Investigating Seismic Events along the Eurasian Plate between Greece and Turkey: 10 Years of Seismological Analysis and Implications

: The North Aegean Sea region in Greece is located at the convergence of the Eurasian, African, and Anatolian tectonic plates. The region experiences frequent seismicity ranging from moderate to large-magnitude earthquakes. Tectonic interactions and seismic events in this area have far-reaching implications for understanding the broader geological processes in the eastern Mediterranean region. This study aims to conduct a comprehensive investigation of the seismic activity of the North Aegean Sea region by employing advanced seismological techniques and data analyses. Data from onshore seismological networks were collected and analyzed to assess the characteristics of the earthquakes in the region. Seismicity patterns, focal mechanisms, and seismic moment calculations were performed to assess current seismic activity. The present study combined spatiotemporal analysis with the analysis of genesis mechanisms, and this resulted in more results than those of previous studies. Detailed analysis of the seismic data showed patterns in the occurrence of earthquakes over time, with periodic episodes of increased seismic activity compared to activities followed by quieter periods. Finally, this study proves that recent earthquakes in the study area (2017, 2020) highlight the complexity of seismicity as well as the consequences of strong earthquakes on people and buildings. Overall, these findings suggest that the North Aegean Sea is becoming increasingly seismically active and is a potential risk zone for adjacent regions


Introduction
The North Aegean Sea has a wide spectrum of seismic activity because of its tectonic complexity, which includes crustal earthquakes, earthquakes connected to subduction, and strike-slip events.Small to moderate quakes can occasionally occur in the area, as well as larger quakes that can have a significant impact on infrastructure and local communities.
A detailed analysis of seismological data from the North Aegean Sea was performed in this study.This is the first time that such an extensive period analysis using the latest state-of-the-art software has been applied to Greece's most seismogenic area.
The North Aegean Sea region is a seismically active area, with many significant seismic events occurring throughout its geological history.
The North Aegean Sea, a geologically dynamic region situated in Greece, has been the focus of extensive seismological investigations over the past decade [1][2][3][4][5].This area is renowned for its complex tectonic setting, characterized by the convergence of major tectonic plates, making it prone to frequent seismic activity [6][7][8][9].Understanding seismicity patterns and trends in this region is of paramount importance for assessing potential seismic hazards and improving earthquake preparedness and mitigation strategies.
Over the last ten years, advancements in seismological monitoring and data collection have provided researchers with a wealth of information on the seismic behavior of the Earth 2024, 5 312 North Aegean Sea.A series of onshore and offshore seismological networks have been established, offering a comprehensive dataset that allows for a detailed analysis of seismic sequences and their associated characteristics.
Figure 1 shows a general structure map of the prefectures of the broader region of the North Aegean Sea.The green stars indicate the strong historical earthquakes from the study area, the purple and yellow triangles represent the seismological stations from the Seismological Laboratory of the University of Thessaloniki (HT), available at http://www.fdsn.org/networks/detail/HT/[10], accessed on 12 August 2023 and the National Observatory of Athens (NOA-HL), available at https://bbnet.gein.noa.gr/HL[11], accessed on 12 August 2023 and with green rectangles represent the station from the Strong Motion Network, available at https://accelnet.gein.noa.gr/[12], accessed on 12 August 2023.The red circles represent the corresponding epicenters.
Uneven seismicity and frequent earthquake clusters and sequences are characteristic of the North Aegean Sea region.To comprehend earthquake processes and stress distribution, scientists have conducted thorough seismological research using methods such as seismic tomography and fault plane solutions.This paper presents a comprehensive seismological analysis of seismicity observed in the North Aegean Sea region over the past decade.By utilizing the wealth of data collected from seismological stations, this study examined the temporal and spatial distribution of earthquakes, investigated the focal mechanisms of seismic events, and assessed seismic moment release during significant earthquakes.
This study aims to provide valuable insights to the scientific community, seismologists, and local authorities, fostering a better understanding of the region's seismic behavior and its significance for earthquake risk assessment in the broader Mediterranean context.The seismicity of the North Aegean Sea is of particular interest because of its implications for regional seismic-hazard assessments.With the expansion of human populations and critical infrastructure located near seismically active zones, a thorough understanding of seismicity patterns is crucial for implementing effective disaster preparedness and response measures.
The present study found that large earthquakes tend to originate in places that are more broken up, whereas smaller ones occur around more active fault zones.This pattern suggests that the fault dynamics of the region are becoming increasingly complex, possibly because of the continuous build-up and release of tectonic stress.
This knowledge is very important for determining how to better prepare for and respond to earthquakes and to understand how they may occur in the future.The 7.0 Mw earthquake that occurred near the island of Samos on 30 October 2020 is an example.
The installation of onshore and offshore seismological networks has made it possible to collect high-resolution data, making it easier to analyze earthquake sequences with greater precision.This improved monitoring ability is important for early warning systems and for reducing the damage caused by future earthquakes.Overall, this paper provides a detailed overview of seismic activity in the North Aegean Sea region and highlights the need for improved seismological monitoring to better understand and assess hazard seismic-hazard potentials within this complex environment.
The analysis found that large earthquakes tended to originate in more fragmented areas, whereas smaller earthquakes tended to be distributed around more active fault zones.Overall, this paper provides a detailed overview of seismic activity in the North Aegean Sea region and highlights the need for improved seismological monitoring to better understand and assess seismic-hazard potentials within this complex environment.This article is structured into six main chapters that describe and analyze the results of our study on the seismotectonics of the North Aegean region.

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Chapter 2: Seismotectonics of the North Aegean region.In this section, the geological structure and seismotectonic activity of the study area are presented.In particular, the main tectonic faults and the history of seismic events affecting the region are discussed.

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Chapter 3: Methodology and Data Collection.The methods used for data collection and analysis are described.The techniques used to monitor seismic activity and the tools used to process the data are analyzed.

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Chapter 4: Seismic Event Analysis.Findings from the analysis of seismic events recorded over the last decade are presented.The analysis focused on the frequency, magnitude, and distribution of earthquakes and their impact on the study area.

