EARTHQUAKES IN JAMAICA ARE INEVITABLE BUT EARTHQUAKE DISASTERS NEED NOT BE?
RAFI AHMAD
UNIT FOR DISASTER STUDIES
DEPARTMENT OF GEOGRAPHY AND GEOLOGY
UNIVERSITY OF THE WEST INDIES
MONA
A recurring theme in all of the earthquakes that have affected the parishes of Kingston and St.Andrew since the Port Royal Earthquake of June 7, 1692 is that the earthquake damage is profoundly influenced by the local geological conditions. In other words, during earthquakes it is the underlying geology that determines how strongly the ground will shake, the sites where landslides, liquefaction, ground cracks and fissures may occur, and where fault ruptures are likely.
These physical processes have generally accompanied all the significant Jamaican earthquakes to date. An understanding of the ground behaviour therefore assumes a great significance if we wish to minimize economic disruption, damages to infrastructure and property, and loss of lives from future earthquakes. Earthquake risks are quantified on this basis.
A number of approaches to reduce losses from future earthquakes are available. However, it is not possible for many of the developing countries to reach the level of sophistication that is currently being practiced in such countries as Japan and USA. We believe that the simplest and most inexpensive approach for earthquake loss reduction in Jamaica is to explore a simple principle "The Past As The Key To The Future".
As geologists we attempt to predict the likelihood of the effects of earthquakes in the years to come on the basis of the distribution of damage and its relation to areas of landslides, liquefaction, ground cracks and fissures, and the site geology.
The lessons learned from the previous earthquakes may be used to adopt wise land use policies, institute proper design and construction practices, strengthen weak structures, and design preparedness plans at national, community and family levels. This proactive response should prevent the hazards becoming disasters.
Stephen Taber in his pioneering analysis of Jamaican earthquakes wrote in 1920".... and it is a general rule that most of the weak shocks of a district originate in the same localities as the stronger ones."
Lessons learned from the January 13, 1993 earthquake
Vulnerability of Kingston to seismic shaking was amply demonstrated by the magnitude 5.4 temblor of January 13, 1993.
Although described as a "moderate" shock with its epicenter located near the Silver Hill Peak in Portland, some 15km northeast of the Half Way Tree Clock Tower, the effects of this earthquake were felt over an area of approximately 500 square kilometers.
The results of a few seconds of ground shaking in eastern Jamaica, with maximum intensities ranging between MMI VII-VIII, were as follows (see Journal of the Geological Society of Jamaica, Volume 30,1996).
1. Economic losses at J$15,810,000.00
2. Two known deaths, one as a result of the collapse of a cliff in Portland.
3. Some 518 families were affected (450 in Kingston and St. Andrew) as their houses were damaged or destroyed.
4. 7, 871 insurance claims reporting losses of about J$152 million dollars were submitted to the insurance companies, and up to June 1993 claims in the value of J$24 million were settled;
5. 2% deductible and the conditions of average resulted in many claims being significantly reduced.
6. Submarine landslides damaged TCSI Digital Cable and Jamaica-Panama Cable; repair costs are not known.
7. Landslides occurred along the Yallahs Water Pipeline route; rock falls covered wash outs and air valves between Hope River and August Town, Rest Haven and Bull Bay, and Cambridge and Eleven Miles.
8. A landslide occurred in the limestone quarry located south of the Mona Reservoir; ground fissures on the embankment road on the southern side of the Mona Reservoir. Damage to NWC Water Treatment Plant building.
9. The Rio Cobre Pipeline in Caymanas Estate was damaged because of liquefaction. Repair costs were estimated at 2 million dollars.
10. Water mains and pipelines in other areas were affected.
11. Electricity system responded very well with only few power failures: 39 MW of power, or 7% of installed capacity was lost for approximately 38 minutes; minor damage to buildings and facilities amounting to $4.65 m.
12. A number of roads were blocked/damaged as a result of landslides.
13. The Ministry of Construction budgeted some $2 m. for the clearance of roads.
14. Liquefaction-related ground cracks were observed in two sections of the north approach road to the Hunts Bay Causeway Bridge.
15. Significant damage was reported to the buildings of various educational institutions.
16. Ground cracks and fissures, ground settlements, and landslides were observed at several places causing damage to building, houses and roads.
17. An abnormally high water discharge was observed at the Rockfort Spring.
18. The figures available suggest that the direct damage due to the moderate earthquake of January 13, 1993 was in excess of J$ 200 m.
"The January 13 event was the tenth Eastern Jamaica Earthquake in the known history (326 years) to have caused intensities of MMI VII and higher" (Margaret Wiggins-Grandison, 1996) .
This earthquake provided an opportunity to study earthquake- induced geological processes and also it was a real test for earthquake preparedness and performance of the lifeline facilities.
