Coda-Q before and after the 1986 Andreanof Islands earthquake     

Zhong-Xian Huang  Carl Kisslinger 《Pure and Applied Geophysics》1992,138(1):1-16

Coda-Q values before and after the May 7, 1986 Andreanof Islands earthquake in the central Aleutian subduction zone were calculated from microearthquake seismograms on the basis of Aki's single backscattering model. Digital waveforms from 329 microeathquakes in 5.4 years before the mainshock and 40 aftershocks recorded by 11 stations of the Central Aleutians Seismic Network were utilized. Before the mainshock, coda-Q in the rupture zone west of the mainshock epicenter was 15% higher than theQ outside the rupture zone to the west. A lowQ in the region east of the mainshock epicenter is inferred, but lacks solid evidence. The highQ region accords with the part of the rupture zone where most seismic moment was released. During approximately two months after the mainshock, coda-Q in the rupture zone decreased about 10%. PrecursoryQ changes were not found in the 5.4 years before the mainshock. It is deduced that a coda-Q precursor, if it existed, was of small magnitude (<10%), or its duration was either shorter than one year or longer than four years.  相似文献   

Anomalous structural evolution of the Shimanto Accretionary Prism at Murotomisaki, Shikoku Island, Japan     

James  Hibbard  Daniel  Karig Asahiko  Taira 《Island Arc》1992,1(1):133-147

Abstract The Late Oligocene-Early Miocene Nabae Sub-belt of the Shimanto Accretionary Prism was created coevally (ca 25-15 Ma) with the opening of the Shikoku back-arc basin, located to the south of the southwest Japan convergent margin. The detailed geology of the sub-belt has been controversial and the interaction of the Shimanto accretionary prism and the opening of the Shikoku Basin has been ambiguous. New structural analysis of the sub-belt has led to a new perception of its structural framework and has significant bearing on the interpretation of the Neogene tectonics of southwest Japan. The sub-belt is divided into three units: the Nabae Complex; the Shijujiyama Formation; and the Maruyama Intrusive Suite. The Nabae Complex comprises coherent units and mélange, all of which show polyphase deformation. The first phase of deformation appears to have involved landward vergent thrusting of coherent units over the mélange terrane. The second phase of deformation involved continued landward vergent shortening. The Shijujiyama Formation, composed mainly of mafic volcanics and massive sandstone, is interpreted as a slope basin deposited upon the Nabae Complex during the second phase of deformation. The youngest deformational pulse involved regional flexing and accompanying pervasive faulting. During this event, mafic rocks of the Maruyama Intrusive Suite intruded the sub-belt. Fossil evidence in the Nabae Complex and radiometric dates on the intrusive rocks indicate that this tectonic scheme was imprinted upon the sub-belt between ～23 and ～14 Ma. The timing of accretion and deformation of the sub-belt coincides with the opening of the Shikoku Basin; hence, subduction and spreading operated simultaneously. Accretion of the Nabae Sub-belt was anomalous, involving landward vergent thrusting, magmatism in newly accreted strata and regional flexing. It is proposed that this complex and anomalous structural history is largely related to the subduction of the active Shikoku Basin spreading ridge and associated seamounts.  相似文献   

益阳火山岩特征及其形成构造环境分析   总被引：11，自引：0，他引：11  

贺安生  韩雄刚 《湖南地质》1992,11(4):269-274

益阳火山岩中的熔岩、辉长辉绿岩和玄武质科马提岩,分别与蛇绿岩套中的熔岩、熔岩中的脉岩或岩墙杂岩和层状堆晶辉长岩有相似或相同的化学成分与微量元素含量,它们具有蛇绿岩套属性。与邻区广西、江西和安徽等省的蛇绿岩套分布在同一带上。因而认为,湖南境内沿通道—淑浦—宁乡—浏阳一带存在一条元古宙的古板块消减带,它控制了湖南中北部地区大地构造的演化和发展。  相似文献   

东北深,浅源地震的相关活动   总被引：1，自引：0，他引：1  

朱兆才 《地震地磁观测与研究》1992,13(4):20-24

本文讨论了东北深、浅源地震在时间上、强度上的相关活动特点,认为东北地震是太平洋板块俯冲与亚欧板块挤压作用的结果。东北深震超前于浅源地震活动,可为浅源地震监测预报提供信息。  相似文献   

中国东南沿海及邻近海区一种独特的大陆增生方式——转换断层向俯冲体系的转变     

周祖翼 《上海国土资源》1992,(1)

闽东沿海构造带—东海陆架西缘断裂、钓鱼岛隆起带(台湾—宍道褶皱带)以及帛琉—九州洋脊在中生代期间先后经历了自转换断层向俯冲系统的转变,这种转变构成了中国东南及毗邻海区独特的大陆增生方式,它表明特提斯和古太平洋的演化对这一地区的中、新生代构造格局起着重要的制约作用。  相似文献   

New radiolarian ages from the Troodos ophiolite and their tectonic implications   总被引：3，自引：0，他引：3  

Soichi  Osozawa Makoto  Okamura 《Island Arc》1993,2(1):1-6

Abstract Newly obtained radiolarian biostratigraphic age combined with previous isotopic age of the Troodos ophiolite shows that the ophiolite becomes systematically younger from east to west: Turonian, early Campanian, and late Campanian. The youngest late Campanian part of the ophiolite is directly covered by the volcaniclastic sediment derived from an active island arc, whereas the older part is covered by pelagic radiolarite. These facts constitute evidence that the Troodos ophiolite was probably emplaced during the subduction of an active spreading ridge.  相似文献   