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Chapter 5: Earthquake Risk Assessment.In this chapter, seismic risk assessment for the North Aegean region is discussed.The data obtained from the research are analyzed, and measures to reduce risk are proposed.

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Chapter 6: Conclusions and Future Directions.The final chapter summarizes the main findings of this study and suggests directions for future research.It also identifies the limitations of the current study and suggests ways for further improvements.

Geological and Tectonic Background
The convergence of several major tectonic plates defines the North Aegean region in Greece as a tectonically complex area [14,15].The North Aegean region is part of the convergence between the Eurasian and African plates, with significant tectonic activity shaping its geological structure.This has had a significant impact on the geological structure of the region.This seismotectonic environment significantly influences the geological This article is structured into six main chapters that describe and analyze the results of our study on the seismotectonics of the North Aegean region.

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Chapter 2: Seismotectonics of the North Aegean region.In this section, the geological structure and seismotectonic activity of the study area are presented.In particular, the main tectonic faults and the history of seismic events affecting the region are discussed.

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Chapter 3: Methodology and Data Collection.The methods used for data collection and analysis are described.The techniques used to monitor seismic activity and the tools used to process the data are analyzed.

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Chapter 4: Seismic Event Analysis.Findings from the analysis of seismic events recorded over the last decade are presented.The analysis focused on the frequency, magnitude, and distribution of earthquakes and their impact on the study area.

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Chapter 5: Earthquake Risk Assessment.In this chapter, seismic risk assessment for the North Aegean region is discussed.The data obtained from the research are analyzed, and measures to reduce risk are proposed.

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Chapter 6: Conclusions and Future Directions.The final chapter summarizes the main findings of this study and suggests directions for future research.It also identifies the limitations of the current study and suggests ways for further improvements.

Geological and Tectonic Background
The convergence of several major tectonic plates defines the North Aegean region in Greece as a tectonically complex area [14,15].The North Aegean region is part of the convergence between the Eurasian and African plates, with significant tectonic activity shaping its geological structure.This has had a significant impact on the geological structure of the region.This seismotectonic environment significantly influences the geological characteristics, earthquake patterns, and seismic hazards of the region.The Hellenic Arc, where the African plate subducts beneath the Eurasian plate, is the main tectonic barrier around the North Aegean Sea [16,17].This subduction process in the region has created deep-sea trenches and volcanic arcs.From the South Aegean Sea to the North Aegean Sea, a major seismic zone recognized for its seismicity and potential for large earthquakes is defined by the subduction zone.The complicated tectonics of the region are also a result of contact between the Anatolian and Eurasian plates [18,19].Compared to the rest of the Eurasian plate, the smaller Anatolian plate, which is a component of the larger Eurasian plate, moves westward.As a result of this movement, strike-slip faults, such as the North Anatolian Fault and the Hellenic Arc Extensional System, emerge, which are responsible for numerous seismic occurrences in the area.
• The North Anatolian Fault (NAF) is one of the most active and long-term seismogenic faults in the region, extending from the Black Sea to the North Aegean Sea, with significant slip movements that cause large earthquakes.

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North Aegean Fault: This fault is responsible for several strong earthquakes in the region, with extensional movements shaping the geology of the Aegean seabed.• The Myrtoo and Chalkidiki faults: Smaller-scale faults are also observed in a wider area, contributing to the overall seismicity of the region.
These zones are responsible for the release of significant seismic energy and are critical for understanding seismic risks in the region.

Seismic Activities and Focal Mechanisms of Earthquakes
Seismicity in the North Aegean region is characterized by a high frequency and intensity of seismic events.The largest seismic events are usually associated with the movement of the main faults such as the North Anatolian and North Aegean faults.The mechanisms of earthquake generation in this region include the following [25]:

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Sliding earthquakes: caused by plate displacement along the North Anatolia and North Aegean faults; • Extensional earthquakes: the expansion and subduction of the Greek microplate, mainly in coastal and submarine segments.
The frequency and magnitude of these earthquakes indicate continuous geodynamic activity in the region, necessitating careful monitoring and study.

Seismotectonic Impacts
The impacts of seismic events in the North Aegean region are multidimensional and include the following.

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Disturbances on the Aegean seabed: Earthquakes cause changes in the seabed geomorphology, affecting submarine flows and structures [26,27].

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Fault movements: Earthquakes can cause significant displacements and movements along faults, thereby affecting the stability of geological formations.

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Risk to settlements: Coastal towns and settlements in the region are exposed to seismic risks, making it imperative to have effective prevention and management measures.
Seismotectonic investigations in the North Aegean Sea region are crucial for seismichazard assessment and earthquake-risk-reduction methods [28,29].It is proposed to continuously monitor seismic activities and enhance research efforts to understand the dynamic changes that occur in the region.Furthermore, the application of advanced techniques and tools for the analysis of seismic data will contribute to a more effective response to seismic risk.Geological formations and fault networks in the region can be understood by scientists to help them locate probable seismic sources and predict the risk of future earthquakes.This knowledge is essential for creating successful earthquake preparedness strategies and robust infrastructure and improving public safety.

Data Processing
Earthquakes are divided into shallow, intermediate, and deep according to the depth value.In Greece, most earthquakes are classified as shallow earthquakes, except those in the Eastern Crete region, Karpathos, and Rodos.The data for the seismic sequences under study were selected based on the following criteria: • The data belong to the area of the North Aegean Sea, Greece; • The time window is defined as 2013-2023; • Shallow mainshocks and a rich aftershock sequence.

