Evaluation of the reliability of a seismic network: the HSSN (Israel) as an example

Under the assumption that an earthquake can be analyzed if it is detected and recorded by at Least four stations, we propose to describe various scenarios leading to the total loss of ability to acquire sufficient data for seismological analysis. These scenarios are presented by constructed fault-trees, to each branch of which is assigned the empirical annual probability of occurrence (equipment malfunction or external disturbance). For each branch of the fault-tree, the probability of occurrence is computed and, eventually, the overall reliability of the seismic network is estimated in terms of annual probability of failure to detect and Locate seismic events. This approach, often used by engineers in safety analysis, has been applied to a seven station local network (HSSN) which operates in parallel with the Israel national seismic network. In this example it is estimated that there is an annual probability of 3*10-4 that an earthquake of magnitude 3.0 or higher would not be detected and analyzed.