Results of NFP 20 seismic reflection profiling along the Alpine section of the European Geotraverse (EGT)     

P. Valasek  St. Mueller  W. Frei  K. Holliger 《Geophysical Journal International》1991,105(1):85-102

  相似文献   

埃达克岩研究的几个问题   总被引：20，自引：0，他引：20  

朱弟成  潘桂棠  段丽萍  夏林  廖忠礼  王立全 《西北地质》2003,36(2):13-19

在简略分析中国埃达克岩研究情况的基础上,讨论了新近在有关埃达克岩研究方面取得的主要进展,探讨了先前埃达克岩研究中很少或者没有注意到的特殊的地球动力学意义。强调O型埃达克岩的出现标志着大洋萎缩消减的开始,C型埃达克岩的出现则暗示地壳在此之前就已经加厚,同时认为要解决埃达克岩研究中存在的一些问题,在很大程度上还有赖于青藏高原的埃达克岩研究。  相似文献   

Seismic Activity Around and Under Krakatau Volcano,Sunda Arc: Constraints to the Source Region of Island Arc Volcanics     

Špičák  A.  Hanuš  V.  Vaněk  J. 《Studia Geophysica et Geodaetica》2002,46(3):545-565

There is general agreement that calc-alkaline volcanic rocks at convergent plate margins are genetically related to the process of subduction (Ringwood, 1974; Maaloe and Petersen, 1981; Hawkesworth et al., 1997). However, opinions on the mode and site of generation of primary magma for island arc volcanism differ substantially. The site of generation of calc-alkaline magma is thought to be either in the mantle wedge (Plank and Langmuir, 1988; McCulloch and Gamble, 1991) or in the subducting slab (White and Dupré, 1986; Defant and Drummond, 1990; Edwards et al., 1993; Ryan and Langmuir, 1993). We present seismological evidence in favour of the latter concept. A distinctive seismicity pattern around and under the Krakatau volcano was identified during systematic studies of the SE Asian convergent plate margins by means of global seismological data. A column-like cluster of events, probably associated with the dynamics of the volcano, is clearly separated from the events in the Wadati-Benioff zone. The accuracy of hypocentral determinations of the events of the cluster does not differ from the accuracy of the events belonging to the subducting slab. The depths of the cluster events vary from very shallow to about 100 km without any apparent discontinuity. On the other hand, there is a pronounced aseismic gap in the Wadati-Benioff zone directly beneath the volcano at depths between 100-150 km. The Krakatau cluster connects this aseismic gap to the volcano at the surface. The pervasive occurrence of earthquakes in the continental wedge between the subducting slab and the Earth surface bears witness to the brittle character of the continental lithosphere and casts doubt on the existence of large-scale melting of mantle material. The aseismic gap (Hanu and Vank, 1985), interpreted by us as a partially melted domain occurring in subducted slabs in practically all active subduction zones that reach depths greater than 100 km, is here used as evidence for the location of the primary source region of island arc volcanics in the subducting plate.  相似文献   

印度大陆板片前缘撕裂与分段俯冲：来自冈底斯新生代火山-岩浆作用证据   总被引：22，自引：16，他引：22  

侯增谦  赵志丹  高永丰  杨志明  江万 《岩石学报》2006,22(4):761-774

青藏高原碰撞造山带不仅呈现南北不均一性,而且显示东西分段性。以横贯高原腹地的NNE向负磁异常带为界,将冈底斯分为三段。在宽约300km的负磁异常带为代表的中段,近SN向的裂谷和正断层系统、重要地震和现代热水活动、古新世林子宗火山岩系和中新世超钾质火山岩系、以及日喀则弧前盆地集中发育,伴有斑岩型Cu-Mo和成因独特的Au-Cu矿化;在85°E以西的西段,主要发育强烈逆冲推覆系、同碰撞期花岗岩和中新世钾质-超钾质火山岩系,伴有造山型Au矿化;而在90°E以东的东段,主要发育走滑断裂系、同碰撞期花岗岩和中新世埃达克质斑岩,伴有斑岩型Cu-Mo矿化。古新世林子宗火山岩的精细定年和地球化学特征揭示,印度大陆板片向北的俯冲-汇聚至少在50Ma前没有表现出明显的时间差异性。然而,中新世钾质-超钾质岩和大规模花岗岩基的时空分布和地球化学特征反映,印度大陆板片前缘可能发生撕裂,并发生分段式差异俯冲,西段(85°E以西)俯冲规模大,距离远,东段(90°E以东)俯冲规模小,可能未跨过雅江缝合带。沿着负磁异常带两侧的边界裂谷带,高SiO_2煌斑岩和念青唐古拉花岗岩基及相伴钾质火山岩的发育,揭示来源于软流圈地幔的岩浆和高热流穿过板片撕裂带并沿耦合上覆的裂谷带上涌,前者侵位和喷发,后者诱发地壳熔融。90°E与85°E之间的俯冲板片可能由于撕裂、断离和破碎,因而导致斜跨高原腹地的大面积通道式负磁异常带。  相似文献