Faculty of Science and Technology
MASTER’S THESIS
Study program/Specialization:
Petroleum Geosciences Engineering Spring, 2019 Open Writer:
Hannah Haugan
(Writer’s signature) Faculty supervisor: Chris Townsend
Title of thesis:
Transverse Faults in the Corinth Rift System, Greece
Credits (ECTS): 30 Keywords:
Structural Geology Transverse Faults Greece
Corinth Rift Evia Rift
North Anatolian Fault Earthquake
Pages: 97 +enclosure: 17
Stavanger, 15.06.2019
Copyright by Hannah Haugan
2019
Transverse Faults in the Corinth Rift System, Greece
by
Hannah Haugan
MSc Thesis
Presented to the Faculty of Science and Technology The University of Stavanger
The University of Stavanger June 2019
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Acknowledgements
I would like to express my gratitude towards my supervisor Chris Townsend for the continuous guidance and helpful discussions. His knowledge of the Corinth Rift system and experience in the field proved very helpful.
A further thank you is directed towards my dear friends, for their support, spell checking and encouragement throughout this thesis – I could not have gotten through this without you.
Finally, I would like to extend my eternal gratitude to my beloved parents for their never-ending support, patience, and encouragement. Thank you for supporting my decisions and for letting me find my own way.
Abstract
Transverse Faults in the Corinth Rift System, Greece
Hannah Haugan
The University of Stavanger, 2019 Supervisor: Chris Townsend
The area around the Aegean Sea contains one of the most seismically active continental regions in the world. The region is composed of two WNW-ESE trending rift systems:
Corinth Rift and the Evia Rift as well as a major strike-slip tectonic fault, the North Anatolian Fault (NAF). All the different structural areas have been investigated in several studies, with the E-W faults as the main focus in the rift systems, and the northern parts of the strike-slip fault for the NAF. Few have looked at the N-S trending faults in the two rift systems together in relation to a potential connection to the North Anatolian Fault, which is what this study had as a main focus.
Observations from both of the rift systems show indications of transverse N-S striking structures, and observations from the river valleys in the southern part of the Corinth Rift system seem to support an underlying fault control for the N-S structures. Field observations, earthquake and previous studies as basis are used to conduct a structural analysis. Through the structural analysis, lineaments were connected and traced through both rift systems, giving indications of one continuous system, with two grabens (GoC and GoE) and a horst structure in the middle (Parnassos Mountain). The lineaments could be continued into the Aegean Sea and a hypothesis of the NAF having “horsetail”
extending down towards the two rift systems have been raised.
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The area is located north of the Hellenic Subduction zone, and the tectonic complexity of the Aegean Sea has previously been explained using the subduction model. The earthquakes in the area does not support subduction model, and another explanation is sought to better explain the area.
Table of Contents
List of Tables ... ix
List of Figures ...x
Chapter 1: Introduction ...1
1.1 Geological challenge and objectives ...5
Chapter 2: Background ...7
2.1 Fault Linkage ...7
2.2 Fault Interaction ...7
2.2.1 Relay zones ...7
2.2.2 Transfer Faults ...8
2.1.3 Transverse Faults ...9
2.1.4 Transform Faults ...10
2.3 Earthquakes ...10
2.3.1 Focal mechanisms ...10
Chapter 3: Regional Geology and Previous Work ...11
3.1 Regional Geology ...12
3.2 Previous Work ...15
3.2.1 Corinth Rift System ...15
3.2.1.1 South of the GoC ...15
3.2.1.2 Offshore GoC ...21
3.2.1.3 North of the GoC ...22
3.2.2 Evia Rift System ...23
3.2.3 The North Anatolian Fault ...24
Chapter 4: Data and Methodology ...27
4.1 Data ...27
4.2 Methodology ...27
4.2.1 Field Work ...27
4.2.2 Earthquake ...29
3.3 Transverse Fault Modelling ...32
Chapter 5: Field Observations ...33
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5.2 South of Gulf of Corinth ...35
5.2.1 Trikala Fault ...35
5.2.2 Krathis Fault...37
5.2.3 Vouraikos Fault ...40
5.2.4 Roghi Fault...43
5.2.5 Kerinthis Fault ...45
5.2.6 Lapanaghi Fault ...48
5.3 Offshore Gulf of Corinth ...51
5.4 North of Gulf of Corinth ...54
5.4.1 Alignment 1 – Amfissa Fault ...57
5.4.2 Alignment 3 ...58
5.4.3 Alignment 5 – Orchomenos Fault ...60
5.4.4 Alignment 8 – Thiva Fault ...62
5.4.5 Alignment 15 - Delphi Fault ...66
5.5 North Anatolian Fault ...69
5.6 Coastal Features ...72
Chapter 6: Structural Analysis ...74
6.1 Introduction ...74
6.2 Connecting The Areas...74
6.3 Earthquake Analysis ...79
6.3.1 Earthquake Data ...79
6.3.2 Focal Mechanisms ...83
Chapter 7: Discussion ...84
7.1 Evidence For Lineaments and Transfer Faults ...84
7.1.1 South of Gulf of Corinth ...84
7.1.2 Offshore Gulf of Corinth ...85
7.1.3 North of Gulf of Corinth ...86
7.1.4 Aegean Sea...87
7.2 Southwestern Termination of the NAF ...87
Chapter 8: Conclusion...92
References ...93
List of Tables
Table 1: An overview of the alignments found on the northern side of the GoC (See Figure 39). Some are based on earthquake data, some
geomorphologically based and some are geologically based. ...55 Table 2: An overview of the river valleys and structures ending in the GoC seen in
Figure 52. ...75
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List of Figures
Figure 1: Figure over the study area from Taymaz et al. (1991). ...2 Figure 2: Map of study areas taken in Google Earth. The study area is highlighted in the red frame. The areas in black represents the areas of fieldwork, seen in Figure 3. ...3 Figure 3: Map of the Corinth Rift (highlighted in green) and Evia Rift (highlighted
in purple) illustrating the major faults related to the rift systems. The areas of fieldwork are concentrated in these two areas. The red area represents the area where most of the previous work in the from the University of Stavanger have been conducted. (Modified after Eliet and Gawthorpe (1995)). ...4 Figure 4: Schematic figures showing the evolutional stages of a relay ramp. Tick
marks on the fault segments illustrate the down-thrown block for normal faults. (a) Stage 1: no interaction between the faults. (b) Stage 2: faults have started to interact, and a relay ramp is beginning to form. (c) Stage 3: accumulated strain in the relay ramp has resulted in fractures beginning to form. (d) Stage 4: the relay ramp is broken by a breaching fault to form a fault zone. (e) Upper ramp is
abandoned, and the two fault segments joined through breaching of the lower ramp. (f) The relay ramp seen in box view. After Ciftci and Bozkurt (2007), modified from Peacock and Sanderson (1995)...8 Figure 5: Conceptual model of transfer fault. a) From map view. b) In box view.
Modified from R. Gawthorpe and Hurst (1993). ...9 Figure 6: Strike-slip faults in the form of focal mechanisms, after Stein and
Wysession (2009) ...11
Figure 7: Tectonic setting of the GoC, the NAF and the Hellenic Subduction zone, illustrating the location of the different plates. EAF = East Anatolian Fault (Modified after Armijo et al. (1999)). ...12 Figure 8: Tectonic setting of the GoC, the NAF and the Hellenic Subduction zone.
