Local and regional earthquake magnitude calibration of Tabuk analog sub-network, Northwest of Saudi Arabia

AbstractThe Seismic Studies Center at the King Saud University has established a seismic sub-network at the NW of Saudi Arabia in 1985. It was named the Tabuk sub-network, after the city of Tabuk in the area. A data set of 194 earthquakes were selected and their corresponding ML values calculated by the nearest seismic network (ISSN). 137 observations of these earthquakes were gathered from AYN station, 82 observations from BADA station, 162 observations from HQL station and 65 observations from SRFA station. Four steps analytical procedure were carried out as follows: (a) Compilation of data for multi-linear regression, (b) linear regression of the common logarithm of the base 10 of the signal duration (τ), (c) smoothing of the data, and (d) multiple linear regressions of the main variables. The following range of values was incorporated for empirical contestant’s a1, a2, a3. a1 vary from −3.05 to −1.68, a2 vary from 2.17 to 2.61 and a3 (which is the epicentral distance correction) vary from 0.003 to 0.004, while the standard deviations vary from 0.17 to 0.22 and the correlation coefficients vary from 0.943 to 0.970. The empirical constants are determined by stepwise multiple linear regression. The local magnitude was assigned as the dependent variable, while the common logarithm of the signal duration, epicentral distance, and the focal depth were assigned as the independent variables. The reasons of using MD in this sub-network are as follows: (a) it does not require any amplitude calibration; (b) it is not affected by instrument saturation; (c) the often-negligible distance-dependence makes the method applicable and (d) this method has an extensive application, especially in micro-earthquake surveys

Focal Mechanism Analyses of the 1993, 1995 Northern red Sea Sequences Activity

On August 3rd, 1993, a sequence of earthquakes began in the central part of the Gulf of Aqaba, northern Red Sea at the Aragonese Deep. The largest event (MD = 5.5) on August 3rd had an origin time of 12:42:43.22 GMT, a latitude of 28.628° N and longitude 34.644° E. This event was followed by more than 15000 events greater than 2 magnitude with some felt earthquakes. On the same spot, another sequence of earthquakes began late 1995. The largest event (MD = 5.9) on November 22 had an origin time of 04:15:12.30 GMT, a latitude of 28.8° N and longitude 34.7° E. This event was followed by more than 8000 aftershocks (1.5 D° N – 29.3° N and 34.6° E – 34.9° E. Focal mechanism were investigated by using data set obtained from the Seismic Network of the Seismic Studies Center, King Saud University, Riyadh, Saudi Arabia and the National Seismic Network at Institute of Astronomy and Geophysics Researches, King Abdulaziz City for Science and Technology. The data set included P-wave first motions of significant earthquake activity in this sequences mainly. A total of 67 events was selected for focal mechanism analysis. The P-wave data from the surrounding seismic networks were also utilized additionally. The structural picture revealed fi-om the focal mechanism solutions shows that the area in general characterized by strike-slip and dip-slip faulting. The mechanism of the first consistent with left-lateral strike-slip on N-NE trending faults of the Dead Sea Transform System. The second consistent with normal faults that generally trend E-W. The main objective of this work is to study the focal mechanism of the recent Northern Red Sea sequences of August 1993 and November 1995 and to associate these sequences with faulting types that were found before using different methods

Environmental Impact of Landfill on Groundwater, South East of Riyadh, Saudi Arabia

The main objective of this work had been given to the environmental impact of landfill on groundwater. The groundwater in the study area had problems caused by the landfill and the high volumes of sewage water percolating into the groundwater. The existing soil stratigraphy at the landfill consisting of sandy sheet and fractured limestone lead to increasing leachate percolation into the groundwater. The groundwater resources are used mainly for crop irrigation in an agriculture dominated area. The chemical analysis of groundwater indicates that nitrate pollution can be a serious problem affecting groundwater due to the infiltration of leachate in landfill downward to groundwater and the use of nitrogen (N) fertilizers in agriculture. The high concentrations of NO3- and Zn especially in landfill site in groundwater, likely indicate that groundwater is being significantly affected by leachate percolation. The nitrate and Zinc concentrations in groundwater samples in landfill site reach 191 ppm and 1473 ? g/L respectively. The groundwater in the study area is exploited from fractured limestone aquifer belonging to several limestone formations and groundwater of the concerned aquifer exists under unconfined conditions. The groundwater flow direction is from the northwest to the southeast direction. The leachate produced by waste disposal sites contains large amounts of substances which are likely to contaminate groundwater. Chemical analyses were carried out on groundwater samples collected from the neighborhood of landfill yard and spread to southeast direction. The effects of dumping activity on groundwater appeared most clearly as high concentrations of total dissolved solids (TDS), electrical conductivity (EC), total hardness (TH), chloride, nitrates and sulphates. Groundwater samples from the wells situated close to the landfill were found to be more contaminated than that of the wells situated farther away. Keywords: Environmental Impact, Landfill, Groundwater, Saudi Arabi

