THE 2014 MW 6.9 NORTH AEGEAN TROUGH (NAT) EARTHQUAKE: SEISMOLOGICAL AND GEODETIC EVIDENCE

A strong earthquake (Mw 6.9) on 24 May 2014 ruptured the North Aegean Trough (NAT) in Greece, west of the North Anatolian Fault Zone (NAFZ). In order to provide unbiased constrains of the rupture process and fault geometry of the earthquake, seismological and geodetic data were analyzed independently. First, based on teleseismic long-period P- and SH- waveforms a point-source solution yielded dominantly right-lateral strike-slip faulting mechanism. Furthermore, finite fault inversion of broad-band data revealed the slip history of the earthquake. Second, GPS slip vectors derived from 11 permanent GPS stations uniformly distributed around the meizoseismal area of the earthquake indicated significant horizontal coseismic slip. Inversion of GPS-derived displacements on the basis of Okada model and using the new TOPological INVersion (TOPINV) algorithm permitted to model a vertical strike slip fault, consistent with that derived from seismological data. Obtained results are consistent with the NAT structure and constrain well the fault geometry and the dynamics of the 2014 earthquake. The latter seems to fill a gap in seismicity along the NAT in the last 50 years, but seems not to have a direct relationship with the sequence of recent faulting farther east, along the NAFZ.

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Two main rupture stages during the 2018 magnitude 7.5 Sulawesi earthquake

Geophysical Journal International ◽

10.1093/gji/ggaa115 ◽

2020 ◽

Vol 221 (3) ◽

pp. 1873-1882

Author(s):

Qi Li ◽

Bin Zhao ◽

Kai Tan ◽

Wenbin Xu

Keyword(s):

Body Wave ◽

Geographical Location ◽

Strike Slip ◽

Inversion Method ◽

The North ◽

Finite Fault Inversion ◽

Strike Direction ◽

Finite Fault ◽

The Moment ◽

North And South

SUMMARY On 28 September 2018, a Mw 7.5 strike-slip earthquake occurred in Sulawesi Island, Indonesia, and it unexpectedly triggered a tsunami. To clearly understand the spatiotemporal evolution process of source rupture, we collected the far-field body wave data and utilized the back-projection method together with finite fault inversion method to investigate the rupture kinematics of this earthquake. Results obtained with the two methods have good consistency and complementarity. We hold that the rupture expanded from the epicentre and propagated bilaterally towards the north and south along the strike direction during the first 24 s, and then to the south. Therefore, the whole rupture process consists of two main stages. For the second stage, the fault segment experienced most of the moment release between 0 and 15 km depth, while the fault plane tended to slip at greater depth (down to 20 km) in the first stage. The total length of the rupture was about 200 km and the seismic moment was ∼2.48 × 1020 Nm, which was equivalent to Mw 7.5. The surface rupture was evident and the maximum slip of 6.24 m was observed in the Palu basin, which was close to Palu city. The rupture was dominated by left-lateral strike-slip with both normal and thrust components as well. The normal slip exhibited in the shallow part of the fault on the north side of Palu bay together with the special geographical location of Palu bay likely favored tsunami genesis.

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Normal Faulting Movement During the 2020 Mw 6.4 Yutian Earthquake: A Shallow Rupture in NW Tibet Revealed by Geodetic Measurements

10.21203/rs.3.rs-120305/v1 ◽

2020 ◽

Author(s):

Jiansheng Yu ◽

Dongzhen Wang ◽

Bin Zhao ◽

Li Qi

Keyword(s):