CHSZ, Central Hellenic Shear Zone; NAT, North Anatolian Trough;
KT, Kephalonia Transform; WASZ, West Anatolian Shear Zone (Royden & Papanikolaou, 2011)...14 Figure 9: The evolution of the Gulf of Corinth. Showing steps from early rift
along the active Chelmos Fault to the present-day evolution of the Chelmos detachment Fault (Sorel, 2000). The Chelmos Fault is marked with a red line. ...16 Figure 10: Structural map of the southern part of the Corinth Rift, highlighting the areas mapped by previous theses and compiled by Egeland (2018). 17 Figure 11: A structural map showing the fault stepping due to relay zones and
individual faults proposed by Ford et al. (2013). The red circle is an example of a relay zone. ...18 Figure 12: Map of the Kalavryta-Eliki area showing the suggested transfer fault
scenario to explain the fault steps (Dahman, 2015). ...19 Figure 13: Location map illustrating the proposed transfer faults in the southern
part of the study area afterEgeland (2018). ...20 Figure 14: Earthquake data in the GoC. Red lines indicate transfer faults
suggested by Mostafa (2017). ...21 Figure 15: Schematic cross section through the GoC (Moretti et al., 2003). ...22 Figure 16: Active faults in the northern GoC, according to Valkaniotis and
Pavlides (2016). Bedrock formations in dark grey and post-alpine sediments in light grey. ...23
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Figure 17: Sketch of the motions in the Aegean region by Taymaz et al. (1991).
Fault are shown as simplified thick lines: those with predominantly normal faulting have blocks in their hanging walls; predominantly strike-slip faults are marked by arrows. ...25 Figure 18: Tectonic setting of continental extrusion in eastern Mediterranean from Armijo et al. (1999). EAF—East Anatolian fault, K—Karliova triple junction, DSF—Dead Sea fault, NAT—North Aegean Trough, CR—
Corinth Rift ...26 Figure 19: List of methodology for the earthquake data. ...30 Figure 20: An example of area in the GoC where identical distance between
earthquakes can be observed. ...31 Figure 21: Structural map of the southern part of the Corinth Rift System,
highlighting the different segments enclosed by inferring high-angle transfer faults by Egeland (2018). ...34 Figure 22: Trikala location. a) Photo of area of contact. b) Trikala fault
interpreted. c) Observed change in lithology. ...36 Figure 23: Overview of the area surrounding the Krathis River. ...37 Figure 24: An overview map of the Krathis river and transfer fault. The red line
represents the proposed transfer fault. ...38 Figure 25: Point a) in Figure 23. Photo taken from the eastern side of the Krathis
river valley, standing on the Valimi Fault, looking towards the north.
...39 Figure 26: The area surrounding the Vouraikos river. ...40 Figure 27: Vouraikos Fault and the main evidence. The thicker red line represents the Vouraikos Transfer Fault. ...41
Figure 28: Roghi Fault and the main evidence. The thicker red line represents the Roghi Transfer Fault, and the thinner red lines are other transfer faults nearby. ...43 Figure 29: Overview of the area surrounding the Kerinthis river. ...45 Figure 30: Kerinthis Fault and the main evidence presented. The thicker red line
represents the Kerinthis Transfer Fault, and the thinner red lines are other transfer faults nearby. The orange square marked the location of Figure 31. ...46 Figure 31: a) Satellite image from Google Earth of one part of the Kerinthis Fault.
b) Structural interpretation showing the Doumena Fault stepping between Doumena Fault West III and Doumena Fault West IV. ...48 Figure 32: An overview of the area surrounding the Lapanaghi Fault. ...49 Figure 33: A map showing the Lapanaghi Fault with proposed continuations of the
fault. ...50 Figure 34: a) Lapanaghi Fault, viewed from the south. b) Interpreted image
showing the change in lithology, with basement in the west side of the fault and basement on the east side. ...51 Figure 35: Google Earth image showing the Lapanaghi Fault and the different
possibilities of continuation. The purple lines represent the fault plane and the stippled line represent the proposed continuations of the fault. ...51 Figure 36: Earthquake data in the GoC. Red lines indicate transfer faults
suggested by Mostafa (2017). Some of the suggested faults lines up with the earthquake data, other which does not relay on earthquake data at all. ...52
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Figure 37: Earthquake data in the GoC. Red lines indicated earthquakes which lines up in an approximately N-S direction, interpreted for this thesis project. ...53 Figure 38: Google Earth image showing earthquake data located in the GoC. Two
types of areas can be seen: two areas with high amount of
earthquakes and two areas with a low amount of earthquakes. ...54 Figure 39: Map showing the alignments found in the GoC and north of it. The
alignments are based on earthquake alignments, changes in topography, or lithology. Due to time constrains, not all the found alignment were visited, but the ones with the strongest evidence were investigated in the field. ...56 Figure 40: a) Google Earth map showing the earthquakes identifying the Amfissa
Fault. b) The Amfissa Fault in purple, following the alignment of the earthquakes. ...57 Figure 41: a) Google Earth map showing Alignment 3. b) The area interpreted,
Alignment 3 marked in red, the Delphi Fault (Alignment 15) and the Amfiliki Fault (Alignment 16) marked in pink, the area where Figure 42 is taken is highlighted in orange. ...59 Figure 42: The transverse fault and the Delphi Fault plane (Alignment 15). ...60 Figure 43: a) The area around the Orchomenos Fault, with the 5 earthquakes
forming the basis of the lineament. b) The Orchomenos Fault
marked, showing the continuation of the fault...61 Figure 44: The two hills terminating in the fault alignment, supporting evidence of
a fault structure. a) photo showing the two hills in a photo, b) the photo interpreted and c) an overview of the area where the photo is taken in Google Earth. ...62
Figure 45: a) The earthquakes which makes up the Thiva Fault seen in Google Earth. b) The lineament marked in pink, showing a continuous alignment. The area marked in orange is the area visited in the field ...63 Figure 46: a) The Thiva Fault seen in the field. b) The fault contact between
conglomerate and ophiolite. c) The fault shown in Google Earth, with the yellow triangle showing the area where the photo in a) is taken. ...65 Figure 47: a) The Delphi Fault seen in Google Earth. b) Interpretations of the
Delphi Fault (marked in red) and the Amfissa Fault and Alignment 3 (marked in purple). Figure 48 is taken from the town of Delphi, located in the corner of the yellow triangle seen. ...67 Figure 48: The Delphi Fault in different scales. a) Photograph showing the valley
below the town of Deplhi, the Deplfi faultplane can be seen in the red stippled square. B) Zoom in on the red stipples box. c) Zoomed in on the outcrop clearly showing the faultplane. d) The faultplane interpreted. ...68 Figure 49: The Mediterranean area shown in a satellite imagery in Google Earth.
a) Figure shows the area from Google Earth. The NAF is can be observed on the seafloor. b) The NAF, marked in red, and other lineaments seen on the sea floor, marked in green. ...70 Figure 50: a) The raw earthquake data from the Aegean Sea area (white points). b)
Collecting the earthquake data lining up with the structure on the sea floor. The earthquake lining up with the NAF alignment (yellow ponits). ...71
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Figure 51: a) The Mediterranean area shown in a satellite imagery in Google Earth. b) The interpreted area. The red lines represents areas where the borders lines up. Each of the faults are named TP and their number, ex. TP 1. ...73 Figure 52: River valleys/ topographic alignments which end up in the GoC, with
an approximate N-S direction. Each river valley/alignment is named with a letter. An explanation for the letters can be found in Table 2.
