Effects of local site and building parameters on damage distribution in Angra do Heroísmo—Azores

During the M_w=6.9 January 1, 1980 earthquake in the Azores, the damage distribution in the town of Angra do Heroísmo, in Terceira Island, had a non-homogeneous spatial character. In order to understand the observed pattern of damage a microtremor survey was carried out, using ambient vibrations, and the data were analysed with the J-Sesame software, following the H/V Nakamura methodology. The results are in good agreement with the surface geology and they show a good correlation with the observed damages. Two building surveys were performed, in 1980 on damage evaluation and in 2000 on characterization of few building parameters. With all these elements (surface geology type, soil peak frequency, building type, number of stories and damage level) for 2111 buildings it was possible to perform several interparameter analysis, which enabled the identification of indicators that could be used to improve the damage estimation for future events.     

Seismic Behaviour of Slightly Reinforced Concrete Walls: Experiments and Theoretical Conclusions

In order to develop new standards related to structures in seismic regions, a series of research programmes has been conducted on slightly reinforced structural walls commonly used in France. Based on these researches, a method of design of such walls submitted to a seismic action has been set up. This method used in the PS92 code differs from that used for ductile walls, where a plastic hinge can develop at the base of the wall. The analysis is similar to the push over analysis presently given in Eurocode 8. These various researches have confirmed the validity of the design concept developed for the PS92 code, on one hand, and highlighted a number of phenomena linked to the non linear behaviour of reinforced concrete walls, on the other hand. The present article aims at presenting a synthesis of the results obtained during these research programmes.     

Types of eruptions of Etna volcano AD 1670–2003: implications for short-term eruptive behaviour

Analysis of the historical records of Etnas eruptive activity for the past three centuries shows that, after the large 1669 eruption, a period of about 60 years of low-level activity followed. Starting from 1727, explosive activity (strombolian, lava fountaining and subplinian) at the summit crater increased exponentially to the present day. Since 1763, the frequency of flank eruptions also increased and this value remained high until 1960; afterward it further increased sharply. In fact, the number of summit and flank eruptions between 1961 and 2003 was four times greater than that of the pre-1960 period. This long-term trend of escalating activity rules out a pattern of cyclic behaviour of the volcano. We propose instead that the 1670–2003 period most likely characterises a single eruptive cycle which began after the large 1669 eruption and which is still continuing.On the basis of the eruptive style, two distinct types of flank eruptions are recognised: Class A and Class B. Class A eruptions are mostly effusive with associated weak strombolian activity; Class B eruptions are characterised by effusive activity accompanied by intense, long-lasting, strombolian and lava fountaining activity that produces copious tephra fallouts, as during the 2001 and 2002–2003 eruptions. Over the past three centuries, seven Class B eruptions have taken place with vents located mainly on the south-eastern flank, indicating that this sector of the volcano is a preferential zone for the intrusion of volatile-rich magma rising from the deeper region of the Etna plumbing system.Electronic Supplementary Material Supplementary material is available for this article at Editorial responsibility: M. Carroll     

The effects of strain rate and saturation on a micro-cracked marble

It is well known rock masses contain several types of weakness planes varying from micro-fissure to fault in size. The fracture frequency, degree of saturation and time are the basic rock parameters affecting its behaviour. However, in most cases, it is practically difficult to test heavily fractured rock in laboratory environment. In this study, the effects of micro cracks, strain rate and water saturation on strength are discussed using a small-scale physical experiments. It is attempted to detach the grain boundaries of coarse-grained rock specimens of the Mu?la marble by thermal treatment that would serve as a small-scale physical simulation of fractures in rock masses and enable a discussion of the variations in time dependent mechanical behaviour. An experimental study was conducted on marble specimens induced thermally by micro-cracks in different frequencies. The thermal treatment periods being 24 h in inert atmospheric condition were varied for each test specimen except categories A and G. Effective porosity increased up to 2.4% after the last thermal cycle of category F. Then conventional compression tests with different strain rates were carried out using a servo-controlled testing machine on both dry and saturated specimens. It is concluded that both lowering strain rates and increasing porosity related with thermally induced micro cracks have important effects on strength and failure path. The progressive failure entirely occurs along the grain boundaries fissured by cyclical treatment and inter-granular deformation depends upon degree of thermal influence. The small-scaled laboratory model enabled to demonstrate that parameters such as joint frequency, time and saturation have a significant effect on mechanical behaviour of rock masses.     