Strike Slip ◽

Model Parameters ◽

Fault Geometry ◽

Normal Faulting ◽

Geometry Model ◽

Radar Images ◽

The North ◽

Altyn Tagh ◽

Finite Fault ◽

Stress Changes

Abstract The ENE striking Longmu Co fault and the North Altyn Tagh left-lateral slip fault have led to the complex regional structure in the northwestern Tibetan Plateau, resulting in a series of normal faulting and strike slip faulting earthquakes. Using both the ascending and descending Sentinel-1A/B radar images, we depict the coseismic deformation caused by the 2020 Yutian Mw 6.4 earthquake with a peak subsidence of ~20 cm. We determine the seismogenic fault geometry by applying the Bayesian approach with a Markov Chain Monte Carlo sampling method, which enables us to find the posterior probability density functions of the source model parameters. The estimation results reveal that the earthquake have dominantly by normal slip with moderate strike slip component. Based on the optimal fault geometry model, we extend the fault plane and invert for the finite fault model dislocation, which indicate that the slip is mainly concentrated at a shallow focal depth of 3–10 km with a maximum slip of ~1.0 m. Our preferred geodetic coseismic model exhibits no surface rupture, which may likely due to the shallow slip deficit in the uppermost crust. We calculate the combined loading effect of the Coulomb failure stress changes induced by the coseismic dislocations and postseismic viscoelastic relaxation of the 2008 Mw 7.1 and 2014 Mw 6.9 Yutian events. Our study demonstrates that the two preceding major Yutian shocks were insufficient to trigger the 2020 Yutian earthquake, which we consider perhaps reflects the natural release of elastic strain accumulated mainly through localized tectonic movement. We attribute the 2020 Yutian event to the release of extensional stress in a stepover zone controlled by the Longmu Co and the North Altyn Tagh sinistral strike slip fault systems. The seismic risk in the southwest end of the North Altyn Tagh fault has been elevated by the Yutian earthquake sequences, which require future attention.

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Consecutive ruptures on a complex conjugate fault system during the 2018 Gulf of Alaska earthquake

Scientific Reports ◽

10.1038/s41598-021-85522-w ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Shinji Yamashita ◽

Yuji Yagi ◽

Ryo Okuwaki ◽

Kousuke Shimizu ◽

Ryoichiro Agata ◽

...

Keyword(s):

Gulf Of Alaska ◽

Source Model ◽

Fault System ◽

Complex Conjugate ◽

Inversion Method ◽

Fault Geometry ◽

Conjugate System ◽

Finite Fault Inversion ◽

Finite Fault ◽

Alaska Earthquake

AbstractWe developed a flexible finite-fault inversion method for teleseismic P waveforms to obtain a detailed rupture process of a complex multiple-fault earthquake. We estimate the distribution of potency-rate density tensors on an assumed model plane to clarify rupture evolution processes, including variations of fault geometry. We applied our method to the 23 January 2018 Gulf of Alaska earthquake by representing slip on a projected horizontal model plane at a depth of 33.6 km to fit the distribution of aftershocks occurring within one week of the mainshock. The obtained source model, which successfully explained the complex teleseismic P waveforms, shows that the 2018 earthquake ruptured a conjugate system of N-S and E-W faults. The spatiotemporal rupture evolution indicates irregular rupture behavior involving a multiple-shock sequence, which is likely associated with discontinuities in the fault geometry that originated from E-W sea-floor fracture zones and N-S plate-bending faults.

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The nucleation of the Izmit and Düzce earthquakes: Some mechanical logic on where and how ruptures began

Geophysical Journal International ◽

10.1093/gji/ggab040 ◽

2021 ◽

Author(s):

Michel Bouchon ◽

Hayrullah Karabulut ◽

Mustafa Aktar ◽

Serdar Özalaybey ◽

Jean Schmittbuhl ◽

...

Keyword(s):

Strike Slip ◽

Seismic Events ◽

Fault Geometry ◽

Brittle Transition ◽

The North ◽

Impending Rupture ◽

Natural Tendency ◽

Ductile To Brittle Transition ◽

Mechanical Logic ◽

Rupture Speed

Summary In spite of growing evidence that many earthquakes are preceded by increased seismic activity, the nature of this activity is still poorly understood. Is it the result of a mostly random process related to the natural tendency of seismic events to cluster in time and space, in which case there is little hope to ever predict earthquakes? Or is it the sign that a physical process that will lead to the impending rupture has begun, in which case we should attempt to identify this process. With this aim we take a further look at the nucleation of two of the best recorded and documented strike-slip earthquakes to date, the 1999 Izmit and Düzce earthquakes which ruptured the North Anatolian Fault over ∼200 km. We show the existence of a remarkable mechanical logic linking together nucleation characteristics, stress loading, fault geometry and rupture speed. In both earthquakes the observations point to slow aseismic slip occurring near the ductile-to-brittle transition zone as the motor of their nucleation.

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Propagation of a strike-slip plate boundary within an extensional environment: the westward propagation of the North Anatolian Fault

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2015-0129 ◽

2016 ◽

Vol 53 (11) ◽

pp. 1416-1439 ◽

Cited By ~ 32

Author(s):

Xavier Le Pichon ◽

A.M. Celâl Şengör ◽

Julia Kende ◽

Caner İmren ◽

Pierre Henry ◽

...

