Page 35 - Jabalpur_EQ

Chapter 2
Selemologlcal Aspects

sional strain and high heat flow. Although, the rate of seismicity in the.Peninsular
India is low in comparison to the Himalayan seismicity, howeve, it can pose con-
siderable seismic hazard due to variety of factors.

GENERAL OBSERVATIONS AND INTENSITY
DISTRIBUTION

The area rocked by the Jabalpur earthquake of May 22, 1997 was surveyed by the
authors. The extent of the affected area was identified based on the available
information from television and
coverage published reports in local newspapers.
Detailed mapping earthquake intensities have been carried out for the purpose
of
of preparing the isoseismal maps of the Jabalpur earthquake. The intensity has
been assigned to a particular locality on the basis of information collected
through the interview of residents in the affected area and also by the visual
inspection of the observed damage.

To assign the intensity values in different localities, MSK as well as MMI scales
have been followed. The intensity was assigned to a specific locality keeping in
view of the structure
type (e.g., A-poor quality such as bricks and mud mortar,
B-good/moderate quality such as bricks and cement mortar or C-good quality
steel), grade damage to each structure (e.g,
of
such as reinforced concrete or the
Grade I to Grade V) and the number of structures suffered to a specific grade of
damage (e-g-, single/few, many or most). The methods adopted to assign inten-
sities are always subjective based on the judgement and it is difficult to apply a
uniform criteria. On account of this the survey team surveyed the epicentral area
jointly and the intensity was assigned after mutual discussion. This filtered out
the individual bias normally involved in assigning intensities and also took into
account the various factors which
may introduce bias. Therefore, while assigning
intensities the team carefully noted the marked difference in the damage to build
ings, type of materials used for construction, and their pre-earthquake condition.
For example, at some localities the similar type buildings built on hard rock/
of
soil suffered lesser damage in comparison to nearby buildings built on loose sed-
iments (or soft soils). The spatial distribution of the earthquake damage in the
Jabalpur area is described along the following tracts:

TRACT : Kosamghat-Barela--Tikarlya--Majgaon
The intensity VIlI has been assigned at Kosamghat village which is situated at a
distance of about 10 km in the SE direction of the
reported earthquake epicenter
(USGS). This village having a population of about 700 people (125 dwelling units)
completely ground both due to the intense shaking as well as the
was razed to the
poor quality of construction. However, about 25 people suffered irnjuries and no
casualty occurred in spite of heavy damage, because villagers were either awake
or sleeping outdoors at the time of the earthquake. Most of the adobe houses suf-
fered grade IV to V damage. There were only three houses constructed in brick
with mud mortar or cement mortar and they also suffered col-
partial/complete
lapse. Figure 2-7 shows a typical damage to adobe house in the village. The roof

Jabalpur Earthquake of May 22, 1997 25