...74 Figure 53: How the different alignments are connected to each other. Green boxes
represents the river valleys and alignments in southern GoC (see Figure 52), blue boxes represents the alignments in the GoC and northern GoC (see Figure 39) and the orange boxes represents the alignments seen on the coastlines (see Figure 51). ...78 Figure 54: The raw earthquake data from the study area displayed in the Petrel
Software. Note the cluster-alignment in the northern part of the area, lining up in the same structure as the NAF seen in Figure 49 and Figure 50. ...79 Figure 55: The earthquake data from the study area displayed in the Petrel
Software after excluding all data with a depth less than 10 000 m.
Note the cluster-alignment indication the NAF is still present, like in Figure 41, but the amount of earthquakes in the central Greece have significantly decreased. ...80 Figure 56: The earthquake data from the study area displayed in the Petrel
Software after excluding all data with a depth less than 20 000 m.
The alignment for the NAF is still visible; much less earthquakes can be seen in the Aegean Sea and the central part of Greece. ...81 Figure 57: The earthquake data seen from the west in Petrel. ...82
Figure 58: An overview of the earthquakes with focal mechanisms. The red circle indicates the earthquakes lining up with the NAF; all the focal mechanisms indicate strike-slip. ...83 Figure 59: The comparison between alignments found in this thesis study, seen in
Figure 32, and Mostafa (2017) seen in Figure 33. ...86 Figure 60: Figure showing the lineaments from topographic to the NAF, this
matched the “horsetail” theory. The two rift systems are marked in their respected graben structures. ...88 Figure 61: The main structures, spatial distribution of earthquakes and focal
mechanisms in the Aegean Sea region, after Console et al. (2013).
CTF: Cephalonia Transform Fault, NAT: North Aegean Trough, NAF: North Anatolian Fault. ...89 Figure 62: Tectonic setting of the GoC, the NAF and the Hellenic Subduction
zone. CHSZ, Central Hellenic Shear Zone; NAT, North Anatolian Trough; KT, Kephalonia Transform; WASZ, West Anatolian Shear Zone (Royden & Papanikolaou, 2011). The orange shading indicates the zones of active oblique extension, which is the study area for this thesis project. ...90
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Chapter 1: Introduction
Western Turkey, central Greece, and the Aegean Sea form one of the most seismically active continental regions with rapidly changing tectonic events (Taymaz et al., 1991).
The region is composed of two main WNW-ESE trending rift systems: the Corinth Rift and the Evia Rift. In addition, the North Anatolian Fault (NAF) creates a crucial E-W structure along the northern border of Turkey. This strike-slip fault clearly changes strike to NE-SW as it approaches the Aegean Sea. The Corinth Rift has been attributed to back-arc extension, caused by the subduction of the African Plate beneath the Anatolian Plate (Jackson, 1994). However, the function of the Evia Rift and how the extension intrudes with the strike-slip structures in the Aegean Sea are rarely discussed.
The Gulf of Corinth (GoC) is located in central Greece, separating continental Greece from the Peloponnesus peninsula in the south (Figure 1). The GoC is a rift system, with a north-south extension of 11-16 mm/year, making it one of the world’s most active rift systems (Ford et al., 2013), consisting of several half-graben structures. Pliocene to Quaternary conglomerate, sand, and marl sedimentary infill characterizes the syn-rift deposition (Ford et al., 2013). Extensive footwall uplift has tilted the adjacent hanging walls and created remarkable rotated fault blocks (Flotté et al., 2005), which have in places been segmented by a NE-SW trend in high angle faults (Zhong et al., 2018).
The North Gulf of Evia (GoE) rift system is the second WNW-ESE striking Quaternary structures accommodating N-S crustal extension in central Greece (Ganas & Papoulia, 2000). The Evia Rift system consists of an asymmetric half-graben, with the dominant faulting on the SW side (Roberts & Jackson, 1991). The rift system consists mainly of Mesozoic limestone and Neogene sediments (Eliet & Gawthorpe, 1995). The southernmost fault in the Evia Rift system has an NW-SE strike and borders the Parnassos Mountain range, where the Corinth Rift system ends.
Figure 1: Figure over the study area from Taymaz et al. (1991).
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This thesis project will investigate the transverse fault structures on a larger regional scale, which include both sides of the GoC as well as earthquake and other published data from Peloponnese peninsula and central Greece, the Evia Rift system, and up to the NAF. In this thesis project, E-W faults will be referred to rift faults, while the N-S faults will be referred to as transverse faults. Evidence supporting the transverse structures will be evaluated with a special focus on trying to explain the nature of how the NE-SW trending structures in the Corinth Rift and Evia Rift interact with the NAF.
Is there a connection between the faults on southern and northern of the GoC? Is there a link between onshore faults and offshore fault structures in the form of earthquakes?
Moreover, can these structures be connected to the NAF?
The study area from this thesis project extends from Lapanaghi and Kandila in the southwest to the peninsula of Gallipoli, Turkey in the northeast (Figure 2). The field area (Figure 3) is separated into three parts: the Corinth Rift system, the Evia Rift system, and the NAF.
Figure 3
Figure 2: Map of study areas taken in Google Earth. The study area is highlighted in the red frame. The areas in black represents the areas of fieldwork, seen in Figure 3.
The southern part of the study area is focused on fieldwork (the red square in Figure 3), with theses from the University of Stavanger and previous publications as a basis (Finnesand, 2013; Ford et al., 2013; Kolbeinsen, 2013; Wood, 2013; Syahrul, 2014;
Dahman, 2015; Lopes, 2015; Rhodes, 2015; Rognmo, 2015; Stuvland, 2015; Bjåland, 2016; Sigmundstad, 2016; Oppedal, 2017; Gawthorpe et al., 2018). The different fault blocks of the southernmost part of the area in Corinth Rift have been investigated in an effort to better understand the structural development and sedimentary infill through time.
Figure 3: Map of the Corinth Rift (highlighted in green) and Evia Rift (highlighted in purple) illustrating the major faults related to the rift systems. The areas of fieldwork are concentrated in these two areas. The red area represents the area where most of the previous work in the from the University of Stavanger have been conducted.
(Modified after Eliet and Gawthorpe (1995)).
5 1.1GEOLOGICAL CHALLENGE AND OBJECTIVES
The Corinth Rift have faults from the early stages preserved both onshore and offshore surrounding the GoC (Armijo et al., 1996). South of the GoC, a series of half-graben structures are exposed, controlled by north-dipping normal rift faults. The half-grabens are cut by perpendicular NNE-SSW river valleys. The various rift faults have displacements of up to 2500 m (Egeland, 2018). Several of these large displacement faults are challenging to trace across the river valleys, indicating a clear cross-cutting mechanism is present.
