Shear Wave Velocities in the Estimation of Earthquake Hazard Over Alluvium in Seismically Active Region

It is well known that the potential hazard during an earthquake is mainly in alluvium or alluvium filled basins; shear wave velocity plays a significant role in estimating the possible hazard during an earth quake in such an area. This paper presents shear wave velocity profile from Jabalpur, Central India mainly dominated by alluvial soil that was moderately affected by an earthquake of magnitude 6.5 in May, 1997. The acquired shear wave velocity by Multichannel Analysis of Surface Wave (MASW) in as many as 36 sites over alluvial soil ranges from 200 m/sec to 400 m/sec and in a few sites marginally less than 200 m/sec corresponding to a sub-surface depth of 30–35 m. Further, the computed N values vary as low as near zero to less than 25. The study is substantiated by the estimation of P-wave velocity by refraction seismic method at the same locations of MASW which ranges from 350 m/sec to 2200 m/sec. The results suggest that the damage during an earth quake appears to be highly unlikely in view of the marginally high Vs up to depth of 30 m. This study on seismic hazard is substantiated by the estimation of frequency of the ground as well as amplification which is found to be a maximum of about 2.5 in the frequency band of 2–6 Hz in west and north western portion of the study area.     

Environmental impact on construction limestone at humid regions with an emphasis on salt weathering,Al-hambra islamic archaeological site,Granada City,Spain: case study

Al-hambra is an immense and valuable archaeological site in Spain built on Sabika hill with red brick and natural sandy limestone. It exhibits weathering features indicating salt weathering process. The main aim of this study is to examine weathering processes and intensity acting on Al-hambra. Rock petrography and mineralogical composition have been examined using thin sections, scanning electron microscope, X-ray diffraction and X-ray fluorescence; limits of rock’s physical parameters using ultrasonic waves and mercury porosimeter; rock salt content through hydrochemical analysis. Salts attacking this structure are mainly from wet deposition of air pollutants on the long term chemical alteration of rock’s carbonate content to its equivalent salts. The salts’ concentration limit within the examined rock samples is considerably low but it is effective on the long run through hydration of sulphate salts and/or crystallization of chloride salts. Rock texture type and its silica as well as clay content reduces its resistance to internal stresses by salts as well as wetting and drying cycles at such humid area. The recession in limits of physical parameters examined for deep seated and weathered limestone samples quantitatively reflects weathering intensity on Al-hambra.     

How Bedrock‐Controlled Channel Migration Can Structure Selective Preservation of Archaeological Sites: Implications for Modeling Paleoindian Settlement

Although Paleoindian sites in Indiana, USA, are commonly located on late Wisconsin (Last Glacial Maximum) outwash terraces, drainage basin development since deglaciation often obscures the visibility of such sites on flood plains by either burying them under alluvium or destroying them through erosion. Significant clusters of Paleoindian and Early Archaic sites, however, have been identified proximal to the modern White River channel in central Indiana on what is mapped as “floodplain.” These site cluster locations are patterned. They typically occur within bedrock‐controlled river reaches but are rare along unconfined meandering reaches. Subsurface reconnaissance and chronology indicate that despite the fact that they often flood, portions of the so‐called flood plains within bedrock‐confined reaches are actually terraces constructed of late Wisconsin outwash with minimal overbank sedimentation. Terrace preservation in these settings is a result of bedrock structure that protects older sediments from lateral erosion and differentially preserves archaeological sites near the modern channel in bedrock‐controlled reaches. Comparisons of archaeological sites within bedrock‐controlled segments of the White River to those in unconfined meandering segments suggests that significant numbers of Paleoindian and Early Archaic sites may be missing from river settings across the midcontinent. These findings demonstrate that bedrock channel controls are important to recognize when assessing prehistoric settlement distributions.     

