Abstract
Abstract. This paper presents a methodological approach to seismic hazard assessment based on a hybrid source model composed of faults as independent entities and zones containing residual seismicity. The seismic potential of both types of sources is derived from different data: for the zones, the recurrence model is estimated from the seismic catalogue. For fault sources, it is inferred from slip rates derived from palaeoseismicity and GNSS (Global Navigation Satellite System) measurements. Distributing the seismic potential associated with each source is a key question when considering hybrid zone and fault models, and this is normally resolved using one of two possible alternatives: (1) considering a characteristic earthquake model for the fault and assigning the remaining magnitudes to the zone, or (2) establishing a cut-off magnitude, Mc, above which the seisms are assigned to the fault and below which they are considered to have occurred in the zone. This paper presents an approach to distributing seismic potential between zones and faults without restricting the magnitudes for each type of source, precluding the need to establish cut-off Mc values beforehand. This is the essential difference between our approach and other approaches that have been applied previously. The proposed approach is applied in southern Spain, a region of low-to-moderate seismicity where faults move slowly. The results obtained are contrasted with the results of a seismic hazard method based exclusively on the zone model. Using the hybrid approach, acceleration values show a concentration of expected accelerations around fault traces, which is not appreciated in the classic approach using only zones.
Highlights
IntroductionActive faults are the main earthquake sources in the crust. their incorporation in seismic hazard assessment is not straightforward since there are not enough data available to adequately model them
Active faults are the main earthquake sources in the crust. Their incorporation in seismic hazard assessment is not straightforward since there are not enough data available to adequately model them. This leads to a limited use of faults as independent sources in seismic hazard analyses and to an extended use of seismic zones that cover a significant portion of the crust, assuming uniform seismic characteristics within each source
Seismic hazard results obtained with the proposed hybrid model (HM) and with the classical method based in zone (CM) are shown in Fig. 6a and b
Summary
Active faults are the main earthquake sources in the crust. their incorporation in seismic hazard assessment is not straightforward since there are not enough data available to adequately model them. This leads to a limited use of faults as independent sources in seismic hazard analyses and to an extended use of seismic zones that cover a significant portion of the crust, assuming uniform seismic characteristics within each source This situation has begun to change in recent years, as more studies on active tectonics, palaeoseismicity and fault deformation rates derived from GNSS and other measurements become available. The seismic potential of faults is characterized based on the slip rate using characteristic earthquake models proposed by Wesnousky (1986) (for instance, Field et al, 2014; Akinci and Pace, 2017) instead of Gutenberg–Richter recurrence models (Parsons and Geist, 2009). The period considered in the catalogue may be too short compared with the recurrence time of the fault to provide an unbiased estimation of fault seismic parameters
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