An example is the Vouraikos River valley: located south of GoC, several faults controlling the half-graben structure seem to terminate in the valley, or stepping and continuing on the other side of the valley (Dahman, 2015). Different explanations have been proposed for this river valley and other valleys in the southern part of the Corinth Rift system. As the valleys reach the coast, very little evidence of their continuation into the GoC has been documented. Mostafa (2017) concluded that some of the transverse faults continue into the GoC; however, no evidence was presented for the fault structures continuing into the north of the gulf.
The continuation of the NAF has been discussed in multiple studies. Barka (1992) interpreted the NAF as a fault zone and terminating in the Aegean Sea. A theory of the NAF splitting into multiple smaller faults towards the south-southwest, as horsetails, was presented. Another theory is that the NAF turns to the north-northwest, continuing into northern Greece (ex. Hubert-Ferrari et al. (2009)). No consensus regarding the fault termination has been reached thus far.
The main objectives of this study are therefore to:
• Assess the evidence for transverse structures in river valleys, by using observations collected in the field and earthquake data, supplemented with data from previous master theses.
• Investigate the relationship between onshore transverse faults and offshore faults, using earthquake data and previous work.
• Evaluate if there is a connection between the transverse structures in the GoC and the GoE, and the NAF.
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Chapter 2: Background 2.1FAULT LINKAGE
In rift settings, it is widely understood that in order for fault systems to develop, a combination of growth, interaction and fault-linkage of individual faults segments over a large range of scales is necessary (Cartwright et al., 1996; Cowie & Roberts, 2001).
Faults grow from microfractures or other elementary weaknesses and create displacement over time as deformations continue (Hills, 1972). Faults do not often grow as individual structures over a long period. As they grow, they are prone to interfere with nearby lying faults, forming fault systems. Extensional systems, such as the Corinth Rift and Evia Rift, are often associated with the creation of half-grabens by normal faulting, where faults form as a response to extensional stress fields.
2.2FAULT INTERACTION
2.2.1 Relay zones
Faults that approach each other and overlap form soft-linked features (Figure 4), as they are not in direct contact with each other. Relay zones form due to faults overlapping, where a decrease in displacement happens because of a decrease in stress at the fault tip interaction points (Peacock & Sanderson, 1995). Relay zones are areas of fault interaction where strain or displacement is relayed from one structure to another (Fossen & Rotevatn, 2016). With continued fault growth, they can eventually link up to form a hard link. The approaching faults sense the presence of a neighbouring fault tip, in which they become kinematically linked. The propagation rate of the fault tips is reduced, causing the local displacement gradient to increase (Fossen, 2016).
2.2.2 Transfer Faults
Large normal faults in extensional basins commonly terminate in structures similar to oceanic transform faults, such as shear zones or orthogonal strike-slip faults (Bally, 1981). These faults are called transfer faults (Gibbs, 1984), where these faults divide the extending surface into segments (Figure 5). Extensional basins developed due to stretching of the continental lithosphere resulting in passive upwelling and thinning of hot asthenosphere where subsidence and block faulting occurred (McKenzie, 1978;
Lister et al., 1986).
Figure 4: Schematic figures showing the evolutional stages of a relay ramp. Tick marks on the fault segments illustrate the down-thrown block for normal faults. (a) Stage 1: no interaction between the faults. (b) Stage 2: faults have started to interact, and a relay ramp is beginning to form. (c) Stage 3: accumulated strain in the relay ramp has resulted in fractures beginning to form. (d) Stage 4: the relay ramp is broken by a breaching fault to form a fault zone. (e) Upper ramp is abandoned, and the two fault segments joined through breaching of the lower ramp. (f) The relay ramp seen in box view. After Ciftci and Bozkurt (2007), modified from Peacock and Sanderson (1995).
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The definition of transfer faults can be ambiguous in some cases. Minor transfer faults can be confined to the upper plate, affecting only the geometry of the fault blocks.
Transfer faults are a general feature of extension zones, and therefore should be expected to generally occur in passive continental margins (Lister et al., 1986).
2.1.3 Transverse Faults
Transverse faults are faults which strike obliquely or perpendicular to the general structural trend in a region. It is the assumption of continuing, high-angle faults going through very widespread areas. The term is loosely used for cross faults in an extensional graben but can also be referred to as strike-slip or transform faults (Sylvester, 1988).
Figure 5: Conceptual model of transfer fault. a) From map view. b) In box view. Modified from R.
Gawthorpe and Hurst (1993).
a) b)
2.1.4 Transform Faults
A transform fault or transform boundary is strike-slip fault where the motion of predominantly horizontal. It often ends abruptly and is connected to another transform fault, a spreading ridge or a subduction zone (Kearey et al., 2009). Most of these faults are hidden in the deep ocean, where they offset divergent boundaries in short zigzags resulting from seafloor spreading. A transform fault is the only type of strike-slip fault that is classified as a plate boundary. The North Anatolian fault is a good example of such a transform fault (Sengör, 1979).
2.3EARTHQUAKES
Earthquakes are caused by rupture of geological faults and often occur along fault structures. The major fault lines of the world are located at the ends of the tectonic plates (Stein & Wysession, 2009), such as in the area for this thesis project, close to the Eurasian plate and the Aegean-Anatolian plate.
There are three main types of fault, which can cause an interplate earthquake: Normal, reverse and strike-slip. Normal and reverse faulting are examples of dip-slip; where the displacement along the fault is in the direction of the dip and the movement involves a vertical unit (Kusky, 2008). Strike-slip faults are high-angle structures where the two sides of the fault slip horizontally past each other (Fossen, 2016). Movement with both dip-slip and strike-slip movements are the cause of many earthquakes; this is known as oblique slip.
2.3.1 Focal mechanisms
The direction of the slip in an earthquake and the orientation of the fault on which it occurs is often referred to as the focal mechanism, typically displayed on maps as a
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“beach ball” symbol (Stein & Wysession, 2009). Figure 6 shows an example of the same N-S fault, but with different slip direction to illustrate the different focal mechanisms.
Figure 6: Strike-slip faults in the form of focal mechanisms, after Stein and Wysession (2009) .
Chapter 3: Regional Geology and Previous Work 3.1 REGIONAL GEOLOGY
The tectonic setting of the Eastern Mediterranean Sea, where the NAF, Evia Rift, and Corinth Rift are located, is the result of the interaction of the African, Arabian, Anatolia-Aegean and Eurasian Plates (Figure 7). These plates have controlled the evolution of the NAF and the GoC since late Paleozoic time (McKenzie, 1972; Taylor et al., 2011). The GoC is located on the northwestern part of the Anatolian and Aegean plates. The African Plate is subducting beneath the Anatolian and Aegean plates, creating the Hellenic Trench in the southwest. In the north, the North Anatolian Fault separates the Anatolian Plate from the Eurasian Plate. In the east, the East Anatolian Fault is located, separating the plate from the Arabian Plate (Jackson, 1994).
Figure 7: Tectonic setting of the GoC, the NAF and the Hellenic Subduction zone, illustrating the location of the different plates. EAF = East Anatolian Fault (Modified after Armijo et al.
(1999)).