基于“双行裂隙”模型的两淮矿区高承压厚松散层突水机理

两淮矿区高承压厚松散含水层覆盖下煤炭储量巨大,在提高上限开采过程中常发生松散层突水事故,采用传统“上三带”理论难以合理解释此类事故发生的机理。本文在分析两淮矿区高承压松散层水文工程地质条件的基础上,建立近高承压松散层开采“双行裂隙”模型,采用室内实验、数值模拟、理论分析和工程应用检验等方法,研究“双行裂隙”发育规律,揭示两淮矿区高承压厚松散层突水致灾机理,结果显示:祁东煤矿松散层第四含水层（简称四含）水压与裂采比呈线性关系;在水压作用下,覆岩“上行裂隙”发育高度增大;利用裂隙受力分析推导的基岩风化带原生裂隙扩展渗透深度计算公式,表明高承压松散含水层对风化裂隙产生劈裂作用,是“下行裂隙”形成的主要因素。“双行裂隙”的综合作用使工作面更易发生松散层水突水事故,研究成果为近松散层煤层开采安全煤（岩）柱的合理留设提供科学依据。      

关于注水地震研究的几个问题

本文认为注水地震是相当复杂的。将注水只看成诱发因素,或将与注水相关的地震都看成构造地震是片面的。对注水过程的微震研究表明,注水可以直接造成地震。对油田地震的研究表明,大量采油造成地下介质的亏空同样可能造成地震。对其它一些地下矿藏的采掘也有类似的情况。错误地把与注水有关的地震都看成是注水诱发的构造地震,将导致对地壳构造活动特点的错误估计。     

Weathering of marbles and granites in marine environment: petrophysical properties and special role of atmospheric salts

 The aim of this paper was to study the weathering mechanism of marbles and granites exposed to the marine environment at the Delos archaeological site. Alterations, as granular disintegration, contour scaling and alveolus formations, can be observed either at the base of blocks and columns, or at the median-high zones of monuments. A white marble, which originated from Naxos Island, had a weak porosity (0.2%). Its porous network was organized into two subnetworks of rectilinear and sinuous cracks, which limited capillary transfer to ∼10 cm. The granite, which originated from Delos Island, had a relatively high porosity (2.15%), and had a well-connected system of cracks and microporous zones of weathered minerals. This homogeneous network allowed good capillary transfer for long distances (1–2 m). For the marble, as for the granite, evaporation occurred mainly at depth in the stone, and encouraged its deterioration. This damage depends on the dissolution and crystallization of salts, which occur in cycles. First, by the capillary transfer of water and salt from the ground, when the stones are located near the sea. This processes can explain the deterioration of the marble and the granite bases, and the decay of granite on all its surfaces. Second, by fixation of water vapor by sea salt deposited on the stone by wind. This phenomenon can explain the degradations observed on the median-high parts of monuments in marble and granite, even though, for the granite, the first mechanism was more active.     

Characterization of Kolar gold field mine tailings for cyanide and acid drainage

The gold mining process at Kolar gold field (KGF) mines has generated about 32 million tons of tailings. Gold was extracted from the mined ores using cyanidation technique that involved dissolution of gold in the ore by water soluble alkali metal cyanides (example, sodium cyanide or potassium cyanide). Of the several dumps that received the mine tailings only the Kennedy’s Line dump was active prior to closure of the KGF mines in the year 2000. The Kennedy’s Line dump received sulfide bearing tailings in slurry form that comprised of spent ore and process water bearing soluble alkali metal cyanide. Depending on the pH of the tailing slurry, the free cyanides may exist as aqueous hydrogen cyanide that can escape to the atmosphere as hydrogen cyanide gas or occur as soluble cyanide (CN⁻) ions that can be leached by infiltrating water to the sub-surface environment. Additionally, the presence of pyrite minerals in the Kennedy’s Line dump makes them susceptible to acid drainage. This study examines the potential of gold tailings of Kennedy’s Line dump to release cyanide ions (CN⁻) and acid drainage to the sub-surface environment by performing physico-chemical and leaching tests with tailing samples collected from various depths of the dump, sub-surface soil samples beneath the dump and groundwater samples from vicinity of Kennedy’s Line dump. The chemical mechanisms responsible for the ambient cyanide and pH levels of the tailing dump, sub-surface soil samples and groundwater are also inferred from the laboratory results.     

