A robust satellite technique for monitoring seismically active areas: The case of Bhuj–Gujarat earthquake

A robust satellite data analysis technique (RAT) has been recently proposed as a suitable tool for satellite TIR surveys in seismically active regions and already successfully tested in different cases of earthquakes (both high and medium–low magnitudes).In this paper, the efficiency and the potentialities of the RAT technique have been tested even when it is applied to a wide area with extremely variable topography, land coverage and climatic characteristics (the whole Indian subcontinent). Bhuj–Gujarat's earthquake (occurred on 26th January 2001, M_S  7.9) has been considered as a test case in the validation phase, while a relatively unperturbed period (no earthquakes with M_S ≥ 5, in the same region and in the same period) has been analyzed for confutation purposes. To this aim, 6 years of Meteosat-5 TIR observations have been processed for the characterization of the TIR signal behaviour at each specific observation time and location.The anomalous TIR values, detected by RAT, have been evaluated in terms of time–space persistence in order to establish the existence of actually significant anomalous transients. The results indicate that the studied area was affected by significant positive thermal anomalies which were identified, at different intensity levels, not far from the Gujarat coast (since 15th January, but with a clearer evidence on 22nd January) and near the epicentral area (mainly on 21st January). On 25th January (1 day before Gujarat's earthquake) significant TIR anomalies appear on the Northern Indian subcontinent, showing a remarkable coincidence with the principal tectonic lineaments of the region (thrust Himalayan boundary).On the other hand, the results of the confutation analysis indicate that no meaningful TIR anomalies appear in the absence of seismic events with M_S ≥ 5.     

Hydrological regime of the Rhône Delta and dynamics of its coastline

Specific features of the hydrological regime of the Rhône River and the nearshore zone of its mouth are discussed. The processes of seawater intrusion into the delta branches are described. The information on the history of the delta evolution and development is presented along with the reconstruction of the Holocene evolution of the Rhône Delta and analysis of formation peculiarities of the present-day delta. Channel processes in the Rhône Delta and the dynamics of the delta coastline are described; characteristics of the deep-water fan are discussed, and the data on sediment balance are given.     

Compression studies of gibbsite and its high-pressure polymorph

Various X-ray diffraction methods have been applied to study the compression behavior of gibbsite, Al(OH)₃, in diamond cells at room temperature. A phase transformation was found to take place above 3 GPa where gibbsite started to convert to its high-pressure polymorph. The high-pressure (HP) phase is quenchable and coexists with gibbsite at the ambient conditions after being unloaded. This HP phase was identified as nordstrandite based on the diffraction patterns obtained at room pressure by angle dispersive and energy dispersive methods. On the basis of this structural interpretation, the bulk modulus of the two polymorphs, i.e., gibbsite and nordstrandite, could be determined as 85 ± 5 and 70 ± 5 GPa, respectively, by fitting a Birch-Murnaghan equation to the compression data, assuming their K_o ^′ as 4. Molar volume cross-over occurs at 2 GPa, above which the molar volume of nordstrandite is smaller than that of gibbsite. The differences in the molar volume and structure between the two polymorphs are not significant, which accounts for the irreversibility of the phase transition. In gibbsite, the axial compressibility behaves as c/c _o > a/a _o > b/b _o. This is due to the fact that the dioctahedral sheets along the c-axis are held by the relatively weak hydrogen bonding, which results in the greater compressibility along this direction. In nord- strandite, the axial compressibility is b/b _o > c/c _o > a/a _o, which can also be interpreted as resulting from the the existence of hydrogen bonds along the b-axis. Received: 28 September 1998 / Revised, accepted: 22 December 1998     

A note on estimating the vertical eddy diffusion coefficient from LANDSAT imagery

Boundary-Layer Meteorology - The vertical eddy diffusion coefficient (K z) for five smoke plumes entrapped in a stable marine layer is estimated from the published LANDSAT imagery data sets of...     

Weak Contrast PP Wave Displacement R/T Coefficients in Weakly Anisotropic Elastic Media

—Approximate PP plane wave displacement coefficients of reflection and transmission for weak contrast interfaces separating weakly but arbitrarily anisotropic elastic media are presented. The PP reflection coefficient for such an interface has been derived recently by Vavry?uk and P?en?ík (1997). The PP transmission coefficient presented in this paper was derived by the same approach. The coefficients are given as a sum of the coefficient for the weak contrast interface separating two nearby isotropic media and a term depending linearly on contrasts of the so-called weak anisotropy (WA) parameters (parameters specifying deviation of properties of the medium from isotropy), across the interface. While the reflection coefficient depends only on 8 of the complete set of the WA parameters describing P-wave phase velocity in weakly anisotropic media, the transmission coefficient depends on their complete set. The PP reflection coefficient depends on "shear-wave splitting parameter" γ. Tests of accuracy of the approximate formulae are presented on several models.     