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During the Early Cretaceous, the Eurasian plate converged with the African plate resulting in alpine mountain ranges in the northern part of the Mediterranean and crustal thickening in the Aegean region (the Hellenides Orogeny). From Eocene to early Miocene, Alpine nappes formed in western Greece, due to the westward migration of thrust activity. This thrusting activity created several NE-SW thrust sheets, which can be seen in the river valleys in the Corinth Rift today (McKenzie, 1972).
The crustal extension, which is responsible for the present-day GoC and GoE, was initiated in the early Pliocene, located on the Alpine basement and is believed to have been formed in relation to the north-northeast subduction of the African plate at the Hellenic Trench (McKenzie, 1972). This subduction resulted in the back-arc extension of the Aegean Sea (Jolivet et al., 1994), and the westward propagation of the NAF (McKenzie, 1972; Jolivet et al., 1994; Armijo et al., 1996). Figure 8 shows the tectonic setting of the GoC, the NAF and the Hellenic Subduction zone. The eastern Mediterranean has long been recognized as an area of active tectonism (McKenzie, 1972).
Interaction of the African, Arabian, Eurasian, Anatolian and Aegean plates and various geometries of convergence result in a broad variety of active tectonic processes, including back-arc extension of the Aegean plate (Bell et al., 2009; Ford et al., 2013).
The opening of the Corinth Rift zone and the Evia Rift zone is part of a crustal extension and widens the Gulf of Corinth and Gulf of Evia as the Peloponnese pulls further apart from mainland Greece (de Boer et al., 2001). This created southeast of the Gulf of Corinth in the onshore Peloponnese, several east-west striking, north-dipping normal faults initiated in Miocene times (Armijo et al., 1996; Moretti et al., 2003).
Figure 8: Tectonic setting of the GoC, the NAF and the Hellenic Subduction zone. CHSZ, Central Hellenic Shear Zone; NAT, North Anatolian Trough; KT, Kephalonia Transform; WASZ, West Anatolian Shear Zone (Royden & Papanikolaou, 2011).
15 3.2PREVIOUS WORK
3.2.1 Corinth Rift System 3.2.1.1 South of the GoC
The geometry of the Corinth Rift system has been discussed for decades. Different theories concerning the structure of the rift and associated fault propagations on the onshore Peloponnese has been suggested.
Doutsos and Piper (1990) proposed a model for the Corinth Rift where the faults are of listric nature. However, due to the lack of evidence supporting such a model, most researches favour a planar fault model (e.g. Moretti et al. (2003); Rohais et al. (2007);
Ford et al. (2013)). Doutsos and Poulimenos (1992) described the structure of the rift and proposed the presence of a low-angle fault at a deeper crustal level connected with the surface normal faults. Sorel (2000) and Chéry (2001) supported the proposal of a low-angle fault and proposed that the Corinth Rift is underlain by a major north-dipping crustal detachment fault, the “Chelmos detachment”, which is underlying the younger faults (Figure 9). Studies of focal mechanisms (Rietbrock et al., 1996) from the Aigion earthquake in 1995, support a model involving an active low-angle crustal detachment, as recorded by micro-earthquakes showing a north-dipping zone of seismicity below the GoC.
Moving to the uppermost crust on the south part of the GoC, an ongoing debate on the rapid fault terminations is still active. Previous work by students at the University of Stavanger has identified a number of faults that step, rapidly terminate or rapidly lose displacement (Dahman, 2015; Lopes, 2015; Rhodes, 2015; Oppedal, 2017; Veiteberg, 2017). Figure 10 shows a structural map of the southern part of the Corinth Rift created by Egeland (2018) based on previous studies conducted in the area. The fault alterations occur in river valleys with NNE-SSW orientations.
Figure 9: The evolution of the Gulf of Corinth. Showing steps from early rift along the active Chelmos Fault to the present-day evolution of the Chelmos detachment Fault (Sorel, 2000).
The Chelmos Fault is marked with a red line.
17
There are different views on fault segmentation and fault terminations, and no consensus has so far been reached. Ford et al. (2013) suggested that each fault step is caused by an individual perpendicular fault or relay zone (Figure 11), the latter supported by Wood (2013). Gawthorpe et al. (2003) indicated that a pre-existing paleo topography was present prior to the rifting, whereas Ghisetti and Vezzani (2005) proposed that the fault segmentation could be controlled by pre-existing structures in the underlying basement.
Figure 10: Structural map of the southern part of the Corinth Rift, highlighting the areas mapped by previous theses and compiled by Egeland (2018).
Figure 11: A structural map showing the fault stepping due to relay zones and individual faults proposed by Ford et al. (2013). The red circle is an example of a relay zone.
19
A proposed alternative explanation for the stepping of the E-W striking, is that each segment may have different extension and different displacement. The river valleys are areas where large structural and depositional changes can be seen from one side of the valley to the other. Dahman (2015), Hadland (2016) and Oppedal (2017) studied some of the river valleys and identified a model involving a several kilometre long transfer faults to explain the fault steps (Figure 12).
Figure 12: Map of the Kalavryta-Eliki area showing the suggested transfer fault scenario to explain the fault steps (Dahman, 2015).
Egeland (2018) investigated the abrupt termination of faults and fault displacement in the rift faults in the Corinth Rift and determined that some faults step, whilst other terminate in the N-S trending river valleys (Figure 13). The findings in the Ladopotamos, Potamia, and Krathis Valley coincide with the conclusions by Dahman (2015) in Vouraikos Valley, Hadland (2016) in the Kerpini Fault Block and Oppedal (2017) east of the Vouraikos Valley.
Figure 13: Location map illustrating the proposed transfer faults in the southern part of the study area afterEgeland (2018).
21 3.2.1.2 Offshore GoC
Mostafa (2017) investigated the west-east direction in the GoC with the use of seismic, bathymetry maps, earthquake data and existing onshore maps (Figure 14). The analysis concluded that there was a continuation of Kerinthis Fault, the Vouraikos Fault, and Ladhopotamos Fault into the gulf.
Moretti et al. (2003) looked at the offshore part of the Corinth Rift and the GoC and concluded that the Gulf is not an asymmetric simple half-graben. There are active normal faults on both sides of the gulf; there are no signs of tilting of the syn-rift sediments in the Aigion area between the active faults Pirgaki, Helike and Aigion (Figure 15).
Transfer fault suggested by Mostafa (2017) Earthquake data
Figure 14: Earthquake data in the GoC. Red lines indicate transfer faults suggested by Mostafa (2017).
The offshore part of the GoC has been the focus for several publications which try to address structural features and basin evolution (Leeder et al., 2005; Bell et al., 2008;
Ford et al., 2016). The structure of the GoC has been described as a graben structure with E-W striking, asymmetric half-grabens and the N-S extension which is controlled by the north-dipping normal faults in the southern part of the GoC.
The faults on the northern part of the GoC were described as south-dipping and active during the early rift phase without any significant footwall uplift (Taylor et al., 2011).
In the central and eastern sector, the structure was described as inherited from the structural grain associated with reactivation of the Parnassos nappe stack in the basement. However, in the western sector, the faults were described as unaffected by the structural grain of the basement (Taylor et al., 2011).
3.2.1.3 North of the GoC
On the northern side of the GoC, Valkaniotis and Pavlides (2016) investigated the onshore fault activity in the northern part of the rift system to further understand the structure of the Corinth Rift and document the transition zone between GoC and the
Figure 15: Schematic cross section through the GoC (Moretti et al., 2003).