Controls on As, Pb, and Mn distribution in community soils of an historical mining district, southwestern Colorado

 Rico, Colorado is a small mountain community that was developed before the turn of the century around and near underground lead-zinc-silver mines. Today, US regulatory concerns in such communities focus on the metal content, particularly of lead, in community soils. This study integrates bedrock geology, surficial geology, mineralogy and geochemistry in order to define the controls on metal distribution in Rico community soils. The principal constituents of concern are As, Pb, and Mn. The results show that mining-related sources are discrete and localized whereas natural sources, including bedrock (mean Pb content of 3 500 ppm), colluvium (mean Pb content of 1 410 ppm), and older alluvium (mean Pb content of 744 ppm) are wider spread and are the principal sources of metals in Rico community soils. Historical mining sites like Rico should be expected to have significant surficial expressions of mineralized bedrock. In these communities, it is important to accurately define the role of all metal sources as a foundation for determining environmental liabilities, cleanup guidelines, and health risk assessments. The application of geology and mineralogy in support of geochemical characterization is necessary to accurately define the origin and distribution of both anthropogenic and natural metal sources at such sites. Received: 27 December 1996 · Accepted: 21 February 1997     

How has coastal erosion affected the prehistoric settlement pattern of the boothbay region of maine?

Erosion of complex, rocky coasts has largely been neglected by geologists. Thus, a geo-archaeological study of coastal erosion was required before analysis of the prehistoric settlement pattern could be undertaken. Along the outer, wave-dominated coast of Maine, erosion is episodic, occurring when large storms raise water levels to new heights. Along the inner, tide-dominated coast, erosion occurs more frequently because unconsolidated sediments are exposed at low elevations in bedrock features. The shell midden archaeological sites of the Boothbay, Maine region are situated in the most rapidly eroding areas; therefore, it can be reasoned that localities without cultural deposits were never occupied. On the other hand, coastal erosion is widespread enough to insure that sites have been exposed to discovery by archaeological survey. Settlement pattern analysis of the study area is, therefore, not biased by differential preservation or discovery of archaeological sites.     

Mechanism of concave “tafoni” and convex “domal shape” formation on TRIASSIC red sandstone of some old buildings, Chester City, UK, Case study

The weathering factors act on the recent and archaeological sites through different processes based on the dominant environmental conditions. The net result of weathering is deformation of the original form of construction rock. In the current case study, the main aim is to find out the mechanism of formation of two different weathering forms recorded on many old buildings taking Chester City as a case study. The construction rock in the case study is arenitic sandstone with carbonate content ranging from 0.0 to 15.6%. The sandstone blocks are cemented together by hydraulic lime mortar that can easily be altered chemically to salts by acid rain that dominates at the study area. In case of mortar with worse geotechnical limits than the sandstone blocks, the net result is convex “domal” shape blocks, but in case of mortar with better geotechnical limits than the construction sandstone, the net result of weathering is tafoni “concave” weathering form.     

Characterisation of groundwater chemistry in an eastern coastal area of Cuddalore district,Tamil Nadu

The groundwater quality detoriation due to various geochemical processes like saline water intrusion, evaporation and interaction of groundwater with brines is a serious problem in coastal environments. Understanding the geochemical evolution is important for sustainable development of water resources. A detailed investigation was carried out to evaluate the geochemical processes regulating groundwater quality in Cuddalore district of Tamilnadu, India. The area is entirely underlined by sedimentary formations, which include sandstone, clay, alluvium, and small patches of laterite soils of tertiary and quaternary age. Groundwater samples were collected from the study area and analyzed for major ions. The electrical conductivity (EC) value ranged from 962 to 11,824 μS/cm, with a mean of 2802 μS/cm. The hydrogeochemical evolution of groundwater in the study area starts from Mg-HCO₃ type to Na-Cl type indicating the cation exchange reaction along with seawater intrusion. The Br/Cl ratio indicates the evaporation source for the ion. The Na/Cl ratios indicate groundwater is probably controlled by water-rock interaction, most likely by derived from the weathering of calcium-magnesium silicates. The plot of (Ca+Mg) versus HCO₃ suggests ions derived from sediment weathering. The plot of Na+K over Cl reflects silicate weathering along with precipitation. Gibbs plot indicates the dominant control of rock weathering. Factor analysis indicates dominance of salt water intrusion, cation-exchange and anthropogenic phenomenon in the study.     

