13 research outputs found
Structural variation from off Shikoku to the Kii Peninsula related to various earhthquake phenomena
南海トラフで繰り返し発生する巨大地震の中には、東海・東南海・南海地震が連動して発生する超巨大地震のケースがあることが指摘されている。このような超巨大地震について、どのような場合に連動し、あるいは非連動性巨大地震となるのかを明らかにすることが必要である。連動型地震の滑り域の範囲がどこまで広がるかを見積もることが重要な課題であり、そのためには南海トラフから沈み込むフィリピン海プレートの形状およびプレート境界周辺の構造、地震活動に関する詳細かつ高精度な情報が必要である。また、南海地震単独で発生した場合についても、深部および浅部低周波地震発生域まで含めた正確な破壊の広がりの把握、複雑な破壊分布の原因を明らかにするために南海地震破壊域とその縁辺での地殻構造や地震活動は重要な情報となる。平成20年度は日向灘、平成21年度は四国沖で調査を実施し、平成22年度は調査海域を東方の紀伊半島沖まで拡大し、沈み込み帯の地殻構造、巨大地震の発生、地震活動の相互関係の解明を目的として、南海・地震破壊域における沈み込みに関する詳細な構造のイメージングおよび地震のアスペリティに関する構造を明らかにするためのデータの取得、および西南日本の付加体先端部付近で発生している低周波地震や微動を含む自然地震観測を実施した。 本講演では、四国沖?紀伊半島沖の平成21~22年度の調査結果について述べる。平成21年10月、および平成22年10~11月、(独)海洋研究開発機構の海洋調査船「かいれい」によって短周期海底地震計各々180台と大容量チューンドエアガン(7800cu. in.)を用いた屈折法・広角反射法探査を実施した(図1)。海底地震計設置期間中に自然地震観測も実施した。四国沖では21観測点、紀伊半島沖では20観測点による約9ヶ月間の長期地震観測も実施した(一部実施中)。なお、本調査は文部科学省からの受託研究「東海・東南海・南海地震の連動性評価のための 調査観測・研究」の個別研究テーマ「南海トラフ域海域地震探査・地震観測」(平成20年度から受託)の一環として実施した。 一部の調査測線の解析の結果、足摺岬沖から日向灘に向かって約6km/sの古い付加体を示す岩体の分布が海側に張り出していること、また、SK05の構造モデルによると、SK03とSK02の中間付近からSK01付近までの付加堆積物が極端に薄いことなど、トラフ平行方向に構造変化があることがわかり、破壊様式の違いに関係する構造ではないかと考えられる。また、測線延長上のHi-net陸上観測点のデータを加えた海陸統合解析を実施しており、これにより深部低周波地震現象と構造との関連性が明らかになると期待されるC11-10発表要旨, 日本地震学会2011年度秋季大会(2011年10月12日~15日, 静岡県静岡市
Erythroderma and Epidermal Necrosis Induced by a Type of Proton Pump Inhibitor in Beagle Dogs
ASOBOI 97: Aso Seismic Observation with Broadband Instruments in 1997
In August 1997, we deployed a total of 24 broadband three-component velocity seismometers temporarily around Aso volcano in Kyushu, Japan. Most of these stations were located within 1 km of the first crater of Naka-dake and provided good azimuthal coverage to constrain the geometry of the source region of long-period (15s) tremors (LPTs). The spatial pattern of the observed LPTs amplitude reveals that the source of LPTs consists of an isotropic expansion (contraction) and an inflation (deflation) of an inclined tensile crack almost parallel to the chain of craters of Naka-dake (Yamamoto et al, 1999). This report summarizes details of the observations, as well as some of the characteristics of the observed data from the ASOBOI 97 expedition
Amplitude modeling of the seismic reflectors in the crust-mantle transition layer beneath the volcanic front along the northern Izu-Bonin island arc
Anomalous depth dependency of the stress field in the 2007 Noto Hanto, Japan, earthquake: Potential involvement of a deep fluid reservoir
We have elucidated depth variations in the stress field associated with the 2007 Noto Hanto, Japan, earthquake by stress tensor inversion using high-quality aftershock data obtained by a dense seismic network. Aftershocks that occurred above 4 km in depth indicated a strike-slip stress regime. By contrast, aftershocks in deeper parts indicated a thrust faulting stress regime. This depth variation in the stress regime correlates well with that in the slip direction derived from a finite source model using geodetic data. Furthermore, the maximum principal stress (σ1) axis was stably oriented approximately W20°N down to the depth of the mainshock hypocenter, largely in agreement with the regional stress field, but, below that depth, the σ1 axis had no definite orientation, indicating horizontally isotropic stress. One likely cause of these drastic changes in the stress regime with depth is the buoyant force of a fluid reservoir localized beneath the seismogenic zone
Crustal structure beneath eastern Kyushu, Japan, derived from a wide-angle reflection and refraction experiment
In 1994 and 1996, seismic refraction experiments were executed in the eastern part of Kyushu, Japan, he target of the experiments was to investigate the crustal structure composed of accretion materials associated with the paleo subduction process. The experiment in 1994 was composed of 3 shots, 195 observation stes, and 195 km measurement line. In the 1996 experiment, there were 3 shots, 236 observation sites, and 228 km measurement line, which extended north. Observation sensors were set at the same places except for the extended line of the second experiment. To establish a P wave crustal structure model, ray-trace forward modeling and inversion technique were used. The final P wave velocity structure model shows that the upper crust is composed of four layers: two sedimentary layers with velocities of 3-4 and 4-5km/s, basement layer, 5.2-5.8 km/s and granitic layer, 6 km/s. The sedimentary layers developed in the southern part of the profile, which corresponds to the North and South Shimant belts. The thickness of the sedimentary layers in the Southern Shimant belt, exceeds 4 km. The basement layer has a complicated form. We found two distinct irregularly folded parts of the basement layer beneath Shimant belts and an abrupt decrease of the amplitudes of seismic waves that pass through beneath those parts. We interpreted the sedimentary layers had developed under a subduction process in Cretaceous (Izanagi plate) and Tertiary (Pacific plate), and the 6 km/s layer rising beneath the Shimant belt might correspond to an under-plating fragment of a plateau
ASOBO197 : 阿蘇山における広帯域地震観測 1997
In August 1997, we deployed a total of 24 broadband three-component velocity seismometers temporarily around Aso volcano in Kyushu, Japan. Most of these stations were located within 1 km of the first crater of Naka-dake and provided good azimuthal coverage to constrain the geometry of the source region of long-period (15s) tremors (LPTs). The spatial pattern of the observed LPTs amplitude reveals that the source of LPTs consists of an isotropic expansion (contraction) and an inflation (deflation) of an inclined tensile crack almost parallel to the chain of craters of Naka-dake (Yamamoto et al, 1999). This report summarizes details of the observations, as well as some of the characteristics of the observed data from the ASOBOI 97 expedition