This report has presented an assessment of earthquake hazards in the Kingston, Jamaica Metropolitan area and was conducted as part of the Kingston Multi-Hazard Assessment under the US Agency for International Development funded Caribbean Disaster Mitigation Program. The assessment included
Within the margin of error or uncertainty, the results of this assessment are consistently equal to or higher than previously published ground motion estimates for the Kingston Metropolitan area. The model presented here incorporates information from the historic record and from the geology and geophysics of the region. We feel that this type of model is more robust in that it does not solely rely on a historic record, which is short compared to the time between large earthquakes. Uncertainties in the basic parameters for a probabilistic seismic hazard assessment led to the use of eight different models, which yielded maximum and minimum ground motion estimates. Within the Kingston Metropolitan area, 'hard rock' ground motions vary by as much as a factor of two and are consistently higher to the north and northeast than the southwest. The 10% probability of exceedence in 50 year acceleration values on hard rock range from 0.35 to 0.70g for the 'worst' case model to 0.15 to 0.40g for the 'best' case model.
Site conditions throughout the Liguanea Plain and Kingston Metropolitan area vary in terms of the types and thickness of soils and the degree of water saturation. Site conditions were evaluated using a number of approaches and techniques including
These site condition data are combined with the 'hard rock' ground motion estimates to develop a regional map of ground response for the Kingston Metropolitan area. Site corrected ground motion values are estimated to be a factor of two to three higher than 'hard rock' values in areas of water-saturated, unconsolidated soils and made-ground. The overall effect, at the regional scale, is to 'level out' the ground motion gradient. In other words, site corrected ground motions in the south and southwest are equivalent to those in the north and northeast. It is important to realize that this assessment represents a regional model of earthquake activity and site response. Site-specific applications require more detailed geo-technical analysis.
Many of the findings and conclusions of this study echo the results of an earlier assessment published by Shepherd in 1971 as part of the United Nations Development Planning Program for Jamaica. This earlier study provides a valuable reference point to assess not only the progress that has been made in understanding earthquake hazards in Jamaica, but also the actions that have been taken to reduce earthquake risk on the island during the last 28 years. Shepherd (1971) made a number of recommendations including:
The following sections discuss these recommendations with a 30 year perspective and present some new directions for policy and research.
The major policy decisions about building codes, earthquake hazard mitigation, and redevelopment of the Kingston metropolitan area were made during an era of historically low seismic activity, following the 1907 earthquake. These policies need to be reevaluated in light of revised information about the likelihood of earthquakes in the immediate vicinity of the Kingston Metropolitan area and revisions of the seismic design criteria in the National Building Code.
The 1907 earthquake is generally responsible for the lack of historic, pre-20th Century architecture in the Kingston area and the initiation of strict building codes. The Building Act of the Kingston and St. Andrew Corporation was introduced in 1907 following the earthquake. These Acts provided mandatory regulations for the planning, design, and construction of buildings. Buildings higher than 60 feet were prohibited. The first buildings to exceed this height limitation were three story buildings on King Street that were constructed of reinforced concrete.
In 1983, the Government published the National Building Code. The National Building Code based structural design requirements on British Standards and Codes of Practice, except for earthquake resistant design, which directed users to the 'The Recommended Lateral Force Requirements of the Structural Engineers Association of California (SEAOC)". The latest revision recommends use of the Caribbean Uniform Building Code (CUBIC) format for earthquake loads and adjusted the design philosophy to conform to the SEAOC code. The current seismic design criteria specify an expected peak acceleration of 30% g with a 10% probability of exceedence in 50 years. CUBIC also recommended a zone factor (Z) of 0.75 for Jamaica, in the absence of information on earthquake sources. This represents effective peak acceleration on rock of 30% g and is equivalent to a distance of 16 miles for M 6.5 and 25 miles for M 7.0.
In 1992, the Government asked the Jamaica Bureau of Standards to set up a Building Code Review Committee. As a result, a new draft Volume 3, Section 3 - Earthquake Loads was prepared in 1993. Based on experience in the 1993 Woodford earthquake, Adams (1996) recommends upgrading the expected peak acceleration to 40% g. The latest revision (1999) increased the level of ground shaking to 40% g with a 10% probability of exceedence in 50 years in the eastern parishes, Kingston, St. Andrew, Portland, St. Thomas, St. Mary and St. Catherine (Adams and Periera, 1998). These suggested changes are consistent with the results obtained from this and other recent analyses of ground motion in the Kingston Metropolitan area.
There is a need for the integration of prevention and multihazard mitigation practices into design and construction. The cost of including earthquake-resistant design features into a building design are estimated to represent less than 3% of the initial construction costs (Pereira, 1995). Direct physical damage and indirect economic losses can easily exceed this initial investment, and in some cases, the actual cost of the building itself. While the Jamaica Public Service Company (JPSCo) experienced moderate damage and relatively few power failures following the 1993 Woodford earthquake, the recognition of high hazard rate from earthquakes and hurricanes, and the high cost of insurance prompted JPSCo to become more proactive and take appropriate mitigation measures (McFarlane, 1996).
