Global Plate Motion Model Research Articles

East African Rift Dynamics

The East African Rift (EAR) is a typical site for the study of dynamic processes leading to continental break-up and dislocation. In the context of global plate motion models, the kinematics of EAR system is less well defined. In this study, the analysis of repeated GPS geodetic data represents a quantum leap in accuracy that allows us to reassess the recent kinematics of EAR. Our results show that the Somali plate rotates at a velocity of 0.076°/m in the Nubian fixed reference frame the velocity increasing from south to north. We also found that the seismotectonic parameters of both sets of plate boundaries are embodied by lithospheric thinning and oceanic accretion, including a scissor-shaped opening. Normal faults are active along a series of fissure boundaries. This NubianSomalian divergence across the East African rift system implies a redistribution of deformation and stress regulation along rift segments connecting rigid blocks that allows for the heterogeneity of the East African basement. We also note the presence of very high-risk seismic zones.

Factors on the Mesozoic Transition From Flat to Steep Subduction of the Paleo‐Pacific Plate Beneath South China: Thickened Oceanic Crust and Subduction Rate

AbstractIn the Mesozoic, the age of Paleo‐Pacific plate that flatly subducted beneath the South China was ∼80 Ma, resulting in a cold and dense oceanic slab. The transition process from flat to steep subduction of this old slab and factors that affect it are still unclear. Using 2‐D thermomechanical numerical models, we investigate the dependence of the transition mode on the size of TOC (length and thickness) and the subduction rate. The results indicate that under low subduction rates (e.g., 1 cm/yr), even a 100‐km long eclogitized TOC can induce slab delamination beneath continental lithosphere. The maximum subduction rate for slab delamination to occur increases with an increasing length or thickness of TOC. However, when the subduction rate is over a certain critical value (e.g., ≥4 cm/yr), oceanic slab rolls back. The presence of the TOC delays the initial rollback time, as compared to cases with no TOC. In addition, with a TOC of small size (e.g., 100‐km length and 20‐km thickness) under a certain range of subduction rate, an 80‐Ma old slab can maintain a long‐lasting flat subduction. The comparisons between the numerical results and global plate motion models indicate that the northwestward motion of South China Block since ca. 195 ± 5 Ma induced the delamination of oceanic slab. The arrival of the TOC in the Paleo‐Pacific Plate to the continental arc should be later than the previously estimated ca. 250 Ma. Determination of the TOC size requires three‐dimensional simulations and more detailed geological records.

Absolute Paleolatitude of Northern Zealandia From the Middle Eocene to the Early Miocene

AbstractThe absolute position during the Cenozoic of northern Zealandia, a continent that lies more than 90% submerged in the southwest Pacific Ocean, is inferred from global plate motion models, because local paleomagnetic constraints are virtually absent. We present new paleolatitude constraints using paleomagnetic data from International Ocean Discovery Program Site U1507 on northern Zealandia and Site U1511 drilled in the adjacent Tasman Sea Basin. After correcting for inclination shallowing, five paleolatitude estimates provide a trajectory of northern Zealandia past position from the middle Eocene to the early Miocene, spanning geomagnetic polarity chrons C21n to C5Er (∼48–18 Ma). The paleolatitude estimates support previous works on global absolute plate motion where northern Zealandia migrated 6° northward between the early Oligocene and early Miocene, but with lower absolute paleolatitudes, particularly in the Bartonian and Priabonian (C18n–C13r). True polar wander (solid Earth rotation with respect to the spin axis), which only can be resolved using paleomagnetic data, may explain the discrepancy. This new paleomagnetic information anchors past latitudes of Zealandia to Earth's spin axis, with implications not only for global geodynamics, but also for addressing paleoceanographic and paleoclimate problems, which generally require precise paleolatitude placement of proxy data.