Diagnosis of weathering damage on rock-cut monuments in Petra, Jordan

Studies of many years—combining in situ investigation and laboratory analysis—have provided comprehensive information on weathering damage on the rock-cut monuments in the ancient city of Petra in Jordan. These rock-cut monuments represent outstanding world heritage. Many hundred monuments were carved by the Nabataeans from bedrock about 2000 years ago. The awareness of increasing weathering damage on the monuments has resulted in international efforts towards their preservation. The damage diagnosis has addressed the complex mutual relationships between stone types, stone properties, monument exposure regimes, environmental influences, weathering phenomena, development and extent of weathering damage and weathering progression. The rocks were classified lithostratigraphically and petrographically. Results on weathering forms, weathering profiles and weathering products obtained from monument mapping, in situ measurements and laboratory studies revealed a complex diversity of weathering phemomena with respect to type and intensity. Damage categories and damage indices were used to create a reproducible quantitative rating of weathering damage. Detailed results on weathering forms allowed the characterization and quantification of weathering progression including weathering prognoses. Stone properties and states of weathering damage were jointly considered for the rating of the rocks’ susceptibility to weathering. The systematic evaluation of weathering damage and monument exposure regimes can enhance the assessment of weathering factors and processes.     

Soil liquefaction susceptibility and hazard mapping in the residential area of Kütahya (Turkey)

This study presents the results of both field and laboratory tests that have been undertaken to assess liquefaction susceptibilities of the soils in Kütahya city, located in the well-known seismically active fault zone. Liquefaction potentials of the sub-surface materials at Kütahya city were estimated by using the geological aspect and geotechnical methods such as SPT method of field testing. And, the data obtained have been mapped according to susceptibility and hazard. The susceptibility map indicated “liquefable” and “marginally liquefable” areas in alluvium, and “non-liquefable” areas in Neogene unit for the magnitude of earthquake of M=6.5; whereas, liquefaction hazard map produced by using of liquefaction potential index showed the severity categories from “very low” to “high.” However, a large area in the study area is prone to liquefy according to liquefaction susceptibility map; the large parts of the liquefable horizon are mapped as “low” class of severity by the use of the liquefaction potential index. It can be said that hazard mapping of liquefaction for a given site is crucial than producing liquefaction susceptibility map for estimating the severity. Both the susceptibility and hazard maps should be produced and correlated with each other for planning in an engineering point of view.     

Salt damage and microclimate in the Postumius Tomb, Roman Necropolis of Carmona, Spain

The necropolis of Carmona (Seville, Spain) is one of the most significant Roman burial sites in southern Spain used during the first and second centuries ad. Of its more than 600 tombs, the Postumius Tomb is one of the best examples of a tomb affected by severe salt damage. To define safe microclimatic conditions for its conservation, environmental parameters were recorded from June 2007 to April 2009, both inside and outside the tomb, and mineralogical, textural, petrophysical, and durability characterization studies of the host-rock were made. Experimental tests revealed a high susceptibility to salt deterioration of a host-rock (calcarenite) with low mechanical properties and a complex porous medium that favors salt weathering, water condensation, and capillary rise. The analysis of the weathered material showed the presence chiefly of gypsum (CaSO₄·2H₂O), thenardite (Na₂SO₄) and halite (NaCl) in the tomb of Postumius, with alteration that was more intensive in spring and autumn, and less so during summer months. Salt damage activity was calculated by quantifying the number of transitions of crystallization–dissolution of saline phases. The calculated seasonality for water condensation and salt damage is coeval. The host-rock alteration is in accord with the estimated salt decay, and was more intensive in spring and autumn and less so during summer. The seasonality of halite transitions is similar to that of the sodium sulfate system, which suggests that salt weathering is produced by the two types of salts. By combining different methodological approaches (pore structure, water condensation, salt and environmental conditions), it is possible to explain why salt crystallization occurs in a tomb with hygrometric conditions that are not suitable for this process to occur. These methodological approaches are also used to other rock-decaying processes, such as the development of microorganisms, clay swelling and calcite dissolution by NaCl- and CO₂-rich pore waters, and can be used to predict safe threshold microclimatic conditions that minimize all rock-decaying processes.     

