排序方式： 共有49条查询结果，搜索用时 15 毫秒
41.
42.
43.
Fuzzy-based method for landslide hazard assessment in active seismic zone of Himalaya 总被引：1，自引：2，他引：1
Landslides in Himalaya cause widespread damage in terms of property and human lives. It the present study, an attempt is made
to derive information on causative parameters and preparation of landslide-susceptible map using fuzzy data integration in
one of the seismically active region of Garhwal Himalaya that was recently devastated by a huge landslide. High-resolution
remotely sensed data products acquired from Indian Remote Sensing Satellite before and after the landslide event were processed
to improve interpretability and derivation of causative parameters. Spatial data sets such as lithology, rock weathering,
geomorphology, lineaments, drainage, land use, anthropogenic factor, soil type and depth, slope gradient, and slope aspect
were integrated using fuzzy gamma operator. The final map was reclassified in to five classes such as highly to lowly susceptible
classes based on cumulative cutoff. The result shows around 72% of known landslide areas including the large Uttarkashi landslide
in the high and very high susceptibility classes comprising of only 37% of the total area. The precipitation data from ground-
and satellite-based observations were compared; the precipitation threshold and the role of seismic activity were analyzed
for initiation of landslide. 相似文献
44.
Northern India is comprised of complex Himalayan mountain ranges having different altitude and orientations. This highly variable terrain is responsible for complexity of the weather systems passing over the region. During winter season, large amount of precipitation is received in this region due to eastward moving low pressure synoptic weather systems called Western Disturbances (WDs). Such heavy precipitation over the region lead to landslides and trigger avalanches in snow bound regions. This causes heavy damage to properties and human lives and therefore poses a great natural hazard threat. In this study an attempt is made to simulate a heavy precipitation event associated with an intense WD using a state of the art mesoscale model. Some important model simulated fields are compared with verifying analysis. Precipitation and circulation features associated with the intense WD are well simulated by the model. Forecast errors indicate that the high resolution mesoscale model could simulate the weather associated with the WD with reasonable accuracy. 相似文献
45.
Use of spectral acceleration data for determination of three-dimensional attenuation structure in the Pithoragarh region of Kumaon Himalaya 总被引：1，自引：0，他引：1
Three-dimensional attenuation structures are related to the subsurface heterogeneities present in the earth crust. An algorithm
for estimation of three-dimensional attenuation structure in the part of Garhwal Himalaya, India has been presented by Joshi
(Curr Sci 90:581–585, 2006b; Nat Hazards 43:129–146, 2007). In continuation of our earlier approach, we have presented a method in which strong motion data have been used to estimate
frequency-dependent three-dimensional attenuation structure of the region. The border district of Pithoragarh in the Higher
Himalaya, India, lies in the central seismic gap region of Himalaya. This region falls in the seismic zones IV and V of the
seismic zoning map of India. A dense network consisting of eight accelerographs has been installed in this region. This network
has recorded several local events. An algorithm based on inversion of strong motion digital data is developed in this paper
to estimate attenuation structure at different frequencies using the data recorded by this network. Twenty strong motion records
observed at five stations have been used to estimate the site amplification factors using inversion algorithm defined in this
paper. Site effects obtained from inversion has been compared with that obtained using Nakamura (1988) and Lermo et al. (Bull Seis Soc Am 83:1574–1594, 1993) approach. The obtained site amplification term has been used for correcting spectral acceleration data at different stations.
The corrected spectral acceleration data have been used as an input to the developed algorithm to avoid effect of near-site
soil amplification term. The attenuation structure is estimated by dividing the entire area in several three-dimensional block
of different frequency-dependent shear wave quality factor Q
β
(f). The input to this algorithm is the spectral acceleration of S phase of the corrected accelerogram. The outcome of the algorithm
is given in terms of attenuation coefficient and source acceleration spectra. In the present study, this region has been divided
into 25 rectangular blocks with thickness of 10 km and surface dimension of 12.5 × 12.1 km, respectively. Present study gives
three-dimensional attenuation model of the region which can be used for both hazard estimation and simulation of strong ground
motion. 相似文献
46.
An endeavor is made to compute peak ground horizontal accelerations at bedrock level in the Delhi region due to the seismogenic sources present around Delhi. The entire area is divided into six seismogenic sources for which seismic hazard analysis is carried out using the complete and extreme part of the seismicity data. Maximum likelihood estimates of hazard parameters viz., seismic activity rate , b value and maximum probable earthquake M
max are made for each zone. The return periods and the probabilities of occurrence of various magnitudes for return periods of 50, 100 and 1000 years are also computed for each zone. The peak ground acceleration (PGA) values for 20% exceedance in 50 years are then computed for the Delhi region from each zone. The maximum PGA value considering all the zones is 0.34 g, which is due to the Mathura fault zone. The seismogenic zones V and VI, i.e., Mathura fault zone and the Sohna fault zone are observed to be contributing maximum PGA values in the Delhi region governing the isoacceleration contours computed for the region. The seismic zonation map for the PGA values at the bedrock level is obtained for the Delhi region. This can be used directly as input for the microzonation of ground motion at the surface by incorporating the local site conditions. 相似文献
47.