PERFORMANCE OF SITE VELOCITY PREDICTION IN SUNDALAND

Abstract. Global Positioning System (GPS) technique has been extensively implemented in determination of crustal deformation globally. With the ability of providing solution up to milimeter (mm) level, this technique has proven to provide a precise estimate of site velocity that represents the actual motion of tectonic plate over a period. Therefore, this study aims to evaluate the site velocity estimation from GPS-derived daily position of station, respective to the global plate motion model and predicted site velocity via Least-Squares Collocation (LSC) method within the tectonically active region of Sundaland. The findings have indicated that stations with precise velocity estimates were consistent with global plate model and predicted velocity, with velocity residuals of 5 mm – 10 mm. However, stations that were severely impacted by continuous earthquake events such as in Sumatra were believed to be induced by the impact with consistently large velocity residuals up to 37 mm. Following the outcomes, this study has provided an insight on the post-seismic decay period plate motion which are induced by continuous tectonic activities respective to modelled plate motion.

Kinematics and extent of the Piemont–Liguria Basin – implications for subduction processes in the Alps

Abstract. Assessing the size of a former ocean of which only remnants are found in mountain belts is challenging but crucial to understanding subduction and exhumation processes. Here we present new constraints on the opening and width of the Piemont–Liguria (PL) Ocean, known as the Alpine Tethys together with the Valais Basin. We use a regional tectonic reconstruction of the Western Mediterranean–Alpine area, implemented into a global plate motion model with lithospheric deformation, and 2D thermo-mechanical modeling of the rifting phase to test our kinematic reconstructions for geodynamic consistency. Our model fits well with independent datasets (i.e., ages of syn-rift sediments, rift-related fault activity, and mafic rocks) and shows that, between Europe and northern Adria, the PL Basin opened in four stages: (1) rifting of the proximal continental margin in the Early Jurassic (200–180 Ma), (2) hyper-extension of the distal margin in the Early to Middle Jurassic (180–165 Ma), (3) ocean–continent transition (OCT) formation with mantle exhumation and MORB-type magmatism in the Middle–Late Jurassic (165–154 Ma), and (4) breakup and mature oceanic spreading mostly in the Late Jurassic (154–145 Ma). Spreading was slow to ultra-slow (max. 22 mm yr−1, full rate) and decreased to ∼5 mm yr−1 after 145 Ma while completely ceasing at about 130 Ma due to the motion of Iberia relative to Europe during the opening of the North Atlantic. The final width of the PL mature (“true”) oceanic crust reached a maximum of 250 km along a NW–SE transect between Europe and northwestern Adria. Plate convergence along that same transect has reached 680 km since 84 Ma (420 km between 84–35 Ma, 260 km between 35–0 Ma), which greatly exceeds the width of the ocean. We suggest that at least 63 % of the subducted and accreted material was highly thinned continental lithosphere and most of the Alpine Tethys units exhumed today derived from OCT zones. Our work highlights the significant proportion of distal rifted continental margins involved in subduction and exhumation processes and provides quantitative estimates for future geodynamic modeling and a better understanding of the Alpine Orogeny.

Redefining East African Rift System kinematics

AbstractEast African Rift System plate geometries and surface motions are some of the least constrained in the context of global plate motion models. In this study, we used GPS data to constrain Somalian plate rotation and to suggest a new tectonic plate geometry for the region. In addition, we tested geologic data from the Southwest Indian Ridge and new GPS data on Madagascar to determine refined kinematics of the Lwandle microplate. A zone of broad deformation was discovered, extending from the eastern boundary of the Rovuma microplate, across the Comoros Islands, and including parts of central and northern Madagascar. Madagascar is fragmenting, with southern Madagascar rotating with the Lwandle microplate and a piece of eastern and south-central Madagascar moving with the Somalian plate. Divergence of the Nubian-Somalian plate system across the East African Rift System involves both diffuse deformation and strain accommodation along narrow rift segments that bound rigid blocks.

