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Our coasts vulnerable to tsunamis
Of late a controversy has surfaced over whether or not Karachi lies in an earthquake-prone area. Some scientists, academics and journalists have also been speculating if Karachi’s beaches are in any way vulnerable to tsunamis. Careful analysis of the real-time data of southern Sindh and the coastal areas of the country, however, reveals that reports of possible major quakes in and around Karachi are greatly exaggerated.
But tsunamis may be another story. The analysis shows that the Murray Ridge area — between 100kms and 200kms from the metropolis — is indeed vulnerable to tsunamis.
Earthquakes, as we all know, have been dreaded by human beings since time immemorial. It has done more damage to life and property than any other natural catastrophe.
Seismology admittedly is a new science, but within a short span of two centuries it has become one of the most developed branches of geophysics. However, detailed seismological studies essentially require the knowledge of geology, along with several allied fields of geophysics like meteorology, geomagnetism, rock magnetism, palaeomagnetism, continental drift, ionosphere physics oceanography, space science and nuclear explosion detection technology. Knowledge about the creation of seismic data, determination of epicentre, magnitude and intensity all have developed gradually during the last two centuries.
It should be pointed out here that seismic information on Karachi gathered by scientists from local or international sources are based on historical records of the last several centuries and not on actual seismic observations of the region. As such, therefore, these can hardly be relied upon.
A study on southern Sindh, the coastal belts of Pakistan and northern Arabian Sea — based on the seismic data of the last 100 years (from 1905 to 2004) — was carried out recently at the Sir Syed University of Engineering and Technology, Karachi, by some scientists and a seismologist. The picture that emerged following this study is depicted in the accompanying map.
Detailed results of the study appears in the university’s reports titled “Disaster preparedness and development of a warning system for coastal region of Pakistan (Part I and Part II)” which can be obtained from the university. However, the following summarizes the important findings:
— Karachi is not prone to a major earthquake. No earthquake originated in the areas comprising the city during the last 100 years. There are no records to show that a quake ever originated there, thereby establishing the fact that no active fault passes underneath the megacity. Director-general of the Pakistan Meteorological Department has repeatedly expressed these views.
— The faults that may be passing are not active ones. The definition of an active fault, as enumerated by the US Panel on Active Tectonic in 1986, is: “Tectonic Movements that are expected to occur within a future time-span of concern to society”. Future time-span was subsequently estimated as 15 to 20 generations.
— About 40 earthquakes of magnitudes ranging from 5.0 to 9.0 on the Richter scale, occurring in the region during the period under review, did jolt Karachi as it lay at a distance between 100kms and 400kms from their epicentres. The effective intensity of all these quakes in Karachi worked out to less than 5.0. Hence, damage was neither expected nor reported (Sci-tech World, Nov 12).
— The Murray Ridge area in northern Arabian Sea is vulnerable to the occurrence of tsunamis. The aforesaid study establishes the presence of an active seismic region in Murray Ridge area, located between 100kms and 200kms south-west of Karachi, where during the last 40 years more than 25 quakes have been recorded. A majority of these seismic events was of moderate intensity (from 7 to 8) on the Modified Mercalli scale.
— The intensity and the frequency of occurrence of earthquakes in this area are evidently on the increase.
— Since the region lies at the junction of three seismic faults, it is vulnerable to devastating high tidal waves. A seismic report issued by some Indian scientists after the Sumatra quake of Dec 26, 2004, stated that the Arabian Sea, about 70-100kms off the Karachi-Balochistan coast, was vulnerable to the generation of a tsunami.
— However, according to historical records, the frequency of tsunamis in North Arabian Sea is small — only once or twice a century. As opposed to this, major earthquakes in the Pacific Ocean generate tsunamis every 10 to 15 years.
— The Pakistani government has been requested to approach Unesco for the provision and installation of a warning system along the Sindh coast. If the geological map of Pakistan does not show any seismic activity, it needs to be corrected in the light of the “active fault definition”.
— Regarding occasional tremors that have been felt in Defence, Clifton and some coastal areas of Karachi, it has already been clarified during some official meetings and in newspapers that this is not due to quakes but rather due to the compression of soaked soil into solid rock.
— This is a normal geologic phenomenon in all cases where large swathes are filled in the coastal areas with loose earth, soil, mud and sand etc instead of concrete. This is a temporary phase and with the passage of time (40-50 years), the alluvial soil will gradually compress into solid rocks and the problem will disappear.
Meanwhile, several letters have appeared recently in newspapers, advocating the launch by Pakistani geologists of research studies on seismology, just as it is done in the developed countries. This issue requires a clarification.
Geophysical subjects, as enumerated in the beginning of this piece, are an essential part of seismic research studies in the developed countries, for which all institutions teaching geology employ qualified geophysicists as staff. In Pakistan, as against hundreds and thousands of geologists, the number of qualified geophysicists hardly exceeds a dozen.
Pakistani geologists neither study geophysical and seismological subjects nor do they possess any experience of the operation, maintenance and interpretation of seismological, geophysical and nuclear detonation instruments and records.
The science of geophysics took its root in Pakistan in 1955 with the arrival of half a dozen Unesco geophysicists, who under an agreement with the Pakistani government established the Geophysical Institute in Quetta. The institute came under the control of the Pakistan Meteorological Department, with a network of fifteen observatories spread throughout the country and dealing with seismology, geomagnetism, iosphere, nuclear explosion detection, and space and upper atmosphere. At that time, the Suparco also came under the administrative control of this department.
Later, a National Committee for Geodesy and Geophysics (NCGG), on the pattern of the International Union of Geodesy and Geophysics, was constituted with experts from the Geological Survey of Pakistan, Pakistan Meteorological Department, Suparco, Pakistan Atomic Energy Commission and engineering universities as members. Several meetings of the NCGG were held in the early 60s.
Soon, Unesco sent six officers from the Pakistan Meteorological Department abroad for training, with a view to helping develop all branches of geophysics in the country. Three geologists were also deputed for specialized seismological/geophysical courses in Japan and China.
What happened thereafter is part of our chequered history. No useful purpose will be served by repeating how and why geophysical sciences could not develop in Pakistan. However, it is pertinent to point out here that in most Asian countries like India, Iran, Saudi Arabia, Sri Lanka, Bangladesh, Malaysia, Thailand, Indonesia and Japan, geophysics continues to be dealt with by meteorological departments.
Nevertheless, it is satisfying to learn that the Quaid-e-Azam University, Islamabad, and the Peshawar University, Peshawar, have set up their own geophysical and seismology departments and have taken rapid measures to produce qualified geophysicists and seismologists in large numbers. Every Pakistani scientist should appreciate the efforts made by these two universities. There indeed is a dire need to introduce earth sciences at the graduate and postgraduate levels in many Pakistani institutions.
In the end, as an active member of the Disaster Management Committee for Sindh, the Sir Syed University of Engineering and Technology, Karachi, would suggest that the federal government constitute as soon as possible a high-powered national committee on geophysics and seismology, comprising members from the Pakistan Meteorological Department, Geological Survey of Pakistan, Oceanographic Survey, Suparco and the engineering universities. The body may be charged with the responsibility of updating the National Zoning Map, and subsequently, revising the regional building code.
The writer is a former director-general of the Pakistan Meteorological Services and a former regional president of the World Meteorological Organization
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