The series of earthquakes that took place on February 6, 2023 caused one of the saddest major calamities in Türkiye. The first major earthquake of magnitude Mw7.7 broke the Pazarcık and Erkenek ...segments moving north on the East Anatolian Fault Zone (EAFZ) between Türkoğlu and Çelikhan. According to the Coulomb failure criterion, the Pazarcık earthquake (Mw7.7) increased stress on the Sürgü-Çardak Fault, a segment on the north splay of the EAFZ, and nine hours later the Elbistan earthquake (Mw7.6) occurred. This great event ruptured the Çardak Fault, the western part of the E-W trending Sürgü-Çardak Fault between Nurhak and Göksun. The Amanos Fault, which extends from Türkoğlu south to Antakya, broke almost simultaneously to the first Pazarcık earthquake. Similarly, the earthquake that broke the Amanos Fault transferred increased stress to its south-western neighbour, the Cyprus-Antakya Transform Fault, triggering the 6.3 magnitude Samandağ earthquake 14 days later. The February 2023 earthquakes, which caused the collapse of >100,000 buildings and the death of >50,000 people, created surface ruptures hundreds of kilometres in length and caused different displacements on different faults, the two largest of which were 4.6 and 6.7 m. On all the faults where the deadly earthquakes occurred in February 2023, inversion of the focal mechanisms of the earthquakes (main shocks and their aftershocks) indicates a transtensional stress regime, or a change from strike-slip to normal slip. For all strike-slip inversions, the R values are <0.45 indicating transtension. The stress tensors obtained indicate left-lateral movement with normal component on all faults where the earthquakes occurred. The transtensional regime, which is thought to reflect regional tectonics, is the result of forces caused by relative movements of Arabia, eastern Mediterranean and Eurasia.
•Earthquakes in February 2023 caused surface ruptures along four different faults.•Every earthquake in February 2023 has a left lateral strike-slip character with a normal component.•The forces brought about by the relative motion of Arabia, Africa and Anatolia resulted in the transtensional stress regime.
On October 30, 2020, an earthquake with a magnitude of 6.8 (Mw) struck the northern coast of Samos Island in the Kuşadası Gulf. The solution to the focal mechanism indicates that the earthquake of 30 ...October 2020 occurred on a normal fault with nodal planes of E-W strike; thus, indicating extension in N-S direction. The fault plane solutions show a N-S trending extension for normal faults, which are obtained by inverting the moment tensor waveforms of 23 earthquakes and the P-wave first motion polarities of 11 aftershocks. A normal fault stress regime of approximately N-S (N6°E) σ3 axis is given by the inversion of slip vectors measured at sites located on land in Kuşadası. The mean R value is 0.84, suggesting that the stress regime is triaxial extensional stress state. The inversion of the focal mechanism of earthquakes occurring on land and in the Gulf of Kuşadası describes an extensional stress regime active today, characterized by an approximately N-S (N9°E) σ3 axis. The calculated R value of 0.31 indicates a triaxial stress state. For the 30 October 2020 earthquake (Mw:6.8), the Coulomb failure stress change analysis shows a substantial reduction in stress in the N-S direction supporting the kinematic results. The N-S extension in Western Anatolia-Aegean is largely influenced by the relatively fast movement of the Hellenic trench southwards, related to the sinking of the African plate beneath Aegean.
•The Samos Earthquake (M:6.8) of 30 October 2020 shows N-S extensional regime character.•This tectonic regime contributes to the development of the E-W gulfs on the coast of the Aegean.•The N-S extension is due to the relative rapid motion of the Hellenic trench towards the south.•The high rate of movement towards the Hellenic trench is related to the roll-back of African slab.
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•Present day stress tensor is determined from seismic fault plane solutions.•The present-day stress regime is extensional with a NNE-SSW direction.•Earthquakes migrated in SSW ...direction along stepped-synthetic normal faults.•The extension is caused by both the Anatolian extrusion and the African subduction.