Global kinematics of tectonic plates and subduction zones since the late Paleozoic Era

Detailed global plate motion models that provide a continuous description of plate boundaries through time are an effective tool for exploring processes both at and below the Earth's surface. A new generation of numerical models of mantle dynamics pre- and post-Pangea timeframes requires global kinematic descriptions with full plate reconstructions extending into the Paleozoic (410 Ma). Current plate models that cover Paleozoic times are characterised by large plate speeds and trench migration rates because they assume that lowermost mantle structures are rigid and fixed through time. When used as a surface boundary constraint in geodynamic models, these plate reconstructions do not accurately reproduce the present-day structure of the lowermost mantle. Building upon previous work, we present a global plate motion model with continuously closing plate boundaries ranging from the early Devonian at 410 Ma to present day.We analyse the model in terms of surface kinematics and predicted lower mantle structure. The magnitude of global plate speeds has been greatly reduced in our reconstruction by modifying the evolution of the synthetic Panthalassa oceanic plates, implementing a Paleozoic reference frame independent of any geodynamic assumptions, and implementing revised models for the Paleozoic evolution of North and South China and the closure of the Rheic Ocean. Paleozoic (410–250 Ma) RMS plate speeds are on average ∼8 cm/yr, which is comparable to Mesozoic–Cenozoic rates of ∼6 cm/yr on average. Paleozoic global median values of trench migration trend from higher speeds (∼2.5 cm/yr) in the late Devonian to rates closer to 0 cm/yr at the end of the Permian (∼250 Ma), and during the Mesozoic–Cenozoic (250–0 Ma) generally cluster tightly around ∼1.1 cm/yr. Plate motions are best constrained over the past 130 Myr and calculations of global trench convergence rates over this period indicate median rates range between 3.2 cm/yr and 12.4 cm/yr with a present day median rate estimated at ∼5 cm/yr. For Paleozoic times (410–251 Ma) our model results in median convergence rates largely ∼5 cm/yr. Globally, ∼90% of subduction zones modelled in our reconstruction are determined to be in a convergent regime for the period of 120–0 Ma. Over the full span of the model, from 410 Ma to 0 Ma, ∼93% of subduction zones are calculated to be convergent, and at least 85% of subduction zones are converging for 97% of modelled times. Our changes improve global plate and trench kinematics since the late Paleozoic and our reconstructions of the lowermost mantle structure challenge the proposed fixity of lower mantle structures, suggesting that the eastern margin of the African LLSVP margin has moved by as much as ∼1450 km since late Permian times (260 Ma). The model of the plate-mantle system we present suggests that during the Permian Period, South China was proximal to the eastern margin of the African LLSVP and not the western margin of the Pacific LLSVP as previous thought.

Ocean Basin Evolution and Global-Scale Plate Reorganization Events Since Pangea Breakup

We present a revised global plate motion model with continuously closing plate boundaries ranging from the Triassic at 230 Ma to the present day, assess differences among alternative absolute plate motion models, and review global tectonic events. Relatively high mean absolute plate motion rates of approximately 9–10 cm yr−1 between 140 and 120 Ma may be related to transient plate motion accelerations driven by the successive emplacement of a sequence of large igneous provinces during that time. An event at ∼100 Ma is most clearly expressed in the Indian Ocean and may reflect the initiation of Andean-style subduction along southern continental Eurasia, whereas an acceleration at ∼80 Ma of mean rates from 6 to 8 cm yr−1 reflects the initial northward acceleration of India and simultaneous speedups of plates in the Pacific. An event at ∼50 Ma expressed in relative, and some absolute, plate motion changes around the globe and in a reduction of global mean plate speeds from about 6 to 4–5 cm yr−1 indicates that an increase in collisional forces (such as the India–Eurasia collision) and ridge subduction events in the Pacific (such as the Izanagi–Pacific Ridge) play a significant role in modulating plate velocities.

Tectonic evolution of the Gulf of Mexico, Caribbean and northern South America in the mantle reference frame: an update

