Clusters of megaearthquakes on upper plate faults control the Eastern Mediterranean hazard (original) (raw)
Related papers
Eastern Mediterranean tectonics and tsunami hazard inferred from the AD 365 earthquake
Nature Geoscience, 2008
Historical accounts describe an earthquake and tsunami on 21 July AD 365 that destroyed cities and drowned thousands of people in coastal regions from the Nile Delta to modern-day Dubrovnik. The location and tectonic setting of this earthquake have been uncertain until now. Here, we present evidence from radiocarbon data and field observations that western Crete was lifted above sea level, by up to 10 m, synchronously with the AD 365 earthquake. The distribution of uplift, combined with observations of presentday seismicity, suggest that this earthquake occurred not on the subduction interface beneath Crete, but on a fault dipping at about 30 • within the overriding plate. Calculations of tsunami propagation show that the uplift of the sea floor associated with such an earthquake would have generated a damaging tsunami through much of the eastern Mediterranean. Measurement of the present rate of crustal shortening near Crete yields an estimate of ∼5,000 yr for the repeat time of tsunamigenic events on this single fault in western Crete, but if the same process takes place along the entire Hellenic subduction zone, such events may occur approximately once every 800 yr.
Journal of Structural Geology, 2001
Most coastal sectors which show evidence of Holocene coseismic uplift in Greece and the Eastern Mediterranean were raised during a short period called here the Early Byzantine tectonic paroxysm (EBTP) between the middle of the fourth and the middle of the sixth century. A.D. The areas uplifted at that time include Cephaloha and Zante in the Ionian Islands, Lechaion and the Perachora Peninsula in the Gulf of Corinth, the Pelion coast of Thessaly, Antikythira and the whole of western Crete, a coastal sector near Alanya in southern Turkey, and the entire Levant coast from Hatay (Turkey) to Syria and the Lebanon. The amount of the EBTP uplift was generally between 0.5 m and 1.0 m but reached a maximum of about 9 m in s0uthwestem Crete.
Reassessing Eastern Mediterranean tectonics and earthquake hazard from the AD 365 earthquake
2021
The hallmark of great earthquakes (Mw ≈ 8.3-8.5) in the Mediterranean is the 21 July AD 365 earthquake and tsunami that destroyed cities and killed thousands of people throughout the Eastern Mediterranean. This event is intriguing because most Mediterranean subduction forearcs exhibit pervasive crustal extension and minimal definitive evidence exists for great subduction megathrust earthquakes, consistent with weak seismic coupling. This conundrum has led many to favor rupture of a previously unrecognized upper plate splay fault south of Crete in an Mw 8.3-8.5 earthquake, uplifting a Holocene paleoshoreline on Crete by up to 9 m. Similar source mechanisms have been adapted and commonly used for seismic and tsunami hazard estimation in the region. We present an alternative model for the uplift of the Cretan paleoshoreline and the AD 365 tsunami that centers on known active normal fault systems offshore of western and southwestern Crete. We use new and published radiocarbon dates, tog...
Active normal faults on the eastern Mediterranean island of Crete form prominent limestone scarps together with basin and range topography. These faults mainly strike E-ESE and N-NNE in southern and northern Crete, respectively, with fault sets commonly intersecting and northern-trending faults a factor of three more abundant. Displacements, lengths and displacement rates have been analysed for 84 active faults sampled over 2±0.5 Ma (long term) and 16.5±2 ka (short term) time-intervals, with about half showing no resolvable short-term activity. Active faults record earthquake processes on timescales of thousands to millions of years and constrain sampling biases, which can lead to under and over estimates of the numbers, rupture lengths, recurrence intervals and single event displacements of paleoearthquakes. The available data indicate no fault propagation and, for the Quaternary, higher displacement rates on longer faults, supporting a model in which fault lengths and maximum eart...
Geophysical Journal International, 2016
Seismological, GPS and historical data suggest that most of the 40 mm yr −1 convergence at the Hellenic Subduction Zone is accommodated through aseismic creep, with earthquakes of M W 7 rupturing isolated locked patches of the subduction interface. The size and location of these locked patches are poorly constrained despite their importance for assessment of seismic hazard. We present continuous GPS time-series covering the 2008 M W 6.9 Methoni earthquake, the largest earthquake on the subduction interface since 1960. Post-seismic displacements from this earthquake at onshore GPS sites are comparable in magnitude with the coseismic displacements; elastic-dislocation modelling shows that they are consistent with afterslip on the subduction interface, suggesting that much of this part of the interface is able to slip aseismically and is not locked and accumulating elastic strain. In the Hellenic and other subduction zones, the relationship between earthquakes on the subduction interface and observed long-term coastal uplift is poorly understood. We use cGPS-measured coseismic offsets and seismological body-waveform modelling to constrain centroid locations and depths for the 2008 Methoni M W 6.9 and 2013 Crete M W 6.5 earthquakes, showing that the subduction interface reaches the base of the seismogenic layer SW of the coast of Greece. These earthquakes caused subsidence of the coast in regions where the presence of Pliocene-Quaternary marine terraces indicates recent uplift, so we conclude that deformation associated with the earthquake cycle on the subduction interface is not the dominant control on vertical motions of the coastline. It is likely that minor uplift on a short length scale (∼15 km) occurs in the footwalls of normal faults. We suggest, however, that most of the observed Plio-Quaternary coastal uplift in SW Greece is the result of thickening of the overriding crust of the Aegean by reverse faulting or distributed shortening in the accretionary wedge, by underplating of sediment of the Mediterranean seafloor, or a combination of these mechanisms.
