並列タイトル等最近のプレート境界地震に続いて隣接セグメントで生じたプレート間固着強化に関する包括的研究
一般注記In general, the concept of a seismic cycle, especially in subduction zones, consists of three phases: interseismic, coseismic, and postseismic. These three phases can be observed through surface crustal movement observations with Global Navigation Satellite System (GNSS) because these three phases have different directions of velocities. During the interseismic stage, all GNSS stations on an arc move landward; during the coseismic stage, they jump seaward, and during the postseismic stage, they slowly move seaward and eventually return to the interseismic regime. During the postseismic phase, the deformation caused by the viscoelastic relaxation results in prolonged seaward movement.Apart from such a classical concept of postseismic seaward movement, several previous studies have also found increased landward surface velocities in the early postseismic stages, especially in segments adjacent along-trench to the megathrust ruptures. Such cases have been found for the 2003 Tokachi-oki and the 2011 Tohoku-oki earthquakes, NE Japan. A similar increase of landward velocities was reported for the segments to the north of the rupture of the 2010 Maule earthquake, Chile. I utilize available GNSS data to find such changes for six megathrust earthquakes in four subduction zones, including NE Japan, central and northern Chile, Sumatra, and Mexico to investigate their common features. My study showed that such increase, ranging from a few mm/yr to ~1 cm/yr, also appeared in adjacent segments of the 2014 Iquique (Chile), the 2007 Bengkulu (Sumatra), and the 2012 Oaxaca (Mexico) earthquakes in addition to the three previously known cases. The region of the increased landward movements usually extends with spatial decay and reach the distance comparable to the along-strike fault length. On the other hand, the temporal decay of the increased velocity is not clear at present. The degree of increase seems to depend on the earthquake magnitude, and possibly scales with the average fault slip in the earthquake. This is consistent with the simple two-dimensional model proposed earlier to attribute the phenomenon to the enhanced coupling caused by accelerated slab subduction. However, these data are not strong enough to rule out other possibilities. In addition to the information above, I also investigated possible increase in background seismicity following the 2011 Tohoku-oki and the 2010 Maule earthquakes in the regions where GNSS stations showed enhanced coupling. Recent studies suggest that relative plate velocity correlates positively with the seismicity and predict that background seismicity increases where plate convergence accelerates. There, I found a moderate but significant increase in seismicity of ~10%, somewhat smaller than the rates of increased landward velocities.
(主査) 教授 日置 幸介, 教授 古屋 正人, 准教授 高田 陽一郎, 教授 高橋 浩晃, 准教授 勝俣 啓
理学院（自然史科学専攻）
コレクション（個別）国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文
受理日（W3CDTF）2021-07-05T22:24:43+09:00
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