Late Quaternary Relative Sea-Level Changes and Vertical GNSS Motions in the Gulf of Corinth: The Asymmetric Localization of Deformation Inside an Active Half-Graben

Abstract

Remains of past sea levels such as tidal notches may provide valuable information for the investigation of relative sea-level changes (RSL) of eustatic/tectonic origin. In this review, we focus on case studies of coastal changes from the Corinth Gulf, where impacts of past earthquakes can be traced through various indicators. The southern coast has undergone a tectonic uplift during the Holocene, whereas the northern coast has undergone subsidence. The magnitude of RSL fall in the south Corinth Gulf is larger than RSL rise in the north. Exploiting previous measurements and datings, we created a geodatabase regarding the relative sea-level changes of the whole gulf, including geodetic data based on permanent GNSS observations. The combination of geomorphological (long-term) and geodetic (short-term) data is a key advance for this area, which is characterized by fast rates of N-S crustal extension and strong earthquakes. The joint dataset fits the tectonic model of an active half-graben where the hanging wall (northern coast) subsides and the footwall (southern coast) is uplifted. The highest uplift rates (3.5 mm/year) are near Aigion, which indicates an asymmetric localization of deformation inside this active rift.

1. Introduction

Studying the geomorphological structure and evolution of an area can aid in the reconstruction of its tectonic history [1]. In tectonically active areas, the geomorphological structure is often controlled by vertical or horizontal tectonic movements [2,3].

The Gulf of Corinth is a major marine basin of Greece, which separates the Peloponnese from central Greece (Figure 1). It is a significant WNW–ESE rift structure [4] and one of the most tectonically active regions of Greece [5,6,7,8,9]. It is a young rift whose length is approximately 120 km. Its width roughly reaches 40 km. The highest width (25–30 km) of the gulf is found in its central–eastern part, where the syn-rift sedimentary sequence also reaches its maximum thickness (up to 3 km) [10]. Its maximum depth reaches 860 m in the eastern part [11]. In the eastern part, it forms two lesser gulfs with a depth of less than 200 m, Lechaion (Figure 1) and Alkyonides Gulfs.

The gulf is undergoing a N-S extension with rates reaching 13 mm/a, rendering it one of the fastest expanding regions on Earth [7,12,13,14,15,16,17,18,19,20,21,22] (Figure 1). This extension is not uniform. In the easternmost part, it undergoes an extension of approximately 6–8 mm/a [17,18,19]. The extensional regime of the gulf is expressed with several generations of segmented normal faults [15,23,24,25,26,27,28,29,30,31], which are mainly oriented E-W [32] and dipping toward north. According to several authors [33,34,35,36,37,38,39,40], the fault activity has migrated northwards. The ongoing extension was initiated during the Upper Miocene. It is due to the combination of lithospheric-scale back-arc extensional processes and gravitational collapse of the Hellenides [41,42]. The eastern part of the gulf has a thinner crust than the western part, which is around 28–30 km [43].

Figure 1. Shaded relief map showing the location of the Gulf of Corinth within Greece (see inset box) along with the main sites discussed in the text. Yellow stars show the epicenters of the 1981 (Alkyonides; [13]) and 1995 (Aigion; [44]) earthquakes. The inset map shows Greece and the red rectangle shows the location of the Corinth Gulf.

Figure 1. Shaded relief map showing the location of the Gulf of Corinth within Greece (see inset box) along with the main sites discussed in the text. Yellow stars show the epicenters of the 1981 (Alkyonides; [13]) and 1995 (Aigion; [44]) earthquakes. The inset map shows Greece and the red rectangle shows the location of the Corinth Gulf.

The southern part of the gulf, i.e., the northern part of the Peloponnese, is subject to uplift [5,45,46,47]. Its uplift rate is not uniform; the sub-basin of Patras (NW Peloponnese) undergoes a 0.8 to 1 mm/a uplift, whereas in Corinth, the uplift rates decrease by 0.4 mm/y. Rio is characterized by the highest uplift rate, which has even been calculated at 4.4 mm/y [48].

The rift’s development followed two stages. The initially shallow marine basin was filled with freshwater and was controlled by tectonics [4,33]. Consequently, the basin was characterized by the presence of Gilbert-type deltas and coarse sediments mainly along the southern shore [33,49,50,51].

The Gulf of Corinth is located in the back-arc domain of the convergence zone between the African and Eurasian plates. Therefore, strong (M6+) earthquakes are common inside the gulf. In fact, it is considered the most seismically active area of Europe [5]. Among the most recent strong earthquake events was the 1981 Alkyonides sequence (24 February 1981 M6.7 and 25 February 1981 M6.4; [13]; Figure 1) and the M6.5 event of 15 June 1995 offshore Aigion (Figure 1; [26,32,44,52,53,54]). To highlight the intense seismic activity, we include a seismicity map with 43 earthquakes of magnitude M ≥ 4.0, including three events with M ≥ 5.0 (see Appendix A, Figure A1; source: National Observatory of Athens catalogue, period 2008–2023; last accessed 16 October 2023).

In terms of tectonic style, the Gulf of Corinth has been identified as a half-graben whose southern coasts have undergone uplift and whose northern ones have been subjected to subsidence, as it was characterized by the presence of landforms that reveal this trend [15,55,56]. In this review paper, we focus on tectonically driven sea-level changes in the Corinth Gulf. We mainly focus on case studies of earthquake-driven coastal changes, where impacts of past earthquakes can be traced mainly through tidal notches but also through biological indicators. For this purpose, an extensive bibliographic review was accomplished, and a geodatabase was developed with the main sea-level indicators of the Corinth Gulf for the Holocene. The tectonic movements that have affected the gulf during the Holocene were concluded not only through geomorphological, archaeological and biological indexes, but geodetic data as well, which were based on permanent Global Navigation Satellite System (GNSS) observations collected from permanent stations around the gulf. Data that arose from both types of surveys were calibrated based on modern data (see Section 2).

2. Materials and Methods

For the purposes of this study, we reviewed and compiled a geodatabase of sea-level indicators reported in the Corinth Gulf for the late Holocene. The geodatabase is composed of sea-level data from the available literature as well as past published research by the authors, mainly focusing on tidal notches and biological indicators. The developed database is presented in a free ArcGIS Online webmap application powered by ESRI (https://www.esri.com (last accessed on 15 September 2023). The webmap application is accessible here: https://evelpidou.maps.arcgis.com/apps/instant/sidebar/index.html?appid=fa9556300b8c433492e7f7e2784eb4f0 (published in 20 September 2023, accessed on 15 September 2023) (e.g., [57,58]).

The database includes spatial information such as locality name, region, and status in relation to m.s.l. A variety of descriptive information is also included, such as the feature and feature type, the relative sea level (RSL), geometrical characteristics depending on the feature, height, genesis (if applicable), age in relation to the dating method, the calibrated age, the age range and errors and the rate of uplift (for features indicating uplift). Finally, the database contains the authors’ comments, if applicable, as well as the corresponding reference and DOI.

