3-D seismic structure of the source area of the 1993 Latur, India, earthquake and its implications for rupture nucleations

The Latur earthquake (M_w 6.1) of 29 September 1993 is a rare stable continental region (SCR) earthquake that occurred on a previously unknown blind fault. In this study, we determined detailed three-dimensional (3-D) P- and S-wave velocity (V_p, V_s) and Poisson's ratio (σ) structures by inverting the first P- and S-wave high-quality arrival time data from 142 aftershocks that were recorded by a network of temporary seismic stations. The source zone of the Latur earthquake shows strong lateral heterogeneities in V_p, V_s and σ structures, extending in a volume of about 90 × 90 × 15 km³. The mainshock occurred within, but near the boundary, of a low-V_p, high-V_s and low-σ zone. This suggests that the structural asperities at the mainshock hypocenter are associated with a partially fluid-saturated fractured rock in a previously unknown source zone with intersecting fault surfaces. This might have triggered the 1993 Latur mainshock and its aftershock sequence. Our results are in good agreement with other geophysical studies that suggest high conductivity and high concentration of radiogenic helium gas beneath the source zone of the Latur earthquake. Our study provides an additional evidence for the presence of fluid related anomaly at the hidden source zone of the Latur earthquake in the SCR and helps us understand the genesis of damaging earthquakes in the SCR of the world.     

The Tornquist Zone, a north east inclining lithospheric transition at the south western margin of the Baltic Shield: Revealed through a nonlinear teleseismic tomographic inversion

From July 1996 to August 1997 the TOR project operated 130 seismographs in North Germany, Denmark and South Sweden, with the aim of collecting signals from local, regional and teleseismic earthquakes. This data set is particularly interesting since the seismic antenna crosses the most significant geological boundary in Europe, the Tornquist Zone, which in the northern part is the border between the Baltic Shield and the younger European lithosphere. Previous studies have shown significant physical changes in the crust and upper mantle across this transition zone, including two independent teleseismic tomographic studies of the TOR data set. But these two studies disagree on the orientation of the slope of the transition. Both studies used an iterative linearized inversion method. We will in this work Preprint submitted to Elsevier Science 27 July 2005 present an inversion based on Bayesian statistics, where the solution space is examined in order to study a very large number of tomographic solutions and to examine the solution uniqueness and uncertainty. The method is applied to measurements of 3345 relative teleseismic P-phase travel times from 48 teleseismic earthquakes with good azimuthal coverage with respect to the great circle arc of the TOR array. We find the lithospheric transition to be a north east inclination of around 30° to 45° off vertical.     

Seismic potential of Southern Italy

To improve estimates of the long-term average seismic potential of the slowly straining South Central Mediterranean plate boundary zone, we integrate constraints on tectonic style and deformation rates from geodetic and geologic data with the traditional constraints from seismicity catalogs. We express seismic potential (long-term average earthquake recurrence rates as a function of magnitude) in the form of truncated Gutenberg–Richter distributions for seven seismotectonic source zones. Seismic coupling seems to be large or even complete in most zones. An exception is the southern Tyrrhenian thrust zone, where most of the African–European convergence is accommodated. Here aseismic deformation is estimated to range from at least 25% along the western part to almost 100% aseismic slip around the Aeolian Islands. Even so, seismic potential of this zone has previously been significantly underestimated, due to the low levels of recorded past seismicity. By contrast, the series of 19 M6–7 earthquakes that hit Calabria in the 18th and 19th century released tectonic strain rates accumulated over time spans up to several times the catalog duration, and seismic potential is revised downward. The southern Tyrrhenian thrust zone and the extensional Calabrian faults, as well as the northeastern Sicilian transtensional zone between them (which includes the Messina Straits, where a destructive M7 event occurred in 1908), all have a similar seismic potential with minimum recurrence times of M ≥ 6.5 of 150–220 years. This potential is lower than that of the Southern Apennines (M ≥ 6.5 recurring every 60 to 140 years), but higher than that of southeastern Sicily (minimum M ≥ 6.5 recurrence times of 400 years). The high seismicity levels recorded in southeastern Sicily indicate some clustering and are most compatible with a tectonic scenario where the Ionian deforms internally, and motions at the Calabrian Trench are small. The estimated seismic potential for the Calabrian Trench and Central and Western Sicily are the lowest (minimum M ≥ 6.5 recurrence times of 550–800 years). Most zones are probably capable of generating earthquakes up to magnitudes 7–7.5, with the exception of Central and Western Sicily where maximum events sizes most likely do not exceed 7.     

