Intrinsic and scattering attenuation in western India from aftershocks of the 26 January, 2001 Kachchh earthquake   总被引：1，自引：0，他引：1  

A. Ugalde  J.N. Tripathi  M. Hoshiba  B.K. Rastogi   《Tectonophysics》2007,429(1-2):111-123

176 vertical-component, short period observations from aftershocks of the M_w 7.7, 26 January, 2001 Kachchh earthquake are used to estimate seismic wave attenuation in western India using uniform and two layer models. The magnitudes (M_w) of the earthquakes are less than 4.5, with depths less than 46 km and hypocentral distances up to 110 km. The studied frequencies are between 1 and 30 Hz. Two seismic wave attenuation factors, intrinsic absorption (Q_i^− 1) and scattering attenuation (Q_s^− 1) are estimated using the Multiple Lapse Time Window method which compares time integrated seismic wave energies with synthetic coda wave envelopes for a multiple isotropic scattering model. We first assume spatial uniformity of Q_i^− 1, Q_s^− 1 and S wave velocity (β). A second approach extends the multiple scattering hypothesis to media consisting of several layers characterized by vertically varying scattering coefficient (g), intrinsic absorption strength (h), density of the media (ρ) and shear wave velocity structure. The predicted coda envelopes are computed using Monte Carlo simulation. Results show that, under the assumption of spatial uniformity, scattering attenuation is greater than intrinsic absorption only for the lowest frequency band (1 to 2 Hz), whereas intrinsic absorption is predominant in the attenuation process at higher frequencies (2 to 30 Hz). The values of Q obtained range from Q_t = 118, Q_i = 246 and Q_s = 227 at 1.5 Hz to Q_t ≈ 4000, Q_i ≈ 4600 and Q_s ≈ 33,300 at 28 Hz center frequencies, being Q_t^− 1 a measure of total attenuation. Results also show that Q_i^− 1, Q_s^− 1 and Q_t^− 1 decrease proportional to f^−ν. Two rates of decay are clearly observed for the low (1 to 6 Hz) and high (6 to 30 Hz) frequency ranges. Values of ν are estimated as 2.07 ± 0.05 and 0.44 ± 0.09 for total attenuation, 1.52 ± 0.21 and 0.48 ± 0.09 for intrinsic absorption and 3.63 ± 0.07 and 0.06 ± 0.08 for scattering attenuation for the low and high frequency ranges, respectively. Despite the lower resolution in deriving the attenuation parameters for a two layered crust, we find that scattering attenuation is comparable to or smaller than the intrinsic absorption in the crust whereas intrinsic absorption dominates in the mantle. Also, for a crustal layer of thickness 42 km, intrinsic absorption and scattering estimates in the crust are lower and greater than those of the mantle, respectively.  相似文献   

Deterministic seismic scenario for Gujarat region, India     

Sumer Chopra  Dinesh Kumar  B. K. Rastogi  Pallabee Choudhury  R. B. S. Yadav 《Natural Hazards》2012,60(2):517-540

In this study, the modified stochastic method based on dynamic corner frequency has been used for the simulation of strong ground motions in Gujarat region. The earthquake-generating faults have been identified in the Gujarat region on the basis of past seismicity of the region. In all, 19 probable faults have been identified with 12 in Kachchh region, 5 in Saurashtra and 2 in Mainland Gujarat region. The maximum magnitude has been assigned to each fault based on the regional tectonic environment and past seismicity. The strong ground motions from these identified sources have been estimated at numerous points distributed all over Gujarat region on a grid. The peak ground acceleration (PGA) values have been extracted from the accelerograms and contoured. The spatial distribution of maximum of 19 PGA values at every grid point have been described and discussed. The ground motions at the surface of 32 important cities of the Gujarat have been estimated by incorporating the site amplification functions. The site amplification functions are obtained using the local earthquake data. These cities are located on various types of geological formations. We note that the site amplification functions have modified the character of the records and amplified the acceleration values at almost all the sites. The Kachchh region can expect surface accelerations between 400 and 800 cm/s², Saurashtra between 100 and 200 cm/s² and Mainland less than 50 cm/s² from a future large earthquake. The obtained results are useful for disaster mitigation measures, strengthening the existing built environment and design of structures in the region.  相似文献   

Chemistry of Precipitation Events and Inter-Relationship with Ambient Aerosols over a Semi-Arid Region in Western India     

N. Rastogi  M. M. Sarin 《Journal of Atmospheric Chemistry》2007,56(2):149-163

The precipitation events (n = 91), collected for 3 years (2000–2002) during the period of SW-monsoon (Jun–Aug) from an urban site (Ahmedabad, 23.0°N, 72.6°E) of a semi-arid region in western India, are found to exhibit characteristic differences in terms of their solute contents. The low solute (<700 μeq L⁻¹) events are either marked by heavy precipitation amount or successive events collected during an extended rain spell; whereas light precipitation events occurring after antecedent dry period are characterized by high solutes (>700 μeq L⁻¹). The ionic composition of low solute events show large variability due to varying contribution of anthropogenic species (: 1%–74%; : 1%–25%; and : 8%–68%) to the respective ion balance. In high solute events, ionic abundances are dominated by mineral dust (Ca²⁺ and ) and sea-salts (Na⁺ and Cl⁻). These differences are also reflected in the pH of low solute events (range: 5.2–7.4, VWM: 6.4) and high solute events (range: 6.6–8.2, VWM: 7.3). The comparison of Ca²⁺/Na⁺ and nss- ratios (on equivalent basis) in rain and aerosols suggests that the ionic composition of high solute events is influenced by below-cloud scavenging; whereas evidence for in-cloud scavenging is significantly reflected in low solute events. The annual wet-deposition fluxes of and are 330 and 480 mg m⁻² y⁻¹, respectively, in contrast to their corresponding dry-deposition fluxes (14 and 160 mg m⁻² y⁻¹); whereas wet and dry removal of Ca²⁺, Mg²⁺ and are comparable.  相似文献   

Equatorial electrojet in east Brazil longitudes     

R. G. Rastogi  H. Chandra  K. Yumuto 《Journal of Earth System Science》2010,119(4):497-505

This paper describes the morphology of the equatorial electrojet (EEJ) along 45°W longitude in east Brazil, where the ground magnetic (dip) equator is associated with the largest declination in the world. Daily range of the horizontal field (ΔH), as expected, was largest at the station in the chain closest to the dip equator, Sao Luiz (inclination −0.25°S). ΔZ was largest positive at Eusebio (inclination 9.34°S) and largest negative at Belem (inclination 7.06°N); both near the fringe of EEJ belt. ΔZ at Sao Luiz during the daytime was unexpectedly large negative in-spite of a small dip and also located south of the dip equator where ΔZ should be positive. Center of EEJ was found to be shifted southward of the dip equator by about 1° in latitude. During southern summer, ΔY started decreasing from 00 h and reached a minimum value in the afternoon, an abnormal feature not discussed for any station so far. The mid-day value of the direction of ΔH vector was 22°–24°W compared to the declination of 19°–21°W in the region.  相似文献