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Source parameters of the small to moderate earthquakes are significant for understanding the dynamic rupture process, the scaling relations of the earthquakes and for assessment of seismic hazard potential of a region. In this study, the source parameters were determined for 58 small to moderate size earthquakes (3.0 ≤ M w  ≤ 5.0) occurred during 2007–2015 in the Garhwal-Kumaun region. The estimated shear wave quality factor (Q β ( f )) values for each station at different frequencies have been applied to eliminate any bias in the determination of source parameters. The Q β ( f ) values have been estimated by using coda wave normalization method in the frequency range 1.5–16 Hz. A frequency-dependent S wave quality factor relation is obtained as Q β ( f ) = (152.9 ± 7) f (0.82±0.005) by fitting a power-law frequency dependence model for the estimated values over the whole study region. The spectral (low-frequency spectral level and corner frequency) and source (static stress drop, seismic moment, apparent stress and radiated energy) parameters are obtained assuming ω −2 source model. The displacement spectra are corrected for estimated frequency-dependent attenuation, site effect using spectral decay parameter “Kappa”. The frequency resolution limit was resolved by quantifying the bias in corner frequencies, stress drop and radiated energy estimates due to finite-bandwidth effect. The data of the region shows shallow focused earthquakes with low stress drop. The estimation of Zúñiga parameter (ε) suggests the partial stress drop mechanism in the region. The observed low stress drop and apparent stress can be explained by partial stress drop and low effective stress model. Presence of subsurface fluid at seismogenic depth certainly manipulates the dynamics of the region. However, the limited event selection may strongly bias the scaling relation even after taking as much as possible precaution in considering effects of finite bandwidth, attenuation and site corrections. Although, the scaling can be improved further with the integration of large dataset of microearthquakes and use of a stable and robust approach. [ABSTRACT FROM AUTHOR]

In the early morning hours of 23 July 2007 at 04 : 32 : 13.5 (IST), a moderate (ML = 4.9, Mw = 5.0) earthquake occurred in the Garhwal Himalaya near Kharsali, about 50 km northwest of the epicentre of the strong (M 6.4) Uttarkashi earthquake of 20 October 1991. Sourced in the upper crust (15 km focal depth), this earthquake was followed by a series of shallow-focused aftershocks of magnitudes ≤ 3.4. Data from the local broadband seismic network were used for understanding the source characterization. The fault plane solutions of the main shock and the biggest aftershock (M 3.4) are almost similar, suggesting that the deformation occurred by reverse faulting with a significant strike-slip component. For the main shock, the trend/plunge of the major and minor principal axes P/T was 166°/1° and 258°/67° respectively. In these solutions one fault plane is dipping to the NE, and the strike of the fault plane coincides with the major tectonic faults as well as the longest axis of isoseismals. The seismic moment, source radius and stress drop of the main shock are estimated to be 4.15 × 1016 Nm, 1660 m and 4.15 MPa respectively. [ABSTRACT FROM AUTHOR]

Abstract: Himalayas, one of the most seismically active belts, have been formed due to continent–continent collision and are probable locations for future moderate to great earthquakes. It is of paramount importance to recognize precursory swarm activity considered to be long predictors of main events. Recently two earthquake swarms occurred across Main Central Thrust (MCT) in Garhwal Himalayan region in a time interval of nearly one month. The first swarm of April 2009 had epicentral locations lying north of MCT on hanging wall side, which has shown less seismic activity in recent times, while the second swarm occurred in May 2009 near Gopeshwar having epicenters on active seismic zone, located south of MCT. The approximate distance between the two swarms is about 50km. In present study preparation zone of 100×100 km2 has been demarcated recognizing these swarms as precursors to moderate to great earthquake in the Garhwal Himalaya. [Copyright &y& Elsevier]