Seismological Analysis of the North Aegean Sea's Strong Earthquakes
Seismological analysis of the North Aegean Sea's strong earthquakes involves the study of various parameters associated with earthquake events.One crucial aspect of the analysis is the determination of the epicenter and depth of the earthquake.This information helps accurately locate the seismic activity and understand the depth distribution of earthquakes in the region.Comprehending earthquake clustering and probable foreshocks or aftershocks requires an in-depth understanding of the temporal characteristics of seismic sequences [30].Seismologists can use it to determine whether a sequence is composed of a mainshock and a series of aftershocks or if it is part of a more intricate seismic process.Investigating the focal mechanisms of earthquakes, which offers insights into the faulting mechanisms and stress regime within the Earth's crust, is a further step in the analytical process [31,32].This knowledge aids in locating active fault systems and understanding how tectonic plates interact in the North Aegean Sea region.
Thirteen broadband stations in the study area were equipped with three seismometer components (Figure 1).Detailed information is presented in Table 1.Strong earthquakes that occurred in the North Aegean region over the last ten years (2013-2023), as well as the aftershocks they triggered, are shown in Figure 2. The main earthquakes are marked with red stars, with orange and blue triangles corresponding to the seismological stations from Seismology Laboratory of Aristotle University (AUTH) [10] and National Observatory of Athens-Institute of Geodynamics (NOA-IG) [11]; finally, red lines represent the main faults for the study area as originated from [33], available at https://land.copernicus.eu/imagery-in-situ/eu-dem.Bathymetry was obtained using Emodnet Bathymetry [33] and DEM.Light blue represents cities near the epicenter.The distribution of the epicenters for 2013-2023 also appears on the map.The size and color of the points depend on their magnitude.The size of the circles indicates the magnitude of seismic events.The larger circles indicate higher magnitudes.
For the seismological stations depicted in the map above, their details (station name, geographic location, altitude, and network to which they belong) are presented in Table 1.The details of the stations that belong to the strong-motion network in the study area are presented in Table 2.

Fault Plane Solutions (FPSs)
Understanding the causes and stress patterns linked to seismic events in the North Aegean Sea region requires the use of fault plane solutions (FPSs) [32,[34][35][36].The interactions of the Eurasian, African, and Anatolian plates in the North Aegean Sea, which result in high seismic activity, make the region tectonically complex.The orientation of fault planes and the types of faulting that contribute to earthquakes are crucial details that FPSs offer, providing important insights into the tectonic processes influencing the seismicity of the region.Seismologists can detect active fault systems and potential seismic dangers in a region by studying FPS data to determine whether an earthquake involves normal, reverse, or strike-slip faulting.FPSs can also be used to investigate the mechanisms that cause earthquakes, redistribution of stress, possibility of aftershocks, and triggered seismicity.This brief introduction investigates the value of fault plane solutions in improving our understanding of seismic activity in the northern Aegean Sea, revealing the complex tectonic processes that affect earthquake occurrence and behavior in this geologically active region.
In this section, the moment tensor solutions for all strong events are calculated and displayed.Therefore, fault plane solutions, moment magnitudes (M w ), and depths (d) of the most powerful earthquakes were determined using seismological broadband data from the Hellenic Unified Seismological Network (HUSN).
A moment tensor inversion methodology was employed using Ammon's software [37], as theoretically reported in [37][38][39].For a specific velocity structure, this method computes synthetic seismograms that are then directly compared with real seismograms.Kennett's reflectivity approach was used to calculate the Green Functions, as performed by Randall [37].A suitable 3D velocity model-in our case, Papazachos' model-is paired with a synthetic model for the three fundamental flaws.
Five broadband stations with three component seismometers, with various azimuth coverages and epicentral distances of less than 3 • , were chosen, and their regional data were examined.The preparation of the data, which includes the deconvolution of the instrument response, integration of velocity to displacement, and rotation of the horizontal components into radial and transverse components, is the first step of the operation.The long-period component of the signal is then added to complete the inversion.By considering the average misfit and compensated linear vector dipole (CLVD; Column 9, Table A1), the quality of the moment tensor solutions can be assessed.The minimal misfit is represented by letters A-D for each solution, and the percentage of CLVD is represented by digits 1-4.

