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be north-dipping. At Vigukot, 10 km north of Allahbund, three large and three or four small
events are inferred based on sand craters and disrupted human settlements found in trenches.
The presence of tidal deposits in the Sindri lake area indicates that the sea has receded
by 100 km from here to the present position. In the eastern part of the ABF near Karimsahi,
several trenches and uplift of paleochannels reveal uplift during last few thousand years.
Due to uplift, the paleochannels could have been formed at 3-4 ka and again uplifted by
2 m at 2 ka, as revealed by OSL dating of samples at different elevations. A trench near
Dharamshala indicates three events in the last 3 ka. Along a streamcut nearby, a highly
deformed zone was identified. OSL dates indicate that a 3 ka bed has thrust over a 2.7 ka bed.
The KMF is found to be south-dipping in a trench at Jhura in the central part of the
KMF, where a cumulative deformation of 5 m has been assessed as due to three events. The
two last events had 70 cm slip each. A rough estimate of the age of formations is 5 ka, as
determined by the optically stimulated luminescence method. At Lodai, in the eastern part
of the KMF, the two large events show slips of 33 cm and 40 cm during the late Pleistocene
to Holocene period and older events along two older faults show a cumulative slip of 98 cm.
The Mesozoic rocks override Quaternary along a south-dipping fault. Identification of a
pressure ridge by remote sensing and thorough ground checks helped in identifying the
activeness of this part of the KMF. Further east, there is cumulative slip of 4 m in the
Quaternary, and the last event at an inferred age of 2 ka indicates a 50 cm slip.
In a trench at Wandhey in the central part of the KHF, Quaternary deformation indicates
three large events during the late Holocene to a few ka along three fault strands, which
displaced the older terrace deposits comprising sand, silt, and gravel units along with
overlying younger deposits from units 1 to 5 made of gravel, sand, and silt.
In the Wagad area, the slips noticed for events possibly in the past few ka are: the Gedi
fault along a rivercut shows slip of 1 m; along the South Wagad fault two events are noticed
with slips of 30 cm and 50 cm along two fault strands in a trench in the Adhoi anticline at
3-4 ka; south of theWagad area, in the Samkhiali basin, slip of 75 cm is measured in a trench.
6.3 Seismicity of Gujarat state
Figure 6.9
shows significant
faults and epicenters of about 200 mainshocks of
magnitude
2 from 1684 to 2000 in Gujarat and the adjoining region bound by 20
°
-25.5
°
N
and 68
E.
Table 6.1
shows the magnitude distribution of mainshocks during the pre-
and post-2001 periods (Rastogi
et al
., 2013a).
About 200 km
°
-75
°
300 km, Kachchh is seismically one of the most active intraplate
regions of the world. It has six major E-W-trending faults of the failed Mesozoic rift, which
are being reactivated by thrusting. Prior to the 2001 M
w
7.7 Bhuj earthquake, Kachchh
had experienced three large earthquakes: 1819 M
w
7.8 Allah Bund (24.00
×
°
N 69.00
°
E),
1845 M
w
6.3 Lakhpat (23.80
E).
Some large earthquakes have been documented based on archeoseismology, such as the
faults (
Figure 6.1
)
. The second seismic region in Gujarat is the Narmada Rift zone, which
°
N 68.90
°
E), and 1956 M
w
6 Anjar (23.30
°
N 70.00
°
