Aftershock activity of Bhuj earthquake of january 26th, 2001     

Ashwani Kumar  S. C. Gupta  A. K. Jindal  Sanjay Jain  Vandana 《Journal of Earth System Science》2003,112(3):391-395

Following a large-sized Bhuj earthquake (M _s = 7.6) of January 26th, 2001, a small aperture 4-station temporary local network was deployed, in the epicentral area, for a period of about three weeks and resulted in the recording of more than 1800 aftershocks (-0.07 ≤M _L <5.0). Preliminary locations of epicenters of 297 aftershocks (2.0 ≤M _L <5.0) have brought out a dense cluster of aftershock activity, the center of which falls 20 km NW of Bhachau. Epicentral locations of after-shocks encompass a surface area of about 50 × 40 km² that seems to indicate the surface projection of the rupture area associated with the earthquake. The distribution of aftershock activity above magnitude 3, shows that aftershocks are nonuniformly distributed and are aligned in the north, northwest and northeast directions. The epicenter of the mainshock falls on the southern edge of the delineated zone of aftershock activity and the maximum clustering of activity occurs in close proximity of the mainshock. Well-constrained focal depths of 122 aftershocks show that 89% of the aftershocks occurred at depths ranging between 6 and 25 km and only 7% and 4% aftershocks occur at depths less than 5 and more than 25 km respectively. The Gutenberg-Richter (GR) relationship, logN = 4.52 - 0.89M_L, is fitted to the aftershock data (1.0<-M _L<5.0) and theb-value of 0.89 has been estimated for the aftershock activity.  相似文献   

Hidden melting signatures recorded in the Troodos ophiolite plutonic suite: evidence for widespread generation of depleted melts and intra-crustal melt aggregation     

L. Coogan  G. Banks  K. Gillis  C. MacLeod  J. Pearce 《Contributions to Mineralogy and Petrology》2003,144(4):484-506

The main plutonic complex of the Troodos ophiolite, north of the Arakapas Fault Zone, has been re-examined both from field and geochemical perspectives. Ion microprobe analyses of clinopyroxene crystal cores show that the range of melt compositions added to the lower crust far exceeds that of published lavas in the main Troodos massif. This suggests that the lower crust acted as a filter into which a large range of melt compositions were added and out of which a homogenised (and generally fractionated) derivative was extracted. This crustal-level aggregation homogenised diverse melt fractions from a broad range of degrees of melting. Depleted melts with U-shaped rare earth element (REE) patterns were a significant component of the melts added to the crust, but because of their low incompatible element abundances, mixing with less depleted melts prior to eruption masked their signature in the lavas. The discovery that highly depleted melts constituted a significant component of the melts added to the Troodos crust, but not of the lavas, demonstrates that the spatial distribution of lava-types is not necessarily a good indicator of where different parental melt compositions are generated within the mantle. Compared with normal mid-ocean ridge basalts, the Troodos parental melts were (1) generally depleted in immobile incompatible trace elements, (2) less depleted in light REE (LREE) than would be expected for the concomitant depletion in middle and heavy REE, (3) enriched in Sr with respect to the LREE and (4) more oxidised. Modelling of these characteristics suggests a mantle source that had previously lost a significant melt fraction under relatively reducing conditions. This was followed by remelting under more oxidising conditions in an environment in which Sr and LREE were added to the source consistent with previous models of a supra-subduction zone setting.  相似文献   

July 2003     

A. K. Dixon  T. J. Vogl 《Environmental Geology》2003,44(4):497-500

  相似文献   

Observed daily large-scale rainfall patterns during BOBMEX-1999     

A. K. Mitra  M. Das Gupta  R. K. Paliwal  S. V. Singh 《Journal of Earth System Science》2003,112(2):223-232

A daily rainfall dataset and the corresponding rainfall maps have been produced by objective analysis of rainfall data. The satellite estimate of rainfall and the raingauge values are merged to form the final analysis. Associated with epochs of monsoon these rainfall maps are able to show the rainfall activities over India and the Bay of Bengal region during the BOBMEX period. The intra-seasonal variations of rainfall during BOBMEX are also seen using these data. This dataset over the oceanic region compares well with other available popular datasets like GPCP and CMAP. Over land this dataset brings out the features of monsoon in more detail due to the availability of more local raingauge stations.  相似文献   

The subsystem of open clusters in the post-hipparcos era: Cluster structural parameters and proper motions     

N. V. Kharchenko  L. K. Pakulyak  A. E. Piskunov 《Astronomy Reports》2003,47(4):263-275

The wide neighborhoods of 401 open clusters are analyzed using the modern, high-precision, homogeneous ASCC-2.5 all-sky catalog. More than 28000 possible cluster members (including about 12500 most probable members) are identified using kinematic and photometric criteria. Star counts with the ASCC-2.5 and USNO-A2.0 catalogs are used to determine the angular and linear radii of the cluster cores and coronas, which exceed the previously published values by factors of two to three. The segregation (differing central concentration) of member stars by magnitude is observed. The mean proper motions are determined directly in the Hipparcos system for 401 clusters, for 183 of them for the first time. The heliocentric distances of 118 clusters are determined for the first time based on color-magnitude diagrams for their identified members.  相似文献   

