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Simulation of strong ground motions of 1991 Uttarkashi (M 7) and 1999 Chamoli (M 6.6) earthquakes using modified hybrid technique

Sharma Anjali, Kumar Dinesh, Paul Ajay, Teotia Satybir Singh

Acta Geophysica

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2023

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Vol. 71, no. 6

2573--2602

EN

In the present study, 1991 Uttarkashi (M 7) and 1999 Chamoli (M 6.6) earthquakes that occurred on October 19, 1991, at 21:23:14 h and March 28, 1999, at 19:05:11 h, respectively, have been simulated using the modified hybrid technique. Hybrid technique is the combination of two existing techniques, i.e., envelope technique and composite source model technique. In the present modified technique, site amplification functions and kappa factor have also been incorporated. The simulated waveforms and their corresponding response and Fourier spectra for each site have been generated. In this study, simulation has been done at 11 and 9 recorded stations of Uttarkashi and Chamoli earthquakes, respectively. Important frequency - and time-domain parameters, i.e., Fourier spectra, response spectra, peak ground acceleration (PGA) and duration at stations, have been estimated and compared with the observed accelerograms. It has been observed that the simulated PGA (231 cm/s2) at the closest distance Bhatwari (22 km) matched with the observed one (248 cm/s2) for the Uttarkashi earthquake. The same has been observed at the nearest most station Gopeshwar (19 km) of the Chamoli earthquake. The simulated PGA (347 cm/s2) for this station has been found well matched with the observed PGA value (352 cm/s2). Similar matching has been observed for other stations also. The present technique is independent of velocity-Q structure of earth’s layered model and past events data of small earthquakes. This study brings light on the site effect and high-frequency decay parameter. This study can be very helpful in the estimation of seismic hazard in a specific region and designing earthquake-resistant buildings.

2

Site Specific Ground Motion Modeling and Seismic Response Analysis for Microzonation of Baku, Azerbaijan

Babayev G., Telesca L.

Acta Geophysica

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2016

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Vol. 64, no. 6

2151--2170

EN

We investigated ground response for Baku (Azerbaijan) from two earthquakes of magnitude M6.3 occurred in Caspian Sea (characterized as a near event) and M7.5 in Shamakhi (characterized as a remote extreme event). S-wave velocity with the average shear wave velocity over the topmost 30 m of soil is obtained by experimental method from the VP values measured for the soils. The downtown part of Baku city is characterized by low VS30 values (< 250 m/s), related to sand, water-saturated sand, gravel-pebble, and limestone with clay. High surface PGA of 240 gal for the M7.5 event and of about 190 gal for the M6.3 event, and hence a high ground motion amplification, is observed in the shoreline area, through downtown, in the north-west, and in the east parts of Baku city with soft clays, loamy sands, gravel, sediments.

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Numerical simulation of the strong ground motion characteristics

Narayan J.

Acta Geophysica Polonica

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2002

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Vol. 50, nr 2

167-178

EN

This paper presents the implementation of point shear dislocation source into 2D parsimonious finite-difference computational grid for simulation of strong ground motion (SGM) characteristics. The procedure used for computing dislocations on the fault plane is identical to both well known kinematic and dynamic models, since dislocation on the fault was computed by solving the equation of motion taking into account the stress drop and the shear strength of the fault. Parsimonious scheme was adopted instead of standard staggered grid scheme since it requires lesser computational memory. The computed numerical radiation patterns of strike-slip, dip-slip and explosive type sources are in good agreement with the respective analytical radiation patterns. The effects of source parameters were studied and the results are in concordance with the existing empirical relations. The simulated results show that impedance decrease, resonance, thickness and geometry of the basin control amplitude amplification and signal duration. The responses for different basin geometry revealed that focusing effect caused by narrow and deep basin causes tremendous increase of amplitude and duration.