Pre-eruption history of phyric basalts from DSDP legs 45 and 46: Evidence from morphology and zoning patterns in plagioclase

Phyric basalts recovered from DSDP Legs 45 and 46 contain abundant plagioclase phenocrysts which occur as either discrete single grains (megacrysts) or aggregates (glomerocrysts) and which are too abundant and too anorthitic to have crystallized from a liquid with the observed bulk rock composition. Almost all the plagioclase crystals are complexly zoned. In most cases two abrupt and relatively large compositional changes associated with continuous internal morphologic boundaries divide the plagioclase crystals into three parts: core, mantle and rim. The cores exhibit two major types of morphology: tabular, with a euhedral to slightly rounded outline; or a skeletal inner core wrapped by a slightly rounded homogeneous outer core. The mantle region is characterized by a zoning pattern composed of one to several spikes/plateaus superimposed on a gently zoned base line, with one large plateau always at the outside of the mantle, and by, in most cases, a rounded internal morphology. The inner rim is typically oscillatory zoned. The width of the outer rim can be correlated with the position of the individual crystal in the basalt pillow. The presence of a skeletal inner core and the concentration of glass inclusions in low-An zones in the mantle region suggest that the liquid in which these parts of the crystals were growing was undercooled some amount. The resorption features at the outer margins of low-An zones indicate superheating of the liquid with respect to the crystal.It is proposed that the plagioclase cores formed during injection of primitive magma into a previously existing magma chamber, that the mantle formed during mixing of a partially mixed magma and the remaining magma already in the chamber, and that the inner rim formed when the mixed magma was in a sheeted dike system. The large plateau at the outside of the mantle may have formed during the injection of the next batch of primitive magma into the main chamber, which may trigger an eruption. This model is consistent with fluid dynamic calculations and geochemically based magma mixing models, and is suggested to be the major mechanism for generating the disequilibrium conditions in the magma.     

On a generalized potential vorticity equation for quasi-geostrophic flow

Summary It is shown that the general nonlinear potential vorticity equation for viscous and conductive fluid in a rotating system can be expressed in terms of the geostrophic stream function for the horizontal velocity alone, provided that the motions are hydrostatic and quasi-geostrophic and the Richardson number is much larger than unity. The form of this equation is identical with that obtained from an asymptotic expansion for a small Rossby number.     

Evaluation of damping reduction factors for estimating elastic response of structures with high damping

The damping reduction factors are used in a few building codes in order to estimate the elastic response spectrum with high damping ratios from its 5%‐damped counterpart. At present, much research regarding this factor has been published. The purpose of this paper is to evaluate the accuracy of five different models of damping reduction factors. In addition, the damping reduction factors adopted in the recent U.S.A. seismic codes are also evaluated. Statistical studies are carried out according to a total of 216 earthquake ground motions recorded on firm sites in California. Considered here are elastic single‐degree‐of‐freedom (SDOF) systems with natural vibrating periods between 0.1 and 6.0 s. Mean ratios and dispersion of approximate to exact maximum elastic displacement demands corresponding to various damping reduction factors are computed as functions of the natural vibrating period and the viscous damping ratio. Copyright © 2005 John Wiley & Sons, Ltd.     

Some isotopic and hydrological changes associated with the 1999 Chi-Chi earthquake, Taiwan

Abstract   The changes in the isotopic composition of, and the groundwater level in, the Choshui River alluvial fan near the ruptured Chelungpu Fault during and following the 1999 ( M _w = 7.5) Chi-Chi earthquake in Taiwan are reported. Three aspects of the hydrological changes are noticed. First, following the Chi-Chi earthquake, the lower aquifers beneath the Choshui River fan showed a significant shift in isotopic composition towards that of the surface water in the Choshui River, suggesting enhanced exchanges of water between the river and the groundwater. Second, in some wells, water levels and isotopic compositions in different aquifers converged to the same respective values during the Chi-Chi earthquake, suggesting coseismic exchanges of water between the different aquifers, which implies enhanced permeability due perhaps to the fracturing and breaching of aquitards between the aquifers. Third, the pattern of the coseismic water-level response is distinctly different from that of the shift in the isotopic composition, suggesting that they were produced by different mechanisms.     