23
northern active extensional basins of Kifissos, Evoikos Gulf and Spercheios Rift (Figure 16).
3.2.2 Evia Rift System
There has been a significant amount of publication on the Evia Rift system, however, the studies are most often concentrated on the E-W striking normal faults (Ganas &
Papoulia, 2000; Jones et al., 2009)
Palyvos et al. (2006) proposed a major topographic feature, the 17 kilometres (km) long and 15 km wide Nileas depression. The proposition was made after geomorphological and geological observation in the northern part of the Evia Island. The Nileas depression is bounded by two NE-SW to ENE-WSW striking fault zones (Prokopi- Pelion fault zone and Kechriae fault zones). The two fault zones strike transverse to the NW-SE active fault zones that bound the northern Evia and aligned to transverse
Figure 16: Active faults in the northern GoC, according to Valkaniotis and Pavlides (2016). Bedrock formations in dark grey and post-alpine sediments in light grey.
structures on the main coast. The fault zones have been the active structures since Middle-Late Quarternary, resulting in uplift and erosion of the Nileas depression.
3.2.3 The North Anatolian Fault
The extent and direction of the right-lateral NAF are widely debated, and for several decades, different theories of the direction and extent of the fault have been proposed.
Using earthquakes as the main form of data, Taymaz et al. (1991) suggested a simple model explain the active tectonics of the north and central Aegean Sea (Figure 17). This model involves three principles to reproduce quantitatively many of the features of the rapid deformation field seen in the central and northern Aegean region. Yolsal et al.
(2007) looked at the plate interactions and crustal deformation in the Eastern Mediterranean region using earthquake and tsunami data. The study concluded that there was an apparent recurring interval of 150-200 years.
25
Armijo et al. (1999) believed in the westward propagation of the NAF and presented evidence for the propagational processes by studying the folding in the Dardanelles Striats region (Figure 18). This allows documentation of the timing of deformation preceding, and the displacement after, which is the passage of the propagating tip of the fault. The observations were made in the Sea of Marmara pull-apart, suggesting long- term kinetics are similar to present-day, and on a larger scale, the westward propagation of the NAF appears to be associated with strain recovery, suggesting that the continental lithosphere retains long-term elasticity.
Figure 17: Sketch of the motions in the Aegean region by Taymaz et al. (1991). Fault are shown as simplified thick lines: those with predominantly normal faulting have blocks in their hanging walls; predominantly strike-slip faults are marked by arrows.
Figure 18: Tectonic setting of continental extrusion in eastern Mediterranean from Armijo et al.
(1999). EAF—East Anatolian fault, K—Karliova triple junction, DSF—Dead Sea fault, NAT—North Aegean Trough, CR—Corinth Rift
27
Chapter 4: Data and Methodology 4.1 DATA
The project utilizes data and observations collected from fieldwork and data compiled from previous master theses at the University of Stavanger (Finnesand, 2013; Dahman, 2015; Hadland, 2016; Sigmundstad, 2016; Mostafa, 2017; Oppedal, 2017; Veiteberg, 2017; Egeland, 2018), along with published work and earthquake data collected from the US Geological Survey. The fieldwork at the end of the study was done to verify previous observations and exploring areas with little to no previous observations.
A multitude of photos and geological mapping of the area, as well as sketches generated in the field, make up most of the collected data. The earthquakes were downloaded from the US Geological Survey website (https://earthquake.usgs.gov/). Earthquakes under magnitude 2.0 were excluded, as they are too small to be of any significance for the thesis project. In addition, satellite imagery from Google Earth is used to filter out earthquake data outside the study area. The satellite imagery from Google Earth combined with a Digitized Elevation Model (DEM) of the study area in Petrel E&P Software Version 2017 (Petrel), were important tools used to conduct the structural analysis of the thesis project.
4.2 METHODOLOGY 4.2.1 Field Work
The fieldwork consisted of two excursions of two-weeks, one in August of 2018 and one towards the end of the study, May of 2019. The first period of fieldwork concentrated on the southern side of the Corinth Rift. Major faults suggested by previous master theses were verified, and less explored areas of interest were investigated. The second period of fieldwork towards the end of the study was
concentrated more on the northern side of the GoC and the southern part of the Gulf of Evia (GoE), and revisiting areas where further investigation was required in the southern side of the GoC, such as the Trikala Fault.
In the field, photos were taken with a Nikon D3400 SD camera with lenses up to 200mm zoom. Faults were photographed from multiple angles, and changes from one side of the fault to the other side were documented. Fault strike and dip measurements were collected using a geological Silva Compass. The measurements are used to aid in identifying fault families across the main faults, whether the fault steps, continue straight across or terminate. The syn-rift deposits and basement were differentiated based on lithology and sedimentological characterization using roundness, grain-size, and orientation. The position of faults and unconformity contacts were mapped, and in areas where the contacts are missing or poorly exposed, the contacts are extrapolated.
The main faults are typically identified by a sudden change in topography and often align with areas of water. These were some of the guidelines used in the field when mapping the main structural features.
The post-fieldwork after both field trips mainly concerned data processing and interpretation of data. GPS points were imported into Google Earth, and further into Petrel. The numerous photos of the different outcrops were merged into larger composite photos and interpreted using Adobe Illustrator.
Post-fieldwork after the second field trip concerned further data processing and interpretation of the gathered data and integrate them into the previous analysis done.
New field observations were organized and plotted into Petrel to compare and integrate with the data used from the previous work.
29 4.2.2 Earthquake
The methodology for acquiring, processing and analyzing earthquake data can be seen in Figure 19. The earthquake data were obtained from the US Geological Survey (https://earthquake.usgs.gov/), a global earthquake database containing earthquake data from 1900 to today. The earthquake database contains information about depth, magnitude, position and time, and for a few data samples – fault plane solution and estimated intensity map. Earthquake data from the period November 8th, 1905 to December 16th, 2018 were used. The total amount of earthquakes processed in this thesis is 13680. Moment tensors or focal mechanisms were not present in the data set, and were obtained from another database; Hellenic Seismic Network (HL) (http://bbnet.gein.noa.gr/HL/), which contains focal mechanisms for all the earthquakes in Greece and adjacent regions from 2005 until today.
The earthquake data was downloaded as a Comma Separated Values (CSV) file and Keyhole Markup Language (KML) files. The CSV file needed to be converted into a .shp-file (SHAPE-file) in order to be able to display the earthquake data in Petrel. When trying to convert the CSV file, a number of tries had to be conducted before successfully creating a .shp-file to use for the earthquake analysis. Different approaches were used, and the best way is described below.
Using Arc Catalog, the CSV file is selected and the option “Create Feature Class From XY Table” is selected. This changes the coordinate system from the geographic coordinate system “WGS 1984” to an X, Y, Z fields that matches with the coordinate system in Petrel. The file can be imported into the Petrel software and displayed as points with attributes. Additional attributes were added to the attribute list, including faults and depths. The workflow of the earthquake process can be seen in Figure 19.
The earthquakes were also downloaded as Keyhole Markup Language files and imported into Google Earth as points of information to display over the satellite imagery. KML files use XML (Extensible Markup Language) files to express geological information like lines, shapes, 3D images and points.
