Abstract
The recurrence time, Tr, of strong earthquakes above a predefined magnitude threshold on specific faults or fault segments is an important parameter, that could be used as an input in the development of long-term fault-based Earthquake Rupture Forecasts (ERF). The amount of observational recurrence time data per segment is often limited, due to the long duration of the stress rebuilt and the shortage of earthquake catalogs. As a consequence, the application of robust statistical models is difficult to implement with a precise conclusion, concerning Tr and its variability. Physics-based earthquake simulators are a powerful tool to overcome these limitations, and could provide much longer earthquake records than the historical and instrumental earthquake catalogs. A physics-based simulator, which embodies known physical processes, is applied in the Southern Thessaly Fault Zone (Greece), aiming to provide insights about the recurrence behavior of earthquakes with Mw ≥ 6.0 in the six major fault segments in the study area. The build of the input fault model is made by compiling the geometrical and kinematic parameters of the fault network from the available seismotectonic studies. The simulation is implemented through the application of the algorithm multiple times, with a series of different input free parameters, in order to conclude in the simulated catalog which showed the best performance in respect to the observational data. The detailed examination of the 254 Mw ≥ 6.0 earthquakes reported in the simulated catalog reveals that both single and multiple segmented ruptures can be realized in the study area. Results of statistical analysis of the interevent times of the Mw ≥ 6.0 earthquakes per segment evidence quasi-periodic recurrence behavior and better performance of the Brownian Passage Time (BPT) renewal model in comparison to the Poissonian behavior.
Highlights
The study of the statistical behavior of strong earthquakes’ occurrence above a given magnitude threshold (e.g., M ≥ 6.0) on specific faults or faults segments is among the key components of the estimation of fault-based probabilistic seismic hazard assessment (PSHA)
The main purpose of such studies is the determination of the mean recurrence time, Tr, between successive strong earthquakes and their variability, the latter of which can be used as an input in the application of either Poissonian or renewal long-term Earthquake Rupture Forecast (ERF) models in a specific time span (Field, 2015)
The Brownian Passage Time (BPT) model is significantly better than the Poisson in the segments with larger numbers of observations, which are those with the lower values of Tr (Ekkara, Farsala, Rigeion, and Volos) and slightly better in the cases of large values of recurrence time and the larger values of coefficient of variation (Cv)
Summary
The study of the statistical behavior of strong earthquakes’ occurrence above a given magnitude threshold (e.g., M ≥ 6.0) on specific faults or faults segments is among the key components of the estimation of fault-based probabilistic seismic hazard assessment (PSHA). An analysis of the implications of the BPT model in the strong earthquakes’ occurrence per fault segment might be useful, highlighting differences between the models in the forecasting of strong earthquakes in the near future This analysis is based on the estimation of the hazard function, H (t), for both the BPT and the Exponential models using the estimated mean recurrence time, Tr, and the corresponding coefficient of variation as obtained from the statistical analysis of the simulated catalog (Table 5). The Exponential model returns a constant hazard rate independently of both the mean recurrence time and the calculated elapsed time (until 01–01-2020; green lines) since the last event in each segment Considering these results, along with the better performance of the renewal BPT model as resulted from the values of the Information Criteria (Table 6), the elastic rebound motivated rupture scenarios is clearly supported. The hazard rate is almost zero and considerably far from their maximum values in the cases of Farsala, Pagasai, Nea Agchialos, and Volos fault segments, whereas for the corresponding values of the Ekkara and Rigeion fault segments, both are at the increasing part of their curves but far enough from their mean recurrence times (about 74 and 142 years, respectively) and their pick values
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