Short-term clustering modeling of seismicity in Eastern Aegean Sea (Greece): a retrospective forecast test of the 2017 Mw = 6.4 Lesvos, 2017 Mw = 6.6 Kos and 2020 Mw = 7.0 Samos earthquake sequences

Short-term earthquake clustering properties in the Eastern Aegean Sea (Greece) area investigated through the application
of an epidemic type stochastic model (Epidemic Type Earthquake Sequence; ETES). The computations are performed in an
earthquake catalog covering the period 2008 to 2020 and including 2332 events with a completeness threshold of Mc = 3.1
and separated into two subcatalogs. The first subcatalog is employed for the learning period, which is between 2008/01/01 and
2016/12/31 (N = 1197 earthquakes), and used for the model’s parameters estimation. The second subcatalog from 2017/01/01
to 2020/11/10 (1135 earthquakes), in which the sequences of 2017 Mw = 6.4 Lesvos, 2017 Mw = 6.6 Kos and 2020 Mw = 7.0
Samos main shocks are included, and used for a retrospective forecast testing based on the constructed model. The estimated
model parameters imply a swarm like behavior, indicating the ability of earthquakes of small to moderate magnitude above Mc
to produce their own offsprings, along with the stronger earthquakes. The retrospective evaluation of the model is examined
in the three aftershock sequences, where lack of foreshocks resulted in low predictability of the mainshocks, with estimated
daily probabilities around 10–
5. Immediately after the mainshocks occurrence the model adjusts with notable resemblance
between the expected and observed aftershock rates, particularly for earthquakes with M ≥ 3.5.