It appears that many of the lessons taught by the previous
earthquakes have been forgotten. The pattern of damage and geologic effects observed in 1993 are very similar to those reported in 1692 and 1907. The sites of ground failures related to landslides, liquefaction, and ground cracks and fissures and the associated damage during 1993 comes as no surprise and should serve as a reminder that these processes can affect the same areas in successive earthquakes.
ANALYSIS:
Our analysis of the geologic signatures of the previous Jamaican earthquakes suggests that any significant earthquake event (magnitude 5.4 and over) to affect the island in future is likely to have an enormous loss
potential, especially for the purposes of earthquake damage underwriting.
The property losses following the January 14, 1907 earthquake were estimated at between 1.5 and 2.5 million pounds (1907 value) and at that time the annual value of Jamaica's export earnings were less than 1.5 million pounds. However, these capital losses were compensated in one form or the other. For example, the British Fire Insurance Companies paid some 85% of the face value of the policies amounting to 1200,000 pounds; the British Parliament provided grants and low-interest loans of some 950,000 pounds (Dr. R. Lobdell, 1993). This type of assistance, however, may no longer be available and a major disaster is likely to set back economic progress considerably.
The adverse social, economic, and environmental impacts of the 1988 hurricane Gilbert are still with us. As far
as earthquake damage scenarios are concerned, Dr. J.F. Tomblin (1976) noted.... "a repeat of the 1692
earthquake in Jamaica might cause property damage, at 1975 prices, in excess of J$2,000 million, plus deaths of up to 10% of the population and injuries to a further 20 to 30%, plus near-total disruption of industrial and agricultural production".
What about the seismic risk for the capital city of Jamaica? In short, both the citizenry and the elected and appointed officials of the state should seriously consider the analysis of Dr. John B. Shepherd (1971) - "From the
seismologists point of view the parishes of Kingston including Port Royal, and lower St. Andrew were probably the worst possible locations to choose for the capital city of Jamaica."
DISASTER TAX:
Unfortunately for Kingstonians, it is not only the seismic hazard that presents them with a risk. They must also deal with hurricanes, landslides, excessive soil erosion, and coastal and riverine flooding. In other words, it is a multiple hazard scenario with strong linkages between the various hazardous phenomena.
However, inspite of all the attendant hazards, risks, and historical disasters (1692 & 1907) people have lived on the Liguanea alluvial fan, Palisadoes tombolo, landslide-prone hills of St. Andrew, marshlands, reclaimed lands, and narrow coastal strips, and will continue to do so, doing the things that they must do in order to earn a living.
The Jamaican government bails out the communities which are hit by natural disasters, e.g., following the earthquake of January 13, 1993, the government provided an emergency relief and rehabilitation grant of 1.2 million dollars to the affected communities.
People have built and re-built, often tragically and painfully but at a cost. We keep on paying an invisible "disaster tax."
The disastrous effects of an earthquake, or for that matter any natural disaster, are a reflection of how aware a society is of its physical environment and how effective is the policy of prudent landuse.
What should be done?
The hazard scenario presented is rather depressing. However, it is always possible to prevent todays hazards in becoming tomorrow's disasters. Earthquake related losses can be minimized if we:
(a) do not forget that Jamaica is a earthquake-prone country and problems related to this hazard can arise at any time, especially in the Kingston Metropolitan Area which is home to some 700,000 people, and
(b) take it as a challenge to apply the lessons learned from the previous events in wise landuse, proper design, and preparedness.
An escalation in vulnerability to natural disasters is often closely related to urbanization in areas with severe landuse constraints and in many instances some of these areas have been subjected to repeated ground failures during past
earthquakes.
Earth scientists have a key role to play in communicating the scientific knowledge on hazards to the public and other potential users and to help mitigate the effects of future disasters.
";We can either proceed vigorously to apply the lessons learned from the (previous) earthquakes or be condemned to relearn them from the next earthquake".
I believe that individuals and agencies would take more interest in mitigation if they could somehow be educated about hazards and risks.
"Natural Hazards can be terrible tragedies - but they can also be "terribly" good opportunities to educate the
public".
RESPONSE:
State-of-the-art, GIS-based hazard maps dealing with landslides, earthquakes, flooding, storm surge etc. are now available in the public domain for Kingston and St.Andrew, Clarendon and St.Catherine, South Coast of Jamaica, Portland, and Montego Bay areas.
Information on natural hazards and disasters may be obtained free of cost from the following UWI websites
(1) Unit for Disaster Studies
(2) Caribbean Disaster Information Network(CARDIN)
Those interested in learning about natural hazards and disasters in the Caribbean may read UWI Dept. of Geography and Geology four- week Summer Course:
Analysis and Management of Geohazards and Risks
offered in the months of June-July.
BLO 20010613 - - - COMMENTS ? - - - Table of Contents
< From: "Rafi Ahmad" <rahmad@uwimona.edu.jm>
To: "Ben Oostdam" <boostdam@hotmail.com>
Subject: Fw: Article on earthquake preparedness.
Date: Tue, 12 Jun 2001 20:07:24 -0500