Decay of earthquake ground motion with distance in Bangladesh is studied from published information and isoseismal maps. A total of seven earthquakes with magnitude varying from 5.1 to 8.1 are considered. Variation of attenuation of earthquake intensity in different directions is studied. A directional concept is used for developing an attenuation law for Bangladesh. Several publications have been examined for identifying appropriate isoseismal and related intensities. This field data is used to develop two equations representing attenuation of intensity: (i) in terms of magnitude and epicentral distance and (ii) in terms of magnitude and hypocentral distance. The second equation is somewhat questionable since it...
Friday, July 27, 2012
Comparison of Attenuation Model with Other Attenuation Laws
12:05 PM
In order to make a comparison with standard attenuation laws based on peak ground acceleration (PGA), the intensity attenuation equations are converted into PGA attenuation relationship using standard intensity PGA relationships. The following intensity PGA relationships have been used:
log (PGA) = 0.14 + 0.300I (Trifunac and Brady, 1975) (4)log (PGA) = -0.430 + 0.350I (Murphy & O’brien, 1977) (5) log (PGA) = 0.453 + 0.273I (Wald et.al., 1999) ...
Wednesday, July 25, 2012
Attenuation in Different Directions
1:20 PM
Attenuation in Different Directions
Epicentral distances have been measured along different directions and it is observed that the distance for the same isoseist is often different in different directions. Fig.2 shows the attenuation of three different earthquakes in different directions. From Fig.2, for 1885 Bengal earthquake it is observed that the intensity in the direction west shows much smaller attenuation. For 1930 Dhubri earthquake, South and S450W directions represent greater attenuation. For 1918 Srimangal earthquake, S450W and east directions show greater attenuation. So the directions affecting Bangladesh (see Fig.3)...
Isoseismals
1:14 PM
The isoseismal maps of different earthquakes have been obtained from different publications. Isoseismal map of five earthquakes (Fig.1) have been taken from Nandy (2001), which are 1918 Srimangal earthquake, 1930 Dhubri earthquake, 1945 Mikirhills earthquake and 1964 Medinipur earthquake. The isoseismal map of 1897 Great Indian Earthquake and mean epicentral distance of different isoseismals have been taken from Ambraseys and Bilham (2003). Isoseismal map for 1999 Moheshkhali earthquake is given by Ansary et al. (1999). Isoseismal map (Oldham Intensity Scale) of 1885 Bengal earthquake is given by Oldham (1899) and ...
Regional Earthquakes
1:00 PM
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