Ioannis Papanikolaou

Fault slip-rate variations during crustal-scale strain localisation, central Italy

Rates of plate motion are generally uniform over 10–102 Myrs timescales. Faults between tectonic plates might, therefore, be expected to show temporally-uniform slip-rates if the same number of faults remain active. For an extending region of the Eurasia-Africa plate boundary, Italy, finite throw values (vertical component of the slip) for seismogenic normal faults are less than that predicted when recent throw-rates are extrapolated over the fault lifetimes. The effect correlates with distance from the fault system tips and demonstrates that the slip-rates on centrally-located faults have increased with time. Neighbouring normal faults were active in the Quaternary but show no signs of surface faulting during the latest Pleistocene to Holocene. Death of these faults has provided the extra strain per unit time to drive the increased slip-rates measured on other faults. Thus, fault interaction and death modify slip-rates and seismic hazards associated with plate tectonics.

New 234U-230Th coral dates from the western Gulf of Corinth: Implications for extensional tectonics

We derive rates of uplift of ∼0.7–0.8 mm/yr for the western end of the Gulf of Corinth, Greece, using geomorphic paleaoshoreline modeling. We calibrate the modeling with new 234U-230Th dates on the coral Cladocora caespitosa collected from raised marine terraces uplifted in the footwall of the active Psathopyrgos fault, the only major active normal fault, reported on published maps controlling the downthrown Rio Straits at the western end of the Gulf of Corinth. In this area of high (15–22 mm/yr) extension rates measured with GPS, the ratio of uplift-rate to extensional velocity is 0.025–0.035, much lower than values of 0.15–0.25 found further east in the gulf. These low values imply that if GPS extension rates are correct then mechanical/kinematic models developed for the eastern and central gulf may not be applicable to the western gulf.

Localization of Quaternary slip rates in an active rift in 105 years: An example from central Greece constrained by 234U-230Th coral dates from uplifted paleoshorelines

Mapping, dating, and modeling of paleoshorelines uplifted in the footwall of the 1981 Gulf of Corinth earthquake fault, Greece (Ms 6.9–6.7), are used to assess its slip rate history relative to other normal faults in the area and study strain localization. The 234U-230Th coral ages from Cladocora caespitosa date uplifted shoreface sediments, and paleoshorelines from glacioeustatic sea level highstands at 76, (possibly) 100, 125, 175, 200, 216, 240, and 340 ka. Uplifted Quaternary and Holocene paleoshorelines decrease in elevation toward the western tip of the fault, exhibiting larger tilt angles with age, showing that uplift is due to progressive fault slip. Since 125 ka, uplift rates varied from 0.25 to 0.52 mm/yr over a distance of 5 km away from the fault tip. Tilting was also occurring prior to 125 ka, but uplift rates were lower because the 125 ka paleoshoreline is at 77% of the elevation of the 240 ka paleoshoreline despite being nearly half its age. Comparison of paleoshoreline elevations and sedimentology with the Quaternary sea level curve shows that slip rates increased by a factor of 3.2 ± 0.2 at 175 ± 75 ka, synchronous with cessation of activity on a neighboring normal fault at 382–112 ka. We suggest that the rapid localization of up to 10–15 mm/yr of extension into the narrow gulf (∼30 km wide) resulted from synchronous fault activity on neighboring faults followed by localization rather than sequential faulting, with consequences for the mechanism controlling localization of extension.

Advances and limitations of the Environmental Seismic Intensity scale (ESI 2007) regarding near-field and far-field effects from recent earthquakes in Greece: implications for the seismic hazard assessment

Abstract The new Environmental Seismic Intensity scale (ESI 2007), introduced by INQUA, incorporates the advances and achievements of palaeoseismology and earthquake geology and evaluates earthquake size and epicentre solely from the earthquake environmental effects (EEE). This scale is tested and compared with traditional existing scales for the 1981 Alkyonides earthquake sequence in the Corinth Gulf (Ms=6.7, Ms=6.4, Ms=6.3), the 1993 Pyrgos event (Ms=5.5) and the 2006 Kythira event (Mw=6.7). These earthquakes were of different magnitudes, focal mechanisms and focal depths and produced well-documented environmental effects. The ESI 2007 intensity values and the isoseismal pattern for the 1993 Pyrgos and the 2006 Kythira events are similar to those resulting from the traditional scales, demonstrating that for moderate intensity levels (VII and VIII) the ESI 2007 and the traditional scales comply well. In contrast, the 1981 Alkyonides earthquake sequence shows that there is an inconsistency between the ESI 2007 and the traditional scales both in the epicentral area, where higher ESI 2007 intensity values have been assigned, and for the far‐field effects. The ESI 2007 scale offers higher objectivity in the process of assessing macroseismic intensities, particularly in the epicentral area, than traditional intensity scales that are influenced by human parameters. The ESI 2007 scale follows the same criteria–environmental effects for all events and can compare not only events from different settings, but also contemporary and future earthquakes with historical events. A reappraisal of historical earthquakes so as to constrain the ESI 2007 scale may prove beneficial for seismic hazard assessment by reducing the uncertainty implied in the attenuation laws, which constitute one of the most important seismic hazard parameters.

