Eliki Fault Research Articles

New constraints on bedrock erodibility and landscape response times upstream of an active fault

Considerable progress has been made in modelling the response of rivers to tectonic perturbation in order to decode the tectonic signals embedded in river long profiles and planform geometry. Whilst studies have showed the importance of rock type on the morphology of rivers responding to tectonics on a local scale, these effects are often not captured in landscape evolution models. In fact, current models of fluvial response to tectonic perturbation such as active faulting require carefully collected data sets to fully constrain or calibrate key parameters, including the effect of bedrock lithology on substrate erodibility and timescales for tectonic signal propagation in bedrock river systems. Here we constrain the role of bedrock in controlling fluvial incision for a 240 km2 catchment draining into the Gulf of Corinth, which has excellent tectonic constraints and a variety of bedrock lithologies. An active normal fault at the downstream end of the catchment (the East Eliki Fault) is known to have initiated at 0.7 Ma, with average Quaternary uplift and incision rates of 1.00–1.25 mm/yr. The initiation of the East Eliki Fault is recorded in the river as a prominent knickzone 7–16 km upstream of the fault. Detailed field data collected within this catchment at 500 m intervals along the main channel length at this tectonically well-constrained field site show an order of magnitude increase in river channel slopes (y/x = 0.02 to 0.18) and stream powers (1 kWm−2 to 27 kWm−2) at the lithological boundary between weak and resistant bedrock. The weak conglomerates and strong limestones have Schmidt hammer compressive strengths of ca. 30 and 50 respectively, based on in-situ rock strength measurements. Consequent erodibility values of 1.8 ± 0.3 × 10−14 and 5–6 ± 2 × 10−15 ms2kg−1 show a factor of three to four decrease in erodibility for a two-fold increase in rock strength. A simple simulation of tectonic signal propagation through the river catchment based on these erodibility values indicates that the observed plan view position of the knickpoint is consistent with our calculated knickpoint positions based on erodibility values derived from incision rate and stream power data. However, the tectonic signal associated with faulting would have propagated completely through the catchment within 1 Ma if it were entirely composed of weak rock for similar climatic and tectonic conditions, indicating that lithology has a major control on landscape response times. Our results help constrain the effect of lithology on river channel geometry and allow erosional parameters to be derived that are crucial for effective modelling of tectonic rates from topography.

Geomorphic and biological indicators of paleoseismicity and Holocene uplift rate at a coastal normal fault footwall (western Corinth Gulf, Greece)

The westernmost part of the Gulf of Corinth (Greece) is an area of very fast extension and active normal faulting, accompanied by intense coastal uplift and high seismicity. This study presents geomorphic and biological evidence of Holocene coastal uplift at the western extremity of the Gulf, where such evidence was previously unknown. Narrow shore platforms (benches) and rare notches occur mainly on Holocene littoral conglomerates of uplifting small fan deltas. They are perhaps the only primary paleoseismic evidence likely to provide information on earthquake recurrence on coastal faults in the specific part of the Rift, whereas dated marine fauna can provide constraints on the average Holocene coastal uplift rate. The types of geomorphic and biological evidence identified are not ideal, and there are limitations and pitfalls involved in their evaluation. In a first approach, 5 uplifted paleoshorelines may be identified, at 0.4–0.7, 1.0–1.3, 1.4–1.7, 2.0–2.3 and 2.8–3.4 m a.m.s.l., probably forming after 1728 or 2250 Cal. B.P. A most conservative estimate for the average coastal uplift rate during the Late Holocene is 1.6 or 1.9 mm/yr minimum (with different amounts of reservoir correction). Some of the obtained radiocarbon ages of Lithophaga sp. allow for much higher Holocene uplift rates, of the order of 3–4 mm/yr, which cannot be discarded but require further research. That the identified paleoshoreline record corresponds to episodes of coastal uplift only, cannot be demonstrated beyond all doubt. Yet, it appears the most likely interpretation given the geological and active-tectonic context and present knowledge on eustatic sea-level fluctuations in the Mediterranean. Proving that the documented uplifts were abrupt (i.e., arguably coseismic) is equally difficult but rather probable. Five earthquakes in the last ca. 2000 yr on the coastal fault zone that is responsible for the uplift, compare well with historical seismicity and the results of recent on-fault paleoseismological studies at the nearby Eliki fault zone. Exact amounts of coseismic uplift cannot be determined precisely unless the rate of non-seismic uplift of Northern Peloponnesus at the specific part of the Corinth Rift is somehow constrained.