中国暴雨中尺度系统发生与发展的诊断分析和数值模拟(Ⅱ)数值模拟

通过改进的MM4中尺度数值模式，对我国三次典型大暴雨过程的模拟，来探讨暴雨中尺度系统发生与发展的问题。主要结果指出:气旋性涡柱在不稳定暖湿气柱内生成和发展，以及与整个涡柱共存的上升运动的持续加强，对暴雨中尺度系统的发展具有重要的作用；地面热通量，凝结潜热释放对暴雨中尺度系统的发展有决定性的作用；各种不同的物理过程和参数化、青藏高原的构形造成的外强迫影响，以及模式空间分辨率等，对暴雨中尺度系统结构与演变以及降雨量的模拟结果均有重要的作用。     

一个同时采用两种地图投影坐标系的大气环流模式

为了进一步研究高原和山地对大气环流的热力和动力作用,我们设计了一个九层的全球原始方程模式.模式中除考虑了地形作用外,还包含了太阳辐射和地、气的长波辐射、大尺度凝结和积云对流等因子的影响.为了能继续采用有限差分近似,并且既能较好地描述中高纬地区的环流状况,又不影响对低纬地区环流的模拟,本模式同时采用了两种地图投影坐标系(麦卡托投影用于中低纬地区,极射赤平投影用于高纬区).文中给出了冬季海平面气压、风场、降水分布和垂直环流的模拟结果,并把它们与观测值作了比较.     

Sustainable groundwater management in Kinmen Island

Kinmen county is located in the southwest of Fujen province, China. It comprises Kinmen, Leiyu and other small islands. Its total area is around 150 km². Kinmen is the largest island, and 95% of the population resides there. The average annual precipitation is 1072 mm. Rainfall is concentrated in a 5 month period from mid‐April to mid‐September. Water resources are limited relative to demand. Eastern Kinmen utilizes surface water, whereas western Kinmen uses groundwater. Moreover, the Kinmen sorghum liquor is brewed using the native groundwater in the west of the island. MODFLOW‐96 was used to simulate the groundwater distribution and determine the annual amount of infiltration, pumping, and boundary inflow and outflow. Additionally, a groundwater management index was adopted to evaluate the status of groundwater level change, thus allowing local government officials to adjust the pumping scheme dynamically. To achieve a sustainable groundwater supply in Kinmen, an integrated groundwater extraction plan was proposed. This plan includes enhancing the infiltration by using treated wastewater from the east of the island, monitoring the groundwater level change, adjusting the groundwater pumping scheme, and constructing seawater desalination plants. If the hostile confrontation between Taiwan and mainland China is resolved, then the water supply through an undersea pipeline from Sharmen, China, to Kinmen can be another potential source of water for Kinmen in the future. Copyright © 2006 John Wiley & Sons, Ltd.     

Holocene thermal optimal and climate variability of East Asian monsoon inferred from forest reconstruction of a subalpine pollen sequence, Taiwan

The East Asian monsoon Holocene optimal period has been debated both about duration and whether conditions were a maximum in thermal conditions or in precipitation. In this study we show Holocene climate variability inferred by a forest reconstruction of a subalpine pollen sequence from peat bog deposits in central Taiwan, based on modern analogues of various altitudinal biomes in the region. A warmer interval occurred between 8 and 4 ka BP (calibrated ¹⁴C years) when the subtropical forests were more extensive. The Holocene thermal optimum is represented by an altitudinal tropical forest at 6.1–5.9 ka BP and 6.9 ka BP and only the latter was accompanied by wet conditions, indicating decoupling of thermal and precipitation mechanism in the middle Holocene. Abrupt and relative severe cold phases, shown by biome changes, occurred at about 11.2–11.0 ka BP; 7.5 ka BP; 7.2 ka BP; 7.1 ka BP; 5.2 ka BP, 5.0 ka BP and 4.9 ka BP. A spectral analysis of pollen of a relatively cold taxon — Salix, reveals that the time series is dominated by a 1500 yr periodicity and similar to the cold cycle reported in the marine records of Indian and western Pacific Oceans. The cold–warm conditions inferred by the change of forests show close relationship to solar energy in comparison with the production rate of Be-10.