17:15 〜 18:45
[MGI31-P11] Application of paleomagnetic secular variation for high-resolution paleoseismology: IODP Expedition 386 Japan Trench paleoseismology
キーワード：日本海溝、巨大地震、古地震学、古地磁気永年変化、長尺ピストンコアラー
IODP Ex386 was conducted in order to establish stratigraphy of event deposits in the deep-sea basins along the Japan Trench and understand spatial and temporal information pertaining to plate boundary megathrust earthquakes based on thei stratigraphy.
In this expedition, a giant piston corer (GPC: max pipe length 40m) equipped on RV KAIMEI, JAMSEC was employed for the first time in IODP operations to collect long sediment samples from ultra-deep sea basin. In contrast to conventional scientific drilling with 10 meters core recovery system, GPC offered continuous samples without gaps between sections, providing an uninterrupted sequence of sedimentary record. While, results of paleomagnetic measurements reveal systematic horizontal rotations in most holes. It was expected that when the long coring pipe penetrated into the seabed, the cores entered into the inner tube with rotation. Although the exact causes of these phenomena are not currently clear, it is presumed that large paleomagnetic directional trend have been caused by linear rotations, therefore it is seemed that reconstructing these rotations is straightforward. After reconstruction of linear trend of paleomagnetic directions, distinct variations in geomagnetic direction changes are observed in holes in the same sites.
These records allow to estimate the precise ages of the event deposits by correlating paleomagnetic secular variation data as demonstrated in the previous works. Consequently, the thick turbidite as proxy of huge earthquake can be correlated in inter-sites. The ages of the thick turbidite determined through this method offer opportunities to study the spatiotemporal distribution of event deposits, along with their precise ages in the Japan Trench.
In this expedition, a giant piston corer (GPC: max pipe length 40m) equipped on RV KAIMEI, JAMSEC was employed for the first time in IODP operations to collect long sediment samples from ultra-deep sea basin. In contrast to conventional scientific drilling with 10 meters core recovery system, GPC offered continuous samples without gaps between sections, providing an uninterrupted sequence of sedimentary record. While, results of paleomagnetic measurements reveal systematic horizontal rotations in most holes. It was expected that when the long coring pipe penetrated into the seabed, the cores entered into the inner tube with rotation. Although the exact causes of these phenomena are not currently clear, it is presumed that large paleomagnetic directional trend have been caused by linear rotations, therefore it is seemed that reconstructing these rotations is straightforward. After reconstruction of linear trend of paleomagnetic directions, distinct variations in geomagnetic direction changes are observed in holes in the same sites.
These records allow to estimate the precise ages of the event deposits by correlating paleomagnetic secular variation data as demonstrated in the previous works. Consequently, the thick turbidite as proxy of huge earthquake can be correlated in inter-sites. The ages of the thick turbidite determined through this method offer opportunities to study the spatiotemporal distribution of event deposits, along with their precise ages in the Japan Trench.