伴随地震和火山喷发的电磁效应

伴随地震和火山喷发引起自然地球物理场的变化,产生了地震电磁效应(SEM),即电场和磁场的扰动。电磁场变化多出现在初始地震发生前几天或几小时内,因此,若对这些现象有进一步认识,电磁场扰动可以作为地震的短期前兆。在研究学者中对SEM的解释历来存在着争论,解释这些     

冰岛火山喷发潜在性的研究

美国研究人员首先详细地勘测了冰岛地下所有的火山,发现情况比他们想象的要复杂得多.他们制定了一个复杂的岩浆分布图.相信这项工作有一天可以更好地了解发生在冰岛和世界其它地方的地震.     

地震触发的远场喷发：火山和间歇泉

约有0.4%的爆发性火山喷发是发生在大的远震后几天之内。偶尔这些"触发的"喷发会比预期的要大很多。人们已经从岩浆超压发生变化当中提出几个机制来解释这种触发,包括气泡增多、气泡上升引起的压力转移,以及岩浆房的翻转。另外,触发喷发也可能是由于岩浆周围的岩石发生破裂而引起的。所有这些机制都需要能够增强由地震引起的小静态应力变化,或者能够将(较大的)瞬变、动态应变转化为永久性压力变化的过程。除了应力的粘弹性松弛外,所有这些过程都可以导致触发喷发的延迟,不过要把地震和延迟触发喷发之间的关系进行量化却不是一件容易的事。泥火山和间歇泉同样会对远震产生反应。能够从超过几百米深处释放出泥浆的泥火山可以被震动所导致的液化作用而触发,因此近似于从地表几米范围内产生的小泥火山。主间歇泉通道周围的岩石骨架由于出现新的破裂而导致其渗透性发生变化。因此这一点可以解释为什么会观测到它们喷发的频度会发生变化。     

广西涠洲岛火山喷发特征

通过对涠洲岛南湾火山火山口的地质地貌、射气喷发基浪堆积、岩浆爆破喷发产物及海蚀火山地貌的研究,表明南湾火山是一巨型射气岩浆喷发火山,火山口位于南湾海中。推测涠洲岛的火山活动始于晚第三纪,更新世南湾火山喷发形成涠洲岛的现代地貌。     

伊兹米特地震前的地震活动性分析

对１９９９年８月１７日土耳其伊兹米特７．４级地震前的地震活动性进行了系统的分析。夺前的地震活动性表现出一定的异常。     

1999年辽宁省岫岩5.4级地震的临震预报及其地震活动研究

１９９９年１１月２９日１２日１０分（北京时间）,中国辽宁省岫岩地区发生一次５．４级地震。这次地震前,在震区记录到丰富的中小地震活动,组成了完整的地震系列。该系列具有小震频度随时间增多,震级上升,ｂ值较低,地震位置集中和地震Ｐ波被动一致,将其判断为震前系列,并抓住了前震活动从密集突然变为相对平静这一大震即将发生的特征,作出了临震预报,于１１月２８日晚入震意见通报给辽宁省地震局有关部门。这次地震的预报     

五大连池火山崩落堆积物研究

五大连池世界地质公园内的老黑山与火烧山火山外围分布有大量圆丘状火山碎屑堆积物,以往人们将其称为"副火山",即认为是独立的火山.本文认为这些堆积物来自这两座火山锥体的破坏.当锥体坡脚处有熔岩流溢出时,在重力作用下坡体发生裂解、崩塌,于是在坡体上形成沟谷,而垮落的坡体碎屑物则随着熔岩流的流动,堆积在火山锥体的外围,虽然有的堆积成较大的锥状体,但它们不是火山,而是火山崩落堆积物.     

Volcanic Debris-avalanche Deposits of the Laoheishan Volcano and Huoshaoshan Volcano in Wudalianchi

Large amounts of volcanic debris-avalanche deposits, which take the shape of hummocks, are distributed around the peripheries of the Laoheishan volcano and Huoshaoshan volcano in Wudalianchi World Geopark. In earlier times, they were called "satellite volcanoes", namely, freestanding volcanoes. This paper points out that these deposits actually came from the collapse of the cones of these two volcanoes. When the lava flow spilled out at the base of the slope of the cones, the slope broke up and collapsed under the action of gravity. Later, ravines were formed on the slope. Caved slope clastics, accompanying lava flow, accumulated at the rims of the volcano cones. Although some accumulations may form very large cones, they are not volcanoes, but deposits of volcanic debris avalanches.     

