M. R. Pandey
Department of Mines and geology, Kathmandu
Peter Molnar
Department of Earth, atmospheric, and Planetary Science,
M. I. T. Cambridge, Massachusetts 02139. U. S. A.
We have recompiled the descriptions of damage and destruction caused by the 15 January 1934 Bihar-Nepal earthquake, given by both Dunn et al. (1939) and by Major General Brahma Sumsher J. B. Rana (1935), to infer bounds on the dimensions of the rupture zone of that earthquake. The distribution of damage in northern India was very uneven, and much of that destruction was closely associatd with slumping, fissuring, and tilting of the ground. The absence of any preferred orientation of the fissures and the prevalence of sand and water issued from fissures suggest that this disruption of the earth’s surface was limited to surficial layers and not to faulting of the basement beneath that area. Thus much of the damage in northern India, perhaps the majority, was not due to shaking or to high accelerations of the ground, but rather to disruption ot the earth’s surficial layers.
Except for three short trips to parts of Nepal by. J. B. Auden, Dunn and his colleagues has access to little information from Nepal, and their descriptions of the effects of the earthquake in Nepal were brief. Rana, however, made extensive compilations both of destroyed buildings and of casualties in various districts and towns in Nepal, and it appears that the greatest destruction lay in the parts of Nepal that Auden did not visit. Where Rana and Auden gave independent assessments of the damage, their reports agreed sufficiently well, that the particularly heavy toll reported to have been taken by the earthquake in the mountainous terrain of east-central Nepal probably is not an exaggeration. This area, in fact, includes the epicenter of the earthquake recalculated from arrival times of P waves.
Thus in contrast to Dunn et al. and others who have followed them, we think that rupture zone of this earthquake lay beneath the lesser Himalaya and not beneath the plains of northern India. The east-west dimensions are difficult to constrain, but surely reach 100 km, the length of the zone of maximum destruction in Nepal. The region for which Dunn et al. assigned an intensity of VIII, on the Rossi-Forel scale, extended as far east as Darjeeling and somewhat west of Kathmandu, for a total distance of about 300 km, however, and the abrupt decrease in destruction west of Kathmandu and east of Darjeeling might indicate that the length of the rupture was this amount. Given the uncertainties in evaluating the dimensions, it probably would be best to allow both extrems, or 200 ± km. in evaluations of recurrence intervals and earthquake hazards.