The west to southwestward motion of the Anatolian block results from the relative motions between the Eurasian, Arabian and African plates along the right-lateral North Anatolian Fault Zone in the north and left-lateral East Anatolian Fault Zone in the east. The Biga Peninsula is tectonically influenced by the Anatolian motion originating along the North Anatolian Fault Zone which splits into two main (northern and southern) branches in the east of Marmara region: the southern branch extends towards the Biga Peninsula which is characterized by strike-slip to oblique normal faulting stress regime in the central to northern part. The southernmost part of peninsula is characterized by a normal to oblique faulting stress regime. The analysis of both seismological and structural field data confirms the change of stress regime from strike-slip character in the center and north to normal faulting character in the south of peninsula where the earthquake swarm recently occurred. The earthquakes began on 14 January 2017 (Mw: 4.4) on Tuzla Fault and migrated southward along the Kocaköy and Babakale's stepped-normal faults of over three months. The inversion of focal mechanisms yields a normal faulting stress regime with an approximately N-S (N4°E) σ3 axis. The inversion of earthquakes occurring in central and northern Biga Peninsula and the north Aegean region gives a strike-slip stress regime with approximately WNW-ESE (N85°W) σ1 and NNE-SSW (N17°E) σ3 axis. The strike-slip stress regime is attributed to westward Anatolian motion, while the normal faulting stress regime is attributed to both the extrusion of Anatolian block and the slab-pull force of the subducting African plate along the Hellenic arc.
The Eskişehir Fault is an active right-lateral widespread intra-continental deformation zone which separates central western Anatolia from the Aegean domain. The inversion of fault slip vectors along ...the Eskişehir Fault yields a strike-slip stress state with NW-trending σHmax (σ1) and NE-trending σHmin (σ3) axes since the Early Pliocene. A change in strike-slip faulting under a compressional stress regime: from old transpression to young transtension, probably occurred in the Quaternary. The inversion of the earthquake source mechanism indicates that the transtensional stress regime continues up to the present. The İnönü and Eskişehir Basins developed under the transtensional stress regime producing consistent and local normal faulting with a continuing NE-trending σHmin (σ3). The stress regime change resulted in a decrease in σHmax (σ1) and/or an increase in σHmin (σ3) stress magnitudes due to coeval influence of the superimposed plate forces and the interaction of three plates (Eurasian/African/Arabian): (1) continental collision of Eurasian/Arabian plates with Anatolian block in the east, (2) westward escape of the Anatolian block by anticlockwise rotation at the west-southwest border of the Eurasian and Arabian/African plates and (3) a complex subduction process between African and Eurasian plates along the Aegean (Hellenic) and the Cyprus arcs which favors western extrusion of the Anatolian block in the eastern Mediterranean region.
•Late Cenozoic to present day stress states by inversion and kinematic analysis of the fault-slip vectors and earthquakes.•A temporal and spatial tectonic regime change in strike slip faulting from transpressional to transtensional due to increase and/or decrease of stress magnitudes (Sigma 1, 2 and 3).•Lateral extrusion and anticlockwise block rotation of Anatolian block to westward from Eurasian/Arabian continental collision in eastern Anatolia.•A complex interaction (roll-back, slab-pull and/or slab break-off) to Eurasian/African plate convergence in eastern Mediterranean.•The active Eskişehir Fault is a right-lateral strike-slip fault presented in a transtensional tectonic regime in present day.
The Isparta Angle is an important area of SW Anatolia where extensions in all directions (N-S, NE-SW, NW-SE and E-W) meet. These extensions were determined by normal faulting structures as well as by ...shallow earthquakes. All extensions, except the E-W one, were attributed to the deviatoric stresses in relation to slab forces and/or extrusion of Anatolia. The moment tensor inversion of 40 shallow earthquakes which occurred in the inner part of the Isparta Angle give focal mechanisms mostly indicating normal faulting. Inversion of all focal mechanisms of the earthquakes obtained from the moment tensor inversion yields normal faulting characterized by an approximately E-W (N268°E) σ3 axis. The calculated stress ratio R is 0.6944 indicating a triaxial stress state. Commonly accepted geodynamic models for the eastern Mediterranean region do not include plate boundary forces acting in the east or west direction. Our hypothesis is that the cause of the E-W extension is the combined forces of Gravitational Potential Energy and the hot asthenosphere upwelling through a tear fault in the subducted African plate between the Hellenic and Cyprus arcs beneath the Isparta Angle.
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•Present day stress tensor is obtained seismic fault plane solution data•We obtained E-W extensional stress regime in the Isparta Angle•The high R value indicates near uniaxial stress state implying that this extension is close radial extension•We suggest a model to explain E-W extensions in the geodynamical context•The cause of the E-W extension is the combined forces of the GPE and upwelling hot asthenospheric material.
