The Town Effect: Dynamic Interaction between a Group of Structures and Waves in the Ground

In a conventional approach, the mechanical behaviour of a structure subjected to seismic or blast waves is treated separately from its surroundings, and in many cases, the dynamic coupling effect between multiple structures and the waves propagating in the ground is disregarded. However, if many structures are built densely in a developed urban area, this dynamic interaction may not become negligible. The first purpose of this contribution is to briefly show the effect of multiple interactions between waves and surface buildings in a town. The analysis is based on a recently developed, fully coupled, rigorous mathematical study, and for simplicity, each building in the town is represented by a rigid foundation, a mass at the top and an elastic spring that connects the foundation and mass. The buildings stand at regular spatial intervals on a linear elastic half-space and are subjected to two-dimensional anti-plane vibrations. It is found that the buildings in this model significantly interact with each other through the elastic ground, and the resonant (eigen) frequencies of the collective system (buildings or town) become lower than that of a single building with the same rigid foundation. This phenomenon may be called the “town effect” or “city effect.” Then, second, it is shown that the actual, unique structural damage pattern caused by the 1976 Friuli, Italy, earthquake may better be explained by this “town effect,” rather than by investigating the seismic performance of each damaged building individually. The results suggest that it may also be possible to evaluate the physical characteristics of incident seismic/blast waves “inversely” from the damage patterns induced to structures by the waves.     

Minerals formed and mineral formation from volcanic ash by weathering

Weathering of volcanic ash and pumice is unique regarding minerals formed and mineral formation. These minerals include allophane, imogolite, opaline silica and some halloysites, and have distinctive structures and properties. Studies on the surface and subsurface weathering of various volcanic ashes in different settings are reviewed. This review illustrates that relatively rapid weathering of finely comminuted volcanic ash well reflects the effects of climate, vegetation and time, and produces various combinations of weathering products. The moisture regime, the nature and amount of organic matter incorporated, the deposition of volcanic ash as overburden, and the chemical and mineralogical composition of parent ash are important in controlling the mineral formation in weathered volcanic ash.     

Modeling of subduction components in the Genesis of the Meso-Cenozoic igneous rocks from the South Shetland Arc, Antarctica

Isotope data and trace elements concentrations are presented for volcanic and plutonic rocks from the Livingston, Greenwich, Robert, King George and Ardley islands (South Shetland arc, Antarctica). These islands were formed during subduction of the Phoenix Plate under the Antarctica Plate from Cretaceous to Tertiary. Isotopically (⁸⁷Sr/⁸⁶Sr)_o ratios vary from 0.7033 to 0.7046 and (¹⁴³Nd/¹⁴⁴Nd)_o ratios from 0.5127 to 0.5129. εNd values vary from +2.71 to +7.30 that indicate asthenospheric mantle source for the analysed samples. ²⁰⁸Pb/²⁰⁴Pb ratios vary from 38.12 to 38.70, ²⁰⁷Pb/²⁰⁴Pb ratios are between 15.49 and 15.68, and ²⁰⁶Pb/²⁰⁴Pb from 18.28 to 18.81. The South Shetland rocks are thought to be derived from a depleted MORB mantle source (DMM) modified by mixtures of two enriched mantle components such as slab-derived melts and/or fluids and small fractions of oceanic sediment (EM I and EM II). The isotopic compositions of the subduction component can be explained by mixing between at least 4 wt.% of sediment and 96 wt.% of melts and/or fluids derived from altered MORB.     

祁连山七一冰川物质平衡的最新观测结果

祁连山七一冰川观测结果表明, 2001/2002年度和 2002/2003 年度冰川物质平衡分别为-810mm和-316 mm水当量, 冰面出现显著的减薄状态. 和过去的观测结果相比较, 20 世纪 70 年代为较大的正平衡, 年平均为360 mm水当量; 80年代年平均为4 mm水当量, 基本接近零平衡状态. 到近两年亏损强烈, 为所有观测资料中负平衡值最大的年份, 零平衡线也达到最高位置. 物质平衡出现较大的负值和零平衡线位置升高的状况, 强烈反映了祁连山冰川对气候变暖过程的响应. 如果气候变暖趋势继续, 冰川物质平衡负值将增大、冰面减薄和雪线的升高, 冰川将继续呈现萎缩状态.     

Observations and modeling of the ice-ocean conditions in the coastal Chukchi and Beaufort Seas

The Chukchi and Beaufort Seas include several important hydrological features： inflow of the Pacific water, Alaska coast current （ ACC ）, the seasonal to perennial sea ice cover, and landfast ice ＇along the Alaskan coast. The dynamics of this coupled ice-ocean system is important for both regional scale oceanography and large-scale global climate change research. A mumber of moorings were deployed in the area by JAMSTEC since 1992, and the data revealed highly variable characteristics of the hydrological environment. A regional high-resolution coupled ice-ocean model of the Chukchi and Beaufort Seas was established to simulate the ice-ocean environment and unique seasonal landfast ice in the coastal Beaufort Sea. The model results reproduced the Beaufort gyre and the ACC. The depthaveraged annual mean ocean currents along the Beaufort Sea coast and shelf hreak compared well with data from four moored ADCPs, but the simulated velocity had smaller standard deviations, which indicate small-scale eddies were frequent in the region. The model resuits captured the sea,real variations of sea ice area as compared with remote sensing data, and the simulated sea ice velocity showed an ahnost stationary area along the Beaufort Sea coast that was similar to the observed landfast ice extent. It is the combined effects of the weak oceanic current near the coast, a prevailing wind with an onshore component, the opposite direction of the ocean current, and the blocking hy the coastline that make the Beaufort Sea coastal areas prone to the formation of landfast ice.