Hydrogeology and Water Quality of Umm Alradhma Aquifer, Eastern Saudi Arabia

Umm Alradhma limestone aquifer represents the most important aquifers in Saudi Arabia. This aquifer is the largest groundwater reservoir in the Arabian Peninsula. It has high potential of groundwater with average saturated thickness of Umm Alradhma 270 m. the average transmissivity, hydraulic conductivity and effective porosity of Umm Alradhma limestone aquifer are 5800 m2/day, 33 m3/day and 30% respectively. The groundwater of the Umm Alradhma limestone aquifer exists under confined condition in the study area. The productivity of the wells reached 704000 m3/day and provided Riyadh City about 300,000 m3/day. The hydrochemical analyses of 52 groundwater samples representing Umm Alradhma limestone aquifer reveal that the groundwater origin is meteoric. The presence of marine salts in groundwater is attributed to the effective leaching and dissolution processes through the flow path within the aquifer materials (limestone, dolomitic limestone and dolomite). The groundwater salinity of the Umm Alradhma limestone aquifer in the study area ranges between 1195-1429 ppm. This suggests that groundwater of Umm Alradhma limestone aquifer is acceptable for domestic, industrial and agricultural purposes. Keywords: Umm Alradhma aquifer, Hydrogeology, Water Qualit

Migration of local earthquakes in the gulf of aqaba, north red sea

ABSTRACTThe Gulf of Aqabah has been considered one of the most seismically-active regions in the Middle East during the last 15 years; a catalogue of 1,415 earthquakes (duration magnitude Md and gt; 2. 8) during 19851995, compiled by Al-Arifi (1996) and Al-Shaabi (1998), mainly based on data from King Saud University. Seismic Studies Center (SSC), Saudi Arabia, for 28°- 30°N and 30°-36°E, has been used for studying local aftershock migration . Aftershocks migrated northwards about 60 km for the 1993 sequence and about 70 km for the 1995 sequence and also to shallow focal depths (15 km focal depth for 1993 main-shock) . Depths reduced as time elapsed until reaching 2 km for the last strong aftershock (Md=5 . 2) which occurred during the late stage of the sequence . The 1993 main-shock caused a redistribution of stresses to the parallel faults' segment where the largest 1993 aftershock occurred triggering these faults' segment to become an area of stress nucleation and generated the 1995 main-shockRESUMENEl Golfo de Aqabah ha sido considerada una de las regiones con más actividad sísmica del Medio Oriente durante los últimos 15 años . Un catalogo de 1415 terremotos (magnitud de duración Md and gt;2. 8) entre 1985-1995, compilado por Al-Arifi (1996) y Al-Shaabi (1998), basado principalmente en datos de la Universidad King Saud, Centro de Estudios Sísmicos (SSC), Arabia Saudita, para la zona ubicada entre 28°- 30°N y 30°-36°E, ha sido usado para estudiar la migración de replicas locales Las replicas migraron unos 60 km al norte para la secuencia correspondiente al año 1993 y unos 70 km para la secuencia por el año 1995 y también hacia bajas profundidades focales (15km de profundidad focal para el evento principal en el año 1993) . Las profundidades se redujeron con el tiempo hasta alcanzar 2 km para la ultima replica fuerte (Md=5 2) que ocurrió durante la última etapa de la secuencia El principal evento del año 1993 causo una redistribución de los esfuerzos hacia el segmento de las fallas paralelas donde la mayor replica en el año 1993 ocurrió, desencadenando el movimiento de estas fallas para llegar a ser un área de nucleación y generando el principal evento en el año 199

Statistical characterization of the hydrochemical data’s of groundwater in the arid land of Wadi AdDawasir area, Saudi Arabia : A probabilistic assessment

The main purpose of this research is to determine the quality of ground water in Wadi AdDawasir by the assessmentof 12 chemical parameters: pH, EC, Eh, TDS, TH, Ca2+, Cl–, HCO3–, Mg2+, Na+, NO3–, and SO42–. Statistical analyseswere carried out using descriptive statistics, histograms, and normal quantile plots. The SPSS 15 software package(SPSS Inc. 2006) and JMPIN (version 4.0.4) were used as the main statistical software. Many locations withinthe study area show thatf pH, EC, HCO3–and Na+ values exceed permissible limits. The concentration of anions isin the order SO42–>Cl–>HCO3–. Some of the analyzed parameters approach a normal distribution, as both their skewnessand kurtoses are close to zero. However, skewness for some parameters such as Mg2+ and HCO3–is high. Kurtosisfor most of the elements varies from moderate to low. Only pH, HCO3– and SO42– have kurtoses. Both the resultsof cluster tree and geochemical features of variables could be generally classifi ed into three main groups. Group1 is comprised of Na and SO42–. The relationships within this group are strong. Group 2 consisted of Mg2+, NO3–,pH, HCO3–, and Ca2+. The fact that this group has a close relationship with group 1 demonstrates that the increase inthe concentration of some elements could be the same. Group 3 is comprised of TH, Cl–, Eh, and EC.</p

