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On October 8, 2005at 8:50(3:50UTC), a large devastating earthquake occurred in Kashmir region of Pakistan.
The depth of the earthquake was estimated to be about 10km and it had the magnitude of 7.6. The earthquake
resulted from the subduction of Indian plate beneath Eurasian plate,and the earthquake was due to thrust faulting.
Although there was no surface fracture as a result of the faulting, extensive slope failures observed along the
expected surface expression of the causative fault.The main faults in the epicentral area are Muzaffarabad-Tanda
fault and Panjal fault. Both of these faults are thrust fault. While Muzaffarabad-Tanda fault dips NE, the Panjal
fault dips SW. The Oct. 8, 2005 earthquake occurred in a place, which may be regarded as a seismic gap. The
computational results for crustal straining using GPS measurements indicated that Indian plate in Pakistan undergoing
much higher straining as compared with that of India. The maximum ground acceleration for Balakot was
inferred to be greater than 0.9g from overturned vehicles in the direction parallel to the axis of the valley. This
probably represents the largest ground acceleration in the epicentral area. Balakot is situated on the hanging-wall
side of the causative fault. In addition, some further analysis of overturned or displaced structures showed that
maximum ground velocity could be more than 280kine, which is probably the highest value so far.
One of the most distinct characteristics of2005Kashmir earthquake is the widespread slope failures all over the
epicentral area. The Kashmir earthquake of October 8, 2005particularly caused extensive damage to housing and
structures founded on sloping soil deposits.Extensive natural and cut slope failures occurred along Neelum,Jhelum
and Kunhar valleys, which obstructed both river flow and roadways. Furthermore, many slope failures associated
with highly sheared and weathered dolomitic limestone occurred along the presumed surface trace of the earthquake
fault. The failures nearby Muzaffarabad were spectacular in both scale and their areal distributions.Slope failures
caused Kashmir earthquake of October 8,2005may be classified into three categories,namely,1)Soil slope failures,
2)Weathered and/or sheared rock slope failures, and 3)Rock slope failures. Soil slopes failures occurred in either
plane sliding mode or circular sliding. Planar sliding modes are generally observed on soil slopes over the bedrock.
Deep-seated circular type soil slope failures observed when the soil thickness was large. Some peculiar soil slope
failures were observed in both Balakot and Muzaffarabad. These slope failures occurred in conglomeratic soil
deposits with rounded large cobbles,which are products of the past glaciation’s period.Since the slope angles were
quite steep (60-80°), these slopes failed on surfaces involving partly vertical tensile cracks and curved shear plane.
The epicentral area is a mountainous terrain and it is highly susceptible to slope failures and rock falls,which may
be very catastrophic sometimes. Furthermore, the slopes are very steep and covered with fallen debris. With due
considerations of topography and possibility of slope failures, several alternative routes involving construction of
viaducts,tunnels and bridges would be desirable for the area in case of blockage of roadways by rock falls or slope
failures.
Kyeword:Kashmir, earthquake, Muzaffarabad, thrust fault, slope failure |
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