06-05-2014, 03:49 PM
A simulation of earthquake induced undrained pore pressure changes with bearing on some soil liquefaction observations following the 2001 Bhuj earthquake
simulation of earthquake.pdf (Size: 183.45 KB / Downloads: 18)
ABSTRACT
The Bhuj earthquake of January 26th, 2001, induced wide spread liquefaction within the Kachch
peninsula. It has been pointed out that inundation due to soil liquefaction was short lived in some
parts than in others in the affected region. Several geological, seismological and hydrological factors
would have cumulatively contributed to these observed changes.
We simulate in this article, undrained or short-term change in pore pressure in a poroelastic half
space, in response to a simplified model of the Bhuj earthquake source. We find that the regions
of relatively shorter lived inundation due to soil liquefaction may fall in the region where pore
pressure responsible for soil liquefaction attributable to strong ground shaking was counteracted
by pore pressure changes due to undrained poroelastic effect and vice versa.
Introduction
The large magnitude (Mw = 7.7) Bhuj earthquake
which occurred on January 26th, 2001, within the
Kachch peninsula in Gujarat, was accompanied
by wide spread liquefaction. Aerial and field sur-
veys reported soil liquefaction and associated phe-
nomena in the Great Rann, Little Rann, Banni
Plains, Kandla River and Gulf of Kachch, between
69.75◦ E and 70.75◦ E at 23.97◦ N, (71.45◦ E, 23.3◦ N),
(70.37◦ E, 22.72◦ N) and (69.67◦ E, 23.5◦ N), covering
an area of tens of thousands of kilometers (Hengesh
and Lettis 2001).
Method
Our estimate of the short-term poroelastic effects
induced by the Bhuj earthquake is based on the fol-
lowing considerations. The drying up phenomena
were observed soon after the earthquake occurred
i.e., during the period of short time response of
the poroelastic earth to the earthquake-induced
stresses, when the poroelastic subsurface rocks
experienced undrained deformation. Since such
type of deformation of a poroelastic medium is
mathematically analogous to the elastic deforma-
tion of a linear isotropic medium, the undrained
perturbations to the ambient pore pressure field,
induced by the Bhuj earthquake immediately after
its occurrence can be estimated in the manner
explained below.
Conclusion
For a detailed understanding of the site-specific
characteristics of soil liquefaction that were
observed during the Bhuj earthquake several fac-
tors related to near surface conditions of the soil
and water table need to be considered. Our study
based on estimates of the short term pore pressure
changes induced by the earthquake suggest that
the quasi-static poroelastic response of the under-
lying rocks of the region may also have a role in
these observed patterns.