Orogen-scale uplift in the central Italian Apennines drives episodic behaviour of earthquake faults

Many areas of the Earth’s crust deform by distributed extensional faulting and complex fault interactions are often observed. Geodetic data generally indicate a simpler picture of continuum deformation over decades but relating this behaviour to earthquake occurrence over centuries, given numerous potentially active faults, remains a global problem in hazard assessment. We address this challenge for an array of seismogenic faults in the central Italian Apennines, where crustal extension and devastating earthquakes occur in response to regional surface uplift. We constrain fault slip-rates since ~18 ka using variations in cosmogenic 36Cl measured on bedrock scarps, mapped using LiDAR and ground penetrating radar, and compare these rates to those inferred from geodesy. The 36Cl data reveal that individual faults typically accumulate meters of displacement relatively rapidly over several thousand years, separated by similar length time intervals when slip-rates are much lower, and activity shifts between faults across strike. Our rates agree with continuum deformation rates when averaged over long spatial or temporal scales (104 yr; 102 km) but over shorter timescales most of the deformation may be accommodated by <30% of the across-strike fault array. We attribute the shifts in activity to temporal variations in the mechanical work of faulting.

Holocene tsunamigenic sediments and tsunami modelling in the Thermaikos Gulf area (northern Greece)

Shallow drill cores in fl at and southerly exposed coastal areas around the Th ermaikos Gulf (Th essaloniki, northern Greece) provided evidence for past high energy sedimentary events, which are interpreted as tsunamites. A tsunamigenic source is located along the western tip of the North Anatolian Fault Zone (NAFZ) in the North Aegean Basin, where water depths ranging between 1.200 and 1.650 m are suffi ciently deep to generate tsunamis. However, the event layers up to now cannot be assigned to individual seismic or landslide sources, but the potential of a tsunami threat in the Th ermaikos Gulf area can now be tested, following both sedimentological and modelling processes. Such potential threat regarding the Th ermaikos Gulf has only recently been notifi ed, but never tested and studied in depth. As a result, several Holocene coarse clastic marine layers have been found intercalated in clayey or gypsiferous lagoonal deposits. Th ese layers have erosive bases, show fi ning-up and thinning-up sequences, and include shell debris, foraminifera and rip-up clasts of lagoonal sediments. A widely observed signifi cant feature of these layers involves mud-coated beach clasts, clasts that rework the high-plasticity clays of lagoons. Such features that indicate highly disturbed sedimentological processes (hyperpycnal fl ows) are rarely described elsewhere. Multiple intercalations of these layers with all the mentioned indicative features downhole are interpreted as paleotsunami deposits from tsunamis generated by earthquakes or earthquake-triggered submarine landslides in the Th ermaikos Gulf. Modelling of the tsunami potential of the basin-bounding fault southwards of the Th ermaikos Gulf provides an example for possible tsunami generation at only one segment of NAFZ along an approx. 55 km normal fault at the southern fault-bound margin of the North Aegean Basin.

Numerical modeling of tidal notch sequences on rocky coasts of the Mediterranean Basin

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Age Constraints and Paleoenvironmental Interpretation of a Borehole Sedimentary Sequence along the Eastern Part of the Corinth Isthmus, Greece

ABSTRACT Pallikarakis, A.; Triantaphyllou, M.V.; Papanikolaou, I.; Dimiza, M.D.; Reicherter, K., and Migiros, G., 2018. Age constraints and paleoenvironmental interpretation of a borehole sedimentary sequence along the eastern part of the Corinth Isthmus, Greece. Borehole Bh-3, located at the eastern part of the Corinth Isthmus (Greece) in a highly active extensional tectonic environment, is studied in detail. The lithology of the 70-m-long borehole is described, and 55 samples extracted from the core are analyzed for their micropaleontological content. Quantitative analysis of foraminiferal fauna assemblages, along with magnetic susceptibility measurements, indicates alternations between different paleoenvironments ranging from upper shoreface and fluvial-terrestrial to lagoon and shallow marine. The borehole site regional paleodepth was estimated, ranging from a few meters to ∼40 m on the basis of foraminiferal assemblages within the borehole, and the vertical stacking of the facies was interpreted as transgressive and regressive system tracts. Calcareous nannofossils found within the core, based on the presence of Emiliania huxleyi specimens, correlated with the glacioeustatic sea-level changes, and the uplift rate of the area indicated a post–240-ka age, corresponding to sea-level highstand marine isotope stages 7 to 5.