Ajay Paul

CODA Q estimates for Kumaun Himalaya

CodaQ (Qc) estimates for the Kumaun Himalaya region have been obtained in high frequency range. Local earthquakes, recorded by a digital seismic network in the region, which fall in the epicentral distances range of 10 to 80 km and with a local magnitude range of 1.4 to 2.8, have been used. The coda waves of 30 sec window length, filtered at seven frequency bands centered at 1.5, 3, 6, 9, 12, 18 and 24Hz, have been analysed using the single backscattering model. The values ofQc estimates vary from 65 to 283 at 1.5 Hz to 2119 to 3279 at 24.0 Hz which showed thatQc is frequency dependent and its value increases as frequency increases.A frequency-dependentQc relationship,Qc = (92 ± 4.73)f(1.07±.023), is obtained for the region representing the average attenuation characteristics of seismic waves for Kumaun Himalaya region.

Amplification of Seismic Waves in the Central Indo-Gangetic Basin, India

Abstract Although the Indo-Gangetic basin is adjacent to rupture areas of largeHimalayan earthquakes (M ≥6), a quantitative study of the amplification of seismicwaves in the region is still lacking. To obtain a first estimate of the amplification, fortwo years we operated an array of 10 broadband seismographs that crossed the centralIndo-Gangetic basin in a north–south direction. Using earthquake recordings ofshallow earthquakes at soft sites and hard reference sites, we computed standard spec-tralratios( SSR s). SSR satsitesneartheHimalayanfoothills,wherethesedimentthick-ness is ∼4 km, reveal a broadband amplification with a fundamental frequency of0.13 Hz. The amplification at this frequency varies between 20 and 60. The funda-mental frequency increases to the south as the thickness of the sediments decreases,becoming ∼0:8 Hz at the southernmost site. The amplification at the fundamentalfrequencies exceeds 10 at all eight soft sites. Calculations based on reasonable earth-quake source and attenuation models and application of random vibration theorysuggest that peak ground acceleration and peak ground velocity at soft sites nearthe foothills, located 100 km from the epicenter, would be amplified by a factorof2–4and6–12,respectively.All ourresultsassumelinear behaviorofthesediments.Although this assumption would not be valid during intense motions resultingfrom large earthquakes, our results, nevertheless, provide basic building block forincorporating nonlinear behavior.Online Material: Supplementary figures of amplification, spectral ratio, andacceleration spectra.Introduction

Seismicity and reservoir induced crustal motion study around the Tehri Dam, India

The Tehri Dam is located in a seismotectonically active region in the Indian Himalayan belt. This 260.5 m high dam has a live water storage of 2615 × 106 m3 and is capable of generating crustal deformation corresponding to water fluctuation. Filling of the reservoir started in October 2005. Seismic data around the dam between 2000 and 2010 shows that seismicity is corresponding to drawdown levels of the reservoir rather than to higher water levels. GPS data at twelve local benchmarks were collected from 2006 to 2008 during filling and drawdown reservoir levels. The velocity vectors show ground motion to be between ∼0.69–1.50 mm in the different filling-drawdown cycles with reference to the permanent station at Ghuttu. The motion appears to be inwards into the reservoir when the reservoir is filled and outwards when the reservoir is drained. This ground motion corresponds to elastic deformation and rebound due to effect of the oscillating water levels.

Timely Prediction of Tsunami Using under Sea Earthquake Signals

The Honshu, Japan earthquake of 11th March 2011, caused severe hazard in Japan and neighboring countries. It revealed the need and importance of warning system for Tsunami generation to minimize the casualties. Seismograms of the Honshu earthquake event (recorded by broadband seismograms, being operated in the NW Himalaya by Wadia Institute of Himalayan Geology, Dehradun) are used for quick prediction of tsunami. The frequency content of these seismograms is studied and energy content in high frequencies is calculated, which is used to give tsunami warning. It is observed that wavelet coefficients for frequencies greater than 0.33 Hz tsunamigenic earthquakes do not show significant energy in the spectrum. However, significant energy is found in wavelet spectrum of non-tsunamigenic earthquake. In this paper we present the wavelet analysis on the Honshu, Japan earthquake of 11th March, 2011. Some other global tsunamigenic and non-tsunamigenic events are also analyzed for test and comparison purpose of the methodology used.