The provided application has an interface friendly to the user, while at the same time, it incorporates various interactive tools supporting the user for easy and simple indexing of the preferable geodata. At the left bar of the application, the user can find tools such as the activation of the map’s legend, and they can change the basemap (with 10 different options, such as satellite images, plain geographical maps etc.), the map of details and the information when clicking on a map’s feature. Further provided tools are the home button in order to reset the map, the compass, the metadata of the online map and a manual for keyboard shortcuts. The map can be zoomed in and out as much as the user desires, while it provides a roller tool for any special measurements. Finally, the user has the ability to share this online map with other users using three different social media, copy the applications URL or even print as a PDF.

Geodetic Data

Dual-frequency geodetic data can be utilized to obtain position time series for tectonic studies. The geodetic data comprise a 3D set of secular velocities provided by permanent GNSS observations from twenty (20) stations around the Gulf of Corinth (

Table 1. List of GNSS stations around the Gulf of Corinth and their vertical velocities (after Briole et al. [19]). V_up is vertical velocity (in mm/a), Sd is standard deviation.

Longitude (°)	Latitude (°)	Vup (mm/a)	Sd (mm/a)	Station Code
23.123	37.939	0.2	2.1	AGTH
22.073	38.242	3.5	1.1	AIGI
23.440	37.734	1.4	0.9	AIGU
22.075	38.255	−0.8	1.7	EGIO
21.928	38.427	−1.4	0.6	EYPA
22.392	38.375	−2.3	1.1	GALA
22.430	38.431	−1.8	0.9	ITEA
22.427	38.434	−1.3	1.1	ITEU
22.102	38.031	−0.7	1.2	KALA
22.750	38.014	−1.7	1.1	KIAT
22.931	37.942	0.5	0.6	KORI
22.046	38.209	−1.0	0.7	KOUN
22.618	37.972	0.6	1.1	KRYO
21.973	38.320	1.7	1.0	LAMB
22.865	38.440	1.3	1.2	LIVA
22.184	38.322	−0.8	0.7	PSAR
21.871	38.329	−3.4	1.0	PSAT
22.073	38.365	−2.1	0.6	TRIZ
22.135	38.234	2.3	0.9	VALI
21.912	38.385	−6.2	1.0	XILI

; Figure 2). The use of GNSS, and particularly the Global Positioning System (GPS), has been used to study the long-term crustal deformation occurring at regional or local scales throughout Greece by use of the analysis of position time series of daily solutions [19,59,60]. Around the Gulf of Corinth, most of the permanent GNSS stations were installed in the early 2000s, and they were continuously occupied over ten (10) years; thus, accurate secular velocities (East, North, Up components) were obtained [19,59].

In this study, we use the vertical velocity dataset of Briole et al. [19] in the global reference frame ITRF2014 [61]. This set of velocities has been corrected for transient effects on the position time series (co-seismic offsets, post-seismic relaxation, etc.). The transient velocity was estimated and was removed from the total velocity field to extract what can be considered as the secular velocity field, which reflects long-term tectonic motion. The earthquakes that have affected the Gulf of Corinth GNSS station positions were the Movri (Achaia) 2008 event [62,63], the Efpalion 2010 events [9,64] and the Zakynthos 2018 subduction event [65,66]. Our data span the period 2000–2020, so we do not consider the shallow, offshore event of 17 February 2021 (Mw = 5.3) east of Rio ([67]; Figure 1; Appendix A, Figure A1). This shallow event ruptured a north-dipping normal fault and did not affect the coastal GNSS stations in the vertical component except station XILI [67]. In terms of data uncertainties, for eleven (11) out of twenty (20) GNSS stations, the uncertainties are ≤1 mm/y, while the uncertainties exceeded the vertical velocity estimates only for four (4) stations (namely AGTH, EGIO, KALA and KRYO; see Table 1). The latter stations are located along the south coast of the gulf (see Figure 2 for a station map). For stations without a clear trend on the vertical, it is usual to observe uncertainties of the same order of magnitude as the signal despite a 6–10 yr longevity of the time series [60].

Satellite radar (SAR) images can also provide data on ground motion patterns especially related to seismic slip along large faults [44,68,69,70]. Radar time-series data achieve great results in minimizing the effects of the atmosphere and in exploring areas with vegetation such as river deltas [69]. The SAR image processing aims to produce Permanent Scatterers (PS) time series or interferogram stacks, so it is possible to obtain the mean ground velocity map and the relative displacement time series in LOS (line-of-sight), E–W and Up–Down components. In the Gulf of Corinth, the analysis by Elias and Briole ([69]; their Figure 16) covers the western part (period 2002–2010) and shows that the south coast is uplifting, while the north coast is subsiding. The mean rates of vertical motion are comparable to GNSS that is from −4 mm/y up to +4 mm/y. The European Ground Motion Service (EGMS) product ([71,72]; 100 m grid), which spans the period 2015–2021, also shows a general subsiding pattern of the north coast of the gulf (Figure 3). The greatest rates of subsidence are observed in the western part of the northern coastline near Trizonia islands (Figure 1; see also GNSS station TRIZ in Table 1). The 1995 Aigion earthquake had a clear InSAR signal of ground subsidence centered in the area of Cape Psaromyta (Figure 1; [44]).

3. Sea-Level Markers

Changes in the sea level can be either owed to eustatic processes, which affect the level of the sea globally [74,75] and are a consequence of the successive melting and accumulation of ice in glaciers, or isostatic and/or tectonic processes, which bear an impact locally. When isostasy and/or tectonics are active in an area, any changes in sea level are owed to them as well, in which case they are referred to as relative sea-level changes [76].

Vertical tectonic movements include either uplift or subsidence, resulting in a fall or rise in the sea-level correspondingly. Such relative sea-level changes can be reflected in several structures and formations known as relative sea-level markers. Such markers can be geomorphological, such as those studied in this paper, archeological, such as submerged or uplifted harbors, or biological ones, such as uplifted or submerged carbonate rocks with Lithophaga holes.

The Gulf of Corinth, as part of Greece and consequently the eastern Mediterranean region, is not only affected by eustatic sea-level changes but vertical or partly vertical tectonic movements as well. It is a very active region, meaning that tectonics has played a very significant role in the changes of the sea level over the last thousand years. Therefore, the coastal zone and other features of the gulf offer several pieces of evidence regarding active tectonic movements, such as uplifted shorelines and earthquake-driven landslides [53,55,77,78,79].

