Reviews on Potash Deposit Metallogenic Conditions

Potash salt is one of key scarce strategic resources. Searching for large scale of potash salt deposit is one big problerm which Chinese academic community faces. Many new discoveries of world potash deposit have been made in recent ten years, which provide abundant practical information and complement the potash metallogenic theory. Through the summary of the potash forming characteristics at home and abroad, the paper studies the potash forming time, tectonic condition, paleogeographic condition, paleoclimate, basin location and salt source. Potash is mainly formed in Permian, Cretaceous, late Jurassic, Cambrian and Devonian. The combination of structure and environment helps to form large scale of evaporation. The climate cycle is related with crust activity. As the other ore deposit, the formation of potash ore also needs dry climate. Potash is the product of final stage in brine evolution, and therefore, it needs persistent drought climate. However, the climate condition is very complicated. Drought climate belt also occurs in humid climate stage, which is controlled by geomorphology. Potash ore can also form in local drought condition. Generally, potash forms in rock salt basin. However, the actual situation is very complicated. Some potash basin is coincided with rock salt basin, some is on one side of rock salt basin; and some are even in the outside of rock salt basin. Salt materials can be from three sources: marine source, terrigenous source and deep source.The paper gives an overview of the research status about the potash deposit forming conditions, which has great guiding significance for searching potash deposit in China. The paper also summarizes the three types of metallogenic models for potash deposit, including epicontinental metallogenic model, abnormal marine evaporation model and rift valley model. The three models are mainly different in material sources, in which the potash in epicontinental metallogenic model is from seawater; the potash in abnormal evaporation model is from nonmarine brine and the potash in rift valley model is mainly from deep material of volcanic activity.     

福建政和铁山铅锌矿床地质特征及成因

福建省政和县铁山铅锌矿床位于闽东中一新生代火山活动带。大地构造上处于建瓯一遂昌上古台拱与浙闽粤沿海断陷交接处。矿体产于晚震旦世一早古生代稻香组与铁山混染正长岩及燕山晚期枫林黑云母花岗岩接触带以及接触带围岩一侧的顺层裂隙之中。矿体与接触带产状基本一致,主要受地层产状及接触带控制。矿体呈似层状、透镜状,部分呈脉状。矿石品位较高,以铅锌矿石为主,次为黄铜铅锌矿石和铅锌磁铁矿石。矿床物质来源于地层、岩体特别是沉积岩中的火山质夹层。矿床成因类型为层控矽卡岩型。     

西藏古大湖成盐模式的提出与分析探讨

根据目前对青藏高原第四系及古环境研究的最新进展,提出了西藏地区盐湖成盐的模式———古大湖成盐模式,并列举了诸多具有说服力的证据,为研究盐湖矿产形成规律和进一步开发利用,促进西藏经济发展,将产生积极的影响。     

经验格林函数法与随机有限断层法在合成近场强地震动中的联合运用

本文采取将经验格林函数法与随机有限断层法相结合的方式,突出体现了各自方法的优点,通过经验格林函数法确定地震震源参数,用随机有限断层法计算参数、检验其合理性。利用1998年新疆阿图什M6．9级地震的肘L4．7级余震记录,合成了这次地震的最大余震Ms6．0级地震的加速度记录,并将合成的结果与实际记录在频域和时域做了对比,分析研究了地震动特征和这次最大余震的可能破裂特征。同时对经验格林函数法需进一步改进的方向进行了探讨。     

Localised coherent response of the La Molina basin (Lima,Peru) to earthquakes,and future approaches suggested by Parkway basin (New Zealand) experience

Earthquake records from a 1984 temporary seismograph array set up in La Molina, Lima, Peru, are re-analysed. The array comprised eight three-component geophones; seven soil based and one rock based. Values of horizontal-to-vertical spectral ratio (HVSR) for two small earthquakes peaked at around 1.3 Hz. In one distant earthquake, four of the seven soil-based stations showed a peak at 1.25 Hz in soil-to-rock spectral ratio (SSR), the same dominant frequency observed during an aftershock of a damaging earthquake. Because this frequency is not compatible with the shear wave velocity profile attributed to La Molina, and because the spectral peak is confined to a small ground area, it is concluded that the peak is caused by a localised deposit of soft soil. Because the area associated with the spectral peak includes the area of great damage in 1974, it is concluded that coherent monochromatic behaviour is responsible for the damage.     