Geometry and slip rate of the Aigion fault, a young normal fault system in the western Gulf of Corinth

The Aigion fault is one of the youngest major normal faults in the Gulf of Corinth, Greece, with an immature displacement profile. Based on geometry, slip rate and comparison with regional faults, we estimate the fault system length at ~10 km. We find the slip rate of the fault system is ~3.5 ± 1 mm/yr decreasing to ~2.5 ± 0.7 mm/yr close to its eastern tip. Complex fault geometry and displacement profiles on the shelf east of Aigion are consistent with the latter as the eastern tip location. Analysis of slip on this fault system and the established fault to the south (Western Eliki Fault) suggests that slip was transferred rapidly but not homogeneously between the two faults during the period of contemporaneous activity. Together with a lack of evidence of lateral propagation at the eastern fault tip in the last 10–13 k.y., we suggest that the fault developed and established its current length rapidly, within its 200–300 k.y. history. These results contribute to our understanding of the process of northward fault migration into the rift and the development of new normal faults.

Palaeoseismic data and their implication for active deformation in Greece

Abstract Results from palaeoseismological trenching for four active faults in Greece are presented. The main target is to determine palaeoearthquake slip and slip associated with events hosted on four active faults: two of them located with the Gulf of Corinth southern part of the Greece (Kaparelli and Eliki) and two in the northern Greece within the Mygdonia and Aliakmon basins. All excavated trenches expose evidence of more than three events, thus enabling to estimate the recurrence interval (RI) of past events and the slip rate (SR) of the faults. Results for the four faults are Eliki fault: RI = 900–400 years, SR = 1.5 mm/a, Kaparelli fault: RI = 2300 years, SR = 0.3 mm/a, Mygdonia fault: RI = 900 years, SR = 0.26–0.7 mm/a, and Paleohori-Sarakina fault: RI = 30,000 (?) years, SR = 0.01–0.03 mm/a. The latter result is under question, because a different dating method was used. From all trenches the inferred earthquake magnitude is in the order of 6.5. On the other hand, both RI and SR range two orders of magnitude with faults located southerly and easterly showing shorter RI and larger SR in reference with the northwesternmost Greece. This palaeoseismological study helps us to propose a model for the behaviour of large seismogenic faults in the Aegean area in response to their geotectonic setting.

Recent history of the Eastern Eliki Fault, Gulf of Corinth: geomorphology, palaeoseismology and impact on palaeoenvironments

The Eliki fault system dominates the landscape of the southwestern shore of the Gulf of Corinth, where rapid extension rates result in frequent earthquakes. These include an event in 373 BC that destroyed the city of Helike and a recent event in 1861. Uplifted Late Pleistocene marine terraces within the Eastern Eliki Fault footwall suggest revised slip rates of ∼3–5 mm yr−1, contributing ∼2–3 mm yr−1 geological extension to a net geodetic extension of ∼10–15 mm yr−1 across this part of the rift. Palaeoseismological trenches indicate two and possibly three earthquakes on the Eastern Eliki Fault in the last 1500 yr, including the 1861 earthquake. One trench (EET1A) reveals displaced stratigraphy, but the main fault trace is thought to lie further south beneath the Old National Road. Trench EET1A reveals liquefied sediments associated with an event between AD 1460 and the present, which may be the 1861 event, and displacement during a second event in the interval AD 440–1410 or AD 1270–1640. A third earlier event identified by liquefaction occurred on the Eliki or a nearby fault in AD 440–1410. Using the 1861 and second event (most likely AD 1270–1640), the interval between recent earthquakes is ∼200–600 yr. Suitable trench sites are rare in this region, compounded by human activity over several thousand years. Borehole and trench data indicate that the Kerynites river frequently flowed eastwards along the Eastern Eliki Fault during the last 20–40 kyr, possibly influenced by tectonic tilting from the Eliki and Aigion fault systems and natural channel avulsion.