3.1. Tidal Notches

Tidal notches are horizontal U- or V-shaped rock undercuttings that have been formed through the simultaneous action of physical, chemical and biogenic erosional processes [80,81], but bioerosion seems to play the key role in their formation [82]. The organisms that primarily facilitate bioerosion are chitons, cyanobacteria and patellaceous gastropods [83]. Bioerosion rate is not uniform, as it fluctuates between less than 0.1 mm/a and more than 1 mm/a, its average value reaching 0.2 to 0.3 mm/a [80,84,85,86]. The primary factors that affect the bioerosion rate include water temperature, salinity and air pressure. These factors do not solely affect the bioerosion rate directly but also the tidal range at a local scale [87]. Additionally, the rock structure affects bioerosion rates. As it was already mentioned, tidal notches are mainly formed in carbonate rocks. Yet, there are several rock characteristics that control a rock’s susceptibility to bioerosion, such as the layers’ slope and the rock’s discontinuities [88]. Bioerosion rate, and thus the rock undercutting, are higher near the mean sea level that is in the midlittoral zone, as it is this area of the coastal zone that hosts the highest number of eroding organisms. The part of the notch that is characterized by the highest undercutting is referred to as the vertex. The undercutting decreases on either side of the notch’s vertex. The overall notch shape is controlled by several factors, including erosion (physical, chemical and biological), wave activity, lithology and resistance to erosion [89].

Tidal notches are usually formed in limestone cliffs in the mid-littoral zone. Tidal notches formed on compact limestones are a very good sea-level indicator for microtidal areas [80]; they are considered to be precise sea-level indicators, and they can attest to the modality of sea-level change (rapid or slow), allowing the identification of palaeo-seismic events. The fact that tidal notches are formed near the sea level renders them a very significant sea-level indicator. In fact, given that different notch profiles reflect different bioerosion rates, tidal range and/or period for which the sea level remained constant, the notch profiles offer valuable information regarding the conditions that prevailed when they were formed and, more specifically, regarding the position of the sea level during their formation, the duration in which the mean sea level remained in the same position (which would be the position of the vertex), as well as the means of the notch’s displacement from its initial position (i.e., whether it was co-seismic, that is rapid or gradual) [80,86,87,90].

Tidal notches can be linked to several co-seismic uplift events, but identifying a single seismic event through studying them is rarely achievable [91,92,93]. Tidal notches of microtidal areas (such as the Gulf of Corinth) can offer an estimation of Holocene relative sea-level changes [94]. It is worth mentioning, however, that uplifted tidal notches are more often used as sea-level indexes (indicating sea-level rise) (see [95,96,97,98,99,100,101,102,103,104]). On the other hand, submerged notches are often difficult to observe and conduct measurements and received less attention [87,105].

The use of tidal notches as sea-level indicators is very common in the Mediterranean region, because it is generally characterized by low tidal range and wave activity, thus minimizing potential errors [88]. In order to identify a palaeo-shoreline, individual erosional marks need to be recognized as formed in the mean tidal zone of the formation period [97].

3.2. Marine Terraces

Marine terraces are wave-cut platforms formed during an episode of sea-level highstand by the combination of both global (eustatic) sea-level changes and tectonic uplift [55,106,107,108]. The morphological features of marine terraces can be associated with the Late Pleistocene sea-level fluctuations in relationship to the tectonic movements [109,110,111,112,113].

The part of a terrace that can safely be associated to a palaeo-shoreline is called the inner edge, which corresponds to the base of the palaeo-cliff in its interface with the surface of the palaeo-platform. The elevation of the inner edge can be correlated with the extent of the total uplift since the time of formation; among a series of marine terraces, each inner edge reflects a sea-level highstand and, as such, it can be linked to a Marine Isotope Stage (MIS) [109,114,115,116,117,118,119].

In areas that undergo a relatively constant and rapid uplift, several successive marine terraces can be formed; in this case, the inner edge of each terrace corresponds to the position of the coast during the period of the terrace’s formation [108], thus allowing the identification of several sea-level fluctuation cycles [120].

3.3. Beachrocks

Beachrocks are coastal formations consisting of beach material (e.g., sand, pebbles, biogenic material) that has been cemented through the precipitation of carbonate salts, i.e., high-magnesium calcite (HCM) or aragonite [121]. Beachrocks are considered as intertidal deposits [122,123]. The granulometry of a beachrock’s material varies according to the environmental conditions. The grains may consist of quartz, flint, feldspars, heavy minerals, clasts, volcanic material, carbonate ooids, mollusk shells and skeletal fragments [124,125,126]. The cementation of beachrocks is very rapid, thus acting auxiliary in their good preservation [127].

Beachrocks are a very good sea-level proxy, because they contain information on both the horizontal and the vertical movements that have taken place in the coastal zone [128,129]. Facies analysis can be successfully utilized to reconstruct past sea-levels and sea-level changes [127].

3.4. Biological Indicators

Lithophaga are mollusks that create bores in rocks (mainly carbonates), which they use for dwelling. The upper limit of Lithophaga holes and, generally, borer shell holes is considered to be an excellent sea-level indicator [130]. Several studies [130,131,132] have shown that the upper limit of the living Lithophaga can provide the limit between the sublittoral zone, where the mollusks are protected against bioerosion and thus preserved, and the biological midlittoral zone, where these species cannot be preserved due to biogenic erosion. The limit of these two zones is frequently referred to as biological mean sea level. If fossil mollusks are found above this level, i.e., due to co-seismic uplift, their shells are well protected against erosion. Vermetids are a good sea-level indicator as well, as they can clearly show rapid, seismic movements [131,132]. An advantage of mollusk shells is that when found and collected, they can be dated with isotope methods (radiocarbon or uranium series).

3.5. Archaeological Indicators

Several archaeological constructions have been used as sea-level indicators when reconstructing an area’s palaeogeographical evolution, such as ancient harbors or fish tanks [133,134,135,136]. It is, however, important to know how an archaeological indicator is to be used. Constructions that were initially built near the sea level (such as ports and fish tanks) can offer valuable information regarding an area’s vertical tectonic movements, both qualitive and quantitative, whereas constructions such as roads do not give accurate clues regarding uplift/subsidence extent or rate [137]; in fact, a road, a cemetery or a temple that are found above the current sea level offer no information regarding the sea-level changes themselves, whereas if they are found submerged, they can only provide an estimation of the minimum subsidence extent, as the absolute altitude of their initial construction is not known. Additionally, different constructions offer different chronology opportunities. For instance, buildings can more easily be dated through archaeological data, given that their form varies through archaeological periods, than harbor facilities and marine constructions such as breakwaters and moles, whose form roughly remains unaltered over the time [137]. Additionally, a single scientific field (e.g., geomorphology, archaeology etc.) can only rarely extrapolate an accurate conclusion when studying the interaction between relative sea-level changes and archaeological markers, but it is rather the combination of these fields that produces accurate results [137].

4. Sea-Level Changes across the Gulf of Corinth

The coastal zone and other features of the Gulf of Corinth offer several pieces of evidence regarding active tectonic movements, such as uplifted shorelines and earthquake-driven landslides [23,46,53,55,77,79,138].

