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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

Kourouklas Christos, Mangira Ourania, Console Rodolfo, Papadimitriou Eleftheria, Karakostas Vassilios, Murru Maura

Acta Geophysica

2021

Vol. 69, no. 3

1085--1099

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 frst 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 ofsprings, 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.

On rapid multidisciplinary response aspects for Samos 2020 M7.0 earthquake

Foumelis Michael, Papazachos Costas, Papadimitriou Eleftheria, Karakostas Vasileios, Ampatzidis Dimitrios, Moschopoulos Giorgos, Kostoglou Anastasios, Ilieva Maya, Minos-Minopoulos Despina, Mouratidis Antonios, Kkallas Charalambos, Chatzipetros Alexandros

Acta Geophysica

2021

Vol. 69, no. 3

1025--1048

Following the M7.0 earthquake that struck the Greek island of Samos and Turkey’s western coast, causing extensive damage and casualties, we combined existing knowledge geodatabases concerning historical seismicity and rupture zones with seismological and geodetic measurements as well as with modelling and in situ observations, to provide an assessment of rapid response to the seismic event. In this paper, we demonstrate that in the frame of the gradual provision of information from the individual scientifc disciplines, taking into account their respective potential and limitations, a multidisciplinary approach is able to address more efciently rapid response issues in order to allow efective preliminary interpretation of the earthquake activity, even within the frst 24 h of the event. It focuses on the assessment of the timely provision of information by each discipline, evaluating the access to primary data sources as well as the maturity of the techniques in terms of accuracy and rapid data processing. Within a period of less than a week, several constraints were partially compensated for, allowing the delivery of more robust results and interpretation. The study highlights the readiness level of the various domains that has been signifcantly improved over the past years, including rapid seismological solutions, systematic availability of free and open Earth Observation data and on-demand online processing through dedicated platforms. Their combination with routinely applied inversion modelling and timely in situ observation is leading to improved operational response levels.

Modeling the earthquake occurrence with time‑dependent processes: a brief review

Mangira Ourania, Kourouklas Christos, Chorozoglou Dimitris, Iliopoulos Aggelos, Papadimitriou Eleftheria

Acta Geophysica

2019

Vol. 67, no. 3

739--752

The complexity of seismogenesis tantalizes the scientific community for understanding the earthquake process and its underlying mechanisms and consequently, precise earthquake forecasting, although a realistic target, is yet far from being a practice. Therefore, seismic hazard assessment studies are focused on estimating the probabilities of earthquake occurrence. For a more precise representation of seismicity-regarding time, space and magnitude stochastic modeling is engaged. The candidate models deal with either a single fault or fault segment, or a broader area, leading to fault-based or seismicitybased models, respectively. One important factor in stochastic model development is the time scale, depending upon the target earthquakes. In the case of strong earthquakes, the interevent times between successive events are relatively large, whereas, if we are interested in triggering and the probability of an event to occur in a small time increment then a family of short-term models is available. The basic time-dependent models that can be applied toward earthquake forecasting are briefly described in this review paper.