Abstract
The frequency-dependent characteristics of P- and S-wave attenuation in the upper crust of NW Himalayas have been estimated using local earthquakes for a frequency range of 1.5 to 18 Hz. A total of 43 local events of magnitude 2.1 - 4.8, mostly from the vicinity of Main Boundary Thrust (MBT) and Main Central Thrust (MCT) have been used in the analysis. The extended coda normalization methods were applied to estimate the quality factors for P- waves (QP) and S-waves (QS) and the single back-scattering model has been used earlier (Kumar et al. [1]) to determine the quality factor for coda waves (QC). The observed quality factors QP and QS is strongly frequency dependent and the estimated average frequency dependent relation is given by QP = (97 ± 3)f (1.06 ± 0.06) and QS = (127 ± 6)f (0.96±0.06) respectively for P- and S-waves. A comparison of QS estimated in this study and QC previously reported shows that QC > QS for entire frequency range. This indicates the enrichment of coda waves and the importance of scattering attenuation to the attenuation of S-waves in the study region infested with faults and fractures. The ratio QS/QP is found to be greater than unity for the entire frequency range indicating that the body waves from source to station paths crossed a crustal volume with dry and rigid rocks. The frequency dependent relations developed in this study can be very useful to ground motion modeling which in turn is required in the seismic hazard assessment of the region.
Highlights
In order to investigate the structure of the interior of the earth and to quantitatively predict the strong earthquake ground motion in engineering seismology, the information on seismic wave attenuation plays an important role
This study is an attempt to understand the attenuation of P, S- and Coda-waves in the NW-Himalayas of the India using the different parts of the seismograms
The frequency-dependent estimates of body waves (QP and Qs) have been obtained using the extended coda normalizetion method, and the single back-scattering model has been used to determine the relation for coda waves
Summary
In order to investigate the structure of the interior of the earth and to quantitatively predict the strong earthquake ground motion in engineering seismology, the information on seismic wave attenuation plays an important role. The information on high frequency wave attenuation in the lithosphere is of particular importance. Attenuation parameter Q–1 is an important factor for understanding the physical mechanism of seismic wave atenuation in relation to the composition and physical condition of the earth’s interior [2]. From the engineering point of view, attenuation of S-waves has been well studied in various regions in the world as compared with that of P-waves. The information on QP 1 is indispensable for evaluating the strong vertical ground motion precisely in view of the earthquake-resistant design of recent huge constructions
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