As far as relative sea-level change patterns are considered, the gulf can be divided into two parts: the northern and the southern. The southern part of the gulf, i.e., the coast of the northern Peloponnese (from the Gulf of Patras–Rio to the Perachora Peninsula; see Figure 1) has been undergoing tectonic uplift at least since 300 ka B.P. [139,140]. The uplift pattern is not uniform across the whole area of the northern Peloponnese, but it varies both in uplift nature (that is, episodic and rapid, co-seismic or gradual, aseismic uplift) and in uplift rates (the latter range from 0.2 to 3 mm/a).

The northern part of the gulf mostly undergoes tectonic subsidence, whose extent is less than the extent of the uplift of the northern Peloponnese. Here too, subsidence is not uniform. The submarine part of the gulf also undergoes subsidence. Subsidence rates were calculated by Moretti et al. [141] for the center of the Corinthian rift at 3.6 mm/a over the last 20 ka. Although uplift evidence is very common and easily observed in the southern part of the gulf, there exists scarce evidence for tectonic subsidence of the northern coasts [142]. In this chapter, we provide uplift and subsidence evidence for the Gulf of Corinth as well as quantitative information (e.g., uplift extent and rates; [142,143,144,145,146,147,148,149,150]). Figure 4 depicts the data collected in this research (geomorphological and geodetic) and shows the confirmed sites undergoing tectonic uplift (Figure 4 blue colors) and those undergoing tectonic subsidence (Figure 4 red colors). Appendix B,

Table A1. The dated sea-level indicators indicating uplift as well as the calculated tectonic rates.

Locality	Region	Sea Level Indicator Type	Rate (mm/y)	Reference
Aegira	South coast	Biological	+23.28	[91]
Aegira	South coast	Biological	+1.57	[91]
Aegira	South coast	Biological	+1.38	[91]
Akrata	South coast	Geomorphological	+0.62	[140]
Akrata	South coast	Geomorphological	+0.67	[140]
Akrata	South coast	Geomorphological	+0.64	[140]
Akrata	South coast	Geomorphological	+0.63	[140]
Akrata	South coast	Geomorphological	+0.60	[140]
Akrata	South coast	Geomorphological	+0.75	[140]
Akrata	South coast	Geomorphological	+0.82	[140]
Akrata	South coast	Geomorphological	+0.72	[140]
Diakofto	South coast	Geomorphological	+3.12	[143]
Diakofto	South coast	Geomorphological	+2.26	[143]
Diakofto	South coast	Biological	+3.12	[91]
Diakofto	South coast	Biological	+2.40	[91]
Diolkos	South coast	Geomorphological	+0.10	[129]
Diolkos	South coast	Geomorphological	+0.04	[129]
Flampouron	Perachora Peninsula	Geomorphological	+0.29	[144]
Flampouron	Perachora Peninsula	Geomorphological	+0.11	[144]
Flampouron	Perachora Peninsula	Geomorphological	+0.15	[144]
Flampouron	Perachora Peninsula	Geomorphological	+0.36	[144]
Heraeon	Perachora Peninsula	Geomorphological	+0.54	[144]
Heraeon	Perachora Peninsula	Geomorphological	+0.12	[144]
Heraeon	Perachora Peninsula	Geomorphological	+0.46	[29]
Heraeon	Perachora Peninsula	Geomorphological	+0.46	[29]
Heraeon	Perachora Peninsula	Geomorphological	+0.46	[29]
Heraeon	Perachora Peninsula	Geomorphological	+0.46	[29]
Heraeon	Perachora Peninsula	Geomorphological	+0.46	[29]
Heraeon	Perachora Peninsula	Geomorphological	+0.55	[29]
Heraeon	Perachora Peninsula	Geomorphological	+0.42	[29]
Heraeon	Perachora Peninsula	Geomorphological	+0.55	[29]
Heraeon	Perachora Peninsula	Geomorphological	+0.55	[29]
Heraeon	Perachora Peninsula	Geomorphological	+0.46	[29]
Heraeon	Perachora Peninsula	Geomorphological	+0.80	[145]
Heraeon	Perachora Peninsula	Geomorphological	+0.25–0.52	[39]
Heraeon	Perachora Peninsula	Geomorphological	+0.49	[55]
Heraeon	Perachora Peninsula	Geomorphological	+0.57	[55]
Heraeon	Perachora Peninsula	Geomorphological	+0.39	[55]
Heraeon	Perachora Peninsula	Geomorphological	+0.38	[55]
Heraeon	Perachora Peninsula	Geomorphological	+0.26	[55]
Heraion	Perachora Peninsula	Geomorphological	+0.55	[97]
Heraion	Perachora Peninsula	Geomorphological	+0.68	[97]
Heraion	Perachora Peninsula	Geomorphological	+0.90	[97]
Lambiri	South coast	Geomorphological	+1.60	[146]
Lechaion	South coast	Biological	+0.68	[147]
Lechaion	South coast	Biological	+0.38	[148]
Lechaion	South coast	Biological	+0.42	[148]
Lechaion	South coast	Biological	+0.36	[148]
Lechaion	South coast	Biological	+0.41	[148]
Mavra Litharia	South coast	Biological	+1.28	[47]
Mavra Litharia	South coast	Biological	+1.47	[47]
Mavra Litharia	South coast	Biological	+1.47	[131]
Mavra Litharia	South coast	Biological	+1.37	[149]
Mylokopi	Perachora Peninsula	Geomorphological	+0.77	[97]
Mylokopi	Perachora Peninsula	Geomorphological	+0.73	[97]
Platanos beach	South coast	Biological	+1.08	[91]
Platanos beach	South coast	Biological	+2.18	[91]
Platanos beach	South coast	Biological	+1.75	[91]
Platanos beach	South coast	Biological	+2.32	[91]
Platanos beach	South coast	Biological	+1.26	[91]
Platanos beach	South coast	Biological	+0.44	[149]
Psatha	Alkyonides Gulf	Geomorphological	+0.29	[150]
Psatha	Alkyonides Gulf	Geomorphological	+0.23	[150]
Psathopirgos	South coast	Geomorphological	+0.70	[46]
Vouliagmeni	Perachora Peninsula	Biological	+0.84	[139]
Vouliagmeni	Perachora Peninsula	Biological	+0.61	[139]
Vouliagmeni	Perachora Peninsula	Biological	+0.79	[139]

presents the dated sea-level indicators showing uplift and the calculated tectonic rates.

4.1. Southern Gulf of Corinth

The southern margin of the gulf has been subject to uplift for the last 300 ka [139] with an average rate of 1.5 mm/a [139,140,151]. Uplift in this part of the gulf is evident through various characteristics. Several sea-level markers have been mapped and used to calculate uplift rates in various areas of the northern Peloponnese, such as marine terraces, uplifted beachrocks, tidal notches, biological indicators, such as Lithophaga shells, and archaeological remains, such as ancient harbors and fish tanks. In several cases, the relief itself confirms that uplift has recently taken place (for instance, downcutting erosion in the southern coast of the gulf; [142]).

