13:45 〜 14:00
[MIS19-01] 火星地殻の地震波不連続面は水で満たされたクラックで説明できるかもしれない
★招待講演
キーワード：火星地殻、地震波不連続面、水、クラック
Recent seismic data acquired by the InSight lander have revealed a seismic discontinuity in the Martian crust, which has been interpreted as a sharp transition in porosity or chemical composition (e.g., Wieczorek et al., 2022). Here we propose an alternative model, based on laboratory measurements and theoretical calculations, that the observed seismic discontinuity may be caused by a transition from dry cracks to water-filled cracks. Our laboratory measurements of thermally cracked rocks show a distinct variation of seismic velocity with crack-filling phases, with water-saturated samples yielding systematically faster seismic velocity than dry samples, consistent with the effective medium theory. This suggests that a change from dry to water-filled cracks in the middle crust can lead to a significant increase in seismic velocity, even for constant porosity, which may explain the seismic discontinuity observed at ~10 km depth in the Martian crust. This is not a unique solution to explain the current observational data, but given the sensitivity of electrical conductivity to aqueous fluids, electromagnetic measurements on Mars may be helpful in further testing the above hypothesis. The present model implies the existence of liquid water in the Martian crust, which may be a local feature around the InSight landing site, but could potentially serve as a subsurface habitat for life.