Hydrogeochemical and isotopic study of groundwater in the Habor Lake Basin of the Ordos Plateau,NW China

Hydrogeochemistry and isotopes were used to understand the origin and geochemical evolution in the Habor Lake Basin, northwestern China. Groundwater samples were taken, and the isotopic compositions δD, δ¹⁸O and major ions were analyzed. The groundwater can be divided into three types: the Quaternary groundwater, the shallow Cretaceous groundwater and the deep Cretaceous groundwater. The groundwater chemistry is mainly controlled by the feldspar weathering and dolomite weathering, the dissolution of Glauber’s salt, and cation exchange. Chemistry of lake water is mainly controlled by evaporation and precipitation. The stable isotopes of oxygen and hydrogen in groundwater cluster along the local meteoric water line, indicating that groundwater is of meteoric origin. Comparing with shallow groundwater, deep groundwater is depleted in heavy isotopes indicating that deep groundwater was recharged during late Pleistocene and Holocene, during which the climate was more wetter and colder than today.     

Seasonality of bedrock weathering chemistry and CO2 consumption in a small watershed, the White River, Vermont

The draw down of CO₂ from the atmosphere during mineral weathering plays a major role in the global budget of this greenhouse gas. Silicate minerals remove twice the CO₂ of carbonate minerals per mole of calcium in runoff during weathering. Bedrock weathering chemistry was investigated in the White River watershed of northeastern USA to investigate whether there are seasonal differences in carbonate and silicate weathering chemistry. Geographic Information Systems analyses of bedrock geology were combined with major element concentrations in river waters to gain an understanding of the consistency of mineral weathering during three seasons. The percent of carbonate mineralogy comprising the bedrock in tributaries of the White River varied from less than 5% to 45% by area. A mass balance calculation using major element concentrations in waters was applied to estimate the seasonal relationships between bedrock geology and bicarbonate flux. In all tributaries and the main stem of the White River the highest calculated percent of bicarbonate from carbonate mineral weathering was measured in the late fall. The results suggest that carbonate and silicate bedrock weathering processes are seasonally controlled. Thus single season sampling could not accurately represent an entire year's geochemical budget. In the White River, water samples obtained solely during the summer would consistently underestimate the total yearly source of bicarbonate from carbonate bedrock weathering. The same sample set would also provide data that would lead to an underestimation of the yearly atmospheric CO₂ draw down by bedrock weathering in the watershed. For example at four of the seven locations studied there was an almost two-fold difference between summer and spring calculated atmospheric CO₂ consumption rates.     

A study of erosion rates on salt diapir surfaces in the Zagros Mountains, SE Iran

Salt exposures and weathering residuum on several salt diapirs in different geographic/climatic settings were studied. Anhydrite, gypsum, hematite, calcite, dolomite, quartz, and clay minerals are the main constituents of the weathering residuum covering the salt diapirs in various thicknesses. Erosion rates of residuum as well as of rock salt exposures were measured at selected sites for a period of 5 years by plastic pegs as benchmarks. Recorded data were standardized to a horizontal surface and to long-term mean precipitation. For the rock salt exposures the following long-term denudation rates were determined of 30–40 mm a⁻¹ for coastal diapirs and up to 120 mm a⁻¹ for mountain salt diapirs. Long-term mean superficial denudation rate measured on weathering residuum of low thickness reached 3.5 mm a⁻¹ on coastal diapirs. The total denudation rate estimated for the thin residuum is close to 4–7 mm a⁻¹ based on apparent correlation with the uplift rate on Hormoz and Namakdan diapirs. Denudation of rock salt exposures is much faster compared to parts of diapirs covered by weathering residuum. The extent of salt exposures is an important factor in the morphological evolution of salt diapirs as it can inhibit further expansion of the diapir. Salt exposures produce huge amounts of dissolved and clastic load, thus affecting the surrounding of the diapir.     