Generally, the Late Quaternary highest uplift rates in the southern part of the gulf are found in the central part of the northern Peloponnese, having a maximum value of approximately 3 mm/a [47]. Lykousis et al. [152] conducted marine measurements (seismic profiling, long piston coring, short gravity and box coring) in the eastern and central Corinthian Gulf. They found evidence of Upper Quaternary prodelta sequences indicating propagation and subsidence since 125 ka, at rates of 0.7–1 mm/a, whereas the vertical displacement between the northern and the southern margin was calculated at 2–2.3 mm/a. Collier et al. [153] have estimated the uplift rate of the area of Corinth and the Isthmus at 0.3 and 0.44 mm/a, but they point out that these values are only minimum. Keraudren et al. [154] mention that the uplift rate in the Xylokastro area (Figure 1 and Figure 4) reaches 1.5 mm/a.

Through the study of marine terraces, Armijo et al. [15] note that in the broader area of Corinth, south of Xylokastro (Figure 1 and Figure 4), maximum uplift rates range from 1.3 to 0.5 mm/a. At least ten marine terraces have been recorded in the northern part of the Peloponnese, thus indicating various stages/phases of tectonic uplift [15,154,155,156,157]. According to Sébrier [155], the area south of Corinth and Kiato is characterized by raised marine terraces at an altitude of up to 150 m.

Morewood and Roberts [29] have mapped two additional marine terraces besides those by Armijo et al. [15]. Their Terrace 1 has been correlated to the 125 ka high sea-level stand, the uplift rate being 0.28–0.64 mm/a [29]. Based on the assumption that the uplift rate was stable along the whole palaeo-coast [15,158], Morewood and Roberts [29] correlated Terrace 2 to the 240 ka highstand (uplift rate 0.33–0.50 mm/a) and Terrace 3 to the 330 ka highstand (uplift rate 0.36–0.74 mm/a). Uplift rates were higher in the period 330 to 240 ka than in the period 240 ka to present. Additionally, uplift rates along the north-dipping South Alkyonides fault decrease toward the end of the fault [29].

In the area of Diolkos (Figure 1 and Figure 5), there exists the homonymous paved road used in antiquity for the transportation of ships from the Gulf of Corinth to the Saronic Gulf and vice versa. The road has been constructed on a beachrock; upon its construction in the 6th century B.C., the beachrock’s development ceased. The area underwent a subsidence phase of approximately 35 cm, leading to the submergence of both Diolkos and the underlying beachrock. Thus, the beachrock continued being developed, covering part of the ancient road. Consequently, after 1569 A.D., the area underwent at least one co-seismic uplift phase, the total uplift being approximately 12 cm [129] (Figure 5).

In areas where tectonic activity is intense, such as the Gulf of Corinth, the pattern and the features of the drainage basins often reflect the impact of tectonics [159,160,161,162]. Fernández-Blanco et al. [163] concluded that the area of the northern Peloponnese has undergone uplift based on the topographical and geomorphological features of the drainage basins. On the condition that the 3D shape of drainage basins offers a well-detailed record regarding an area’s tectonics, Demoulin et al. [164] conducted morphometric measurements in the main Peloponnesian rivers flowing into the gulf in order to unwrap the area’s uplift history during the Quaternary. One of the features used by Demoulin et al. [164] was the hypsometric curve, which is used to describe the cumulative distribution of elevations of a drainage basin. The curve can be correlated to the rock volume of the catchment in comparison to the catchment’s area. The integral of the hypsometry can offer a rough estimation regarding the catchment’s evolutionary stage. The results for the drainage basins of northern Peloponnese show landscape rejuvenation. More specifically, the most recent uplift has taken place in the Aigion–Derveni area (central part of the northern Peloponnese; see Figure 1) [164].

Another metric Demoulin et al. [164] used was the Geophysical Relief. According to Small and Anderson [165], the geophysical relief is the mean elevation difference between the surface that connects the highest points of the landscape and the actual topography. It indicates the valley deepening and erosion. Demoulin et al. [164] found that the Aigion–Derveni is the most actively and most recently uplifted region, the maximum values reaching 410–420 m. According to their findings, the largest uplift rates, at least regarding the most recent event, are observed in the central area (Aigion–Derveni), while the lowest are observed in the eastern part and intermediate rates are observed in the western part. They estimated that the most recent uplift event of the northern Peloponnese occurred at about 10–20 ka. In conclusion, upon studying the topographical features of the studied drainage basins, Demoulin et al. [164] show that the uplift began in the eastern part and propagated westwards. During the Early Pleistocene uplift phase, the rates of uplift were higher in the western part of the northern Peloponnese. The Middle Pleistocene uplift phase only had an impact on the Akrata–Derveni area and, during the Holocene, only the eastern and central part continued being uplifted.

Archaeological remains (mainly uplifted harbors) have also been found in the northern Peloponnese [148,166]. The most typical ones include Lechaion (Figure 1) and Aigeira. Riddick et al. [167] conducted various sediment corings in the ancient port of Lechaion for sediment, micropalaeontology and isotope (C, O) analyses. They suggested that the harbor underwent one or more phases of rapid (co-seismic) uplift in the 6th century A.D., which led to its abandonment. After the uplift, the coastal environment switched to lacustrine, with a simultaneous increase in terrestrial sediments, which was attributed to the lowering of the base level [167]. The uplift of Lechaion could also be identified through rocks bearing mollusk borings (Figure 6a) and through uplifted beachrocks (Figure 6b). According to Mourtzas et al. [157], the area of the ancient port has not only undergone uplift phases but at least one intermediate subsidence phase. After the construction of the harbor around 360 A.D., the first sea-level changes that seem to have occurred in the area were due to seismic events around 360–370 A.D. and 520–580 A.D.; the latter period is possibly related to subsidence [157]. Turner et al. [144] attributed the uplift at Lechaion to isostatic processes.

Stiros [166], based on biological indicators, notes that the ancient port of Aigeira has undergone rapid Holocene uplift due to several individual seismic events. He calculated the sea-level drop rate at 2.15 to 2.3 mm/a from 150 to 250 A.D. (which was the period when the harbor was constructed). Converting it to uplift rate, he estimated that the latter was 2.4–2.5 to 3 mm/a. Papageorgiou et al. [131] reported an uplift of 1 m between 1088 and 1451 A.D., also confirming that the uplift was rapid and episodic, whereas Stewart and Vita-Finzi [91] found an uplift of 6 m in approximately 2400 to 2700 years.

In the Aigeira area, the uppermost boundary of Holocene emergence has been identified by Pirazzoli et al. [47] at +9.3 m. They suggest that the sea level did not remain stable for a significant time period during the Quaternary but underwent constant changes. They estimated the time period prior to which the uplift did not exceed the eustatic sea-level rise around 7035–7542 B.P. After this age, the vertical (uplift) tectonic movements were more significant than the eustatic ones, thus leading to a rapid uplift of the area [47]. The latter also suggests that the uplift rate of Aigeira was not stable; they mention that it was faster during the period to 1451 A.D. and slower in the intermediate periods. In the nearby area of Platanos beach, uplift rates were calculated at 2.4 mm/a, which could also have reached 3.2 mm/a during some periods [47].