A Holocene coral–algal reef at Mavra Litharia, Gulf of Corinth, Greece: structure, history, and applications in relative sea-level change

A Holocene coral–algal reef at Mavra Litharia, south-central coast of Gulf of Corinth, Greece, is exposed from ca. 2 to 9.3 m above sea level on an uplifting footwall associated with the Eliki Fault. The reef lacks sea-level-critical species but its coralline algal assemblage indicates a ca. 10 m water depth. Reef-frame components date from 9280–8730 years BP to 6343–5993 years BP, so the reef frame grew between ca. 10,000 and 6000 years BP. The youngest dated shells (1860–305 years BP) from the site are accessory organisms collected from the lowest 2 m of outcrop, one of which ( Dendropoma) grew at sea level [Stiros, S.C. and Pirazzoli, P., 1998. Late Quaternary coastal changes in the Gulf of Corinth, Greece: tectonics earthquake, archaeology. Guidebook for the Gulf of Corinth Field Trip, Patras University, Greece, Patras, September 14–16, 1998]. Reef history has four phases: a) growth and lithification of reef; b) development of smooth-walled dissolution pipes and caves in the reef; c) colonisation of dissolution surfaces by Mn–Fe crusts (that may be bacterially formed), barnacles, serpulid worms, and rock-boring bivalves; and d) uplift to present position where much of the reef is eroded. Sea-level history after 11,500 years BP, when rising post-glacial sea level overtopped the Rio sill and returned the Gulf of Corinth to a marine environment, is reconstructed. Calculations of interplay between sea-level rise and tectonic uplift suggest that between 11,500 and 10,000 years BP sea level rose very quickly, associated with deglaciation at the close of the Younger Dryas, MWP-1B, at a maximum of 25.6 mm/year (broadly consistent with other studies), then slowed to ca. 4.4 mm/year until 6000 years BP when sea level was ca. 3 m below modern, after which sea level rose at ca. 0.5 mm/year to modern day. Tectonic uplift rate of maximum 3 mm/year, slower than sea-level rise, means that the reef could not catch up to sea level until recent times, explaining its fossil assemblage. The pipe/cave system is interpreted as having formed when the reef top was emerged, but much dissolution occurred beneath sea level because of insufficient time to allow uplift and resubmergence. Intense rainfall during the mid-Holocene pluvial phase, ca. 6000 years BP for the eastern Mediterranean, which affected large areas of the Mediterranean, is suggested as the mechanism and timing of submarine dissolution.

Dating recent colluvial sequences with 210Pb and 137Cs along an active fault scarp, the Eliki Fault, Gulf of Corinth, Greece

Reliable dating is an essential element of palaeoseismological studies, yet whilst a suite of geochronological methods can now provide late Quaternary age control it remains very difficult to date modern events (i.e., those occurring within the last 150 years). This is significant because the starting point for many palaeoseismological investigations is a modern surface-rupturing event, whose geological effects need to be disentangled in trench stratigraphies from palaeoseismic ruptures. Two dating methods which, in combination, can provide robust dating control in recently deposited sediments are the 210Pb and 137Cs dating methods. Here, we test the applicability of using 210Pb and 137Cs to date colluvial sediments exposed in three trenches excavated across an earthquake fault—the Eliki fault, Gulf of Corinth, Greece—which ruptured in an earthquake in 1861. The 210Pb and 137Cs profiles observed in these colluvial sequences are relatively erratic due to the mixed nature of the sediments, i.e., their deposition in an environment where the supply of slope sediments is driven by seasonal rainfall, causing non-uniform sediment accretion and sediment reworking. In one trench, however, 210Pb dating, corroborated by 137Cs dating, indicates that a proposed post-1861 surface colluvial unit has been deposited over the period 1950 AD–present (at a rate of ca. 9 mm/year), and overlies a significantly older unit (>120 years old). The dating control provided here by 210Pb and 137Cs dating corroborates the published interpretation of the trench stratigraphy, and refines the 14C-based estimated dates for the upper unit. At two other trenches 210Pb and 137Cs dating only provided minimum ages (based on the presence or absence of 210Pb excess and 137Cs). Such approximate ages, however, may still useful in corroborating interpretations made using the trench stratigraphy, or, at sites which have long earthquake recurrence intervals, determining which earthquake event was responsible for a particular bed offset.