Kingston ranks as the 7th largest natural harbor in the world. The large concentration of infrastructure throughout the Kingston Metropolitan area, including the Norman Manley International Airport, marine port facilities, oil refineries, and power generation plants is situated in the areas that sustained the greatest damage in previous earthquakes and has the highest concentration of reclaimed land. The region's demonstrated susceptibility to liquefaction and ground failure during moderate sized earthquakes makes it extremely vulnerable to economic disruption as well as loss of life. Damage to port facilities during even a moderate sized earthquake, can delay post-earthquake relief efforts and have a significant long-term economic impact to industries dependent on air and marine commerce. A recent example of the impact even moderate sized earthquakes can have on national economies is the magnitude 6.8 Hyogoken Nanbu (Japan) earthquake of January 17, 1995. This moderate sized event resulted in the extended closure of the Port of Kobe and repair costs estimated to be on the order of $5.5 billion. Indirect costs due to port damage were estimated to be $6 billion during the first year after the earthquake (Werner, 1998). Many of these facilities were located on reclaimed land.
Many of the facilities in the Kingston Harbor area that were built on engineered ground will perform better than those built on fill and unconsolidated soils, yet many of these structures were built 30 years ago. Is there a need for seismic retrofitting of critical facilities in the Harbor area, given the upgraded ground motion estimates discussed in this Assessment? The vulnerability of the Palisadoes to strong ground shaking has been demonstrated in previous earthquakes. While the Norman Manley International Airport may remain functional following a moderate earthquake, the single road connecting the airport to the mainland, the Norman Manley Highway, may become impassable due to liquefaction and ground failure. Road access to the Portmore Kingston Causeway also lies in areas of reclaimed land, as does the rail line into Kingston.
Water and wastewater supply and distribution systems are critical infrastructure for both sanitation and fire fighting. The fire following the 1907 Kingston earthquake swept over 10-15 blocks of the business and warehouse district. Gas supply and distribution systems need automatic shut-off valves to reduce the likelihood of fires. The installation of shutdown values at both water reservoirs and throughout water distribution systems can reduce losses from pipe breakage due to ground failure and help to speed restoration of service in the critical hours following a damaging earthquake.
Activities are underway to develop nationally consistent seismic guidelines for lifelines and other infrastructure in the United States (e.g., Werner, 1998). The two sets of ground motion values developed in this study, for example, are consistent with practice at the Port of Los Angeles in California (10% and 50% probabilities of exceedence in 50 years). CUBIC provisions (1203.2) recommends the installation of at least 3 strong motion instruments in all buildings six stories and higher. This recommendation should be extended to critical facilities and infrastructure, as well.
This Assessment has attempted to develop a geologic framework for seismic hazard assessment in Jamaica and the Kingston Metropolitan area. Expanded support for scientific and engineering research, coupled with the continued collection of earthquake data, is essential to 'fill the gaps' and reduce the uncertainties in the current state of knowledge and to improve future estimates of earthquake hazard in the Kingston Metropolitan area and Jamaica. Table 5.1 lists the relevant parameters, their importance and the types of data needed to reduce the uncertainty
Knowledge about rates of regional deformation and fault motion are critical parameters in evaluation and monitoring of seismic hazards in Jamaica. The fault systems used in this study were identified based on geologic information only. The installation of GPS stations, coupled with data from the Jamaican geodetic network, can begin to document current day rates of fault motion and reduce the uncertainties in seismic hazard models. Geologic and paleoseismic investigations are needed to determine the capability of the major on-island fault systems and document the earthquake history.
While the Jamaican seismograph network has existed for close to 40 years, the intermittent quality and quantity of the data collected has compromised the usefulness of the data. The new digital network with computer based state of the art data processing described in Appendix 1, needs to be maintained and expanded. The data collected by the network in critical to understanding the seismotectonics of Jamaica. Similarly, the collection of strong motion data from engineered structures, critical facilities and lifelines is an investment in the economic sustainability of the country.
|Parameter||Precision or Uncertainty||Regions Affected||Value Used||Over/Under Estimate Hazard||Data Needed to Reduce Uncertainty|
|b-value||± 0.3||All of KMA||0.7 and 1.0||Bounding extremes||Higher quality magnitude scale calibration, earthquake locations over decade time scale|
|Slip on Central or Northern faults||± 4mm/yr||Northern and Northwestern KMA||Two extreme models (511 and 151) using 1 and 5 mm/yr||Bounding extremes||Paleoseismic investigation of appropriate faults|
|Strong Motion Variability||Factor of Two||All of KMA||Factor of Two||May overestimate Hazard||Strong Motion Recording of Local Earthquakes|
|Attenuation of seismic waves||Real attenuation law for Jamaica unknown||All of KMA||Joyner -Boore, and Woodward- Clyde formulas||? Leads to 0.4g uncertainty in final acceleration maps||Measure attenuation of seismic waves using digital data from seismic network|
|Total slip rate for Active Faults Crossing Jamaica||4mm/yr to 8mm/yr||All of KMA||6 and 8 mm/yr||Middle to upper extremes||GPS rate|
|Location of Active Faults in Blue Mountains||Location of faults known, slip rates unknown||Northern and Eastern KMA||Used faults and sources zone; Estimated fault slip rates||? Source regions appears to underestimate hazard||Paleoseismic investigation of appropriate faults|
In closing, attention should be given to defining an acceptable level of earthquake risk for the Kingston Metropolitan area. In spite of our best efforts to mitigate against earthquakes, we will never be able to eliminate the problem entirely. How much economic disruption can Jamaica tolerate following a moderate earthquake? How fast can Jamaica recover from a natural disaster and reenter the competitive world market place?
|CDMP home page: http://www.oas.org/en/cdmp/||Project Contacts||
Page Last Updated: 20 April 2001