S-wave velocity profiling from refraction microtremor Rayleigh wave dispersion curves via PSO inversion algorithm

The refraction microtremor method has been increasingly used as an appealing tool for investigating near surface S-wave structure. However, inversion, as a main stage in processing refraction microtremor data, is challenging for most local search methods due to its high nonlinearity. With the development of data optimization approaches, fast and easier techniques can be employed for processing geophysical data. Recently, particle swarm optimization algorithm has been used in many fields of studies. Use of particle swarm optimization in geophysical inverse problems is a relatively recent development which offers many advantages in dealing with the nonlinearity inherent in such applications. In this study, the reliability and efficiency of particle swarm optimization algorithm in the inversion of refraction microtremor data were investigated. A new framework was also proposed for the inversion of refraction microtremor Rayleigh wave dispersion curves. First, particle swarm optimization code in MATLAB was developed; then, in order to evaluate the efficiency and stability of proposed algorithm, two noise-free and two noise-corrupted synthetic datasets were inverted. Finally, particle swarm optimization inversion algorithm in refraction microtremor data was applied for geotechnical assessment in a case study in the area in city of Tabriz in northwest of Iran. The S-wave structure in the study area successfully delineated. Then, for evaluation, the estimated Vs profile was compared with downhole data available around of the considered area. It could be concluded that particle swarm optimization inversion algorithm is a suitable technique for inverting microtremor waves.     

High-resolution shallow seismic and ground penetrating radar investigations revealing the evolution of the Uemachi Fault system, Osaka, Japan

Abstract Ground penetrating radar (GPR) and high‐resolution shallow reflection seismic surveying were carried out to investigate the subsurface geology in and around the Uemachi Fault zone in the Yamato River area, Osaka, Japan. Shallow drilling in the area showed a major displacement event during the middle Pleistocene. The main Uemachi Fault plane could be clearly imaged on the seismic section, except for the most shallow 200 m. Several shallow normal fault planes with less displacement could be detected on both sides of the fault plane. GPR profiles confirmed the presence of several shallow normal faults within the area near the fault zone. These shallow faults could be followed in all of the GPR profiles crossing the fault zone. The integration of seismic section, GPR profiles and drilling data led to a conceptual model that explains the evolution of the Uemachi Fault system. The proposed model suggests the occurrence of several cycles of small vertical displacement along the deep part of the fault plane caused by the regional east–west compressional stress. The ductile nature of the shallow sedimentary cover and the absence of confining pressure in the shallow part allow for a considerable amount of plastic bending before failing in the shallow sedimentary layers. This bending generates stretching force within the shallow sedimentary cover, which in time, along with gravitational force, gives rise to the formation of the swarm of normal faults within the shallow layers near the fault zone. Some of the detected faults extend to a depth of less than 3 m below the ground surface, suggesting that the last tectonic activity along the fault plane may have occurred recently.     

Adaptive boxcar background filtering for real-time GPR utility detection

Ground Penetrating Radar (GPR) investigation tools are increasingly used for real-time detection of underground utilities. Background noise is an annoying problem, because it sometimes masks the reflection from objects of interest. This study introduces an efficient background removal algorithm, which is so simple that it can be incorporated into GPR logging devices. The algorithm is based on the recently published outliers-out algorithm for stacking seismic data. Experiments conducted on both synthetic and field GPR data show that proposed background removal algorithm yields much better results than the commonly used average trace subtraction algorithm in a relatively comparable computational time.     

An Assessment of Flood Forecasting in Bangladesh: The Experience of the 1998 Flood