Acquiring earthquake
data
• Earthquake is downloaded from US Geological Survey (USGS)
• CSV files
• KML files
Conversion of data
• CSV files need to be converted to .shp-file
• Arc Catalog
• Changes geographic coordinate system
• WGS1984 --> GCS WGS1984 (EPSG:4326)
Display the data
• CSV file (now Shapefile) displayed in Petrel
• KML file displayed in Google Earth
Process data
• Add attributes in Petrel
• Earthquake alignments
• Eliminate "noise"
Earthquake analysis
• Transverse alignments
• Rift alignments
• Connect the system
Figure 19: List of methodology for the earthquake data.
31 Errors:
The data showed areas of problems that weakened the reliability of the earthquake data set:
• Regular spacing
In some areas, the earthquakes are quite clustered, indicating high activity.
After taking a closer look, a suspicious regular spacing can be identified (see Figure 20). The earthquakes all have different depth and magnitude, which makes it difficult to determine the reliability of this data.
• Reliability of the older data
Earthquake data from before 2000 have significantly fewer details than data from the last 20 years. The earthquake data from before 2000 consist of date and time of earthquake, position and depth, magnitude and magnitude type.
earthquakes have been monitored in Greece since the 1900s, a national seismological network, Hellenic Unified Seismological Network (http://www.gein.noa.gr/en/networks/husn), was not established before 2006- 2007. Before that, the institutes had their own measurement-stations and data were not shared openly.
Figure 20: An example of area in the GoC where identical distance between earthquakes can be observed.
3.3TRANSVERSE FAULT MODELLING
Data collected from published work and fieldwork from several master theses from the University of Stavanger have been used to conduct 3D structural models of the study area. The models are used to analyze and investigate the alignments and earthquakes data. The 3D geological model representing the study area was built using Petrel.
Within Petrel, a Digitized Elevation Model (DEM), representing the topography of the entire Peloponnesus and central Greece, was used to form a basis for the model construction of the transverse faults in the study area. The surfaces defining the 3D model are the DEM, constructed faults and a base surface that limits the model. The DEM used in Petrel has a grid size of 90 x 90 m, which is satisfactory to resolve the main topographic features of the study area.
For the offshore area in this study, the Aegean Sea, a geopolygon set containing the country borders in the Mediterranean form the basis, with earthquake data and Google Earth as the main data input, as less information was gathered in that area. This was the base for structural and earthquake analysis.
33
Chapter 5: Field Observations 5.1INTRODUCTION
This chapter will describe the observations done in the field during the two field trips executed during this thesis project. The southernmost part of the study area has been investigated by previous master projects at the University of Stavanger, and a structural map has been compiled from them as a help in the field. Egeland (2018) compiled a structural map for the area from Kalavryta to Helike (Figure 21). The map was in the southern part (Chelmos and Kalavryta Fault Block) compiled from Finnesand (2013), and the Kerpini Fault Block from Hadland (2016). The Doumena Fault Block was from Veiteberg (2017) and Oppedal (2017), including the eastern segments of the Mamousia- Pirgaki Fault. The Mamousia-Pirgaki Fault Block and the Eiliki Fault were compiled from Dahman (2015) and Ford et al. (2016) (Seen in Figure 21). The structural map for the area around the Trikala fault is compiled from Gawthorpe et al. (2018). The faults mapped in these studies were given specific names, and the same fault names are used in this study where possible.
The river valley has been described previously in different master theses from the University of Stavanger, and as the focus of this thesis project is not to map them in detail, a thorough field description has not been conducted. Each transverse fault is presented as a geologic sketch map, and the main evidence is highlighted and included in a short bullet point description.
Students from UiS have not yet studied the north of the GoC areas; the northern part of the Corinth Rift and the whole Evia Rift. Furthermore, no recent structural studies have been conducted, and few appear to have carried out detailed fault mapping in the N-S direction on a larger scale. Rift faults have been assimilated from previous studies plus
Figure 21: Structural map of the southern part of the Corinth Rift System, highlighting the different segments enclosed by inferring high-angle transfer faults by Egeland (2018).
35
some additional field observations. Very few transverse faults have previously been mapped. However, in this study several possible transverse faults were identified, using the earthquakes and applying techniques used by previous studies south of the GoC. In addition, these faults were backed up by the earthquake data, with the database being used to identify additional potential transverse faults.
Possible transverse faults were marked for earthquake alignments where three or more earthquakes line up in a NE-SW direction. Some of these alignments were visited in the field to check if additional evidence can be seen, while the rest are based entirely on the investigation done in Google Earth and with earthquake analysis.
5.2SOUTH OF GULF OF CORINTH
5.2.1 Trikala Fault
The Trikala Fault has previously been described by Gawthorpe et al. (2018), which interpreted the fault to be located approximately 4.5 km west of Kefalari. The fault was observed to be 6.7 km long, linking the E-W striking Kyllini and Kefalari faults, with an NNW-SSE trend.
When the area surrounding the proposed transfer fault was visited, finding the fault proved challenging. Approximately 200 m north of the town of Kefalari, a change in lithology can be seen (Figure 22), however no change in topography was observed and no other evidence to support it was found. No earthquakes have been recorded in the area. Taken into account the observations for this fault, the evidence for this transfer structure is weak.
Figure 22: Trikala location. a) Photo of area of contact. b) Trikala fault interpreted. c) Observed change in lithology.
Basement
Conglomerate Transfer fault
37 5.2.2 Krathis Fault
The Krathis Fault was proposed by Oppedal (2017) who investigated the Krathis Valley and interpreted a transfer structure running along the river valley. The fault follows the river valley from Zarouchla in the south to the coast of Paralia Porovitsis in the north, giving the Krathis Fault a length of approximately 26 km. There are no earthquakes lining up with the river valley, and the fault was visited in the field (Figure 23 and Figure 24).
Figure 23: Overview of the area surrounding the Krathis River.
N
The main evidence for the Krathis Fault is, going from north to south:
a) Figure 25:
• Basement outcropping on the western side, conglomerate in the eastern side.
N
Figure 24: An overview map of the Krathis river and transfer fault. The red line represents the proposed transfer fault.
b) a)
N
39
• Approximately 600 m higher elevation of the basement on the west side, compared to the east.
• On the eastern side, a thick succession of conglomerate is dipping to the east, the opposite way of the fault and the basement seen on the western side.
b) The Kalavryta Fault comes into the Krathis river valley in the west, ending abruptly.
Figure 25: Point a) in Figure 24. Photo taken from the eastern side of the Krathis river valley, standing on the Valimi Fault, looking towards the north.
5.2.3 Vouraikos Fault
The Vouraikos Fault was previously described by Dahman (2015) and Oppedal (2017), who investigated the Vouraikos Valley. The fault stretches from the town of Kalavryta in the south to coast of Diakopto in the north, having a length of 19 km (Figure 26 and Figure 27). There are no earthquakes aligning with the fault, but the Vouraikos Fault was visited in the field and tracked by foot most of the way.
N
Figure 26: The area surrounding the Vouraikos river.
41
The main evidence for the Vouraikos Fault includes:
a) Multiple fault stepping:
• The Kerpini Fault left steps in the Vouraikos Fault.
o A 430 m difference in displacement from east to west (Egeland, 2018).