Ge-bearing coals of the Luzanovka Graben, Pavlovka brown coal deposit, southern Primorye

Results of the study of a new Ge-bearing area of the Pavlovka brown coal deposit are presented. Ge is accumulated in bed III₂ lying at the bottom of the Late Paleogene-Early Neogene coal-bearing sequence adjacent to the Middle Paleozoic granite basement. The Ge content in coals and coal-bearing rocks varies in different sections from 10 to 200–250 ppm, reaching up to 500–600 ppm in the highest-grade lower part of the bed. The metalliferous area reveals a geochemical zoning: complex Ge-Mo-W anomalies subsequently grades along the depth and strike into Mo-W and W anomalies. Orebodies, like those at many Ge-bearing coal deposits, are concentric in plan and dome-shaped in cross-section. Coals in their central parts, in addition to Ge, W, and Mo, are enriched in U, As, Be, Ag, and Au. Distribution of Ge and other trace elements in the metalliferous sequence and products of gravity separation of Ge-bearing coals is studied. These data indicate that most elements (W, Mo, U, As, Be) concentrated like Ge in the Ge-bearing bed relative to background values are restricted to the organic matter of coals. The electron microscopic study shows that Ge-bearing coals contain native metals and intermetallic compounds in association with carbonates, sulfides, and halogenides. Coal inclusions in the metalliferous and barren areas of the molasse section strongly differ in contents of Ge and associated trace elements. Ge was accumulated in the coals in the course of the interaction of ascending metalliferous solutions with organic matter of the buried peat bogs in Late Miocene. The solutions were presumably represented by N₂-bearing thermal waters (contaminated by volcanogenic CO₂) that are typical of granite terranes.     

A soil chronosequence in Late Glacial and Neoglacial moraines, Humboldt Glacier, northwestern Venezuelan Andes

Late Glacial and Neoglacial (Little Ice Age) deposits on the Humboldt Massif were analyzed for relative-age dating parameters, including geomorphic and weathering characteristics, geochemical and soil properties. The soil chronosequence, formed in chemically uniform parent materials, provides an important database to study soil evolution in a tropical alpine environment. Extractable and total Fe and Al concentrations, examined to assess their use in relative-age determination, and as paleoenvironmental indicators, provide an important measure of the accumulation and downward profile movement over time of organically-bound Al, ferrihydrite and other crystalline forms (hematite and goethite) of extractable Fe. Ferrihydrite is particularly useful in determining former perched water levels in soils with relation to paleoclimate. The ratios of most Fe extracts are time dependent. The Fe_d/Fe_t ratio, within statistical limits, shows a slow increase from LIA (Little Ice Age) to Late Glacial soils, which closely correlates with other alpine soil studies in the middle latitudes and other tropical alpine locales. Values of Al_d (dithionite) and Al_o (oxalate extractable) generally do not correlate with time; however, Al_p (pyrophosphate extractable) measured against Al_t (total) provides insight on the downward translocation over time of organically-bound Al. Low leaching rates in this chronosequence are further supported by clay mineralogy trends and the geochemical data.     

An integrated approach to investigate saline water intrusion and to identify the salinity sources in the Central Godavari delta, Andhra Pradesh, India

The Central Godavari delta is located along the Bay of Bengal Coast, Andhra Pradesh, India, and is drained by Pikaleru, Kunavaram and Vasalatippa drains. There is no groundwater pumping for agriculture as wells as for domestic purpose due to the brackish nature of the groundwater at shallow depths. The groundwater table depths vary from 0.8 to 3.4 m and in the Ravva Onshore wells, 4.5 to 13.3 m. Electrical Resistivity Tomography (ERT) surveys were carried out at several locations in the delta to delineate the aquifer geometry and to identify saline water aquifer zones. Groundwater samples collected and analyzed for major ions for assessing the saline water intrusion and to identify the salinity origin in the delta region. The results derived from ERT indicated low resistivity values in the area, which can be attributed to the existence of thick marine clays from ground surface to 12–15 m below ground level near the coast and high resistivity values are due to the presence of coarse sand with freshwater away from the coast. The resistivity values similar to saline water <0.01 Ω m is attributed to the mixing of the saline water along surface water drains. In the Ravva Onshore Terminal low resistivity values indicated up coning of saline water and mixing of saline water from Pikaleru drain. The SO ₄ ^?2 /Cl^?and Na⁺²/Cl^?ratios did not indicate saline water intrusion and the salinity is due to marine palaeosalinity, dilution of marine clays and dissolution of evaporites.