Explosive volcanic eruptions—X. The influence of pyroclast size distributions and released magma gas contents on the eruption velocities of pyroclasts and gas in Hawaiian and Plinian eruptions

Previous treatments of the relationship between the mass fraction of released magma volatiles and the eruption speeds of gas and pyroclasts in steady explosive eruptions have not taken detailed account of the dynamic effects associated with the finite size distribution of the pyroclasts. When this is done, it is found that previously published estimates of exsolved magma volatile contents obtained from the analysis of pyroclast size distributions in near-vent deposits overestimate the volatile content by approximately 20 per cent in the case of Plinian eruptions. The discrepancy is much worse for pyroclast size distributions skewed towards coarse clasts, as is common in basaltic lava fountains; in such cases pyroclast dispersal studies may overestimate the exsolved magma volatile content by at least 200 per cent. An analogous problem arises if released magma volatile amounts deduced from studies of fluid inclusions in pyroclasts are inserted into most current computer models of eruption dynamics, but the gas eruption speeds deduced have an even larger error, being underestimated by up to 300 per cent in the case of coarse-grained eruptions. The more sophisticated of the currently available numerical models of eruption dynamics can in principle avoid this problem, but practical implementation limitations have so far prevented such models being run with a sufficiently wide range of grain sizes for the importance of these effects to be fully appreciated.     

地震危险性分析中确定潜在震源的反思

在区域稳定性评价中,其主要内容之一就是地震稳定性评价。近年来,国内外多采用地震危险性分析的概率方法作为区域地震稳定性评价的主要方法。 在地震危险性分析中,首要问题是确定区域潜在震源,但至今尚缺乏完整、科学的理论和实践。作者认为有必要从地震地质角度进行一次深刻的地质反思。 本文从构造变形的动力源、区域及局部应力场、地震断裂活动带的地震重复周期,地震断裂的活动特征及区域地震强度衰减规律等几个方面提出了若干看法,作为地震危险性分析的基础地震地质工作加以考虑。至于常见的非发震断裂在区域地震稳定性评为中所起的作用,则需对这些断裂的地质特征与周围地质体的介质特征进行具体的对比分析,才能判定其对地震波传播的影响,不能一概而论。     

海岸沙丘沙运动特征若干问题的研究——以闽江口南岸为例

在海岸带,沙粒粒径和水分含量是决定沙粒起动风速的最主要因素。闽江口南岸海滩沙的平均粒径为2.0Φ,水分含量多在0.3%~1.0%之间。运用Johnson的经验公式,可计算出海滩沙的起动风速为6~7m/s。这一结果与实际观测值十分吻合。由于海岸环境因素的影响,使得同等条件下海岸带沙粒的起动风速明显大于内陆沙漠沙,而风沙流的输沙率明显小于内陆沙漠沙。海岸带是风速剧变带,在引用陆地气象台站的风速记录分析海岸风况和研究风沙运动规律时,必须对风速进行订正。     

不同密度镜质组的热解色谱特征及生烃潜力的研究

摘要：用热解色谱（Ｒｏｃｋ－Ｅｖａｌ）对２个褐煤样、３个气煤样的２８个分离组分进行了研究,揭示了不同密度镜质组组分之间生烃潜力具有较大的差异性;镜质组不仅可以作为重要的生气母质,而且还可以作为重要的生油母质。     

波速线性变化介质中地震波传播特征

根据变速介质中地震波传播所满足的变系数波动方程,推导出波速线性变化介质中一维波动方程的解析解,讨论了波速不均匀性对地震波传播的影响：地震波振幅衰减大小与介质速度梯度有关;频率转折点两侧地震波传播性质;频率与地震波波速关系。     

流速逆变张量隐式求解方法及其在航道港池流场计算中的应用

运用高分辨率的边界适应网格进行流体动力学数值计算时,如何提高计算稳定性和减少计算量成为数值求解的关键性问题.在非正交的边界适应坐标系中,每个动量方程中同时出现了两个交叉方向的水位偏导数项,给隐式求解带来困难,而显式格式下的时间步长由于受与空间步长有关的Courant-Friedrichs-Lewy条件限制,计算量成倍增加.本文从广义曲线坐标系下浅海动力学方程组出发,导出了流速的逆变张量所满足的动量方程组,使方程中的水位偏导数项变成了沿某一协变基向量方向占优的形式,方便地采用了交替方向隐式差分格式,从而提高了计算稳定性并减小了计算量.本文通过对澳门海域航道和港池中流场的计算,证实了该模式是一种进行高分辩率数值计算的有效方法.     

直立堤前海床的局部冲刷

对不规则波作用下直立堤前海床的局部冲刷进行了研究。研究了由于波浪作用导致床面的底沙运动,从而造成提前海床的局部冲刷,即所谓的“相对粒沙”的情况。报导了;(1)堤前海床面为水平、堤下无基床情况下的堤前局部冲刷,以及堤下有明基床时基床尺度对堤前局部冲刷的影响;(2)堤前海床面为斜坡面时堤前的局部冲刷,以及当堤下有明基床时基床尺度对堤前局部冲刷的影响;(3)从波浪作用下床面边界层的理论分析出发,对于在不规则波作用下,离堤面愈远处的冲刷坑深度愈小的事实给出了解释。     

海底沉积物孔隙度与声速的关系

给出大陆架海底沉积层中声速(压缩波)V_p依赖于沉积物孔隙度n的一个新的经验公式,该公式当n=100时,V_p=V₀,V₀为海底水声速.公式的计算值与我国周边大陆架测量值吻合较好,并将其结果与国内外成果作了对比讨论.     

The Statistical Distribution of the Horizontal Velocities of Water Particles at Wave Surface Maxima

On the basis of the linear model of random sea waves presented by Longuet-Higgins,the statis-tical distribution of the horizontal velocities of water particles at wave surface maxima is derivedtheoretically.The derived distribution is similar to that of wave surface maxima,and a new spectral widthε_u,which is defined as(1-(m_3~2/m_2m_4))~(1/2),is introduced in the distribution.When ε_u tends to zero,the distribu-tion is reduced to Rayleigh distribution and it is reduced to the normal distribution when ε_u tends to unity.For a narrow spectrum,it is proved that ε is equal to 1/2ε,where ε is(1-(m_2~2/m_0m_4))~(1/2)and is the commonlyused spectral width..     

The Kuroshio East of Taiwan and in the East China Sea and the currents East of Ryukyu Islands during early summer of 1996

Using hydrographic data and moored current meter records and the ADCP observed current data during May–June 1996, a modified inverse method is applied to calculate the Kuroshio east of Taiwan and in the East China Sea and the currents east of Ryukyu Islands. There are three branches of the Kuroshio east of Taiwan. The Kuroshio in the East China Sea comes from the main (first) and second branches of the Kuroshio east of Taiwan. The easternmost (third) branch of the Kuroshio flows northeastward to the region east of Ryukyu Islands. The net northward volume transports of the Kuroshio through Section K₂ southeast of Taiwan and Section PN in the East China Sea are 44.4×10⁶ and 27.2×10⁶ m³s⁻¹, respectively. The western boundary current east of Ryukyu Islands comes from the easternmost branch of the Kuroshio east of Taiwan and an anticyclonic recirculating gyre more east, making volume transports of 10 to 15×10⁶ m³s⁻¹. At about 21°N, 127°E southeast of Taiwan, there is a cold eddy which causes branching of the Kuroshio there.