Mining Thick Coal Seams Under Thin Bedrock–Deformation and Failure of Overlying Strata and Alluvium

In underground coal mines, the failure of overlying strata can have disastrous effects where the working face is overlain by thin bedrock covered with thick alluvium. Roof failure under these conditions can cause a massive water and sand inrush. This paper presents a case study for a design to prevent such disasters in the Baodian mine, China. First, the engineering geological and hydrogeological conditions of the overlying lithified strata and the alluvium were obtained from field and laboratory studies. Numerical models were then built with different bedrock thicknesses using distinct-element modelling software. The deformation, failure, and subsidence of the overlying strata during simulated coal mining were studied using these computer models. Finally, the results of the model studies were combined with the geological data to design a reasonable layout for the longwall panel to be mined in the Baodian mine. Initial results showed that the alluvium was somewhat impervious and water-poor. The models showed that the first caving and weighting intervals of the roof decreased with decreasing bedrock thickness, and decreasing bedrock thickness also increased maximum subsidence of the alluvium. The maximum height of the caving zone and the minimum height of the sand-prevention coal and rock pillars were 34 m and 46 m, respectively. Knowing this allowed a somewhat shorter (204 m) but safe working face to be designed. This research provides a good background for the design of safe mines under similar conditions.     

Sr isotopic signature of the Ganga Alluvial Plain and its implication to Sr flux of the Ganga River System

The influx of Sr responsible for increase in marine Sr has been attributed to rise of Himalaya and weathering of the Himalayan rocks. The rivers draining Himalaya to the ocean by the northern part of the Indian sub-continent comprising the Ganga Alluvial Plain (GAP) along with Central parts of the Himalaya and the northern part of the Indian Craton are held responsible for the transformation of Sr isotopic signature. The GAP is basically formed by the Himalayan-derived sediments and serves as transient zone between the source (Himalaya) and the sink (Bay of Bengal). The Gomati River, an important alluvial tributary of the Ganga River, draining nearly 30,500 km² area of GAP is the only river which is originating from the GAP. The river recycles the Himalayan-derived sediments and transport its weathering products into the Ganga River and finally to Bay of Bengal. 11 water samples were collected from the Gomati River and its intrabasinal lakes for measurement of Sr isotopic composition. Sr concentration of Gomati River water is about 335 μg/l, which is about five times higher than the world’s average of river water (70 μg/l) and nearly three times higher than the Ganga River water in the Himalaya (130 μg/l) The Sr isotopic ratios reported are also higher than global average runoff (0.7119) and to modern seawater (0.7092) values. Strong geochemical sediment–water interaction appearing on surface is responsible for the dissolved Sr isotopic ratios in the River water. Higher Sr isotopic rations found during post-monsoon than in pre-monsoon season indicate the importance of fluxes due to monsoonal erosion of the GAP into the Gomati River. Monsoon precipitation and its interaction with alluvium appear to be major vehicle for the addition of dissolved Sr load into the alluvial plain rivers. This study establishes that elevated ⁸⁷Sr/⁸⁶Sr ratios of the Gomati River are due to input of chemical weathering of alluvial material present in the Ganga Alluvial Plain.     

The Bhuj, India, earthquake: lessons learned for earthquake safety of dams on alluvium

The Bhuj, India, earthquake of 26 January 2001, M_s 7.9, caused dams built on alluvium to sustain damage ranging from cosmetic to severe. Major damage was caused almost entirely by soil liquefaction in the alluvium. The critical factor was the level of earthquake ground motion.

The Bhuj earthquake showed that peak horizontal accelerations (PHAs)≤0.2 g were generally safe. PHAs>0.2 g were hazardous, when unconsolidated granular foundation soils were water saturated. N values of <20 are indicative of susceptibility to soil liquefaction. The Bhuj experience showed that alluvial foundation soils, subject to a PHA>0.2 g, must be evaluated over the full area beneath a new dam and all soils deemed susceptible to liquefaction must be either removed or treated. For remediating an old dam, reliable options are removal and replacement of liquefiable alluvium beneath upstream and downstream portions of the dam, combined with building berms designed to provide stability for the dam should there be a strength loss in soils beneath the dam.