Low Slip-Rate Faults Around Big Cities: A Challenging Threat. The Afindai Fault as a Case Study for the City of Athens

Abstract eng:
Low slip-rate faults tend to have large recurrence intervals and are usually regarded that they represent a low hazard probability. However, when these faults neighboring a large city, the risk becomes high. The Afidnai fault is a low slip-rate fault that bounds the northern edge of the Athens Plain and represents such an example. Due to the long recurrence intervals these faults are often absent from the historical catalogues, therefore are usually excluded from the seismic hazard assessment. In such cases only geological data can extend the history of a fault back in time, depicting the long-term deformation pattern of slip. Offset Pleistocene terraces have been used to calculate a long-term throw-rate of 0.1 to 0.3 mm/yr for the Afidnai fault, depending on our location along strike the fault. Based on a worst-case scenario the 14 km long Afidnai fault can generate events of the maximum magnitude (M=6.4), about every 2000 years. Considering that the completeness of the historical record in Greece for such magnitude events is about 200 years, it is evident that it represents only a small fraction of the mean earthquake recurrence interval of the Afidnai fault. The Afidnai fault is a typical case study concerning the threat posed by low slip rate faults around big cities and priorities should be given in tracing and assessing such structures worldwide. In such cases, paleoseismology and earthquake geology have an important role to play.

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