Ups and downs in western Crete (Hellenic subduction zone)
Sci. Rep., 2014
Studies of past sea-level markers are commonly used to unveil the tectonic history and seismic behavior of subduction zones. We present new evidence on vertical motions of the Hellenic subduction zone as resulting from a suite of Late Pleistocene -Holocene shorelines in western Crete (Greece). Shoreline ages obtained by AMS radiocarbon dating of seashells, together with the reappraisal of shoreline ages from previous works, testify a long-term uplift rate of 2.5-2.7 mm/y. This average value, however, includes periods in which the vertical motions vary significantly: 2.6-3.2 mm/y subsidence rate from 42 ka to 23 ka, followed by ,7.7 mm/y sustained uplift rate from 23 ka to present. The last ,5 ky shows a relatively slower uplift rate of 3.0-3.3 mm/y, yet slightly higher than the long-term average. A preliminary tectonic model attempts at explaining these up and down motions by across-strike partitioning of fault activity in the subduction zone.
Quaternary International, 2010
An up to 9 m uplift of western Crete, a cluster of coastal uplifts in the East Mediterranean radiocarbon dated approximately w1500 BP, as well as historical and archaeological data are evidence for major, although poorly documented seismic destruction on a nearly-Mediterranean scale in the 4th to 5th c. AD, including the destruction of the Nile Delta in Egypt by a tsunami in AD365. These data represent parts of a puzzle for historians, archaeologists, geologists and seismologists.
Earth and Planetary Science Letters, 2019
Quaternary paleoshorelines are common landforms on the island of Crete, a forearc high above the Hellenic Subduction Zone. These geomorphic markers are useful on Crete and elsewhere in determining coastal uplift rates, the identification of active geologic structures, and to constrain geodynamic models and seismic hazards. Controversy exists in the literature regarding the formation mechanisms and age of late Pleistocene paleoshorelines on Crete that has led to competing models of the uplift history, tectonic evolution, and seismic hazards of the Hellenic forearc. We present new mapping and results from luminescence and radiocarbon geochronology of paleoshoreline deposits that constrain the spatial and temporal pattern of rock uplift around the Cretan coastline. Existing and new radiocarbon data are variable and show no obvious age-elevation trends within individual terrace sequences. By contrast, nearly all luminescence ages, some from shorelines dated with radiocarbon, show positive age-elevation trends and range from 60-220 ka suggesting that all dated paleoshorelines are beyond the limits of radiocarbon. We propose that the inconsistencies between the different geochronological methods are the result of secondary contamination of young carbonate, possibly from meteoric waters, that bias radiocarbon in Cretan Pleistocene marine fossils. Most luminescence ages closely correlate with the timing of mid-to-late Pleistocene relative sea level highstands, consistent with stratigraphic observations. Calculated coastal uplift rates using a Monte-Carlo error analysis range from ∼0-1.2 mm/yr; the lowest uplift rates are found along the northern and eastern coasts of the island, while the most rapid are focused along the southern and western coasts where active normal faults are observed offsetting paleoshoreline sequences. Based on this new data, we favor a tectonic model where slip along upper crustal normal faults acts to locally augment a steady regional signal of uplift along the south and west coast, interpreted to result from the deep underplating of rock at the base of the subduction wedge beneath Crete. Arcward of the contact between the upper plate Moho and the top of the subducting slab, crustal thinning will occur in the orogenic wedge resulting in subsidence along the north coast of Crete.
Geochemistry, Geophysics, Geosystems, 2020
Active fault traces generally form due to displacement of the ground surface or seabed during surface-rupturing earthquakes (Gilbert, 1884; McCalpin, 2009; Stein et al., 1988; Wallace, 1987) (Figure 1). Repeated surface-rupturing earthquakes can produce topography, the height of which depends on the total fault displacement and the relative rates of fault displacement and surface processes (i.e., deposition or erosion) (Figure 1, block diagram). Where sedimentation rates exceed fault displacement rates, the faults are buried and their growth histories can be recovered from subsurface information, including seismic reflection lines and trenches (
A model for the Hellenic subduction zone in the area of Crete based on seismological investigations
Geological Society, London, Special Publications, 2007
The island of Crete represents a horst structure located in the central forearc of the retreating Hellenic subduction zone. The structure and dynamics of the plate boundary in the area of Crete are investigated by receiver function, surface wave and microseismicity using temporary seismic networks. Here the results are summarized and implications for geodynamic models are discussed. The oceanic Moho of the subducted African plate is situated at a depth of about 50-60 km beneath Crete. The continental crust of the overriding Aegean lithosphere is about 35 km thick in eastern and central Crete, and typical crustal velocities are observed down to the upper surface of the downgoing slab beneath western Crete. A negative phase at about 4 s in receiver functions occurring in stripes parallel to the trend of the island points to low-velocity slices within the Aegean lithosphere. Interplate seismicity is spread out about 100 km updip from the southern coastline of Crete. To the south of western Crete, this seismically active zone corresponds to the inferred rupture plane of the magnitude 8 earthquake of AD 365. In contrast, interplate motion appears to be largely aseismic beneath the island. The coastline of Crete mimics the shape of a microseismically quiet realm in the Aegean lithosphere at 20-40 km depth, suggesting a relation between active processes at this depth range and uplift. The peculiar properties of the lithosphere and the plate interface beneath Crete are tentatively attributed to extrusion of material from a subduction channel, driving differential uplift of the island by several kilometres since about 4 Ma.