Heterogeneous growth of cordierite in low P/T Tsukuba metamorphic rocks from central Japan

This paper examines the spatial statistics of matrix minerals and complex patterned cordierite porphyroblasts in the low‐pressure, high‐temperature (low P/T) Tsukuba metamorphic rocks from central Japan, using a density correlation function. The cordierite‐producing reaction is sillimanite + biotite + quartz = K‐feldspar + cordierite + water. The density correlation function shows that quartz is distributed randomly. However, the density correlation functions of biotite, plagioclase and K‐feldspar show that their spatial distributions are clearly affected by the formation of cordierite porphyroblasts. These observations suggest that cordierite growth occurred through a selective growth mechanism: quartz adjacent to cordierite has a tendency to prevent the growth of cordierite, whereas other matrix minerals adjacent to cordierite have a tendency to enhance the growth of cordierite. The density correlation functions of complex patterned cordierite porphyroblasts show power‐law behaviour. A selective growth mechanism alone cannot explain the origin of the power‐law behaviour. Comparison of the morphology and fractal dimension of cordierite with two‐dimensional sections from a three‐dimensional diffusion‐limited aggregation (DLA) suggests that the formation of cordierite porphyroblasts can be modelled as a DLA process. DLA is the simple statistical model for the universal fractal pattern developed in a macroscopic diffusion field. Diffusion‐controlled growth interacting with a random field is essential to the formation of a DLA‐like pattern. The selective growth mechanism will provide a random noise for the growth of cordierite due to random distribution of quartz. Therefore, a selective growth mechanism coupled with diffusion‐controlled growth is proposed to explain the power‐law behaviour of the density correlation function of complex patterned cordierite. The results in this paper suggest that not only the growth kinetics but also the spatial distribution of matrix minerals affect the progress of the metamorphic reaction and pattern formation of metamorphic rocks.     

莺琼盆地岩石弹性物性规律的研究

利用岩芯实验室测试数据、全波列测井数据和地震资料对莺琼盆地纵横波地震参数及衍生参数的变化规律进行了详尽地分析和研究。含气岩芯的刚性模量、纵横波速度比和泊松比比含盐水岩芯的低得多;砂岩的纵横波速度比和泊松比比泥岩的低得多。当地层埋深超过2500m时,纵横波速度比、泊松比基本不受深度的影响。岩石密度和孔隙度的相关性很好;含盐水岩芯的纵横波速度比与孔隙度的相关性很差;含气岩芯的纵横波速度比与孔隙度的相关性稍好于含盐水岩芯;高温高压状态下的纵横波速度比和泊松比的变化也是有规律的。     

Simulation of liquefaction beneath an impermeable surface layer

A joint element is proposed, which can simulate the three phases of behaviour of an impermeable layer over a liquefied sand layer. The analysis tracks the post-liquefaction reconsolidation of the sand, the simultaneous development of a water film between the layers and the settlements resulting from the subsequent drainage of the water film. The element is incorporated in a finite element program, which can be used to simulate the behaviour of layered systems. The effectiveness of the program is demonstrated by simulation of the performance of a model soil deposit of two layers in a centrifuge test.     

一阶弹性波方程交错网格高阶差分解法

提高计算精度和运算效率是所有波场正演方法所追求的目标,本文通过将速度 （应力）对时间的奇数阶高阶寻数转化为应力（速度）对空间的导数,运用时间和空间差分精度 均可达任意阶的高阶差分法,通过交错网格技术,对一阶速度－应力弹性波方程进行了数值求 解．波场快照以及实际模型的正演结果表明,这种求解一阶弹性波方程的高阶差分解法,和 常规的差分法相比网格频散显著减小,精度明显提高,而且可以取较大的空间步长,提高计算 效率。     

双相各向异性研究、问题与应用前景

地球内部流体的存在和岩石各向异性是地下介质的两大表征,考虑地下流体和介质各向异性问题的双相各向异性理论是当今地震学和地球物理学理论与应用研究的前沿和难题之一。孔隙流体的存在、固体和流体之间的相互作用会弱化或硬化岩石的力学属性,上起声波或弹性声波速度的频散的振幅的衰减,并产生第二类压缩波。裂缝或裂隙的定向分布、岩层的旋性沉积、应力场的定向排列,都会引起传播速度的各向异性、横波发生分裂等重要现象,这些