Keyword(s):

Plate Boundary ◽

Strike Slip ◽

Fault System ◽

Plate Boundaries ◽

Sea Of Marmara ◽

The North ◽

Gulf Of Corinth ◽

Northern Border ◽

North Aegean ◽

Narrow Plate

We document the establishment of the Aegea–Anatolia/Eurasia plate boundary in Pliocene–Pleistocene time. Before 2 Ma, no localized plate boundary existed north of the Aegean portion of the Anatolia plate and the shear produced by the motion of Anatolia–Aegea with respect to Eurasia was distributed over the whole width of the Aegean – West Anatolian western portion. In 4.5 Ma, a shear zone comparable to the Gulf of Corinth was formed in the present Sea of Marmara. The initial extensional basins were cut by the strike-slip Main Marmara Fault system after 2.5 Ma. Shortly after, the plate boundary migrated west of the Sea of Marmara along the northern border of Aegea from the North Aegean Trough, to the Gulf of Corinth area and to the Kefalonia Fault. There, it finally linked with the northern tip of the Aegean subduction zone, completing the system of plate boundaries delimiting the Anatolia–Aegea plate. We have related the change in the distribution of shear from Miocene to Pliocene to the formation of a relatively undeforming Aegea block in Pliocene that forced the shear to be distributed over a narrow plate boundary to the north of it. We attribute the formation of this block to the northeastward progression of the oceanic Ionian slab. We propose that the slab cuts the overlying lithosphere from asthenospheric sources and induces a shortening environment over it.

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NEOGENE TECTONIC ROTATIONS IN THE VICINITY OF THE NORTH AEGEAN TROUGH: NEW PALAEOMAGNETIC EVIDENCE FROM ATHOS AND SAMOTHRAKI (GREECE)

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.16590 ◽

2018 ◽

Vol 40 (1) ◽

pp. 343 ◽

Cited By ~ 1

Author(s):

D. Kondopoulou ◽

I. Zananiri ◽

A. Michard ◽

H. Feinberg ◽

A. Atzemoglou ◽

...

Keyword(s):

Magnetic Susceptibility ◽

Remanent Magnetization ◽

Strike Slip ◽

Isothermal Remanent Magnetization ◽

Northern Greece ◽

The North ◽

Low Field ◽

Palaeomagnetic Data ◽

North Aegean ◽

Major Strike

The present study focuses on two post-orogenic plutons, the Athos (Grigoriou) and Samothraki granites, as well as the Samothraki volcanics, located in the vicinity of the North Aegean Trough. A detailed palaeomagnetic study was carried out, with the aim of constraining the age and mechanism of tectonic rotations. In addition, anisotropy of low field magnetic susceptibility (AMS) was studied and isothermal remanent magnetization (IRM) and thermomagnetic analyses were performed. Finally, a radiometric age for the Athos granite was obtained (43.3 ± 1.0 Ma K/Ar biotite). The measured declinations indicate clockwise rotations of the Athos (16.6°) and Samothraki (36.3°) blocks. The age of rotation is constrained to be <18 Ma at Samothraki, whereas the much smaller rotation of the Athos block can only be dated as younger than Eocene. Comparing the new palaeomagnetic data to the published dataset for Northern Greece, we suggest that the palaeomagnetically determined rotations in the vicinity of the North Aegean Trough are dominantly of post-Early Miocene age, and are controlled by major strike-slip faults and distributed "small" or minor faults.

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Construction of fault geometry by finite-fault inversion of teleseismic data

10.31223/osf.io/92hsw ◽

2020 ◽

Author(s):

Kousuke Shimizu ◽

Yuji Yagi ◽

Ryo Okuwaki ◽

Yukitoshi Fukahata

Keyword(s):

Fault Geometry ◽

Finite Fault Inversion ◽

Teleseismic Data ◽

Finite Fault

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Rupture Kinematics of the 11 January 2021 Mw 6.7 Hovsgol, Mongolia, Earthquake and Implications in the Western Baikal Rift Zone

Seismological Research Letters ◽

10.1785/0220210061 ◽

2021 ◽

Author(s):

Gang Liu ◽

Xuejun Qiao ◽

Pengfei Yu ◽

Yu Zhou ◽

Bin Zhao ◽

...

Keyword(s):

