Abhey Ram Bansal

Wavelet and rescaled range approach for the Hurst coefficient for short and long time series

The calculation of Hurst coefficient (H) by different techniques is sensitive to the length of the profile and noise. Synthetic fractional Brownian motions with different values of H have been generated and the effectiveness of the techniques has been tested on these time series. H values are calculated by wavelet transform (WT), power spectrum (PS), roughness length (RL), semi-variogram (SV), and rescaled range (R/S) methods. On the basis of the error estimates two methods: R/S analysis and WT are suggested for calculation of H for short/long datasets. Further, WT method is applied to geophysical data of the Bay of Bengal. The gravity, magnetic and bathymetry data indicate the self-affine nature with H=0.8, 0.8 and 0.9, respectively.

Depth Estimation from the Scaling Power Spectral Density of Nonstationary Gravity Profile

Abstract— A technique to estimate the depth to anomalous sources from the scaling power spectra of long nonstationary gravity profiles is presented. The nonstationary profile is divided into piecewise stationary segments based on the criterion of optimum gate length in which the time-varying and time-invariant autocorrelation functions are similar. The division of a nonstationary into piecewise stationary allows identification of the portion of the crust with different geological histories, and using the stationary portion of the gravity profiles, more consistent depths to the anomalous sources have been obtained. The technique is tested with the synthetic gravity profile and applied along the Jaipur-Raipur geotransect in western and central India. The geotransect has been divided into four stationary parts: Vindhyan low, Bundelkhand low, Narmada rift and Chhattisgarh basin; each section corresponding to a different geological formation. Forward modeling of gravity data using results of each stationary section is carried out to propose the subsurface structure along the Jaipur-Raipur transect.

Gravity evidence for mid crustal domal structure below Delhi fold belt and Bhilwara super group of western India

A scheme to interpret nonstationary gravity profile is proposed in two steps (1) divide the entire nonstationary gravity profile into piecewise stationary sub-profiles, and (2) apply the scaling power spectral analysis to each sub-profile. The scheme is applied to gravity data along a well studied Nagaur- Jhalawar transect in western India. The profile has been subdivided into three sub-profiles; each sub-profile corresponds to a geological unit. Gravity data delineated a 2-D mid crustal domal structure below the Delhi fold belt and Bhilwara super group. Further, forward gravity modelling is carried out to model the subsurface along the entire profile.

No evidence of unusually large postseismic deformation in Andaman region immediately after 2004 Sumatra-Andaman earthquake

[1] Static offsets due to the 26 December 2004 Sumatra-Andaman earthquake have been reported from the campaign mode GPS measurements in the Andaman-Nicobar region. However, these measurements contain contributions from postseismic deformation that must have occurred in the 16-25 days period between the earthquake and the measurements. We analyse these and tide gauge measurements of coseismic deformation, a longer time series of postseismic deformation from GPS measurements at Port Blair in the South Andaman and aftershocks, to suggest that postseismic displacement not larger than 7 cm occurred in the 16-25 days following the earthquake in the South Andaman and probably elsewhere in the Andaman Nicobar region. Earlier, this contribution was estimated to be as large as 1 m in the Andaman region, which implied that the magnitude of the earthquake based on these campaign mode measurements should be decreased. We suggest an Mw for this earthquake as 9.23.

Isolated Regions of Remote Triggering in South/Southeast Asia Following the 2012 Mw 8.6 Indian Ocean Earthquake

Large earthquakes are capable of triggering either shallow earthquakes or deep tectonic tremors at long-range distances. So far most of remotely triggered tremors were found along major plate boundary faults around the Pacific Rim. Here we conduct a systematic search for remotely triggered earthquakes and tremors in South/Southeast Asia following the April 11, 2012 Mw 8.6 Indian Ocean Earthquake. We find additional evidence of triggered tectonic tremors beneath the Java Island and the Molucca Island in Eastern Indonesia and triggered earthquakes in Vietnam. Tremors mostly occurred during the large-amplitude Rayleigh waves of the Indian Ocean mainshock, and were also triggered by several other large distant earthquakes. Although we are unable to locate them, they were recorded at stations close to major tectonic faults, suggesting that they are likely of tectonic origin. However, we find no evidence of triggered tremor/earthquakes along the Sumatra subduction zone and eastern portion of Himalaya frontal thrusts, indicating that remote triggering was not as widespread as previously thought.