Landslide susceptibility zonation mapping and its validation in part of Garhwal Lesser Himalaya, India, using binary logistic regression analysis and receiver operating characteristic curve method Abstract A landslide susceptibility zonation (LSZ) map helps to understand the spatial distribution of slope failure probability in an area and hence it is useful for effective landslide hazard mitigation measures. Such maps can be generated using qualitative or quantitative approaches. The present study is an attempt to utilise a multivariate statistical method called binary logistic regression (BLR) analysis for LSZ mapping in part of the Garhwal Lesser Himalaya, India, lying close to the Main Boundary Thrust (MBT). This method gives the freedom to use categorical and continuous predictor variables together in a regression analysis. Geographic Information System has been used for preparing the database on causal factors of slope instability and landslide locations as well as for carrying out the spatial modelling of landslide susceptibility. A forward stepwise logistic regression analysis using maximum likelihood estimation method has been used in the regression. The constant and the coefficients of the predictor variables retained by the regression model have been used to calculate the probability of slope failure for the entire study area. The predictive logistic regression model has been validated by receiver operating characteristic curve analysis, which has given 91.7% accuracy for the developed BLR model.

Long‐period magnetotelluric (MT) data were collected at 15 stations on a 250 km long profile in the northwest Indian Himalaya to study the structure of this continent‐continent collision zone. Two‐dimensional MT inversion was used to find a resistivity model that fit the data. In the upper crust low resistivity was imaged on the limbs of the Tso‐Morari dome and may originate in serpentenization or zones of graphite. The Indus Tsangpo Suture was imaged as a sub‐vertical conductive structure that dips northeast and merges with a mid‐crustal conductor. A north dipping zone of low resistivity is imaged at the top of the underthrust Indian Plate and is likely due to fluids expelled from the underthrust sedimentary rocks. North of the Indus Suture zone this layer is located at 20–25 km depth with a conductance around 3000 S. The resistivity of 5–10 Ωm can be attributed to the presence of fluids, likely partial melt or aqueous fluids. This layer is underlain by a relatively resistive Indian crust that extends from the High Himalaya to north of the Indus suture. A decrease in deep resistivity was observed at the northern end of the profile, and is similar to the structures observed further east in the region of the INDEPTH study, despite the smaller north‐south extent of the orogen in the Indian Himalaya.

No abstract

No abstract

Abstract.A new approach is developed to find the source azimuth of the ultra low frequency (ULF) electromagnetic (EM) signals believed to be emanating from well defined seismic zone. The method is test applied on magnetic data procured from the seismoactive region of Koyna-Warna, known for prolonged reservoir triggered seismicity. Extremely low-noise, high-sensitivity LEMI-30 search coil magnetometers were used to measure simultaneously the vector magnetic field in the frequency range 0.001-32 Hz at two stations, the one located within and another ∼100 km away from the seismic active zone. During the observation campaign extending from 15 March to 30 June 2006 two earthquakes (EQs) of magnitude (M L >4) occurred, which are searched for the presence of precursory EM signals.Comparison of polarization ellipses (PE) parameters formed by the magnetic field components at the measurement stations, in select frequency bands, allows discrimination of seismo-EM signals from the natural background ULF signals of magnetospheric/ionospheric origin. The magnetic field components corresponding to spectral bands dominated by seismo-EM fields define the PE plane which at any instant contains the source of the EM fields. Intersection lines of such defined PE planes for distant observation stations clutter in to the source region. Approximating the magnetic-dipole configuration for the source, the magnetic field components along the intersection lines suggest that azimuth of the EM source align in the NNW-SSE direction. This direction wellCorrespondence to : Gautam Rawat (rawatg@wihg.res.in) coincides with the orientation of nodal plane of normal fault plane mechanism for the two largest EQs recorded during the campaign. More significantly the correspondence of this direction with the tectonic controlled trend in local seismicity, it has been surmised that high pressure fluid flow along the fault that facilitate EQs in the region may also be the source mechanism for EM fields by electrokinetic effect.