Slip rates of the Aigion and Eliki Faults from uplifted marine terraces, Corinth Gulf, Greece

Along the southern coast of the Gulf of Corinth, important coastal uplift is illustrated by raised Late-Pleistocene marine platforms. Terrace remnants preserved on the footwall of the Aigion and Eliki Faults were mapped in detail. To derive cumulative uplift rates, the individual terraces were tentatively correlated with the eustatic sea-level curve, constrained by some direct dating of the deposits blanketing the terraces. We obtain uplift rates of 1.05–1.2 mm yr−1 for the Aigion Fault footwall and of 1.0 and 1.25 mm yr−1 for the East and West Eliki Fault footwalls respectively. A forward modelling procedure was adopted to fit the best-preserved terrace transects, using a code based on standard dislocation theory and assuming reasonable scenarios of regional uplift. We obtained maximum slip rates consistently in the range of 7–11 mm yr−1 for the West and East Eliki Faults and of 9–11 mm yr−1 for the Aigion Fault. To cite this article: P.M. De Martini et al., C. R. Geoscience 336 (2004).

Uplift and slip rates of the eastern Eliki fault segment, Gulf of Corinth, Greece, inferred from Holocene and Pleistocene terraces

Uplifted Pleistocene and Holocene marine and fluvial deposits are preserved in the footwall of the Eliki fault, western Gulf of the Corinth, where geodetic extension rates exceed 10 mm a −1 . Up to 10 Pleistocene terraces are distinguished in the footwall block of the eastern Eliki fault segment, discontinuously preserved along strike. Terraces are depositional, forming by the progradation of clastic fan deltas, or predominantly erosional, between fan deltas. Correlation of terrace profiles with Late Pleistocene eustatic sea level suggests an uplift rate of c . 1 mm a −1 , with an alternative of c . 1.5 mm a −1 . On average, higher rates are obtained from uplifted Holocene deposits ( c . 1–2 mm a −1 ). To determine slip rates, a long-term ratio of uplift to subsidence of c . 1:2–3.2, derived from net footwall altitude and basin subsidence–fill and a fault dip of 50° are applied to uplift of c . 1 mm a −1 . These produce a slip rate of c . 4–7 mm a −1 contributing c . 2–4 mm a −1 to extension across the Gulf, significantly less than geodetic rates. This discrepancy may result from strain taken up on faults to the north and offshore. Uplift rates decrease little at the Eliki fault tips. Uplift rates are broadly consistent in the central–western Gulf but show a decrease in average uplift from Corinth eastward.

MORPHOTECTONIC ANALYSIS IN THE ELIKI FAULT ZONE (GULF OF CORINTH, GREECE)

Morphotectonic analysis using geomorphic indices has been developed as a basic reconnaissance tool in order to identify areas experiencing rapid tectonic deformation or estimate relative variations of tectonic activity in a specific area. We applied this analysis in Eliki fault zone, which is located in the western part of the Gulf of Corinth. Eliki fault zone was selected because it displays a spectacular geomorphic expression and hosts historic and recent seismicity. The intensity of active tectonics is interpreted through a detailed geomorphic study of the fault-generated mountain fronts and fluvial systems. Tectonic geomorphology analysis of the Eliki footwall area includes the application of the most commonly used geomorphic indices, such as the mountain front sinuosity index (Smf), the valley floor / width ratio index (Vf), the stream gradient index (SL) and the transverse topographic symmetry factor (T). These indices were estimated on topographic maps and aerial photographs of the study area in order to correlate active tectonics and erosional processes. Our results imply that the Eliki fault zone can be assigned to a tectonic class of the higher tectonic activity. However, spatial variations of tectonic activity along the segmented studied fronts point to a general trend of increasing activity towards the east, which is gradually decreasing towards the west.