1.
The Mw = 7.0 30 October 2022 Samos Earthquake An earthquake with a moment magnitude of Mw = 7.0 occurred on 30 October 2020, at 11:51 UTC (13:51 local time), in an offshore region about 16 km north of Samos Island in Greece and about 60 km southwest of Izmir in Western Turkey.On both sides of the Aegean Sea, the Mw 7.0 magnitude earthquake caused extensive damage, leading to fatalities and injuries.The location was estimated by USGS [40], available at https://earthquake.usgs.gov/earthquakes/eventpage/us7000c7y0/executive, to be near 37.897 • N, 26.784 • E at a hypocentral depth of 11.5 km and the focal mechanism solution with φ = 276 • , δ = 29 • and λ = 88 • .Two people died, and nineteen people were injured on Samos Island as a result of the generated disasters, which also included strong ground shaking, tsunami run-up, liquefaction, rockfalls, and landslides.In Western Turkey, 116 people were killed, and over 1030 were hurt.Buildings and infrastructure in the impacted areas sustained significant damage because of the strong shocks that produced landslides [41].Numerous homes and buildings were rendered unusable, forcing residents to flee, and this necessitated rapid assistance.Samos and the other Greek islands as well as other coastal locations in Western Turkey experienced tsunami flooding [42].Greek citizens on the eastern Aegean Sea islands received a tsunami warning via text message from the general secretary for civil protection, available at https://civilprotection.gov.gr/[42], via emergency number 112.The alert was transmitted at 12:15 UTC (14:15 local time).
The earthquake occurred when COVID-19 was a pandemic worldwide, necessitating a different kind of response than would normally be required for an earthquake of this size.International organizations did not send reconnaissance teams to the area because international travel was limited.Reconnaissance was performed.A 12-person team from Greece's Hellenic Association of Earthquake Engineering (HAEE/ETAM), available at https: //www.eltam.org/klimakio-etam-sti-samo/[43,44], was dispatched in two subsequent trips to Samos Island and the surrounding islands.Similarly, the Earthquake Engineering Association of Turkey and the Earthquake Foundation of Turkey (EEAT/EFT), available at https://www.tdmd.org.tr/[45,46], dispatched teams to the Aegean coast's devastated areas, with Izmir as the main emphasis due to its severe damage.
International organizations with US roots (Earthquake Engineering Research Institute, EERI, available at https://www.eeri.org/what-we-offer/webinars/9312-quick-quakebriefing-m7-0-samos-island-offshore-greece-and-turkey-earthquake-october-30-2020[45,46], and Geotechnical Extreme Events Reconnaissance Association, GEER, available at https:// geerassociation.org/component/geer_reports/?view=geerreports&id=96&layout=build [45]) facilitated and encouraged conversations between HAEE/ETAM and EEAT/EFT while these reconnaissance missions were in progress.The information exchange was fruitful, and it became clear that the only way to fully comprehend this important occurrence was to mobilize scientists on both sides of the fault while integrating data and collectively analyzing field findings.Furthermore, throughout these three-way dialogues (between Greece, Turkey, and the USA), a sincere desire to work together and create collaborative reports for upcoming events that reflect our shared goal of transforming catastrophes into knowledge emerged.Initially, papers detailing their reconnaissance efforts were written by EEAT/EFT, HAEE, and several university research centers.Four members from the collaborating organizations were tasked with planning, enabling the creation and revision of a joint document to aid in the development of this study.The outcome of that effort is this paper, which combines the key seismological, engineering, and societal effects of this significant event on both the Greek islands and the Aegean region of Turkey's mainland.
The Anatolian microplate, which is one of the seismically active regions of the world because of the interaction between the Eurasian, African, and Arabian plates, is related to the motion of the Samos earthquake tectonic setting.The Anatolian microplate accommodates the relative movement of the three major plates and is bounded by the Hellenic Trench, East Anatolian Fault, and North Anatolian Fault (NAF, EAF).Although the Eurasian and African plates collided and subducted, the entire Aegean Sea has been experiencing tectonic tension since 25 Ma as a result of back-arc spreading on the Mediterranean crust and slab rollback of the subducting African plate, which is responsible for the crustal extension between Samos and Western Anatolia (the larger Izmir area) at a spreading rate of 7.4 mm/yr [47].
The Kaystrios Fault, which has been previously mapped in the GEM-Faults database, available at https://blogs.openquake.org/hazard/global-active-fault-viewer/[48], is known as the main seismogenic fault of the 2020 Samos earthquake.They form part of a complicated fault system located close to and around the islands of Samos and Ikaria, along with the nearby Ikaria Fault (IKF), Fourni Fault (FOF), and Pythagorio Fault (PYF).
A visual and spatial representation of earthquake activity in a certain area was provided via 3D visualization of the epicenters.This three-dimensional depiction adds depth to the visualization in place of just showing epicenters on a 2D map, allowing for a more thorough comprehension of seismic events.The depth, latitude, and longitude of each earthquake epicenter are shown in a 3D representation to create a geographical distribution of seismic activity.It is possible to transmit additional information, such as the magnitude or timing of an earthquake, using the size and color of the data points.
The source parameters (φ, δ, λ), moment magnitude (Mw), seismic moment (M 0 ), and depth (d) were estimated for the strong event of the 30 October 2020 in Samos Island, Greece, using the procedure outlined in Section 3.1.The results are shown in Figure 3.For this purpose, the data of eight stations with three components, each one at epicentral distances less than 500 km, were used.For the main event, inversion indicates the activation of a normal faulting type.The best-fit solution was strike = 290 • , strike = 30 • , rake = −85 • , and the focal depth was calculated at 12 km.The seismic moment was determined as M 0 = 3.16 × 10 26 dyn * cm, and the calculated double couple (DC) was found to be equal to 5%, while the compensated linear vector dipole (CLVD) was 95%.These geometric features of the fault plane are consistent with the seismotectonic setting of the area [49].
According to the kinematic findings, the entire rupture process takes place over approximately 25 s, producing a total seismic moment of 3.16 × 10 19 N*m (Mw = 7.0) with a peak moment rate of 3.11018 Nm/s at approximately 10 s.The major slide area was shallowly distributed and exhibited a complementary pattern with aftershocks, with a maximum amplitude of three meters.While a pure normal faulting mechanism dominated the slip in the first six seconds, a strike-slip component was also present in the subsequent rupture.The shift in the focal mechanism, which is also visible in the aftershock mechanisms, corresponds to a tectonic transition from lateral shearing to dilatation.These geometric features of the fault plane are consistent with the seismotectonic setting of the area [51,52].