• The Mamousia-Pirgaki Fault has a small step to the right.
Figure 27: Vouraikos Fault and the main evidence. The thicker red line represents the Vouraikos Transfer Fault.
N
b)
a)
a)
c) b)
Roghi Doumena
b) Fault termination:
• The Doumena Fault terminates in the Vouraikos Fault.
• Multiple minor faults terminate.
c) Different lithology on each side of the fault.
43 5.2.4 Roghi Fault
The Roghi Fault was previously described by Syahrul (2014) and Hadland (2016), to provide a better explanation for the steps in both the Doumena and the Kerpini faults.
The Roghi Fault is located in a valley to the west of the Vouraikos Fault (Figure 26), with a length of 7.70 km. There are no earthquakes lining up with the valley, but the fault was visited in the field and evidence for the Roghi Fault being a transfer fault was confirmed, shown in Figure 28.
Roghi
Doumena
N
b) a)
a)
Figure 28: Roghi Fault and the main evidence. The thicker red line represents the Roghi Transfer Fault, and the thinner red lines are other transfer faults nearby.
The main evidence for the Roghi Fault includes (See Figure 28):
a) Faults are stepping from one side of the structure to the other:
• The Kerpini Fault has a small step to the right.
o 320 m difference in displacement from the east side to west side (Egeland, 2018).
• The Doumena Fault steps to the left.
o Drops 150 m in displacement between the two segments.
d) A clear change in elevation can be seen in the field.
• The basement is observed on the west side of the fault, and conglomerate can be observed on the east side suggesting the unconformity is much lower on the eastern side.
45 5.2.5 Kerinthis Fault
The Kerinthis Fault has been previously described by Dahman (2015), Hadland (2016) and Veiteberg (2017) to explain the steps in the Doumena Fault, the Mamousia-Pergaki Fault, and the Eiliki Fault. The fault is located in the Kerinthis Valley (Figure 29 and Figure 30) and extends from Skepasto in the south to the coast of Rodia in the north, which gives the fault a length of 19 km. The fault splits in two, named Kerinthis Fault and Kerinthis Fault II. There are no earthquakes measured that line up with this fault structures, but the fault was visited in the field and evidence for a transfer structure was observed.
Figure 29: Overview of the area surrounding the Kerinthis river.
N
The main evidence for the Kerinthis Fault (Figure 30) includes:
a) Rift faults stepping:
• Kerpini Fault steps to the right in the eastern fault and terminates in the western fault.
o There is a 540 m difference in displacement (Egeland, 2018).
N
Figure 30: Kerinthis Fault and the main evidence presented. The thicker red line represents the Kerinthis Transfer Fault, and the thinner red lines are other transfer faults nearby. The orange square marked the location of Figure 31.
Figure 31
47
o The westernmost end of the Kerpini Fault terminated, and abruptly drops 480 m in displacement (Egeland, 2018).
• Doumena Fault steps 850 m to the right (Figure 31).
• Mamousia-Pirgaki Fault steps to the left.
• Eliki Fault steps approximately 2000 m to the right, separating Eliki Fault East and West.
b) Change in lithology:
• Basement in the west and conglomerate in the east.
c) Rift fault termination.
• The Kerpini Fault terminated in the Kerinthis Fault West.
Figure 31: a) Satellite image from Google Earth of one part of the Kerinthis Fault. b) Structural interpretation showing the Doumena Fault stepping between Doumena Fault West III and Doumena Fault West IV.
W E
49 5.2.6 Lapanaghi Fault
The area surrounding the Lapanaghi Fault was described by Rhodes (2015), however, this fault has not been described before (Figure 32). The fault is located immediately west of the town of Lapanaghi, in the Dhemesticha Basin (Figure 33). The length of the fault is interpreted to be 2.70 km, but as the continuation of the fault is unclear. There are no earthquakes lining up with the fault, and the area was visited in the field.
3 km
N
Figure 32: An overview of the area surrounding the Lapanaghi Fault.
The main evidence for the Lapanaghi Fault (Figure 33) includes:
a) Change in lithology. Lapanaghi town is located on basement, and the other side of the fault, at the same elevation conglomerate is observed (Figure 34 a, b).
b) A clear change in elevation of base-syn rift unconformity, deeper to the west (Figure 34 a, b).
Figure 33: A map showing the Lapanaghi Fault with proposed continuations of the fault.
N
51
The fault has been observed to continue over the valley, and up on the left side of the monastery (Figure 35); however, no evidence other than a topographic change was observed when visiting the mountainside.
Figure 35: Google Earth image showing the Lapanaghi Fault and the different possibilities of continuation. The purple lines represent the fault plane and the stippled line represent the proposed continuations of the fault.
a) b)
Figure 34: a) Lapanaghi Fault, viewed from the south. b) Interpreted image showing the change in lithology, with basement in the west side of the fault and basement on the east side.
5.3OFFSHORE GULF OF CORINTH
The observations for the GoC are based on earthquake data and changes in the sea floor.
Mostafa (2017), which looked at the GoC in an E-W direction, found multiple NNE- SSW fault structures, some that line up with the earthquake data, others that line up with changes in topography and onshore river valleys (Figure 36).
Multiple alignments of three or more earthquake can be seen in the north-south direction (Figure 37). Some of these alignments line up with the proposed fault of Mostafa (2017), while others are only based on seen alignments in the GoC. A few of them can be lined up with the river valleys on the southern side.
Transfer fault suggested by Mostafa (2017) Earthquake data
Figure 36: Earthquake data in the GoC. Red lines indicate transfer faults suggested by Mostafa (2017).
Some of the suggested faults lines up with the earthquake data, other which does not relay on earthquake data at all.
53
Looking at the earthquakes in the GoC, two different types of overall seismic zones can be seen (Figure 38). The red squares show areas with high earthquake activity, while the yellow squares show areas where there is low earthquake activity. The boundaries between these zones tend to have a NNE-SSW trend, parallel to the onshore fault of the Peloponnesus (Figure 37) and the offshore fault in the GoC (Figure 36). Some of the areas with a large amount of earthquake data show that a noticeable amount of earthquake is located with an identical distance to each other and with identical depth and similar magnitude (Figure 20). Therefore, the reliability of these observations alone could be open to question.
Transverse faults suggested based on earthquake alignments Earthquake data
Figure 37: Earthquake data in the GoC. Red lines indicated earthquakes which lines up in an approximately N-S direction, interpreted for this thesis project.
5.4NORTH OF GULF OF CORINTH
Multiple fault structures were observed on the northern side of the Gulf of Corinth. The alignments are separated into earthquake-based alignments, geomorphologically based and geologically based – or a mixture of two or all of them. Some of the alignments were visited in the field, to examine whether the earthquake alignments can be observed in the topography in the area. Table 1 and Figure 39 give an overview of the observations in the area, separated into rift faults (E-W orientation) and transverse faults (N-S orientation). Goldsworthy and Jackson (2001) and Jones et al. (2009) have previously investigated the area, but the N-S striking transverse faults were not investigated in the paper.
Figure 38: Google Earth image showing earthquake data located in the GoC. Two types of areas can be seen: two areas with high amount of earthquakes and two areas with a low amount of earthquakes.