Late Holocene evolution of the East Eliki fault, Gulf of Corinth (Central Greece)

Trench stratigraphy and morphotectonic analysis was used to examine the recent evolution of the Helike (Eliki) Plain and Eliki Fault. The entire alluvial plain of the Kerynites and Vouraikos Rivers, which cross the Eliki Fault, has subsided at rate of 1.4 mm/yr, resulting in the burial of the Late Hellenistic-Roman occupation horizons under ⩽3 m of fluvial and colluvial sediments. Along the eastern segment of the Eliki Fault five trenches have been excavated and their 5000-yr old fluvial and colluvial deposits have been studied in association with the fault strand imprinted on them. The Kerynites River crosses at high angle the Eliki Fault and appears to be sensitive in tectonic movements related with the Eliki Fault. Sedimentation in the alluvial plain and the fluvial geomorphology of the Kerynites River is important for understanding the fault evolution and the burial of the ancient (4th century BC) Helike city. The Kerynites River course highlights breaching deformation is the more likely to connect East and West Eliki Fault segments and that postseismic deformation is a significant mechanism for stress accommodation for part of the west end of the Gulf of Corinth.

A late Holocene record of environmental changes from the Aliki lagoon, Egion, North Peloponnesus, Greece

Aliki lagoon is a small lagoon located on the micro-tidal south coast of the Gulf of Corinth, Greece. The sediments of the lagoon recovered in three cores provide a record of late Holocene environmental change, including tectonic subsidence, tsunami layers, and change in local vegetation and sedimentation. Four periods of rapid environmental changes were identified over a 5000-yr-long record. These date from about 4700, 3000, 2500 and 2000 yr BP. Each change is linked to activity on the Egion fault, a deepening of the lagoonal bottom and a rise in relative sea level. Six tsunami events are recorded and have been caused by earthquakes on the Egion fault (three events ∼4700, ∼3000 and ∼2500 BP), Eliki fault (2350±40 yr BP) and two more distal fault ruptures. The vegetation history and pollen zones are similar to those recognised by Jahns (Vegetation Hist. Archaebot. 2 (1993) 187) on the Argive Plain, 100 km southeast of the lagoon. Five successive sedimentological configurations are established in relation to the time frame provided by the tectonic activity: (1) crevasse splay; (2) fresh to brackish water marsh; (3) and (4) brackish to hypersaline “blind” lagoon, and (5) brackish to hypersaline “blind” lagoon or brackish open lagoon.

A palaeoseismological and geoarchaeological investigation of the Eliki fault, Gulf of Corinth, Greece

Palaeoseismological and morphotectonic analyses enable us to define a 400-m-wide actively deformed zone associated with the active Eliki normal fault, central Greece, bounded on the south by a second-order fault and on the north by a composite and prominent fault scarp. This scarp is further analysed by trenching. Based on colluvium stratigraphy, displacement of distinct horizons and deposition of sedimentary layers, three faulting events have been identified along four fault strands affecting unconsolidated sediments in the trench. The two younger events, with throws of 0.93 and 1.37 m, respectively, the third event, with a throw of 0.44 m, and the penultimate 373 BC event suggest a variable seismic history. The entire alluvial plain of the Kerynitis and Vouraikos rivers, which cross the Eliki fault, has subsided at a rate of 1.4 mm/year, resulting in the burial of the Late Hellenistic–Roman occupation horizons under 3 m of fluvial and colluvial sediments in places. Extension in the broader area is accommodated by the seismically active Eliki and Egion faults. Structural and palaeoseismological analysis of those two faults indicates that they accommodate 1.5 mm/year, or about 10% of the geodetically estimated extension of up to 13 mm/year.

