of ±0.3 g/cm3. The resultant location of the southern low-density body is consistent with a magma reservoir reported in previous studies. No Kumamoto aftershocks occur in the southern low-density body; this aseismic anomaly may indicate a ductile feature due to high temperatures and/or the presence of partial melt. Comparisons of the location of the southern low-density body with rupture models of the mainshock, obtained from teleseismic waveform and InSAR data, suggest that the rupture terminus overlaps the southern low-density body. The ductile features of a magma reservoir could have terminated rupture propagation. On the other hand, a northern low-density body is resolved in the Asodani area, where evidence of current volcanic activity is scarce and aftershock activity is high. The northern low-density body might, therefore, be derived from a thick caldera fill in the Asodani area, or correspond to mush magma or a high-crystallinity magma reservoir that could be the remnant of an ancient intrusion.

Characteristics of the surface ruptures associated with the 2016 Kumamoto earthquake sequence, central Kyushu, Japan

The 2016 Kumamoto earthquake sequence started with a M J (Japan Meteorological Agency magnitude) 6.5 event on April 14, and culminated in a M J 7.3 event on April 16. Associated with the sequence, approximately 34-km-long surface ruptures appeared along the eastern part of the Futagawa fault zone and the northernmost part of the Hinagu fault zone. We carried out an urgent field investigation soon after the earthquake to map the extent and displacement of surface ruptures with the following results. (1) The rupture zone generally consisted of a series of left-stepping en echelon arrays of discontinuous fault traces of various lengths. (2) Slip exceeding 100 cm occurred on previously unrecognized fault traces in the alluvial lowland of the Kiyama plain and on the western rim of the Aso volcano caldera. (3) Large slip with maximum dextral slip of 220 cm was measured throughout the central section of the rupture zone along the Futagawa segment, and the slip gradually decreased bilaterally on the adjoining northeastern and southwestern sections. (4) The surface rupture mostly occurred along fault traces mapped in previous active fault investigations. (5) Most of the surface ruptures were produced by the mainshock, and significant postseismic slip occurred after the mainshock.

Crustal deformation associated with the 2016 Kumamoto Earthquake and its effect on the magma system of Aso volcano

An MJMA6.5 earthquake (foreshock) and MJMA7.3 earthquake (mainshock) struck Kumamoto Prefecture on April 14, 2016, and April 16, 2016. To evaluate the effect of crustal deformation due to the earthquake on the Aso magma system, we detected crustal deformation using InSAR and GNSS. From InSAR analysis, we detected large crustal deformations along the Hinagu Fault, the Futagawa Fault, and the northeast extension of the latter fault. It extended to more than 50 km, and the maximum slant-range change exceeded 1 m. Although the obtained crustal deformation was approximately explained by the right-lateral strike-slip on the fault, its details could not be explained by such simple faulting. Additionally, we found complex surface deformation west of the Aso caldera rim, suggesting that shallow fault slips occurred in many known and unknown faults associated with the earthquake. Most of the crustal deformation could be reasonably explained by four rectangle faults located along the Futagawa Fault, in the northeast extension of the Futagawa Fault, alongside the Hinagu Fault, and in the eastern part of the Futagawa Fault. The first three of faults have high dip angles and right-lateral slip. The other was a fault with a low dip angle that branched from the shallow depth of the fault along the Futagawa Fault. The normal-dip right-lateral slip was estimated for this segment. Based on the estimated fault model, we calculated the displacement and stress field around the Aso volcano by the finite-element method (FEM) to evaluate the effects on the Aso magma system. In this calculation, we assumed a spherical soft medium located at a 6-km depth beneath the area south of the Kusasenri region as the magma system and considered only static effects. The result shows complex distributions of displacements and stresses, but we can notice the following significant points. (1) The spherical magma system deformed to an ellipsoid, and the total volume was slightly increased, less than 1%. (2) The differential stress around the upper portion of the magma system was as large as 3.5 MPa. This is strong enough to open pre-existing cracks and can cause the migration of magma.

豪雨と地震に伴う阿蘇火山・仙酔峡での斜面崩壊 -UAVとSfM多視点ステレオ写真測量を用いて-

豪雨と地震に伴う阿蘇火山・仙酔峡での斜面崩壊 -UAVとSfM多視点ステレオ写真測量を用いて-

Sediment Yields Triggered by Heavy Rainfall in July 2012 at Aso Volcano: Application of High-Definition Topography Data Using Unmanned Aerial Vehicles and Structure-from-Motion Multi-View Stereo Photogrammetry

Sediment Yields Triggered by Heavy Rainfall in July 2012 at Aso Volcano: Application of High-Definition Topography Data Using Unmanned Aerial Vehicles and Structure-from-Motion Multi-View Stereo Photogrammetry