2.
The Mw = 6. 3 12 June 2017 Lesvos Earthquake The Greek island of Lesvos was hit by a strong Mw 6.5 magnitude earthquake on 12 June 2017.Injuries and structural damage were caused by the earthquake's extensive damage to the island's structures and infrastructure.Due to the earthquake's proximity to Lesvos, the residents of the island were greatly affected.Many structures, including historical and cultural heritage monuments, sustained structural damage as a result of the earthquake, raising questions about the future preservation of Lesvos's extensive past.The earthquake added to the immediate difficulties that local authorities and rescue personnel already faced by inflicting casualties on some island residents.While rescue personnel attempted to guarantee the safety of earthquake-affected communities, medical teams were quickly organized to help those in need.
The mainshock's aftershock activity created a focus zone that corresponded to a 600meter-deep marine basin south of Lesvos.Active normal faulting dominates the central and eastern portions of the Aegean Sea, and the region has experienced numerous earthquakes over the past 2.000 years.Because no significant normal faulting earthquakes have struck this region in the past few decades, when current seismological and crustal deformation data are accessible, many elements of seismicity in this region are still unknown.
Next, we present the results of the inversion based on the inversion of regional waveform data for the strong event of 12 June 2017, with a magnitude of Mw 6.3 on Lesvos Island.Because of its location, this earthquake demonstrated the applicability of this method, with particularity.According to the Disaster and Emergency Management Presidency, Earthquake Department (AFAD) [54], available at https://deprem.afad.gov.tr/home-page, the epicenter was located in the northwest corner of Lesvos Island (38.8511 • N, 26.2565 • E).Due to insufficient azimuthal coverage of the Greek stations, attempts were made to recalculate some fault plane solutions by including records from Turkish stations that were located at mixed epicentral distances of more than 300 km, thereby expanding our azimuthal coverage to the west and south of the epicenter.
personnel already faced by inflicting casualties on some island residents.While rescue personnel attempted to guarantee the safety of earthquake-affected communities, medical teams were quickly organized to help those in need.Each station was employed in the calculation of the focal mechanism of the six stations for the three components at epicentral distances between 130 and 380 km.The moment tensor inversion technique described previously was used to determine source parameters.The best-fitting solution is φ = 130 • , δ = 50 • , λ = -60 • rake, and the depth at a focal depth of 10 km.The computed double couple (DC) was found to be equal to 73%, while the compensated linear vector dipole (CLVD) was found to be equal to 27%.The seismic moment is derived as M 0 = 3.46•10 25 dyn × cm. Figure 4 shows the procedural outcomes.
of Lesvos Island (38.8511°N, 26.2565° E).Due to insufficient azimuthal coverage of the Greek stations, attempts were made to recalculate some fault plane solutions by including records from Turkish stations that were located at mixed epicentral distances of more than 300 km, thereby expanding our azimuthal coverage to the west and south of the epicenter Each station was employed in the calculation of the focal mechanism of the six sta tions for the three components at epicentral distances between 130 and 380 km.The mo ment tensor inversion technique described previously was used to determine source pa rameters.The best-fitting solution is φ = 130°, δ = 50°, λ = -60° rake, and the depth at a focal depth of 10 km.The computed double couple (DC) was found to be equal to 73% while the compensated linear vector dipole (CLVD) was found to be equal to 27%.The seismic moment is derived as M0 = 3.46•10 25 dyn × cm. Figure 4 shows the procedural out comes.

Statistical Analysis
Another crucial component of this study is seismicity rate analyses, which considers the frequency and distribution of seismic occurrences across time.Researchers want to understand the fundamental properties of seismic sequences, such as the frequency, magnitude, and spatial distribution of earthquakes, using cutting-edge statistical approaches to seismic data.Seismologists have used information obtained from a network of seismometers placed around the area to conduct this type of investigation.These devices provide a comprehensive dataset for seismological investigations by continually recording the ground vibrations resulting from seismic events.Statistical correlations known as Gutenberg-Richter and Omori's laws are frequently used in seismological analyses.While Omori's law describes the aftershock decay rate following a mainshock, Gutenberg-Richter's law describes the logarithmic relationship between the frequency of earthquakes and their magnitudes.
In this study, a large volume of seismological data was used to draw reliable conclusions regarding the rate of change in seismicity.The graph showing the rate of seismicity in the North Aegean region over time offers important details regarding the region's tectonic processes and seismic activity.Figure 5 shows a visualization of the seismicity rate of the North Aegean region for the period 2013-2023.The x-axis represents the scale of the recorded magnitude, whereas the y-axis represents the number of records.In total, for the last 10 years, 8.138 events were manually located.
meters placed around the area to conduct this type of investigation.These devices provide a comprehensive dataset for seismological investigations by continually recording the ground vibrations resulting from seismic events.Statistical correlations known as Gutenberg-Richter and Omori's laws are frequently used in seismological analyses.While Omori's law describes the aftershock decay rate following a mainshock, Gutenberg-Richter's law describes the logarithmic relationship between the frequency of earthquakes and their magnitudes.
In this study, a large volume of seismological data was used to draw reliable conclusions regarding the rate of change in seismicity.The graph showing the rate of seismicity in the North Aegean region over time offers important details regarding the region's tectonic processes and seismic activity.Figure 5 shows a visualization of the seismicity rate of the North Aegean region for the period 2013-2023.The x-axis represents the scale of the recorded magnitude, whereas the y-axis represents the number of records.In total, for the last 10 years, 8.138 events were manually located.The distribution of the number of events concerning their magnitude is shown in Figure 5. Here, we observed that most earthquakes occurred between 2.0 and 3.0 M L .The distribution of earthquakes, as shown in the diagram, follows a normal distribution.
Figure 6 shows the relationship between the duration of the event across the years and its magnitude in the North Aegean Sea of Greece, with the three stars (blue and green; these colors are proportional to the size of the earthquakes) indicating three strong earthquakes that occurred in the last decade in the study area.From the diagram of a post-seismic sequence, there are often too many overlapping earthquakes.It is difficult to separate many facts and find reliable and small facts.Over time, the sequence slows, and individual events become more easily detectable.and its magnitude in the North Aegean Sea of Greece, with the three stars (blue and green; these colors are proportional to the size of the earthquakes) indicating three strong earthquakes that occurred in the last decade in the study area.From the diagram of a postseismic sequence, there are often too many overlapping earthquakes.It is difficult to separate many facts and find reliable and small facts.Over time, the sequence slows, and individual events become more easily detectable.Figure 6.For the 8.138 seismological records, the location with time is represented as a function of magnitude.Each occurrence from the events that occurred in the broader area of the North Aegean Sea is represented by its date (years) on the x-axis and its magnitude (ML) on the y-axis.

Sensor Technologies for Detecting Seismic Events
Seismic sensors are critical tools for detecting and monitoring seismic events and provide vital data for understanding earthquakes and mitigating their effects.The use of these sensors allows the detection of ground motions caused by seismic waves and the conversion of these motions into signals that can be analyzed to derive various properties of seismic events.The main objective of seismic sensors is to detect and record the ground movements caused by seismic waves.These sensors convert mechanical movements into electrical signals, which are then analyzed to determine earthquake characteristics, such as the size, location, and depth of the epicenter.Figure 6.For the 8.138 seismological records, the location with time is represented as a function of magnitude.Each occurrence from the events that occurred in the broader area of the North Aegean Sea is represented by its date (years) on the x-axis and its magnitude (ML) on the y-axis.