Paleoseismological investigation of the eastern "segment" of the Heliki fault, Gulf of Corinth, Greece

Paleoseismological analysis based on geological data enable us to understand the recent seismic history of the Eliki fault. Along the eastern "segment (or strand)" scarp 5 trenches have been excavated (8x5x2m), their walls were mapped in scale 1:20 and further analyzed by precise tectono-stratigraphic methodology. The Kerynitis river, which crosses the Eliki fault from S to Ν and supplies the alluvial plain, has subsided at a rate of 1.4 mm/ yr. The river was running from west to east, resulting the fluvial conglomerates in the trenches, which have buried under the colluvial sediments. Based on colluvium stratigraphy, displacement of distinct horizons, deposition of sedimentary layers and C14 dating, faulting events have been identified affecting unconsolidated sediments in the trench. The penultimate 373 BC event and the two younger events with a throw of 0.93 m and 1.37 m respectively, the third event, with a throw of 0.44 m, suggest a variable seismic history.

Barriers on seismogenic faults in central Greece

Structural mapping, morphotectonic analysis and existing seismological data are synthesized to characterize barriers—regions of high strength along the fault which can impede or arrest rupture propagation—on the most active and prominent traced fault zones in central Greece. Inhomogeneous and non-conservative barriers are the two different structures that have been identified on the Eliki fault (in northern Peloponnesos), and the Kaparelli and Atalanti fault zones (in Sterea Hellas), respectively. The Eliki fault consists of two colinear segments of different rupture characteristics that intersect at an inhomogeneous barrier. The eastern fault segment has had, in Late Quaternary, repeatedly activated earthquake sequences, whereas the western segment remained unaffected by these events. The Kaparelli and the Atalanti fault zones are the WNW and ENE fault segments of a single primary fault zone with a surface trace bent. The fault zone bends represent asperities—strong stable barriers—that effectively blunt the fault displacements and permit independent deformation of the fault segments. Earthquakes on these fault zones occur when the asperities fail. Repeated deformation and evolution of faulting change these asperities into non-conservative barrier structure. That is, surface rupturing is accommodated by a new, third direction of faulting developed in the zone of intersection between the two adjacent oblique segments of the primary fault zone. This third direction of faulting involves a major cumulative dip slip within the barrier region and it is responsible for repeated earthquakes during the Quaternary time. In response to this faulting process, a primary bent fault zone activated by repeated earthquake events tends to be curvilinear in trace and preserves a perched basin on its footwall block. The proposed rupture model of fault zone bends by a third direction of faulting during large earthquake events and is suitable for widespread application in Greece, regarding: (1) the interpretation of the distribution of fault strikes between dominant WNW and ENE inherited strikes; and (2) the initiation of earthquakes from the fault zone bends.

Coastal uplift on active normal faults: The Eliki Fault, Greece

The Eliki Fault forms part of a system of major normal fault segments that borders the southern margin of the Gulf of Corinth half graben. Radiocarbon dating of elevated marine fossils reveals broadly uniform Holocene coastal uplift, at a time‐averaged rate of 1.5 mm/yr, both along the Eliki Fault and in the transfer zone that separates it from the neighbouring fault segment. Coseismic uplift increments are considered to account for only a minor part of the 6 m of emergence recorded here in the last 3000 years. Reappraisal of shoreline data from the Perachora Peninsula at the eastern end of the Gulf of Corinth indicates a similar, though less rapid (0.7 mm/yr), pattern of uniform Holocene emergence. As these Holocene coastal records embody both coseismic and interseismic deformation they can be used to characterise long‐term tectonic strain.

Holocene uplift and palaeoseismicity on the Eliki Fault, Western Gulf of Corinth, Greece

Radiocarbon dating of elevated coastal phenomena along the emergent footwall of the Eliki Fault in the West- em Gulf of Corinth has established a chronology of tectonic emergence during Holocene times. The results confirm -6 m of coastal uplift over the last 3000 years at sites both immediately adjacent to, and more distant from, the offshore l'ault. Although revealing little or no spatial vm.iation along the fault, temporally the data de- fine two phases of enhanced tectonic activity (0-3000 year B.P. and pre- 7-8000 year B.P.) separated by a 4- 5000 year period of tectonic quiescence. Well documented historical surface faulting during the most recent lclive phase testify to the contribution to net uplift played by coseismic increments, but these are considered to be superimposed on significant aseismic movements. While asesismic uplift confuses the palaeoseismic .ecord, correlation of prominent notch levels with dated raised shoreline fauna provides evidence for at least 3 surface faulting events during the past 2500 years.