Stewart and Vita-Finzi [91] identified uplifted erosional notches in the areas of Diakofto, Platanos beach and south of Aigeira. They also conducted a C isotope study (and locally, U-series) on Lithophaga and other mollusks across this area and found additional evidence of tectonic uplift. The minimum uplift rate was calculated at 0.8–2.5 mm/a in Aigeira, 1–2.3 mm/a in Platanos beach and 1–2 mm/a in Diakofto. The uplift was not solely co-seismic but aseismic as well [143]. According to the area’s morphological features, there have been at least three faulting events in the last 2500 years. Τhere were two periods of rapid uplift (2–2.5 mm/a) and an intermediate phase, lasting for 4 to 5 ka, when the tectonic activity and the consequent uplift were almost inexistent. Stefatos et al. [168] mention that the uplift of the Diakofto, Platanos and Aigeira coastal areas was not due to Helike fault slip solely but rather to more faults, which could also explain the differential uplift extent.

Collier et al. [153] used uranium-series disequilibrium dating of Scleractinian corals collected from the isthmus of Corinth and the Gulf of Alkyonides to calculate the uplift rate for these areas. Uplift rates varied according to the sampling location. They found a minimum uplift rate of 0.2 mm/a over the last 312,000 years to 0.3 mm/a over the last 205,000 years for the area of Corinth and the Isthmus. The average rate was calculated at 0.44 mm/a for the last 205 ka [153]. The Alepochori coast has been uplifted by 0.1 mm/a for the past 127,000 years. The mean rate for the broader area is 0.3 mm/a [153].

Verrios et al. [169] studied the morphometric parameters of the west and east Helike faults in order to assess the recent tectonic movements. Their results confirm the uplift regime that characterizes the area during Holocene. Another morphotectonic study was conducted by Tsimi et al. [170] along the footwall of the Psathopyrgos normal fault at the western end of the Gulf near Rio, indicating high tectonic activity. Mouyaris et al. [149] mention that the two segments of the Helike fault zone have either undergone differential tectonic movements or periodic uplift and subsidence events. In any case, they concluded that the region has been uplifted by at least 6.5 m in the last 4–5 ka, resulting from at least three individual uplift events [149].

Rohais et al. [38] divided the sedimentary formations of the northern Peloponnese into three groups. The Upper Group consists of formations such as slope breccia, present and perched fan delta, slope deposits and fluvial and marine terraces. The older fluvial/marine terraces are dated from the footwall of the eastern Helike fault at 307–312 ka [140,153]. The small fan deltas, terraces and slope deposits of this group were attributed to rapid uplift of the northern Peloponnese [38].

According to McNeil and Collier [140] and McNeil et al. [171], raised marine terraces exist in the footwall of the East Helike fault that show an uplift rate of 1.1 mm/a along the fault, which decreases in the eastern edge of the fault. This rate is similar to that found by Dufaure and Zamanis [172] and Rigo [173] and to the rate of 1.3 to 1.6 mm/a for the Corinth–Xylokastron terraces found by Armijo et al. [15]. In that way, McNeil et al. [171] estimated the fault’s age at 0.7 to 1.1 Ma. They also suggested that the fault has contributed to a 2–3 mm/a extension rate of the overall extension of the Corinthian rift. Activation (earthquake occurrence) frequency for this fault was estimated at two or three events per 1500 years with a probable magnitude of M > 6.6 [171].

Various dating methods have been applied in the terraces of the western part of the south gulf, and several dates and uplift rates have been estimated. Palyvos et al. [45] suggest that west of the Rio area, the uplift rate was not stable during the Middle-Late Pleistocene and calculated on average 1.8 mm/a for the last 350 ka or more. De Martini et al. [151] also mapped raised marine terraces in the footwalls of west Helike, east Helike and Aigion faults. They calculated the uplift rates at 1.05 to 1.2 mm/a for the Aigion fault and 1 to 1.25 mm/a for Helike faults for the last 200 to 300 ka. In the area of Aravonitsa (Figure 1), the uplift rate was found to be 1.74 to 1.85 mm/a [174].

Perachora Peninsula

Perachora Peninsula is located in the eastern part of the gulf that segregates it from the Gulf of Alkyonides. The western part of Perachora Peninsula is a deformed segment boundary between the Xylokastro and the South Alkyonides faults, which both have an approximately E–W direction [30]. In the broader area of Perachora Peninsula and Lechaion, several uplifted geomorphological and biological indicators have been identified, such as beachrocks [147,148], marine terraces [29] (Figure 7), Lithophaga shells and other bioerosion marks [147,148].

In Perachora Peninsula, four uplifted coastlines exist (Figure 8a). The lowest, youngest, and best preserved has an inner edge at altitudes varying from 35 to 80 m, which is correlated with OIS 5e (125 ka) [29]. The second terrace is located at an altitude of 80–120 m, which is correlated with stage 7e (240 ka) [29]. The third one is located at an altitude of 120–245 m, which is correlated with stage 9c (330 ka) [29]. Maroukian et al. [145] identified another older marine terrace in Perachora Peninsula, at elevations of 280–360 m, with an age of 400 ka (OIS 11c).

Robertson et al. [55] studied the sea cliffs, palaeo-sea cliffs and wave-cut platforms of Perachora Peninsula and conducted several measures and datings. They mainly used ²³⁰U/²³⁰Th dating of corals as well as ³⁶Cl. They found uplifted marine terraces at elevations of 6 to 99 m in Cape Heraion. Their findings, together with their observations of uplifted notches, limestone blocks bearing Lithophaga holes, etc., suggest indeed that these terraces were a result of wave erosion and subsequently uplifted through the action of normal faults. One of the terraces, at 44 m elevation, was dated at 136–137 ka, corresponding to the MIS 5e stage (125 ka-highstand) [55]. Regarding bioerosion, they found rates between 0.1 and 6 mm/ka, which gave ages that agree with the above date (125 ka-highstand) for this terrace [55].

Maroukian et al. [145] conducted a geomorphological survey in Perachora Peninsula in order to assess the impact of neotectonic movements on the relief of the drainage basins and reconstruct the area’s palaeogeography. They mainly focused on knick points, gorges, planation surfaces, alluvial fans, talus cones and slope changes. Upon mapping the geomorphological features of the peninsula’s two drainage basins, Maroukian et al. [145] concluded that the peninsula has been affected by both local and regional tectonics and, to a lesser extent, by eustasy. Locations of knickpoints and gorges in the basin of Perachora were investigated in relation to uplifted coastlines corresponding to Oxygen Isotope Stages 5e, 7e and 9c (125, 240 and 330 ka, respectively [145]. Maroukian et al. [145] found two depositional surfaces, which they linked to the sea-level highstand of OIS 11c (400 ka) and the 7e highstand (240 ka). The apex of the lowest alluvial cone was linked to the most recent Tyrrhenian sea-level stage (5e) [145]. Perachora basin has been affected by both Loutraki (south-dipping) and East Xylokastro (north-dipping) normal faults [55]. The Xylokastro fault has caused an uplift of the northern part of the basin [145].

