日本地球惑星科学連合2019年大会

講演情報

[J] ポスター発表

セッション記号 S (固体地球科学) » S-SS 地震学

[S-SS14] 地震発生の物理・断層のレオロジー

2019年5月29日(水) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:岡崎 啓史(海洋研究開発機構)、向吉 秀樹(島根大学大学院総合理工学研究科地球資源環境学領域)、野田 博之(京都大学防災研究所)、吉田 圭佑(東北大学理学研究科附属地震噴火予知研究観測センター)

[SSS14-P06] 二軸摩擦試験機によるSlide-Hold-Slide実験中の反射波と透過波の時間変化

*植村 美優1伊藤 喜宏2片山 郁夫3 (1.京都大学大学院理学研究科、2.京都大学防災研究所、3.広島大学大学院理学研究科地球惑星システム学専攻)

キーワード:スロースリップ、二軸摩擦試験、ガウジ

Slow slip events (SSEs), which is one of the slow earthquakes differing from regular earthquakes, have been detected at both shallower and deeper portions of the seismogenic zones, such as Japan and New Zealand. We carried slide-hold-slide experiments with gouge layer under a slip velocity of an SSE using a biaxial friction testing machine under the condition with the temperature and the humidity of room. We measured temporal changes of acoustic impedance in the gouge layer with reflected and transmitted wave during slides and holds. As a result, we detected variations in travel time, amplitude, and cross-correlation coefficient on first arrival of reflected and transmitted wave.

The features of observed waveforms were classified clearly by a slide-hold-slide conditions into two categories: sliding and holing. We chose two materials as gouge powder, which were clay mineral (Ca- montmorillonite) and quartz. Regardless of the kinds of the gouge powder, the amplitude both of reflected and transmitted waves showed opposite temporal variation during the slide-hold-slide sequences; the amplitude of transmitted wave decreased during slides and increased during holds, respectively. This suggests that the amplitudes of reflected and transmitted waves indicate a change of an elastic-wave speed in the gouge layer.

The travel times of transmitted waves increased during slides and decrease during holds. According to Birch (1961), a propagation speed of elastic waves normally decreases as the density of media decreases, or as the porosity increases. Increasing travel times of transmitted waves in our experiments may indicate the change of the density, or porosity in the gouge layer. Although the travel times of reflected waves decreased during slides and increased during holds in the case of clay mineral, the travel time on quartz powder did not change through our experiment.

The temporal change on correlation of observed transmitted wave also shows significant changes from a slide to a hold. The change of travel time, the amplitude, and the cross-correlation coefficient of transmitted waves were more sensitive to a slide-hold-slide condition, such as slip rate on the gouge later than those of reflected wave. Those result suggests that a transmitted wave is more suitable for monitoring SSE although a reflected wave is also useful for monitoring, and that a beginning and an end of an SSE can be detected by reflected and transmitted waves.