An earthquake that shook Karachi on late hours of October 11 was recorded at 4 on the Richter scale. A large part of the city felt jerks and many people spent the night outside from their houses.
In fact 4-point tremor is considered a moderate one as compared to the 7.6 jolts on October 8 earthquake which shook Kashmir and NWFP.
The citizens of Karachi already frightened due to the recent disaster in northern parts of the country took these mild jerks quite seriously and to avoid any mishap spent the night out on roads.
In Karachi, earthquake is not a new phenomenon because for the last three years low intensity tremors have been felt time to time.
Karachi and its neighbouring areas surrounded by some hill ranges are sitting on an active fault. It means the largest city may receive more jerks in the future.
Experts suggest that the possibility of any sizeable earthquake cannot be ruled out because large intraplate earthquakes may occur in unexpected places.
In such a perspective, the geologist underscored the need for taking a thorough study of Karachi region with respect to micro-seismicity, detailed geology, hydrology, man-made activities of multi-disciplinary urban development.
Global distribution of destructive earthquakes and nature of tectonic elements indicate that a major part of Pakistan is also in active zone of significant seismicity, besides the north-western margin of the Indo-Pakistan sub-continent is characterised by all kinds of earthquake events.
The south-eastern part of Pakistan and adjoining Rann of Kutch area were considered to be the part of the stable continental crust, the historical and the modern seismicity records of the Kutch region show significant earthquake activities, indicating active intra-continental tectonic deformational process.
The 16 June 1819 Rann of Kutch earthquake was one of the disastrous of the series, which was felt throughout India.
Significant vertical movements of the ground caused flooding of regions near sea level, damming of a distributory of the Indus river, widespread liquefaction, and a tsunami, however, the geometry of the fault plane has hitherto remained obscure. Dislocation models based on deformation data gathered 7 and 25 years after the earthquake suggest that a near-surface reverse fault slipped locally more than 11 metre.
The absence of significant uplift on a ENE trending extension of surface trace of the fault in 1819, may signify that slip on the fault was directed to the north-east, consistent with focal mechanisms of recent earthquakes in the region.
The inferred 50-70° N-dipping fault plane beneath the Allah Bund is unfavourably steep for reverse faulting, presumably requiring high fluid pressures in the nucleation zone. A geometric moment magnitude of 7.7±0.2 is obtained from the inferred slip parameters, consistent with a magnitude estimated empirically from the intensity distribution.
While a recurrence of the Kutch earthquake is unlikely soon because of low inferred contractional strain rates in the region, the Indus Delta and Kutch rift zones could host several ruptures contiguous with the 1819 event, with important consequences for the city of Karachi.
An International report prepared in 1982 warned that some large earthquake might hit Karachi. Other studies on the subcontinent have also warned that the shift of a great earth mass might increase seismic activity in the area, including Pakistan and India, causing disasters.
The alerts were given years back that we witnessed now on October 8, morning when a massive jolt turned a large area into graveyard and perished around 38,000.
Karachi and its adjoining areas have been rocked for a number of times during its available history. But despite expert studies and warnings during the past decades, the authorities neither have been taken any practical measures to monitor the seismic activity nor such measures have been initiated that could lessen the magnitude of damage in case an earthquake of severe magnitude hits the highly populated city of Pakistan.
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