تجزیه و تحلیل حساسیت از پتانسیل هشدار سونامی

Tsunamis are normally generated by underwater earthquakes. The earthquakes are normally easily detected by seismographs. However, the earthquake may not always generate a tsunami. Further, the severity of the earthquake is not linearly related to the severity of the tsunami. The tsunami may be detected by a deep-sea pressure transducer communicating through a surface rider buoy, through satellites to a tsunami warning centre. The detectors are expensive to build and maintain, need to be placed near surface-rider buoys, and the placement of these detectors needs to be optimal. The provision of adequate warnings from the network of detectors, called the tsunami warning potential, depends on the network of the deployed detectors, the number of detectors used, and the response times of the detectors, warning centre, and of the emergency services which need to convey the warning. The warning potential is also a function of the number in the population at risk. The sensitivity of the warning potential is analysed for first-order effects, particularly with respect to time delays arising from detection and operation of the emergency services to deliver the warning to the population. The sensitivity of the warning potential to population shifts is also considered. Areas for improvement are identified, together with suggestions of how the system can be optimised.

In the past, tsunamis have caused considerable loss of life and destruction of property in coastal areas [1]. Various tsunami warning systems have been designed and used to detect the generation of a tsunami, and to warn of its approach to coastal regions [2]. Currently, seismic observations are used to detect the occurrence of earthquakes, act ‘at a distance’, and communications are rapid. The real-time detection of a tsunami is usually through direct observation. This is a hazardous operation, as the observer needs to be near the destructive zone, and the means of communication are often destroyed, disrupted or utilised by non-essential traffic. Fortunately, tsunamis are far less damaging in the open ocean and may be detected by suitable sea-floor-mounted detectors [3]. These detectors use acoustic coupling to communicate to the surface, to wave-rider buoys which can then communicate via satellite [3]. The detectors and wave-rider buoys are expensive to make and are currently limited in number. Some six possible sites have been selected, after consideration of regular NOAA ship passages and other maintenance and cost factors (Tsunami Hazard Mitigation Federal/State Working Group, 1996 [THM]). The problem is to locate a small number of detectors at a selection of the possible communication-buoy locations, so as to give the maximum warning of the generation of a tsunami, i.e. to maximise the warning potential function. This problem has been formulated and solved; it leads to an integer programming problem which can be solved using standard enumeration techniques [4]. The solution for the optimal warning potential function depends on parameters such as population numbers at risk, and response times for detection of the tsunami and for conveying the warning to the population. These parameters can be considered to vary continuously in their ranges. The maximum warning potential function also depends on the number of buoys which are deployed, and this is a discrete variable with up to six buoy locations. The aim of this paper is to investigate the sensitivity properties of the maximum warning potential function to its input parameters. This will assist in determining the subset of more influential parameters with respect to sensitivity. The results will provide valuable feedback to the operation of a tsunami warning system.