プレート境界における地震活動と沈み込む海洋性地殻の地震波速度構造との関係について : 特集「地震発生の物理からみた地震発生帯堀削」

Ipresent a seismic velocity structure model to explain strong seismic reflections from the aseismic part of the plate boundary recently reported from an airgun-OBS survey in the northern Japan trench subduction zone. Although no P wave velocity anomaly models could explain the reflection amplitudes and the first arrival travel times consistently, it is possible to simulate significant amplitudes observed in relative small offset ranges using a model with a low S wave velocity in the subducting oceanic crust. The upper oceanic crust with the low S wave velocity anomaly may reduce the shear strength of the plate boundary thrust, as fault damaged zones with a considerably low S wave velocity make faults weak. The result of this study indicates the importance of clarifying the S wave structure in the vicinity of the plate interface to understand the frictional propeties of subduction megathrust seismogenic zone. Not only conventional seismic surveys but also seismic observations in deep boreholes are required to do this

The Role of Genetic Analysis in Distinguishing Multifocal and Multicentric Glioblastomas: An Illustrative Case

Introduction: Glioblastomas can manifest as multiple, simultaneous, noncontiguous lesions. We genetically analyzed multiple glioblastomas and discuss their etiological origins in this report. Case Presentation: We present the case of a 47-year-old woman who presented with memory impairment and left partial paralysis. Radiographic imaging revealed three apparently noncontiguous lesions in the right temporal and parietal lobes extending into the corpus callosum, leading to diagnosis of multicentric glioblastomas. All three lesions were excised. Genetic analysis of the lesions revealed a TERT promoter C228T mutation, a roughly equivalent amplification of EGFR, and homozygous deletion of CDKN2A/B exclusively in the two contrast-enhanced lesions. Additionally, the contrast-enhanced lesions exhibited the same two-base pair mutations of PTEN, whereas the non-enhanced lesion showed a partially distinct 13-base pair mutation. The other genetic characteristics were consistent. Rather than each having arisen de novo, we believe that they had developed by infiltration and are therefore best classified as multifocal glioblastomas. Conclusion: Our findings underscore anew the possibility of infiltration by glioblastomas, even within regions devoid of signal alterations on T2-weighted images or fluid-attenuated inversion recovery images. Genetic analysis can play a crucial role in differentiating whether multiple glioblastomas are multifocal or multicentric

地震発生帯における深部掘削孔を用いた長期計測

Large earthquakes occur frequently in subduction zones. Most earthquakes are generated in the seismogenic zone, a fairly limited area confined to the shallower regions of the subduction plate boundary. To understand the processes of earthquake generation, it is essential to monitor the physical and mechanical properties of the seismogenic zone over long periods. At present, there are no deep borehole observations of the seismogenic zone more than 3km below seafloor, because it has, until now, been impossible to penetrate to such depths below the sea floor. The Integrated Ocean Drilling Program (IODP), scheduled to begin in 2003, plans to drill boreholes beneath the ocean floor using a multiple-drilling platform operation. The IODP riser-quipped drilling ship (Chikyu) enables the emplacement of boreholes up to 0km beneath the ocean floor, and will provide opportunities to conduct long-term deep borehole observations in the seismogenic zone. Long-term borehole observations in the seismogenic zone are expected to require the development of advanced sampling, monitoring, and recording technology. Here, we discuss the scientific objectives, engineering and technical challenges, and experimental design for a deep borehole, long-term deepborehole monitoring system aimed at understanding the processes of earthquake generation in the seismogenic zone of subduction plate boundaries. We focus specifically on the relationships between environmental conditions in the deep subsurface, details of monitoring and recording, and design and implementation of scientific tools and programs

Relation between seismic velocity structure of subducting oceanic crust and interplate micro-seismicity

Ipresent a seismic velocity structure model to explain strong seismic reflections from the aseismic part of the plate boundary recently reported from an airgun-OBS survey in the northern Japan trench subduction zone. Although no P wave velocity anomaly models could explain the reflection amplitudes and the first arrival travel times consistently, it is possible to simulate significant amplitudes observed in relative small offset ranges using a model with a low S wave velocity in the subducting oceanic crust. The upper oceanic crust with the low S wave velocity anomaly may reduce the shear strength of the plate boundary thrust, as fault damaged zones with a considerably low S wave velocity make faults weak. The result of this study indicates the importance of clarifying the S wave structure in the vicinity of the plate interface to understand the frictional propeties of subduction megathrust seismogenic zone. Not only conventional seismic surveys but also seismic observations in deep boreholes are required to do this