Physico-chemical characteristics of Jharkhand and West Bengal thermal springs along SONATA mega lineament, India

The chemical and isotopic compositions of thermal springs located along the Son–Narmada–Tapti (SONATA) mega lineament in central India have been investigated. The issuing temperatures of the thermal waters vary from 31° to 89°C for the thermal springs and 24° to 25°C for the cold springs. These thermal springs are located on the Archean Chotanagpur Gneissic Complex (CGC) in the eastern part of peninsular India. The thermal springs are mostly alkaline in nature with pH varying from 7.5 to 9.5. Piper diagram suggests that the chemistry of the thermal waters is compatible with the granitic host rocks through which the waters circulate. Mineral saturation index suggests that the thermal waters are saturated with cristobalite and quartz at lower temperatures (less than ∼130 to 150°C), and calcite and forsterite at higher temperatures (∼160° to 250°C). The estimated reservoir temperature based on chemical geothermometers is in the range of 132°–265°C, which favours a medium enthalpy geothermal system. Oxygen isotope fractionation of Bakreswar and Tantloi thermal springs highlights a higher reservoir temperature than estimated by chemical geothermometer. Positive gravity anomalies over Bakreswar and Tantloi areas strongly suggest a basement/mantle upliftment or mafic intrusion which could account for the heat source close to the surface. However, the large negative gravity anomaly depression around the Surajkund and Katkamsandi thermal springs indicates presence of deep seated faults

The feeder system of the Toba supervolcano from the slab to the shallow reservoir

The Toba Caldera has been the site of several large explosive eruptions in the recent geological past, including the world’s largest Pleistocene eruption 74,000 years ago. The major cause of this particular behaviour may be the subduction of the fluid-rich Investigator Fracture Zone directly beneath the continental crust of Sumatra and possible tear of the slab. Here we show a new seismic tomography model, which clearly reveals a complex multilevel plumbing system beneath Toba. Large amounts of volatiles originate in the subducting slab at a depth of ∼150 km, migrate upward and cause active melting in the mantle wedge. The volatile-rich basic magmas accumulate at the base of the crust in a ∼50,000 km3 reservoir. The overheated volatiles continue ascending through the crust and cause melting of the upper crust rocks. This leads to the formation of a shallow crustal reservoir that is directly responsible for the supereruptions

Multivariate statistical analysis of urban soil contamination by heavy metals at selected industrial locations in the Greater Toronto area, Canada

A good understanding of urban soil contamination with metals and the location of pollution sources due to industrialization and urbanization is important for addressing many environmental problems. The results are reported here of an analysis of the metals content in urban soils samples next toindustrial locations in the Greater Toronto Area (GTA) in Ontario, Canada. Theanalyzed metals are Cr, Mn, Fe, Ni, Cu, Zn, and Pb. Multivariate geostatistcalanalysis (correlation matrix, cluster analysis, principal component analysis) is used to estimate soil chemical content variability. The correlation matrix exhibits a positive correlation with Mn, Fe, Cu, Zn, Cd, and Pb. The principal component analysis (PCA) displays two components. The first component explains the major part of the total variance and is loaded heavily with Cr, Mn, Fe, Zn,and Pb, and the sources are industrial activities and traffic flows. The second component is loaded with Ni, and Cd, and the sources could be lithology andtraffic flow. The results of the cluster analysis demonstrate three major clusters: 1) Mn-Zn, 2) Pb-Cd-Cu and Cr, 3) Fe-Ni. The geo-accumulation index and the pollution load index are determined and show the main I geovalues to be in the range of 0-1.67; the values indicate that the soil samples studied for industrial locations in the GTA are slightly to moderately contaminated with Cr, Fe, Cu, Zn, and Cd, and moderately contaminated with Pb,while Ni, and Mn fall in class "0". Regarding the pollution load ingindex (PLI), the lowest values are observed at stations 6, 7, 9, 10, 11, 12,25, 27 and 28, while the highest values are recorded for stations 1, 5, 6, 13,14, 16, 17, 18, 20, 22 and 24, and very high PLI readings are seen for stations 5, 13, 16, 17, 18, 22 and 24. These data confirm that the type of industries, especially metallurgical and chemical related ones, in the study area, in addition to high traffic flows, are the main sources for soil pollution in the GTA