Pirazzoli et al. [97] conducted several measurements in the tidal notches of the archaeological site of Heraion, Perachora Peninsula, including erosional landforms (e.g., tidal notches and shell Lithophaga holes), in situ bioconstructions from vermetids and barnacles and beachrocks (Figure 8b). According to their findings, in the archaeological area of Heraion, raised tidal notches are present at altitudes of +3.2 m (4157–3681 B.C.), 2.6 m (2106–1588 B.C.), 1.7 m and +1.1 m (455–989 A.D.). These researchers also found Lithophaga holes below the level of +3.1 m, but their clearest appearance was above +2 m, where shell remnants were also found. Pirazzoli et al. [97] attributed this to a very rapid, possibly co-seismic uplift event, which led to the uppermost notches being raised to a level where the impact of waves is non-existent and thus protected by further bioerosion [130]. The +1.1 m shoreline reflects the most recent uplift event, which was also rapid [97]. The uplift that took place between 455 and 989 A.D. was the last major uplift event, even though the area may have been slightly uplifted in 1981 [97]. Pirazzoli et al. [97] found no evidence of subsidence (such as submerged notches) for the area of Heraion. In the area of Mylokopi (see Figure 1 for location), they also found Lithophaga holes. A shell at +3.0 m, corresponding to the uppermost notch of the area, was dated 4336–4808 B.C. [97]. They dated a vermetid shell at 0.8 m, which reflected the sea-level prior to the recent uplift, at 663–1036 A.D. In conclusion, the uppermost notch was raised after 4157 B.C. in Heraion and after 2859 B.C. in Mylokopi. There seems to have been a period of high seismicity between the 4th and the 6th century B.C. not only in this area but also in other areas such as the southern Hellenic arc, Turkey, Cyprus and the Lebanon [97,175,176].

Mitzopoulos [177] describes of a shoreline of the last interglacial (Tyrrhenian) stage at +28 m in the area of Heraion with an average uplift rate of either 0.2 mm/a since 125 ka, if it corresponds to the OIS stage 5e, or 0.3 mm/a since 100 ka if it corresponds to the OIS stage 5c [97]. Pirazzoli et al. [97] mention that such rates would have only caused an uplift of 1.3 to 2 m since 6400 BP, therefore concluding that during the Holocene, the uplift rate accelerated. Alternatively, it remained stable at around 0.5 mm/a during the last 81 ka, but this would only be the case if the shoreline mentioned by Mitzopoulos [177] belongs to the 5a stage, but this still does not seem to be the case [97]. Uplift rates seem to have been higher during the Holocene than during the Pleistocene [97].

Vita-Finzi [139] has stated that the uplift of Perachora Peninsula was uniform. On the other hand, according to Kershaw and Guo [178], the notches of Lake Vouliagmeni, Heraion and Mylokopi (Figure 1) do not share the same morphological characteristics (profiles), and this is owed to differentiations in bedrock resistance and wave activity, but differential uplift has also had an impact on the notches’ profile both regarding uplift rates and uplift characteristics [178].

The uplift events in Perachora Peninsula were, according to Pirazzoli et al. [97], owed to seismic movements. Specifically, the uplift at Heraion was caused by three earthquakes, namely in 4157 B.C., 2859 B.C. and sometime between 455 and 989 A.D. In Mylokopi, the uplift was caused by two seismic events, namely 2859 B.C. and sometime between 663 and 1036 A.D. [97]. Stewart and Vita-Finzi [91] calibrated their data and found that the uplift was uniform in the two areas and mainly (but not solely) aseismic.

According to Turner et al. [144], the rates of uplift near Heraion reach at least 0.5 mm/a and decrease to 0.22 mm/a toward the southeast based on uplifted notches. The marine terraces of Heraion that were dated to the MIS 5e show an uplift rate of 0.18 mm/a, contrary to those dated at MIS 7e, whose rate is faster, at 0.25 mm/a [144]. The average uplift rate for the south coast of Perachora peninsula was found to be 0.31 mm/a [144].

To the east of Perachora, Jackson et al. [13] suggested that the coast from Schinos to Alepochori is characterized by subsidence as well as along the coast of Psatha (Figure 1; north from Alepochori). The intermediate coast (between Alepochori and Psatha) undergoes uplift. Through the study of beachrocks, Karkani et al. [150] suggest a rate of tectonic uplift of ~0.26 mm/a on average, since 4160 ± 320 years BP. Leeder et al. [179], based on an accumulation of raised beach gravels, considering a sea level at about −10 ± 4 m at MIS 5a at ~83,000 years BP, and they estimate a mean uplift of 0.24 ± 0.05 mm/a.

4.2. Northern Gulf of Corinth–Gulf of Alkyonides

Evelpidou et al. [142] studied the submerged tidal notches of the northern Corinthian Gulf. Vertex depths range from 20 to 120 cm below sea level except for two sites, where depths of more than 200 cm have been measured. As they found no tidal notches in the present-day sea level, they concluded that the sea reached this level only recently, whereas the most recent subsidence event was co-seismic and led to a vertical displacement of approximately 0.5 m. Evelpidou et al. [142] emphasize that the subsidence was not uniform along their study area and probably not owed to the same earthquake across all the coast. Yet, some of the studied notches were characterized by a significant vertical development, which could indicate that in these cases, the relative sea-level rise was gradual [142] (Figure 9). During their research, Evelpidou et al. [142] found no evidence of uplift in the northern Corinthian Gulf.

Emmanouilidis et al. [180] conducted a survey in the area of Domvraina Gulf (Gulf of Alkyonides) using various methods. They performed boreholes in the Alyki lagoon, which were later analyzed regarding their sedimentological and mineralogical characteristics. At 1600 B.C., they found evidence of tectonic uplift of the lagoon’s beachrock barrier, which resulted in the closing of the lagoon and its separation from the sea.

5. Discussion

Based on the above review on the relative sea-level changes in the Gulf of Corinth during the Holocene, one can observe that the gulf has followed a mixed pattern regarding the rates of tectonic movements, yet an overall pattern (trend) of vertical motions seems clear. In active rifting settings such as the Gulf of Corinth, one would expect different rates in different locations at the same time due to the partitioning of crustal extension accommodated by normal faulting both onshore and offshore (cf. [6,8,15,18,39,43,86,142]), while the variation in late Quaternary fault activity across the strike of the rift controls the rift flank topography [163]. The along-strike variation may be reflected in the distribution of uplift rates because footwall uplift is a result of seismic motion along normal faults [9,15,26,34,36,133,181]. Therefore, by studying the distribution of footwall uplift along an active rift, we may infer the pattern of a symmetric or asymmetric localization of strain along the active faults. In the Gulf of Corinth, the GNSS data have established that horizontal crustal extension is oriented roughly N–S, and it peaks at 11–13 mm per year near Aigion [16,18,19,21] with decreasing values eastwards. We discuss below this set of observations in relation to uplift rates along the south coast of the gulf (recorded by sea-level indicators and GNSS data).