The chemically distinct nucleus and structure of the S0 galaxy NGC 80     

O. K. Sil’chenko  S. E. Koposov  V. V. Vlasyuk  O. I. Spiridonova 《Astronomy Reports》2003,47(2):88-98

The giant lenticular galaxy NGC 80, which is the brightest member of a rich group, possesses a central evolutionarily-distinct region: the stars in the nucleus and in a circumnuclear ring of radius 5″t–7″ have a mean age of only 7 Gyr, whereas the stellar population of the bulge is older than 10 Gyr. The nucleus of NGC 80 is also chemically distinct: it is a factor of 2–2.5 richer in metals than its immediate neighborhood and is characterized by a high magnesium-to-iron abundance ratio [Mg/Fe]≈+0.3. The global stellar disk of NGC 80 has a two-tiered structure: its outer part has an exponential scale length of 11 kpc and normal surface density, while the inner disk, which is also exponential and axisymmetric, is more compact and brighter. Although the two-tiered structure and the chemically distinct nucleus obviously have a common origin and owe their existence to some catastrophic restructuring of the protogalactic gaseous disk, the origin of this remains unclear, since the galaxy lacks any manifestations of perturbed morphology or triaxiality.  相似文献   

Impact of Sea-level Rise and Storm Surges on a Coastal Community   总被引：7，自引：7，他引：7  

K. L. Mcinnes  K. J. E. Walsh  G. D. Hubbert  T. Beer 《Natural Hazards》2003,30(2):187-207

A technique to evaluate the risk of storm tides (the combination of a storm surge and tide) under present and enhanced greenhouse conditions has been applied to Cairns on the north-eastern Australian coast. The technique combines a statistical model for cyclone occurrence with a state-of-the-art storm surge inundation model and involves the random generation of a large number of storm tide simulations. The set of simulations constitutes a synthetic record of extreme sea-level events that can be analysed to produce storm tide return periods. The use of a dynamic storm surge model with overland flooding capability means that the spatial extent of flooding is also implicitly modelled. The technique has the advantage that it can readily be modified to include projected changes to cyclone behaviour due to the enhanced greenhouse effect. Sea-level heights in the current climate for return periods of 50, 100, 500 and 1000 years have been determined to be 2.0 m, 2.3 m, 3.0 m and 3.4 m respectively. In an enhanced greenhouse climate (around 2050), projected increases in cyclone intensity and mean sea-level see these heights increase to 2.4 m, 2.8 m, 3.8 m and 4.2 m respectively. The average area inundated by events with a return period greater than 100 years is found to more than double under enhanced greenhouse conditions.  相似文献   

Impact of horizontal resolution on prediction of tropical cyclones over Bay of Bengal using a regional weather prediction model     

M. Mandal  U. C. Mohanty  K. V. J. Potty  A. Sarkar 《Journal of Earth System Science》2003,112(1):79-93

The present study is carried out to examine the performance of a regional atmospheric model in forecasting tropical cyclones over the Bay of Bengal and its sensitivity to horizontal resolution. Two cyclones, which formed over the Bay of Bengal during the years 1995 and 1997, are simulated using a regional weather prediction model with two horizontal resolutions of 165 km and 55 km. The model is found to perform reasonably well towards simulation of the storms. The structure, intensity and track of the cyclones are found to be better simulated by finer resolution of the model as compared to the coarse resolution. Rainfall amount and its distribution are also found to be sensitive to the model horizontal resolution. Other important fields, viz., vertical velocity, horizontal divergence and horizontal moisture flux are also found to be sensitive to model horizontal resolution and are better simulated by the model with finer horizontal grids.  相似文献   

Mercury-bearing black shales and human Hg intake in eastern Finland: impact and mechanisms   总被引：1，自引：0，他引：1  

K. Loukola-Ruskeeniemi  M. Kantola  T. Halonen  K. Seppänen  P. Henttonen  E. Kallio  P. Kurki  H. Savolainen 《Environmental Geology》2003,43(3):283-297

  相似文献   

Flood Management in India     

Mohapatra  P. K.  Singh  R. D. 《Natural Hazards》2003,28(1):131-143

In this paper, flood problems in India, regional variabilityof the problem, present status of the ongoing management measures, their effectiveness and futureneeds in flood management are covered. Flood problems in India are presented by four zonesof flooding, viz. (a) Brahmaputra River Basin, (b) Ganga River Basin, (c) North-WestRivers Basin, and (d) Central India and Deccan Rivers Basin. Some special problems,related to floods like dam break flow, and water logging in Tal areas, are also mentioned.Progress of various flood management measures, both structural and non-structural, arediscussed. In addition, future needs to achieve efficient and successful flood managementmeasures in India are also pointed out.  相似文献