[P-PS05] 月の科学と探査

[PPS05-04] Recent boulder falls within the Finsen crater, an assessment of ongoing geological activities

*Trishit Ruj¹、Goro Komatsu²、Kenji Kawai¹、Hanaya Okuda³、Zhiyong Xiao⁴、Deepak Dhingra⁵ (1.Department of Earth and Planetary Science, School of Science, The University of Tokyo、2.International Research School of Planetary Sciences, Università G. d'Annunzio, Viale Pindaro 42, 65127, Pescara, Italy、3.Department of Ocean Floor Geoscience, Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8564, Japan、4.Planetary Environmental and Astrobiological Research Laboratory, School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, China、5.Department of Earth Sciences, Indian Institute of Technology Kanpur, Kanpur, UP 208016, India)

キーワード：Moon, TECTONICS, BOULDER FALL, SOUTH POLE AITKEN BASIN

To better understand the necessary triggers for the origin of the lunar boulder tracks, we report over 400 tracks. The tracks were identified on the southern inner wall and the central peak region of the Finsen crater, located within the South Pole-Aitken basin on the lunar far side. We assessed two main possibilities of triggers, 1) ground shaking excited by the recent impact crater formation events, and 2) moonquakes generated from recent fault reactivation associated with the lobate scarps identified inside and in the vicinity of Finsen. Our assessments revealed that the impact-induced seismicity could have generated the moonquake with the maximum moment magnitude of 3.67. We also estimated that the moonquakes excited by the movements along the lobate scarps had an estimated upper limit of moment magnitude between 7.85 and 7.90, i.e., for the basaltic and noritic basement respectively. The geological mapping and the spatial distribution of the boulder tracks indicate a higher concentration around the vicinity of the lobate scarps. Considering the location of the Finsen crater positioned over the structural discontinuity along the boundary of the central and mid rings of the South Pole-Aitken basin and higher moment magnitude generated from the fault movements, we propose that the region is seismotectonically active, and reactivation of pre-existing faults possibly triggered/triggers the necessary ground motion for the boulders to initiate their movements.