Floods are among the most costly natural disasters interms of human sufferings and economic losses inBangladesh. Approximately 20% of the countryexperiences normal annual flooding while all thehistorical catastrophic floods inundated more thanfifty percent of the country's total area. The recentflood in 1998 has been found to be more severe thanall previous floods. During the flooding season of1998, the Flood Forecasting and Warning Center (FFWC)of the Bangladesh Water Development Board (BWDB)prepared daily flood bulletin and incorporatedinformation about rainfall, rise/fall of riverwater, flood forecasting for 24 and 48 hr inadvance and warning messages (if any). The FFWCattempted to provide adequate services to the localand national level decision-making process. Theforecasting procedure adapted by the FFWC was based onhydrological information, forecaster's experience, andmodel simulation. This paper primarily examines therole and activities of the FFWC, especially in floodforecasting and warning. Identification of the causesand consequences of 1998 flood is the other pertinentarea of discussion of the paper.Findings of this research revealed that the flood of1998 was caused by heavy downpour in the upstream thatwas drained out through the major rivers inBangladesh. Three major rivers' peak was synchronizedand characterized it as the most prolonged flood inthe history of Bangladesh. It also revealed that,despite various limitations, the flood forecasts ofthe FFWC were reasonably adequate to meet nationaldemand during the crises of 1998.     

Delay in the onset of South Asian summer monsoon induced by local black carbon in an AGCM

The influence of local black carbon (BC) on monthly mean precipitation and the associated circulation in South Asia is investigated. The results show that the amplified shortwave radiative heating rate by BC absorption enhances convective activity near the Himalayas and the southern Tibetan Plateau with increased rainfall anomalies in April and May, which is consistent with previous studies. However, the enhanced vertical motions and the precipitation ultimately lead towards cooling of the lower troposphere especially in May, which is extended till June. This favored negative rainfall responses in June, implying delay in the onset of South Asian summer monsoon rainfalls over Arabian Sea and western parts of the subcontinent. The negative precipitation response is further associated with the prevailing anomalous high pressure and the anticyclonic wind circulations induced by BC. Thus, we present here one different feature associated with BC-induced elevated heat pump-like circulations in South Asia.     

Physico‐Chemical and Bacterial Characteristics of Water Quality in Three Villages West of Lake Nasser,Egypt

The present study aims to investigate physico‐chemical and bacterial characteristics of Nasser Lake water and houses drinking water, as well as fish cultures and its wastewater, in three villages west of Lake Nasser, Egypt. Fifteen representative water samples (Nasser Lake, different drinking water, fish cultures, and wastewater sources) were collected from three villages (Garf Hussein, Bashaier, and Kalabsha) in the west of Lake Nasser. Physico‐chemical, total viable counts, and bacterial qualification of water were achieved. The obtained results indicated that the produced water, supposed to be for domestic use in the three villages, contained all the tested organisms. The investigated water samples of the lake and drinking water in the selected three villages are supposed to be chemically safe according to World Health Organization and to Egyptian standards for drinking water. Water pollution index (WPI) was used in this study and the result concluded that for irrigation canals from the lake to the agriculture site, fish cultures (both concrete and earth pond systems), and drainage canal of fish ponds need to be treated before it is discharged to the lake. It is better to reuse it after treatment for agricultural purposes or recycled it to the fish cultures.     

Analysis of South Asian Monsoons within the Context of Increasing Regional Black Carbon Aerosols

South Asian monsoons were analyzed within the context of increasing emissions of black carbon(BC) aerosols using a global atmospheric general circulation model.The BC aerosols were allowed to increase only over the south Asian domain to analyze the impacts of regional black carbon over the climatological patterns of monsoons.The black carbon significantly absorbed the incoming short wave radiation in the atmosphere,a result that is consistent with previous studies.Pre-monsoon(March-April-May) rainfall showed positive anomalies,particularly for some coastal regions of India.The summer(June-July-August) rainfall anomalies were negative over the northern Himalayas,Myanmar,southern China,and most of the regions below 20°N due to the decrease in temperature gradients induced by the absorption of radiation by BC aerosols.The vertical wind speed anomalies indicated that these regions experienced less convection,which reduces the precipitation efficiency of the monsoon system in South Asia.     

