Page 19 - Jabalpur_EQ

Chapter 1
Introduction

APPENDIX: APPROXIMATE ESTIMATES OF PEAK
ACCELERATIONS

Tipping of shivlings in Bheraghat
In Bheraghat area, approx. 24 km from the epicenter, in a store full of shivlingsof
varying sizes arranged on the floor, overtoppled from the seat except one weigh-
ing about 40 kg. For a shivling to unseat, it has to overturn about the edge of a very
shallow bowl in which it sits as shown in Fig. A1-1 and the overturning moment
due to inertial forces must be greater than the stabilizing moment due to gravity
Therefore, the acceleration, a at the c.g. of a shivling which will cause it to over-
turn can be related to geometrical distances.r and y between the centre of gravity
and the centre of rotation (Fig. A1-la) as,

a2(x/y)g8 (EQ A.1)

For the largest shivling that was overturned, x=45 mm and y=140 mm, which
implies that the acceleraion, a was at least equal to 0.3g. For the largest shivling
that was not overturned but slightly tilted, x and y were measured to be 75 mm
and 180 mm, repectively, which means that the acceleration was less than 0.4g.

Rocking ofa granary at Chattarpur

Peak acceleration at Chattarpur village can be estimated from the observd rock-
ing of a brick granary (schematic shown in Fig. A1-2). Horizontal cracks in mud
plaster at the base of granary and the pedestal on which it was supported indi-
cated the rocking of the granary during the quake. Since there was no mechanical
connection between the base of granary and the pedestal, the acceleration that
would be required for "just lift" condition can be given by Eq. A.1. Using the
dimensions shown in Fig. A1-2, the acceleration to which the granary was sub-
jeced is estimated to be 0.4g.

Centre of
gravity

Uia
Centre of
rotation

Figure A1-1. Overturning of a
shuvling.
777777T77 T

Jabalpur Earthquake of May 22, 1997 9