Sensor Technologies for Detecting Seismic Events
Seismic sensors are critical tools for detecting and monitoring seismic events and provide vital data for understanding earthquakes and mitigating their effects.The use of these sensors allows the detection of ground motions caused by seismic waves and the conversion of these motions into signals that can be analyzed to derive various properties of seismic events.The main objective of seismic sensors is to detect and record the ground movements caused by seismic waves.These sensors convert mechanical movements into electrical signals, which are then analyzed to determine earthquake characteristics, such as the size, location, and depth of the epicenter.
Seismic sensors are generally divided into two main categories: conventional and advanced sensors.Conventional seismic sensors include seismometers, accelerometers, and geophones.Accordingly, advanced sensors include broad-spectrum seismometers, distributed acoustic sensors, and fiber-optic sensors.
Seismometers [55,56] are used to measure the speed of ground movements.These are essential tools for detecting and recording seismic activity and are placed in fixed facilities to monitor earthquakes over large geographic areas.Accelerometers [57,58] record ground acceleration and are vital for monitoring strong earthquakes and studying and assessing their effects on infrastructure and communities.Seismometers and accelerometers are installed on both onshore and offshore seismic networks to monitor earthquakes.Finally, geophones [59,60] convert ground movement into voltage and are widely used in local and regional networks for the reliable detection of seismic events.In recent years, significant advances have been made in seismic sensor technology to enhance the accuracy and coverage of seismic monitoring systems.
Broad-spectrum seismometers can detect a wide range of frequencies, from lowfrequency tectonic movements to high-frequency tremors caused by smaller seismic events.These are essential for providing a comprehensive understanding of seismic activity at different scales [61,62].Distributed Acoustic Sensing (DAS) technology uses fiber optics to detect and measure vibrations along cables, providing high-resolution data for monitoring large areas [63,64].The DAS can monitor large areas and provide high-resolution data, making it an ideal choice for both regional and local seismic monitoring.
Fiber Bragg Grating (FBG) sensors represent another class of advanced sensors.FBG sensors measure deformations along optical fibers and are particularly sensitive to ground changes [65,66].Fiber-optic sensors represent a significant advancement in the field of seismic monitoring owing to their high sensitivity, wide dynamic range, and immunity to electromagnetic interference.The use of seismic sensors is crucial for the early detection of seismic events, assessment of their impact, and improvement in earthquake preparedness and community resilience.These sensors contribute to the prevention and reduction in damage by providing reliable data for analyzing and understanding seismic events.They are particularly useful in areas that are prone to tectonic shifts and landslides.Fiber-optic sensors are increasingly used in underwater settings to monitor seismic activity and assess potential tsunami hazards.For example, the deployment of DAS in the Mediterranean region could significantly enhance the detection of undersea earthquakes.FBG sensors can provide valuable ground stress data and help predict seismic hazards in areas such as the North Aegean region, where tectonic activity prevails.Seismic sensors are widely used in research programs and earthquake monitoring networks.The development and integration of new technologies, such as fiber optics, continue to improve the accuracy and efficiency of monitoring systems, enabling a better understanding of seismic hazards and the implementation of measures to protect communities.
The integration of conventional and advanced sensor technologies provided a robust framework for seismic monitoring.The combination of traditional seismometers and modern fiber-optic sensors ensures a comprehensive coverage and high-resolution data acquisition.This integration enables the detection of a wide range of seismic activities, from small tremors to large earthquakes, thereby improving earthquake preparedness and mitigation strategies [67][68][69][70].

Discussion
The North Aegean area of Greece is known to have a complex tectonic structure.Seismic activity frequently occurs because different tectonic plates collapse into each other.This study shows how the complex interaction of tectonic movements at the point where the Eurasian, African, and Eastern plates meet is shown by seismic activity in this area.Throughout history, the North Aegean region has been hit by numerous major earthquakes that have damaged nearby towns and infrastructure.The Izmit earthquake in 1999 and the Bodrum-Kos earthquake in 2017 are well-known events that have had a significant effect on the area.Studying earthquakes in this area is a unique opportunity to determine how tectonic plates move and the associated earthquake risks.
Our in-depth study, which examines the timing and location of earthquakes, focal mechanisms, and the release of seismic moments, provides important information about the seismic characteristics of this area.Our results show that there has been more seismic activity over the last ten years, which makes sense given both the complex tectonic environment of the region and the increase in installations of seismological and other categories of stations (accelerometers, etc.).
The data show that large earthquakes tend to come from places that are more broken up, whereas smaller ones occur around more active fault zones.This pattern suggests that the fault dynamics of the region are becoming increasingly complex, possibly because of the continuous accumulation and release of tectonic stresses.
It is very important to conduct a seismic risk assessment of the North Aegean region because more people are moving there, and important infrastructure is being built near areas prone to earthquakes.Using advanced methods to study earthquakes, like fault plane solutions (FPSs) and moment tensor solutions (MTSs), can tell us a lot about how stress is distributed and how cracks form in the area.This knowledge is very important for determining how to better prepare for and respond to earthquakes and for understanding how they might occur in the future.The Mw 7.0 earthquake that occurred near the island of Samos on October 30, 2020, is one example.Not only did this event cause a lot of damage and death, but it also showed the importance of understanding how ruptures occur in the area.This information is vital for understanding the potential of future seismic events and improving disaster preparedness and response strategies.One such case is the Mw 7.0 earthquake that occurred near the island of Samos on October 30, 2020.This event not only caused significant damage and casualties but also highlighted the importance of understanding rupture processes in the region.The focal mechanism of the earthquake indicated a normal rupture that was consistent with regional tectonics.Aftershocks occurred and their processes were studied later.This shows that the transformation from lateral shear to extension occurred more clearly.This also indicates the dynamics of the tectonic environment of the area.
In the last ten years, improvements in seismological monitoring have allowed us to learn a lot about how earthquakes have occurred in the North Aegean Sea.Installing seismological networks on land and at sea has made it possible to collect high-resolution data, making it easier to analyze earthquake sequences more accurately.This improved tracking ability is important for early warning systems and for making future earthquakes less damaging.For more accurate seismic-hazard models, it is important to keep tracking and collecting data along with using more advanced analytical methods.To solve the complicated problems that earthquakes in this area cause, it is also important to conduct studies that include geological, geophysical, and technical points of view.
The seismic activity in the North Aegean Sea presents unique challenges and opportunities for future research.Understanding seismotectonic processes, fault mechanics, and the impact of seismic risk assessments is critical.Although this study provides a comprehensive overview of seismicity in the North Aegean Sea, further research is required to improve our understanding of the underlying tectonic processes.The key directions for future research are as follows:

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Detailed well mapping: Conducting detailed geological and geophysical surveys to map active fault systems more accurately is a fundamental direction for research.
Understanding the geometry and segmentation of faults is essential for evaluating the potential for large earthquakes to occur.Through these investigations, we will be able to identify areas that are more likely to be affected by future seismic activity, and better prepare response and mitigation plans.