Assessing vulnerability to earthquake hazards through spatial multicriteria analysis of urban areas

Assessing urban vulnerability to natural hazards such as earthquakes can be regarded as an ill-structured problem (i.e. a problem for which there is no unique, identifiable, objectively optimal solution). A review of the literature indicates a number of contrasting definitions of what vulnerability means, as well as numerous conflicting perspectives on what should or should not be included within the broad assessment of vulnerability in cities. This paper reports on the findings from a project in which a GIS methodology has been developed to assess urban vulnerability through a spatial analytical procedure. First, we highlight the deficiencies of current GIS approaches to urban vulnerability analysis and discuss the ill-structured nature of the vulnerability problem. We then propose a working definition for vulnerability assessment in which vulnerability is thought of as a spatial decision problem under the conditions of uncertainty. Next, we present a methodology to incorporate this definition into a GIS framework that combines elements from the techniques of spatial multicriteria analysis and fuzzy logic. The application of this methodology is then illustrated with a case study from Los Angeles County. The results suggest that the proposed methodology may provide a new approach for analyzing vulnerability that can add to our understanding of human/hazards interaction.     

Seasonal flooding in Bangladesh – variability and predictability

At present, Bangladesh has a flood forecasting lead time of only 3 days or so. There is demand for a forecasting lead time of a month to a season. The primary objectives of this paper are to study the variability and predictability of seasonal flooding in Bangladesh, as revealed by large‐scale predictors of the climate across the watersheds. To explore the source of predictability, accessible Bangladesh hydrological indicators are related to large‐scale oceanic variability and to large‐scale atmospheric circulation patterns predicted by general circulation models (GCMs). Correlation analyses between the flood‐affected area (FAA) for July–September and tropical sea‐surface temperature (SST) indicate connections to tropical Pacific and Indian Ocean SSTs, at a short lead time of a month or so. These are related to El Niño–southern oscillation (ENSO). Correlations between the SSTs of the preceding October–December and the July–September FAA are weaker but notable. Forecasts of the FAA using the leading principal components (PCs) of SST were made, which provided good skill with a lead time of a month or so. The streamflows and rainfall observed in Bangladesh have been added to these prediction models. Finally, the SST PCs were replaced with PCs of GCM prediction fields (precipitation). The prediction models at short lead time that were constructed for FAA were of generally similar levels of skill to that for SST. This is encouraging, as it suggests that linkages with SST can be successfully recovered in a physical model of the climate system in Bangladesh. This study concludes that seasonal flood prediction in Bangladesh is possible from the unusually warm or cold SST in parts of the tropics. This predictability can be enhanced with the information achievable from monitoring the downstream streamflows (which are generated mainly from upstream rainfall conditions) in advance of the flooding season. Finally, this study recommends formalizing a regional cooperation among the countries in the principal co‐basin areas of the Ganges–Brahmaputra–Meghna to achieve this goal. Copyright © 2006 John Wiley & Sons, Ltd.     

Geochemistry of lamprophyres associated with uranium mineralization, Southeastern Desert, Egypt

Two brecciated shear zones (NNW-SSE) are found crosscutting cataclastic rocks. The cataclastic rocks (3.0 km2) occupy the core of the granitic pluton and enclose a roof pendant of mafic-ultramafic rocks. The NNW-SSE-extending lamprophyre dykes vary in thickness from 0.5 m to 1 m and up to 800 m long, cutting the cataclastic rocks and are composed mainly of plagioclases, amphiboles, relics of pyroxenes and K-feldspar phenocrysts embedded in fine-grained groundmass. They are characterized as being peraluminous, calc-alkaline in composition (chemical trap) and enriched in calcite, sulfide and P2O5. The lamprophyres were affected by hydrothermal alteration (chlorite-carbonate alteration) while the cataclastic rocks were affected by diagenetic alteration (K-feldspar-albite alteration). Uranium mineralization is the product of hydrothermal events and has been investigated by X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM), involving primary uranium minerals (U3O8) and secondary uranium minerals (uranophane and beta-uranophane, kasolite, torbernite, autonite and meta-autonite) in addition to U- bearing minerals (astrocyanite, betafite and fergusonite). The presence of different mineral parageneses associated with clay minerals indicates that the lamprophyres were subjected to acidic and alkaline mineralizing solutions. Moreover, the U-Zr/U, U-Ce/U values show negative correlations, confirming U-enrichment in both cataclastic rocks and shear zones while the Th-eU/eTh, Th-Zr/Th and Th-Ce/Th values show negative correlations, indicating that the U-bearing solutions are rich in Th in the cataclastic rocks only.