— Analysis of the Koyna-Warna earthquake catalog (1968–1996) shows that on an average there is a positive correlation between the b value (decrease) and fractal dimensions (decrease in both D2s and D2t) of earthquake epicenters 0.5 and 2.5 years prior to 1973 (M5.2) and 1980 (M5.5) events, respectively, except a negative correlation for about five years (1988–1993) prior to the 1993/1994 sequence (M5.4). This positive correlation indicates a weaker clustering, or that the epicenters tend to fill the two-dimensional plane. While the origin of the negative correlation seems to be that during periods of large events (low b value), there is strong clustering around the main shock epicenter (high fractal dimension). Interestingly, during the last year (1995–1996) of the studied period both the b value and correlation dimensions rose significantly, suggesting that stress release occurs through increased levels of low magnitude and increasingly scattered seismicity, suggesting an increased risk of larger magnitude events. Incidentally, during 2000 three earthquakes of magnitude M 5.0, one earthquake of M 4.0, 45 earthquakes of magnitude M 3.0–3.9, and several thousand earthquakes of M < 3 have occurred in the region. Thus it can be inferred that at local scales the relationship yields both positive and negative correlation that appears to be controlled by different modes of failure within the active fault complex.Acknowledgement. The authors are grateful to Dr. B.K. Rastogi of NGRI for providing the catalog of Koyna earthquakes and for useful scientific discussions. The comments of Dr. I. G. Main have improved the quality of paper for which we extend to him our sincere thanks. One of the authors (AOM) thanks the Third World Academy of Science and the Council of Scientific and Industrial Research, India for the Postdoctoral Fellowship award under which this work was carried out. 相似文献
48.
The conventional spectral analysis method for interpretation of magnetic data assumes stationary spatial series and a white‐noise source distribution. However, long magnetic profiles may not be stationary in nature and source distributions are not white. Long non‐stationary magnetic profiles can be divided into stationary subprofiles following Wiener filter theory. A least‐squares inverse method is used to calculate the scaling exponents and depth values of magnetic interfaces from the power spectrum. The applicability of this approach is demonstrated on non‐stationary synthetic and field magnetic data collected along the Nagaur–Jhalawar transect, western India. The stationarity of the whole profile and the subprofiles of the synthetic and field data is tested. The variation of the mean and standard deviations of the subprofiles is significantly reduced compared with the whole profile. The depth values found from the synthetic model are in close agreement with the assumed depth values, whereas for the field data these are in close agreement with estimates from seismic, magnetotelluric and gravity data. 相似文献
49.
Western disturbances (WDs) are extratropical synoptic scale weather systems which cause significant precipitation over the Himalayas and surrounding areas during winter (December, January and February, DJF). Three intense WDs, 13–17 January 2002, 05–08 February 2002, and 11–13 February 2002, are chosen as two of the WDs are extensively studied by Hatwar et al. (Curr Sci 88:913–920, 2005) and one independent WD (Indian Meteorological Department, Delhi, Mausam 54(1):346–347, 2003) is considered. Firstly, it is planned to study model sensitivity with these WD cases, which are simulated with different combinations of cloud microphysics, planetary boundary layer and cumulus parameterization schemes in weather research and forecasting model to assess a better suite for the WD simulations. Sensitivity and error analyses carried out with different observations, show that the combination of Eta Ferrier or Eta Grid-scale cloud and precipitation microphysics scheme, Yonsei University scheme and Kain-Fritsch scheme has shown consistently lower error values. Further, the results suggest, that the model simulations of a WD capture the spatial distribution of precipitation, locations of low pressure region and the circulation patterns very well. It is observed that the WD system comprises of low pressure region in the vertical atmospheric column in form of a stationary surface low and a depression in the subtropical westerly jet moving eastwards. Further, the growth of convective cyclonic systems over the steep topographical region of the Himalayas is depicted by the increased positive vorticity and high values of CAPE, alluding to the propensity of WDs to cause orographically forced precipitation. WDs and associated precipitation show varied but significant impacts on the Indian winter climate such as snow cover variation and cold wave or fog conditions along with impact on winter crop production. 相似文献