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Installation of additional seismometers: Increasing the density of seismic stations (Appendix A), particularly in under-monitored areas, will improve the detection and characterization of seismic events.Enhanced spatial coverage provides more comprehensive datasets for the analysis.For more accurate seismic-hazard models, they need to be constantly monitored and require data collection, along with the need for more advanced analytical methods.To deal with the complicated problems that seismic risks in this area cause, it is also important to conduct studies that include geological, geophysical, and technical points of view.

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3D seismic velocity models: The development of high-resolution 3D models of the crust and upper mantle is critical for better understanding seismic wave propagation and heterogeneities in the Earth's structure.These models can assist in the simulation and prediction of earthquakes more accurately.They will also help us to find places where large earthquakes are most likely to occur.Three-dimensional models will also help improve early warning systems and make towns more able to handle earthquakes.

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Integration of new technologies: The use of cutting-edge technologies such as satellite remote sensing and ground-based LIDAR can complement traditional seismological methods.These technologies offer detailed information about how the ground is changing shape and how faults are moving.Researchers can find small changes in the Earth's surface caused by earthquakes using satellite systems such as Interferometric Synthetic Aperture Radar (InSAR).This technology allows continuous monitoring of large areas and the analysis of ground deformation with millimeter precision.Light Detection and Ranging (LIDAR) on the ground can also provide exact 3D data of the ground surface.In places prone to earthquakes, this technology is particularly helpful for mapping faults and studying geomorphology.Researchers can create full models of seismic activity by mixing data from ground-based LIDAR, satellite remote sensing, and regular seismographs.This combination provides a fuller picture of the events that happen to cause earthquakes.

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Integration with climate studies and studying socioeconomics: This involves looking into how climate change might affect seismicity, mainly in terms of rising sea levels and how they affect fault systems along the coast, and working with social scientists to learn about the human aspects of earthquake risk, such as how prepared communities are, how people think about risk, and the best ways to communicate about public safety.• Analysis of historical seismicity: This involves compiling and analyzing historical and paleoseismic records to identify long-term patterns and cycles of seismic activity.This can provide information on the recurrence intervals of major earthquakes.

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Sequences of aftershocks and foreshocks: This involves studying the temporal and spatial characteristics of aftershock and foreshock sequences to improve earthquake prediction models and early warning systems.
By taking these research directions, the scientific community can improve their understanding of seismic hazards in the North Aegean region and beyond.These efforts will contribute to more effective earthquake preparedness and risk-reduction strategies, ultimately improving public safety and resilience to future seismic events.

Conclusions
The collision of Eurasian, Anatolian, and African plates in the North Aegean Sea region demonstrates a complex tectonic context.This complexity causes a vast variety of seismic events, including shallow and deep earthquakes, strike-slip, thrust, and normal faulting.According to our investigation, the North Aegean Sea region is seismically active and frequently experiences earthquakes of various magnitudes.The continuous convergence and collision of tectonic plates are principally responsible for the increased seismicity.The main objective of this study was to investigate the earthquakes that occurred in Greece's North Aegean Sea region over the last 10 years and compare them statistically and from a seismological point of view.Some patterns in seismic activity that can be found through statistical analysis include the number of earthquakes, their size, and how they propagate out in space.This knowledge is important for identifying places with a high risk of earthquakes and determining how likely it is that an earthquake may occur soon.Scientists can determine the correlation between the earthquake frequency and magnitude through statistical analysis.The probability of larger, potentially more damaging earthquakes occurring during a specific timeframe is estimated using this information.Only a few examples of seismic activity patterns that can be discovered by statistical analyses include the frequency, magnitude, and spatial distribution of earthquakes.This information is essential for identifying areas with high seismic risk and for calculating the probability of future earthquakes.
Two strong events that occurred in the broader area of the North Aegean Sea, Greece, were analyzed.The first seismic event was a strong earthquake that occurred on 12 June 2017, on Lesvos Island, Greece, with magnitude ML 6.1, and the second occurred on 30 October 2020, Samos Island.Moment tensor inversion using regional data was used for both the events.The analysis indicates activation for both events of a normal fault, a fact confirmed by corresponding geodetic studies.Additionally, the focal mechanisms indicated an extensional stress field oriented differently than previously reported.
During the study period, more than 8.000 events were recorded and analyzed.It was deemed necessary to carry out a statistical study on the one hand because it is the first time that a seismological catalog of the area has been studied for such a long period (10 years).In addition, scientists can identify any variations in the frequency and intensity of earthquakes by analyzing the seismicity rate over several years, and researchers can identify long-term seismic trends by comparing data from several decades or even centuries.This knowledge advances our understanding of geological processes and earthquake cycles.
In our study, the magnitude and relative time distribution of the earthquakes indicated a normal distribution.Scientists have recognized variations in earthquake frequency and intensity by examining the seismicity rate over several years.
In conclusion, the present study concluded the following.
• The North Aegean area has experienced a significant number of earthquakes, considering the complicated tectonic reactions between the colliding plates.Most earthquakes that have occurred in the last ten years have been very strong.• A detailed analysis of seismological data revealed patterns in the occurrence of earth- quakes over time, with periodic episodes of enhanced seismic activity followed by quieter periods.• This comprehensive study, which combines a spatial-temporal analysis with research on source mechanisms, provides more information than previous studies on the seismic processes that control this very active area.

