Shin'ya Okamoto

Modern and ancient seismogenic out-of-sequence thrusts in the Nankai accretionary prism: Comparison of laboratory-derived physical properties and seismic reflection data

[1] To investigate characteristics of a seismogenic out-ofsequence thrust (OOST) imaged as a strong reflection on seismic profiles in the Nankai accretionary prism, we determined acoustic properties of discrete samples from an fossil Nobeoka OOST outcrop under confining pressures, and compared the acoustic properties with those of an active OOST in the Nankai accretionary prism. We observed anisotropy of velocity and attenuation in the hanging wall of Nobeoka OOST attributed to foliation of pelitic-phyllite. In contrast, the footwall is composed of brittlely deformed, chaotic shales and fine sandstones, and velocities in the footwall are lower than those in the hanging wall. Amplitude variation with offset (AVO) modeling utilizing contrasts in P- and S-wave velocities and densities between the hanging wall and footwall of the Nobeoka OOST indicates that fractures filled with overpressured fluid likely account for angle-dependent reflection amplitudes of the active OOST in the Nankai Trough. Citation: Tsuji, T., G. Kimura, S. Okamoto, F. Kono, H. Mochinaga, T. Saeki, and H. Tokuyama (2006), Modern and ancient seismogenic out-ofsequence thrusts in the Nankai accretionary prism: Comparison of laboratory-derived physical properties and seismic reflection data, Geophys. Res. Lett., 33, L18309, doi:10.1029/ 2006GL027025.

SCF Ensures Meiotic Chromosome Segregation Through a Resolution of Meiotic Recombination Intermediates

The SCF (Skp1-Cul1-F-box) complex contributes to a variety of cellular events including meiotic cell cycle control, but its function during meiosis is not understood well. Here we describe a novel function of SCF/Skp1 in meiotic recombination and subsequent chromosome segregation. The skp1 temperature-sensitive mutant exhibited abnormal distribution of spindle microtubules in meiosis II, which turned out to originate from abnormal bending of the spindle in meiosis I. Bent spindles were reported in mitosis of this mutant, but it remained unknown how SCF could affect spindle morphology. We found that the meiotic bent spindle in skp1 cells was due to a hypertension generated by chromosome entanglement. The spindle bending was suppressed by inhibiting double strand break (DSB) formation, indicating that the entanglement was generated by the meiotic recombination machinery. Consistently, Rhp51/Rad51-Rad22/Rad52 foci persisted until meiosis I in skp1 cells, proving accumulation of recombination intermediates. Intriguingly bent spindles were also observed in the mutant of Fbh1, an F-box protein containing the DNA helicase domain, which is involved in meiotic recombination. Genetic evidence suggested its cooperation with SCF/Skp1. Thus, SCF/Skp1 together with Fbh1 is likely to function in the resolution of meiotic recombination intermediates, thereby ensuring proper chromosome segregation.