THE INFLUENCE OF FERTILIZERS, NaHCO3,SOIL TYPE ON CHEMISTRY OF FLOODED SOILS AND RICE PLANT GROWTH

1 INTRODUCTIONQuality of chemical properties of flooded soils isgenerally determined by salinity and alkalinity,bothof these acts as inhibiting factors of plant growth.Thecorrelation of electrical conductivity and other analysisindex has been reported by …     

Rock fracturing by explosive energy: review of state-of-the-art

A study of the dynamic rock fracture initiation and propagation due to explosive energy is presented through a detailed state-of-the-art review. Explosive energy dissipation in crushing and fracturing is examined and the various means to enhance the explosive energy utilization for dynamic rock fracturing are reviewed. The study highlights the need for a better understanding of the dynamic fracturing process particularly in the presence of in situ stresses in the rock mass.     

2D Self-Potential tomographies for studying groundwater flows in the Varco d''Izzo landslide (Basilicata, southern Italy)

A geoelectrical monitoring activity has been carried out to improve the geological and hydrogeological knowledge about the Varco d'Izzo landslide (Potenza, Basilicata, Southern Apennine, Italy), an active rotational–translational slide evolved in earth-flow. In this work we have focused on the Self-Potential (SP) method by applying three different SP measuring techniques and combining modern technologies for data acquisition and new methods for tomographic inversion. A SP map and three static SP tomographies have been carried out to better analyse the groundwater circulation system and to better reconstruct the geometry of the landslide body. In the accumulation zone, which is the area more exposed to the geomorphological activity, a new SP measuring strategy has been applied. This strategy, based on time-continuous 2D SP tomographies, helps identify water flow changes in subsurface by studying the time series of SP tomographic images. The analysis of time-dependent changes of water infiltration in near surface is the key to better understand the hydrogeological processes underlying the ground instability phenomena. The time-lapse analysis of tomographic images has allowed us not only to investigate the correlation between the temporal changes of SP signals and rainfall events, but also to quantify the range of these changes. The modification of the distribution of the SP source accumulation zones is associated with the dynamics of the groundwater flows. These preliminary results allow us to consider the SP tomographic method as a tool for geophysical monitoring of landslide areas and encourage to develop new measuring systems for near-real time applications.     

Partial melting and P–T evolution of the Kodaikanal Metapelite Belt, southern India

The Kodaikanal region of the Madurai Block in southern India exposes a segment of high-grade metamorphic rocks dominated by an aluminous garnet–cordierite–spinel–sillimanite–quartz migmatite suite, designated herein as the Kodaikanal Metapelite Belt (KMB). These rocks were subjected to extreme crustal metamorphism during the Late Neoproterozoic despite the lack of diagnostic ultrahigh-temperature assemblages. The rocks preserve microstructural evidence demonstrating initial-heating, dehydration melting to generate the peak metamorphic assemblage and later retrogression of the residual assemblages with remaining melt. The peak metamorphic assemblage is interpreted to be garnet + sillimanite + K-feldspar + spinel + Fe–Ti oxide + quartz + melt, which indicates pressure–temperature (P–T) conditions around 950–1000 °C and 7–8 kbar based on calculated phase diagrams. A clockwise P–T path is proposed by integrating microstructural information with pseudosections. We show that evidence for extreme crustal metamorphism at ultrahigh-temperature conditions can be extracted even in the cases where the rocks lack diagnostic ultrahigh-temperature mineral assemblages. Our approach confirms the widespread regional occurrence of UHT metamorphism in the Madurai Block during Gondwana assembly and point out the need for similar studies on adjacent continental fragments.     

On the Importance of Geolithological Features for the Estimate of the Site Response: The Case of Catania Metropolitan Area (Italy)

The evaluation of seismic site response in the urban area of Catania was tackled by selecting test areas having peculiar lithological and structural features, potentially favourable to large local amplifications of ground motion. The two selected areas are located in the historical downtown and in the northern part of Catania where the presence of a fault is evident. Site response was evaluated using spectral ratio technique taking the horizontal- to-vertical component ratio of ambient noise. Inferences from microtremor measurements are compared with results from synthetic accelerograms and response spectra computed at all drillings available for this area. Such method is particularly suitable in urban areas where the nature of the outcropping geological units is masked by city growth and anthropic intervention on the surface geology. The microtremor H/V spectral ratios evaluated at soft sites located within the downtown profile tend to be smaller than that usually reported in the literature for such soils. A tendency for amplifications to peaks near 2 Hz is observed only in some sites located on recent alluvial deposits. Evidences for amplifications of site effects (frequency range 4–8 Hz) were observed in the sampling sites located on the fault, with a rapid decrease of spectral amplitude just a few tenths of metres away from the discontinuity. Numerical simulations evidenced the importance of geolithological features at depth levels even greater than 20–30 m. Besides this, the results strongly confirm the importance of the subsurface geological conditions, in the estimate of seismic hazard at urban scale.