Regarding vertical tectonic motions in Corinth, our combined dataset suggests that the gulf can be divided into two sections: the northern part of the basin that is generally undergoing tectonic subsidence and the southern part that is undergoing uplift (Appendix B, Table A1; Figure 4, Figure 10 and Figure 11). On the northern part, several geomorphic indexes of tectonic subsidence have been found, but no uplift indexes have been identified [86,142].

On the contrary, the northern coast of the Peloponnese, that is the southern section of the gulf, shows a general tendency for tectonic uplift. However, we note that only a few sites indicate a “pure”—that is, continuous—uplift during the Holocene. A few sites have undergone repetitive phases of subsidence and uplift (cf. Diolkos [129]; Lechaion [157]; Helike fault system (Figure 4; [149])). This localized behavior may be due to the competition of motions due to seismic slip along neighboring normal faults, as it depends on the location of the coastal site with respect to the displaced block (i.e., footwall vs. hanging wall location). This investigation is interesting but beyond the scope of this regional review. Therefore, based on geomorphological and archaeological indexes, as well as carbon and OSL dating, we can conclude that the long-term tendency for the south coast is uplift ([139,140,151]; Appendix B, Table A1 and Figure 10). Most authors have suggested an average uplift rate of 1.5 mm/a, yet this is not a firm rate. From east to west, the uplift rate shows significant divergence (Figure 10). The eastern part exhibits rates rarely exceeding 0.2 to 0.5 mm/a. In particular, mean uplift rates have been calculated at 0.4 mm/a for Corinth town and the Isthmus [153], 0.3 mm/a for Alepochori [153], and 0.2 to 0.5 mm/a in Heraion [97,144].

The central–western part of the coastline of the northern Peloponnese shows the highest uplift rates, fluctuating between 0.8 and 3.11 mm/a (Figure 10). In the area of Xylokastron (Figure 1), the rates are, 0.5 to 1.6 mm/a [15,154,172,173], which are followed by the Helike and Aigion fault systems (1–1.3 mm/a; [151]). The highest uplift rates have been found in the area of Aigeira–Diakofto–Platanos [47,91,131,166]. We did not include the +23.2 mm/y site of Stewart and Vita-Finzi [91] near Aigeira on the map of Figure 10, as we consider it as an outlier (an order of magnitude greater than that of neighboring sites). Further west, i.e., the northwestern part of the Peloponnese, shows intermediate uplift rates, ranging from 0.7 to 1.8 mm/a (Figure 10; [45,46,174]).

In addition, the most recent geodetic data [19] indicate that all seven (7) GNSS stations on the northern coast are subsiding with rates exceeding 1 mm/a (Figure 11; stations ITEA, ITEU, GALA, PSAR, TRIZ, EYPA, XILI). Along the south coast stations, KORI, KRYO, VALI, AIGI, AIGU and LAMB show uplift with rates 0.5 ≤ V_up ≤ 3.5 mm/a, which is comparable to the geological data. Stations KRYO and KORI are also reported with positive vertical velocities by Serpeloni et al. [60] (0.77 ± 0.77 and 0.47 ± 0.92 mm/a, respectively) which also indicate an upwards, yet small, motion of the crust. Two stations (KOUN and PSAT; Figure 11) indicate subsidence, but these trends are attributed to local effects such as the compaction of sandy soils [19]. Station KIAT also indicates subsidence; however, this station is located next to a pier at the Kiato harbor where local effects are also possible. We note that the Kiato port also appears subsiding at the European Ground Motion Service dataset (EGMS [73]; Layer Ortho-Level 3, period 2015–2021; Figure 4). Uplift rates are higher in the western part of the gulf, near the city of Aigion where station AIGI moves with a rate of +3.5 ± 1.1 mm/a (Figure 10).

The spatial correlation between high uplift rates and amount (rate) of extension is the highest near the city of Aigion (up to Akrata–Derveni (Figure 1)). This pattern is followed by both sea-level and GNSS data (Figure 10 and Figure 11) with comparable rates. This key observation points to an asymmetric tectonic control on the Upper Pleistocene–Holocene configuration of uplift along the rift axis and demonstrates that the highest tectonic uplift (~3 mm/a) is found where the present-day rate of the crustal extension is the highest, i.e., around Aigion.

The joint consideration of the geomorphological (long-term) and geodetic (short-term) data is a key advance for this area of central Greece that is characterized by fast rates of N–S crustal extension and strong earthquakes that rupture normal faults. We suggest that these data fit the model of an active half-graben structure (120 km long) where the hanging wall (northern coast) subsides while the footwall (southern coast) is undergoing uplift.

6. Conclusions

In the Gulf of Corinth, several geomorphological, geodetic, archaeological and biological features testify to the intense tectonic activity of the area. An overview of published sea-level indicators, with a focus on tidal notches and biological features, clearly reveals that the southern part of the Corinth Gulf has undergone a tectonic uplift over the last thousand years, whereas the northern part has undergone a tectonic subsidence. The evidence suggests that the magnitude of RSL fall in the south Corinth Gulf is larger than that of RSL rise in the north. The highest uplift rates (~3.1 mm/a) are found in the western part of the Corinthian Gulf’s southern margin, i.e., the west–central part of the northern Peloponnese, that is in the area of Aigion–Aigeira (Figure 10). The northwestern Peloponnese is characterized by lesser uplift rates, whereas the northeastern Peloponnese is characterized by even smaller uplift rates, even though relatively higher uplift rates can be locally found. The geodetic rates of land motion are comparable to the geological ones. The joint dataset indicates an asymmetry in strain localization inside the Gulf of Corinth.

It is important to mention that as the Corinth Gulf is rich in sea-level indicators, a very large proportion of them, including sites of particular interest that could potentially offer many pieces of information, are undated up to the present day. In future work, the undated sea-level indicators from the Corinth Gulf need to be dated, so that they confirm our results or reconsider them and contribute to a better understanding of past sea-level changes in the Corinth Gulf and other areas of similar tectonic regime.

As new data (sea-level, GNSS, InSAR, etc.) keep on appearing, this review will be updated in the future to include more dense observations on the ground motion patterns (uplift vs. subsidence). The gap in geodetic data that exists on the eastern gulf (Figure 11) is one of the issues that needs to be looked at. Another point is the need for more geomorphological observations along the northern coast of the gulf opposite Aigion (Figure 4). The accumulation of additional data in the Gulf of Corinth will contribute toward testing models for rift development and normal fault growth.