IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS006 Poster presentation 1937
Identifying active faults and obtaining their seismic parameters in low
strain zones: The northwester margin or the Valencia trough
Dr. Hector Perea
Eullia Masana, Pere Santanach
The detection of the active faults and the determination of the parameters that describe their seismic
cycle (maximum magnitude earthquake, recurrence period and time elapsed since the last event) is one
of the key points that could help to the improvement of the seismic hazard studies in zones of low
seismicity. The faults localized in these regions are characterized by low slip rates (< 0.01 mm/yr) and
long seismic cycles (10 to 3 to 10 to 5 years). We propose different approaches with the objective of
identifying the active faults in a zone of low strain rates, the north-western margin of the Valencia
trough: a) spatial association between earthquakes, instrumental and historical, and faults to detect
those responsible of the present and historical earthquakes; b) paleoseismological studies; c)
geomorphological analysis of mountain fronts to identify the main patterns of those associated to active
faults, those associated to non active faults and those not associated to faults; and d) analysis of
seismic reflection profiles in offshore zones to localize the faults that are offsetting the seismic reflectors
corresponding to the plio-quaternary sedimentary layers. Using this information the faults are classified
in five different groups according with the observed characteristics: a) seismogenic faults (2 in the study
area); b) faults that record present and accumulated activity (8); c) faults that record accumulated
activity (18); d) faults that record present activity (32); and e) faults that do not record activity (186).
The next step is the obtainment of the seismic parameters of the detected active faults. Maximum
magnitude earthquake and recurrence interval are obtained from the length and slip rate of the faults.
However, these parameters can only be obtained for faults classified in groups a, b and c. The time
elapsed since the last event can only be get trough paleoseismological studies and these are not always
feasible in low slip rate faults. The knowledge of these parameters allows the inclusion of some of the
active faults in a probabilistic seismic hazard assessment. This study highlights the importance of
identifying active faults and studying their seismic parameters to be included in any probabilistic seismic
hazard assessment.
Keywords: active faults, fault seismic parameters, seismic hazard