Baikal Rift Zone ◽

Tien Shan ◽

Deformation Pattern ◽

Convergence Region ◽

The North ◽

Finite Fault Inversion ◽

Teleseismic Data ◽

Finite Fault ◽

The Right ◽

Rupture Kinematics

Abstract The Mongolia plateau is the farthest intracontinental region of the India–Eurasia collision and is a transition zone between north–south convergence to the south in the Tien Shan and northwest–southeast extension to the north in the Baikal rift. Mongolia has experienced four M 8 earthquakes since 1905, but due to limited observations, the mechanism of these strong earthquakes and regional tectonics are poorly understood. The 11 January 2021 Mw 6.7 Hovsgol, Mongolia, earthquake is the largest event that has occurred in the Hovsgol graben, which is noted for being the northernmost convergence region of the India–Eurasia collision and the youngest extension region of the Baikal rift. In this article, the coseismic displacements are retrieved by space geodesy for the first time in this region, providing good constraints for the deformation pattern. We use a finite-fault inversion of InSAR and teleseismic data, and a backprojection analysis to reveal the rupture kinematics of this event. The geometry of the Hovsgol fault is determined as east-dipping with a dip of 45°. The rupture process is characterized by a northwestward propagation with a moderate average rupture velocity of ∼2.0 km/s and a complex slip pattern composed of two major slip patches with dimensions of 40 km×20 km. The oblique slip, illustrated by predominate extension and significant dextral striking, confirms the right-lateral-striking faulting in the Hovsgol rift, which indicates that the eastwardly north–south convergence across the southwest segment of the Baikal rift has decreased.

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Construction of fault geometry by finite-fault inversion of teleseismic data

Geophysical Journal International ◽

10.1093/gji/ggaa501 ◽

2020 ◽

Vol 224 (2) ◽

pp. 1003-1014

Author(s):

Kousuke Shimizu ◽

Yuji Yagi ◽

Ryo Okuwaki ◽

Yukitoshi Fukahata

Keyword(s):

Fault Plane ◽

Seismic Source ◽

Rupture Process ◽

Inversion Method ◽

Source Inversion ◽

Fault Geometry ◽

Waveform Data ◽

Finite Fault Inversion ◽

Finite Fault ◽

Double Couple

SUMMARY Conventional seismic source inversion estimates the earthquake rupture process on an assumed fault plane that is determined a priori. It has been a difficult challenge to obtain the fault geometry together with the rupture process by seismic source inversion because of the nonlinearity of the inversion technique. In this study, we propose an inversion method to estimate the fault geometry and the rupture process of an earthquake from teleseismic P waveform data, through an elaboration of our previously published finite-fault inversion analysis (Shimizu et al. 2020). That method differs from conventional methods by representing slip on a fault plane with five basis double-couple components, expressed by potency density tensors, instead of two double-couple components compatible with the fault direction. Because the slip direction obtained from the potency density tensors should be compatible with the fault direction, we can obtain the fault geometry consistent with the rupture process. In practice we rely on an iterative process, first assuming a flat fault plane and then updating the fault geometry by using the information included in the obtained potency density tensors. In constructing a non-planar model-fault surface, we assume for simplicity that the fault direction changes only in either the strike or the dip direction. After checking the validity of the proposed method through synthetic tests, we applied it to the MW 7.7 2013 Balochistan, Pakistan, and MW 7.9 2015 Gorkha, Nepal, earthquakes, which occurred along geometrically complex fault systems. The modelled fault for the Balochistan earthquake is a curved strike-slip fault convex to the south-east, which is consistent with the observed surface ruptures. The modelled fault for the Gorkha earthquake is a reverse fault with a ramp-flat-ramp structure, which is also consistent with the fault geometry derived from geodetic and geological data. These results exhibit that the proposed method works well for constraining fault geometry of an earthquake.

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Strike slip tectonics and transtensional deformation in the Aegean region and the Hellenic arc: Preliminary results

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.11098 ◽

2017 ◽

Vol 47 (2) ◽

pp. 647 ◽

Cited By ~ 6

Author(s):

D. Sakellariou ◽

J. Mascle ◽

V. Lykousis

Keyword(s):

Aegean Sea ◽

Strike Slip ◽

Volcanic Arc ◽

Swath Bathymetry ◽

The North ◽

Crustal Block ◽

Hellenic Arc ◽

North Aegean ◽

North Aegean Sea ◽

Lateral Escape

Recently acquired offshore seismic and swath bathymetry data from the Hellenic Arc, the Ionian Sea and the South and North Aegean Sea, including the Hellenic Volcanic Arc and the Cyclades plateau, along with geological and tectonic data from Plio-Quaternary basins exposed on the Hellenic Arc indicate that strike slip tectonics has played a major role in the southwestward extension of the Aegean crustal block, the development of the offshore neotectonic basins and the spatial distribution of the volcanic activity along the Volcanic Arc. Transtensional deformation, accommodated by (sinistral or dextral) strike slip zones and related extensional structures, prevail throughout Plio-Quaternary, since the North Anatolian Fault broke westwards into the North Aegean. Incipient collision of the Hellenic Forearc south of Crete with the Libyan promontory and consequent lateral escape tectonics led to the segmentation of the Hellenic Arc in distinct blocks, which move southwestwards independently from each other and are bounded by strike slip faults.

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