Volcano Seismology

— A fundamental goal of volcano seismology is to understand active magmatic systems, to characterize the configuration of such systems, and to determine the extent and evolution of source regions of magmatic energy. Such understanding is critical to our assessment of eruptive behavior and its hazardous impacts. With the emergence of portable broadband seismic instrumentation, availability of digital networks with wide dynamic range, and development of new powerful analysis techniques, rapid progress is being made toward a synthesis of high-quality seismic data to develop a coherent model of eruption mechanics. Examples of recent advances are: (1) high-resolution tomography to image subsurface volcanic structures at scales of a few hundred meters; (2) use of small-aperture seismic antennas to map the spatio-temporal properties of long-period (LP) seismicity; (3) moment tensor inversions of very-long-period (VLP) data to derive the source geometry and mass-transport budget of magmatic fluids; (4) spectral analyses of LP events to determine the acoustic properties of magmatic and associated hydrothermal fluids; and (5) experimental modeling of the source dynamics of volcanic tremor. These promising advances provide new insights into the mechanical properties of volcanic fluids and subvolcanic mass-transport dynamics. As new seismic methods refine our understanding of seismic sources, and geochemical methods better constrain mass balance and magma behavior, we face new challenges in elucidating the physico-chemical processes that cause volcanic unrest and its seismic and gas-discharge manifestations. Much work remains to be done toward a synthesis of seismological, geochemical, and petrological observations into an integrated model of volcanic behavior. Future important goals must include: (1) interpreting the key types of magma movement, degassing and boiling events that produce characteristic seismic phenomena; (2) characterizing multiphase fluids in subvolcanic regimes and determining their physical and chemical properties; and (3) quantitatively understanding multiphase fluid flow behavior under dynamic volcanic conditions. To realize these goals, not only must we learn how to translate seismic observations into quantitative information about fluid dynamics, but we also must determine the underlying physics that governs vesiculation, fragmentation, and the collapse of bubble-rich suspensions to form separate melt and vapor. Refined understanding of such processes—essential for quantitative short-term eruption forecasts—will require multidisciplinary research involving detailed field measurements, laboratory experiments, and numerical modeling.     

Volcano height and plate thickness

When the height of major young oceanic volcanoes above the basaltic basement are corrected for the buoyancy of their submerged bases, the heights are shown to increase as the square root of basement age. This is compatible with an isostatic model for the height of the magma in the volcanic conduit: As plates thicken with increasing age, the length of magma columns in isostatic equilibrium with the adjacent plate also increases. Volcano height is therefore primarily limited by plate thickness rather than, for example, the speed of a plate over a hot spot or the hot spot's productivity.     

本活跃期以来山西地震带地震活动的基本特点

1815年平陆6~(3/4)级地震揭开了华北本活跃期的序幕,其后的175年中山西地震带虽未发生7级以上强震,但是中强地震频度较高。它们主要分布在大同-平陆北北东向剪切段内。时间序列的幕式活动特点和华北活跃幕的划分是一致的。应变释放速率显示了明显的加速现象。1989年大同-阳高6.1级地震的发生,进一步说明地震活动性的增强。本活跃期尚余的1～2个活跃幕中,山西地震带是值的注意的一个地区。     

Results of repeated leveling surveys at Newberry Volcano, Oregon, and near Lassen Peak Volcano, California

 Personnel from the U.S. Geological Survey's Cascades Volcano Observatory conducted first-order, class-II leveling surveys near Lassen Peak, California, in 1991 and at Newberry Volcano, Oregon, in 1985, 1986, and 1994. Near Lassen Peak no significant vertical displacements had occurred along either of two traverses, 33 and 44 km long, since second-order surveys in 1932 and 1934. At Newberry, however, the 1994 survey suggests that the volcano's summit area had risen as much as 97±22 mm with respect to a third-order survey in 1931. The 1931 and 1994 surveys measured a 37-km-long, east–west traverse across the entire volcano. The 1985 and 1986 surveys, on the other hand, measured only a 9-km-long traverse across the summit caldera with only one benchmark in common with the 1931 survey. Comparison of the 1985, 1986, and 1994 surveys revealed no significant differential displacements inside the caldera. A possible mechanism for uplift during 1931–1994 is injection of approximately 0.06 km³ of magma at a depth of approximately 10 km beneath the volcano's summit. The average magma supply rate of approximately 1×10^–3 km³/year would be generally consistent with the volcano's growth rate averaged over its 600,000-year history (0.7–1.7×10^–3 km³/year). Received: 10 September 1998 / Accepted: 4 December 1998     

Geology and petrology of Mahukona Volcano,Hawaii

The submarine Mahukona Volcano, west of the island of Hawaii, is located on the Loa loci line between Kahoolawe and Hualalai Volcanoes. The west rift zone ridge of the volcano extends across a drowned coral reef at about-1150 m and a major slope break at about-1340 m, both of which represent former shoreines. The summit of the volcano apparently reached to about 250 m above sea level (now at-1100 m depth) did was surmounted by a roughly circular caldera. A econd rift zone probably extended toward the east or sutheast, but is completely covered by younger lavas from the adjacent subaerial volcanoes. Samples were vecovered from nine dredges and four submersible lives. Using subsidence rates and the compositions of flows which drape the dated shoreline terraces, we infer that the voluminous phase of tholeiitic shield growth ended about 470 ka, but tholeiitic eruptions continued until at least 435 ka. Basalt, transitional between tholeiitic and alkalic basalt, erupted at the end of tholeiitic volcanism, but no postshield-alkalic stage volcanism occurred. The summit of the volcano apparently subcided below sea level between 435 and 365 ka. The tholeiitic lavas recovered are compositionally diverse.     

长白山天池火山监测与灾害防御

对吉林省长白山天池火山历史喷发灾害进行了分析,指出了火山灾害可能带来的后果,并根据长白山天池火山现状和火山灾害特点．提出了火山灾害防御对策。