Engineering source model for strong ground motion

A new engineering source model consistent with seismological concepts for simulating strong-motion accelerograms (SMAs) is presented in this paper. The source region is modeled as a horizontally layered elastic medium to cater for site dependency. The moment field acting on the rupture plane is decomposed into space and time functions, which is a novel concept. The spatial and temporal components are determined for six well-recorded earthquakes using the corresponding recorded SMA. The obtained spatial variations indicate that they can be modeled as an anisotropic random field. The temporal components of all the six events are transients, with typical frequency spectra. Based on these results, a simplified source model is proposed for the synthesis of SMA during strong earthquakes. The model is validated by simulating strong-motion acceleration time histories at stations deliberately kept out of the modeling exercise. It is found that the present model is efficient in simulating observed time histories. The proposed model is also illustrated by simulating an ensemble of acceleration time histories for the Kutch earthquake of 26th January 2001 using only the few known source parameters.     

Empirical site-specific response-spectra correction factors for the Gubbio basin (central Italy)

Providing quantitative microzonation results that can be taken into account in urban land-use plans is a challenging task that requires collaborative efforts between the seismological and engineering communities. In this study, starting from the results obtained by extensive geophysical and seismological investigations, we propose and apply an approach to the Gubbio basin (Italy) that can be easily implemented for cases of moderate-to-low ground motion and that takes into account not only simple 1D, but also more complicated 3D effects.     

A study on feasibility of SI for identification of earthquake damages in Taiwan

Using the actual damage data of the strong earthquakes in Taiwan, the effectiveness of the earthquake risk indices, namely, peak ground acceleration (PGA) and spectral intensity (SI), is verified. PGA and Housner's [Housner GW. Spectrum intensity of strong-motion earthquakes. In: Proceedings of symposium on earthquakes and blast effects on structures. EERI, UCLA; 1952] definition of SI are directly compared. A three-parameter spectral intensity system with spectral intensities SI_a, SI_v, and SI_d in the acceleration, velocity, and displacement regions, respectively, is discussed. Here, the effectiveness of SI, SI_a, SI_v, and SI_d has been compared by using the available earthquake-damage data in Taiwan. Three period ranges, namely, 0.1–0.6, 0.6–1.6, and 1.6–3.0 s were used for structures of 1–6 stories, 7–20 stories, and 21 and more stories, respectively. The results indicate that the three-parameter system is a good risk index of the damage potential of earthquakes.     

昆仑8.1级地震同震形变特征及其对响应地震活动的制约机制

本文定义”响应地震”的概念统一表述昆仑山口西8.1级地震所引发的主破裂两侧临近构造及部分块体边界上的显著地震活动.其主体活动区域集中在昆仑地震主破裂的西南侧和东北侧及祁连山断裂.同时,地壳运动在主破裂北侧的甘青块体中西部出现与背景运动场反向的特征性变化,祁连山断裂出现应变弱化.弹性位移-应力阶跃模型模拟结果显示,昆仑地震造成其东北侧甘青块体中西部地壳运动的反向运动(相对背景场).并形成东北部和西南部两个体应变张性区域,绝大部分响应地震都发生在应变张性区中和块体张性边界上.这种强烈挤压剪切背景中出现的相对松弛状态与昆仑地震后青藏块体地震弱活动背景中出现的显著活跃的响应地震活动的正相关性可能反映了断层约束状态的相对减弱对滑动的触发作用.说明在考虑地震发生条件时,不能只着眼于应力场是否增强,断层摩擦强度,或更广义地说,构造约束条件的变化也是一个不容忽视的重要因素.