Multifractal Analysis of Earthquakes in the Southeastern Iran-Bam Region

Earthquakes in Iran and neighbouring regions are closely connected to their position within the geologically active Alpine-Himalayan belt. Modern tectonic activity is forced by the convergent movements between two plates: The Arabian plate, including Saudi Arabia, the Persian Gulf and the Zagros Ranges of Iran, and the Eurasian plate. The intensive seismic activity in this region is recorded with shallow focal depth and magnitude rising as high as M_w = 7.8. The study region can be attributed to a highly complex geodynamic process and therefore is well suited for multifractal seismicity analysis. Multifractal analysis of earthquakes (m_b ≥ 3) occurring during 1973 – 2006 led to the detection of a clustering pattern in the narrow time span prior to all the large earthquakes: M_w = 7.8 on 16.9.1978; M_w = 6.8 on 26.12.2003; M_w = 7.7 on 10.5.97. Based on the spatio-temporal clustering pattern of events, the potential for future large events can be assessed. Spatio-temporal clustering of events apparently indicates a highly stressed region, an asperity or weak zone from which the rupture propagation eventually nucleates, causing large earthquakes. This clustering pattern analysis done on a well-constrained catalogue for most of the fault systems of known seismicity may eventually aid in the preparedness and earthquake disaster mitigation.     

Framboidal — colloform — recrystallised pyrite in the granitoids of Wahkyn area,West Khasi hills,Meghalaya

Petrographic studies of Proterozoic pyriteferous granitoids forming basement for upper cretaceous Mahadek sediments from Wahkyn area reveal interesting textural peculiarities of Pyrite. These pyrites also reveal interesting structural peculiarities. The three textural pyrite varieties found in the granitoids are: framboidal, colloform and recrystallised which appear both as composite aggregate as well as independent units. Various textures and variation in reflectivity, microhardness and elemental distribution of the pyrites are described. Average Co/Ni ratio along with the textural manifestation of these pyrites attests their sedimentary origin.     

The Himalayan foreland basin crust and upper mantle

Modeling of multimode surface wave group velocity dispersion data sampling the eastern and the western Ganga basins, reveals a three layer crust with an average V_s of 3.7 km s^?1, draped by ～2.5 km foreland sediments. The Moho is at a depth of 43 ± 2 km and 41 ± 2 km beneath the eastern and the western Ganga basins respectively. Crustal V_p/V_s shows a felsic upper and middle crust beneath the eastern Ganga basin (1.70) compared to a more mafic western Ganga basin crust (1.77). Due to higher radiogenic heat production in felsic than mafic rocks, a lateral thermal heterogeneity will be present in the foreland basin crust. This heterogeneity had been previously observed in the north Indian Shield immediately south of the foreland basin and must also continue northward below the Himalaya. The high heat producing felsic crust, underthrust below the Himalayas could be an important cause for melting of midcrustal rocks and emplacement of leucogranites. This is a plausible explanation for abundance of leucogranites in the east-central Himalaya compared to the west. The uppermost mantle V_s is also significantly lower beneath the eastern Ganga basin (4.30 km s^?1) compared to the west (4.44 km s^?1).     

Fluoride occurrence and mobilization in geo-environment of semi-arid Granite watershed in southern peninsular India

Plausible forms of fluoride (F) responsible for the persistence of fluoride toxicity in ground water of a granitic terrain of semi-arid region, which is the main source of drinking water, have been studied. The study area in Anantapur District of Andhra Pradesh, India, is one of the chronic regions with excess fluoride in groundwater and the region is under transformation into aridity due to poor rainfall and over-exploitation of groundwater. Geochemical analysis of soil, groundwater, and rock samples of the study area revealed the presence of other toxic elements also in addition to fluoride which need to be addressed in drinking water sector in near future. Soil fluoride leaching experiments demonstrated the probable mode of mobilization of F into the groundwater through natural recharge process during monsoon. Analysis of saturation indices indicates that the fluorite solubility alone is not attributable to the high fluoride content in groundwater. The groundwater flow controls fluoride mobilization in the study area as it is evidenced through fluoride concentration and electrical conductivity increase from catchment to downstream region. Creation of lesser fluoride groundwater sources through rainwater harvesting and artificial recharge of groundwater in catchment areas is suggested as a long-term sustainable safe drinking water strategy.