•
Major earthquakes that occurred in both 2017 and 2020 indicated the complexity of the seismicity and risk of earthquakes in this area, which affected people and buildings nearby.A close study of these types of events helps us learn more about how earthquakes occur and the dangers that come with them.• To become more accurate at determining how dangerous earthquakes are and to prepare for them, we need to keep an eye on them and perform more advanced seismological research.For effective methods to reduce risks, we need to study the long-term patterns, cycles, and triggers of earthquakes.
recording smaller tremors using electronic technology.This technology has improved our understanding of seismic waves and their characteristics.Simultaneously, international observation networks, such as the World Wide System of Seismographic Stations (WWSSN), were established in the 1960s, enabling data collection worldwide and improving forecasts and analyses.
The following table (Table A1) provides data on the number and type of stations, as well as data availability and the time of station installation.

Figure 1 .
Figure 1.General structure map of the North Aegean Sea.Red circles represent prefectures.The green stars indicate strong historical earthquakes.Purple and yellow triangles indicate the permanent stations of the Unified Seismological Network (HUSN), from the Seismological Laboratory of Thessaloniki (HT) and National Observatory of Athens (HL), and finally, red lines indicate the main active faults for the study area, available at https://land.copernicus.eu/imagery-in-situ/eu-dem[13].

Figure 1 .
Figure 1.General structure map of the North Aegean Sea.Red circles represent prefectures.The green stars indicate strong historical earthquakes.Purple and yellow triangles indicate the permanent stations of the Unified Seismological Network (HUSN), from the Seismological Laboratory of Thessaloniki (HT) and National Observatory of Athens (HL), and finally, red lines indicate the main active faults for the study area, available at https://land.copernicus.eu/imagery-in-situ/eu-dem[13].

Figure 2 .
Figure 2. General structure map of the broader area of the North Aegean Sea; purple squares represent prefectures, while red lines are the main active faults in the study area.Bathymetry was obtained using Emodnet Bathymetry [33] and DEM.Light blue triangles represent the permanent stations of the Unified Seismological Network (HUSN) [11], orange stations represent the corresponding seismological stations from the Seismological Laboratory of the Aristotle University of Thessaloniki [10], and the two red stars indicate strong earthquakes (12 June 2017, ML 6.1, and 30 October 2020, ML 6.7) that occurred in the region of Lesvos Island and Samos Island.The distribution of epicenters for the period 2014-2019 is indicated via the size and color of the points according to magnitude and depth.

Figure 2 .
Figure2.General structure map of the broader area of the North Aegean Sea; purple squares represent prefectures, while red lines are the main active faults in the study area.Bathymetry was obtained using Emodnet Bathymetry[33] and DEM.Light blue triangles represent the permanent stations of the Unified Seismological Network (HUSN)[11], orange stations represent the corresponding seismological stations from the Seismological Laboratory of the Aristotle University of Thessaloniki [10], and the two red stars indicate strong earthquakes (12 June 2017, ML 6.1, and 30 October 2020, ML 6.7) that occurred in the region of Lesvos Island and Samos Island.The distribution of epicenters for the period 2014-2019 is indicated via the size and color of the points according to magnitude and depth.

Figure 3 .
Figure 3. Moment tensor solution of the 30 October 2020 (11:51 UTC) earthquake.The green arrow in the misfit/compensated linear vector dipole (CLVD)-versus-depth graph (center-up) indicates the selected solution.The center-lower portion displays a summary of the answers together with the accompanying beach ball.At the inverted stations for the radial, tangential, and vertical components, the observed and synthetic displacement waveforms are shown on the left as continuous and dotted lines, respectively.A summary of the solution and the fault plane solution as a lower-hemisphere equal-area projection is shown at the left-center-right and upper-middle-lower portions, respectively.

Figure 3 .
Figure 3. Moment tensor solution of the 30 October 2020 (11:51 UTC) earthquake.The green arrow in the misfit/compensated linear vector dipole (CLVD)-versus-depth graph (center-up) indicates the selected solution.The center-lower portion displays a summary of the answers together with the accompanying beach ball.At the inverted stations for the radial, tangential, and vertical components, the observed and synthetic displacement waveforms are shown on the left as continuous and dotted lines, respectively.A summary of the solution and the fault plane solution as a lower-hemisphere equal-area projection is shown at the left-center-right and upper-middle-lower portions, respectively.

Figure 4 .
Figure 4. Moment tensor solution of the 12 June 2017 (15:28 UTC) earthquake.The center-lower portion displays a summary of the answers together with the accompanying beach ball.At the inverted stations for the radial, tangential, and vertical components, the observed and synthetic displacement waveforms are shown on the left as continuous and dotted lines, respectively.The summary of the solution and the fault plane solution as a lower-hemisphere equal-area projection are shown at the left-center-right and upper-middle-lower portions, respectively.

Figure 5 .
Figure 5. Visualization of the seismicity rate of the North Aegean region for 2013-2023.The number of seismological recordings of 8.138 manually located events.The green line indicates the normal distribution that follows the number of earthquakes relative to the magnitude.

Figure 5 .
Figure 5. Visualization of the seismicity rate of the North Aegean region for 2013-2023.The number of seismological recordings of 8.138 manually located events.The green line indicates the normal distribution that follows the number of earthquakes relative to the magnitude.

Table 1 .
Characteristics of seismological stations in the study area.Station coordinates are in decimal degrees, and elevation is in m.Sources: [10,11].

Table 1 .
Characteristics of seismological stations in the study area.Station coordinates are in decimal degrees, and elevation is in m.Sources: [10,11].

Table 2 .
[12]acteristics of stations belonging to the Strong Motion Network in the study area.Station coordinates are in decimal degrees, and elevation is in m.Sources:[12].

Table A1 .
Summary of Station Data.