The 1897 Assam Earthquake

Hough, Bilham, and Ambraseyes, fall 2003 AGU

Ambraseys and Bilham (in review, BSSA) present a reinterpretation of original felt reports of the great Assam earthquake of 12 June, 1897. Intensity values (MSK) are based on effects that are considered to reflect primary mainshock ground motions rather than secondary effects such as liquefaction. We use a simple mathematical interpolation approach to construct a Historic ShakeMap for this earthquake.

Using mainshock source parameters determined from geodetic data we calculate predicted shaking intensity at hard rock sites using the method of Beresnev and Atkinson (1997). A comparison between the predicted hard rock intensities and the observed values yields a map of residuals which corresponds to site response in the Ganges Basin. Our results illustrate that if historic earthquake accounts are interpreted carefully, with consideration of local building types and a focus on primary shaking effects, they can provide valuable direct constraint on strong motion site response.