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•Late Cenozoic stress tensor is determined using microtectonic data.•Present day stress tensor is obtained from seismic fault plane solution data.•We obtained temporal/spatial change ...within extensional stress regime on the SW Turkey.•We determined the NW-SE and NE-SW extensions acting in SW Anatolia.•We suggest a model to explain these nearly orthogonal extensions in the geodynamical context.
The history of the Late Cenozoic stress regime was determined for an area between the gulfs of Fethiye and Antalya. Fault kinematic analysis and inversion of focal mechanisms of shallow earthquakes reveal significant evolution of the regional stress regime in SW Anatolia, i.e., the area of interaction between the Hellenic and Cyprus arcs, from the Mio-Pliocene to the present time. Fault kinematic analysis yields two different normal faulting stress regimes along the southwestern part of Fethiye-Burdur Fault zone, e.g., in and around Çameli Basin (Zone A1) and two different strike-slip to normal faulting stress regimes characterized by a roughly orthogonal set of extensional axes between Fethiye and Demre (Zone B) with an older NW–SE σ3 axis for Mio-Pliocene and a younger NE–SW σ3 axis for Plio-Quaternary time. Inversion of focal mechanisms of the earthquakes occurring in Zone A1 provides an extensional stress state with approximately N-S σ3 axis. Inversion of those occurring in Zone B, south of Zone A1, yields a dominantly strike-slip stress state with a NE-SW σ3 axis and a NW-SE σ1 axis respectively. The inversion slip vectors from fault planes yield a consistent normal faulting stress regime in Burdur Basin and its surroundings (i.e., along the northeastern part of Fethiye-Burdur Fault Zone, (Zone A2)) during Plio-Quaternary, continuing into recent time as indicated by earthquake focal mechanism inversions. Both states have a consistent NW–SE σ3 axis. Fault kinematic analysis indicates NW-SE extension acting in Zone C (subarea between Demre and Antalya), south of Zone A2, during Mio-Pliocene time. The inversion of focal mechanisms yields normal faulting also characterized by a consistent NW-SE σ3 axis. The nearly orthogonal extensional stress regimes (NW-SE and NE-SW) obtained by inversion of both measured and seismic faults seem to have been acting contemporaneously with each other at different intensities from the Mio-Pliocene onwards in SW Turkey. This may be attributed to the geodynamic effects related to the subduction of the African plate beneath Anatolia diffusing along the Hellenic and Cyprus arcs and in the west-southwestward extrusion of Anatolia. The cause of the early NW–SE extension is the slab-pull force due to the subduction process along the Cyprus arc, considered to be dominant until the Plio-Quaternary in the western part of the study area in zones A1 and B. The dominant status of the Cyprus arc continues today in the eastern part of study area in zones A2 and C. The later NE–SW to present day approximately N–S extension, dominant since the Plio-Quaternary, is related to the combined forces of the Anatolian extrusion and the subduction process along the Hellenic arc.
In the Aegean Sea, the western part of Gökova Gulf, Kos and Bodrum were struck by a 6.6 (Mw) earthquake on July 20, 2017. The fault plane solution for the main shock shows an E-W striking normal type ...fault with approximately N-S (N4°E) tensional axis (T-axis). Fault plane solutions of 33 aftershocks show two groups of normal type fault with E-W and NE-SW to ENE-WSW orientations. The inversion of the focal mechanisms of the aftershocks yields two different normal faulting stress regimes: one is characterized by an approximately N-S (N5°E) σ3 axis (minimum horizontal stress axis). This extension is obtained from 13 focal mechanisms of aftershocks with approximately E-W direction. The other is characterized by approximately NW-SE (N330°E) σ3 axis. The latter is calculated from 21 seismic faults of aftershocks with approximately NE-SW direction. These aftershocks occurred on relatively small-scale faults that were directed from NE-SW to ENE-WSW, and possibly contributed to expansion of the basin in the west. The 24 focal mechanisms of earthquakes which occurred since 1933 in and around Gökova Basin are introduced into the inversion analysis to obtain the stress state effective in a wider region. The inversion yields an extensional stress regime characterized by an approximately N-S (N355°E) σ3 axis. The E-W directional metric faults, measured in the central part of Gökova Fault Zone bordering the Gökova Gulf in the north, also indicate N-S extension. The NE-SW extension obtained from NE-SW aftershocks appears to be more local and is responsible for the expansion of the western part of the asymmetric Gökova Basin. This N-S extension which appears to act on a regional-scale may be attributed to the geodynamic effects related to the combined forces of the southwestward extrusion of Anatolia and the roll-back process of African subduction beneath Anatolia.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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