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

Episodic tremor and slip near the Japan Trench prior to the 2011 Tohoku-Oki earthquake

Change in the rates of aseismic deformation prior to large earthquakes is a major area of interest in earthquake physics. Here we present evidence that episodic tremor and slip occurred in the shallow subduction zone within the source region of the 2011 Tohoku-Oki earthquake prior to the main shock. Ocean bottom seismometers near the Japan Trench recorded some excitations in amplitude of ambient noise level accompanying both the 2008 and 2011 slow slip events. The observed signals show that low frequencies of 5–8 Hz dominated, suggesting that the excitations were due to small low-frequency tremors accompanying the slow slip events. The largest amplitude tremor was observed just before the 2011 event. The estimated sources of tremors were possibly distributed within the coseismic slip area of the 2011 event, suggesting the shallow plate-boundary thrust near the trench is a general location of slow earthquakes

Hakuho-maru Cruise Report KH17-J02

調査海域: 日本海溝南部・福島沖 / Area: Axial part of the southern Japan Trench ; 期間: 2017年3月6日～2017年3月12日 / Operation Period: March 6, 2017～March 12, 201

KAIREI and KAIKO Mk-IV Cruise Report KR17-06

調査海域: 宮城県沖, 福島県沖日本海溝 / Area: Japan Trench, off Miyagi Prefecture and off Fukushima Prefecture ; 期間: 2017年4月14日～2017年4月20日 / Operation Period: April 14, 2017～April 20, 2017http://www.godac.jamstec.go.jp/darwin/cruise/kairei/kr17-06/