Seismicity patterns before the M=5.8 2002, Palermo (Italy)earthquake: seismic quiescence and accelerating seismicity

Seismic quiescence and accelerating seismic energy release are considered as possible spatio-temporal patterns of the
preparation process of the 6 September 2002 Palermo, Italy, earthquake (M 5.8). The detailed properties of the quiescence are
analyzed applying the RTL algorithm. The RTL algorithm is based on the analysis of the RTL prognostic parameter, which is
designed in such a way that it has a negative value if, in comparison with long-term background, there is a deficiency of events
in the time–space vicinity of the tested point. The RTL parameter increases if activation of seismicity takes place. The RTL
algorithm identified that a seismic quiescence started from the beginning of November 2001 and reached its minimum at the end
of May 2002. The Palermo 2002 earthquake occurred 2 months after the RTL parameter restored its long-term background
level. The application of a log-periodic time-to-failure model gives a ‘‘predicted’’ (in retrospect) magnitude M= 6.2 main shock
on 5 May 2002.

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