Abstract We present an updated synthesis of the widely accepted ‘single-arc Pacific-origin’ and ‘Yucatán-rotation’ models for Caribbean and Gulf of Mexico evolution, respectively. Fourteen palaeogeographic maps through time integrate new concepts and alterations to earlier models. Pre-Aptian maps are presented in a North American reference frame. Aptian and younger maps are presented in an Indo-Atlantic hot spot reference frame which demonstrates the surprising simplicity of Caribbean–American interaction. We use the Müller et al. ( Geology 21 : 275–278, 1993) reference frame because the motions of the Americas are smoothest in this reference frame, and because it does not differ significantly, at least since c. 90 Ma, from more recent ‘moving hot spot’ reference frames. The Caribbean oceanic lithosphere has moved little relative to the hot spots in the Cenozoic, but moved north at c. 50 km/Ma during the Cretaceous, while the American plates have drifted west much further and faster and thus are responsible for most Caribbean–American relative motion history. New or revised features of this model, generally driven by new data sets, include: (1) refined reconstruction of western Pangaea; (2) refined rotational motions of the Yucatán Block during the evolution of the Gulf of Mexico; (3) an origin for the Caribbean Arc that invokes Aptian conversion to a SW-dipping subduction zone of a trans-American plate boundary from Chortís to Ecuador that was part sinistral transform (northern Caribbean) and part pre-existing arc (eastern, southern Caribbean); (4) acknowledgement that the Caribbean basalt plateau may pertain to the palaeo-Galapagos hot spot, the occurrence of which was partly controlled by a Proto-Caribbean slab gap beneath the Caribbean Plate; (5) Campanian initiation of subduction at the Panama–Costa Rica Arc, although a sinistral transform boundary probably pre-dated subduction initiation here; (6) inception of a north-vergent crustal inversion zone along northern South America to account for Cenozoic convergence between the Americas ahead of the Caribbean Plate; (7) a fan-like, asymmetric rift opening model for the Grenada Basin, where the Margarita and Tobago footwall crustal slivers were exhumed from beneath the southeast Aves Ridge hanging wall; (8) an origin for the Early Cretaceous HP/LT metamorphism in the El Tambor units along the Motagua Fault Zone that relates to subduction of Farallon crust along western Mexico (and then translated along the trans-American plate boundary prior to onset of SW-dipping subduction beneath the Caribbean Arc) rather than to collision of Chortis with Southern Mexico; (9) Middle Miocene tectonic escape of Panamanian crustal slivers, followed by Late Miocene and Recent eastward movement of the ‘Panama Block’ that is faster than that of the Caribbean Plate, allowed by the inception of east–west trans-Costa Rica shear zones. The updated model integrates new concepts and global plate motion models in an internally consistent way, and can be used to test and guide more local research across the Gulf of Mexico, the Caribbean and northern South America. Using examples from the regional evolution, the processes of slab break off and flat slab subduction are assessed in relation to plate interactions in the hot spot reference frame.

Oblique rifting at oceanic ridges: Relationship between spreading and stretching directions from earthquake focal mechanisms

The relationship between spreading and stretching directions is investigated at oblique-spreading oceanic ridges using earthquake focal mechanisms. The stretching direction at ridge axes corresponds to the direction of the greatest principal strain ɛ 1 taken as the mean trend of the seismic T-axes of extensional earthquake focal mechanisms. It is compared with the spreading direction provided by global plate-motion models. We find that the stretching direction trends approximately halfway between the spreading direction and the normal to the ridge trend, a result in line with analogue experiments of oblique rifting. This result is satisfactorily accounted for with an analytical model of oblique rifting, for which the direction of ɛ 1 is calculated with respect to rifting obliquity for different amounts of stretching using continuum mechanics. For low stretching factors, typical of incremental seismic deformations, ɛ 1 obliquity is two times lower than rifting obliquity. For higher stretching factors, the stretching and spreading directions become parallel.

Seismic Strain rate along the Middle America Trench reveals significant differences between Cocos-North America and Cocos-Caribbean convergence

SUMMARY Centroid-moment tensor solutions for thrust-faulting earthquakes in the last 27 yr are used to obtain and compare seismic strain rate associated to the subduction process along the Cocos‐North America and along the Cocos‐Caribbean convergent margins. In both cases, the eigenvectors of the strain-rate tensor align along radial and tangential directions with respect to their respective Euler Pole. Seismic strain rate along the Cocos‐North America plate boundary is about 2.8 × 10 −7 yr −1 , a value close to those previously found along the Japan and Aegean convergent margins. Strain rate along the Cocos‐Caribbean margin is one order of magnitude smaller, namely 3.7 × 10 −8 yr −1 . The relative plate velocity is also calculated using seismic moment tensors. We find a relative plate convergence of 1.13 ◦ Myr −1 for the Cocos‐North America plate margin, and 0.13 ◦ Myr −1 for Cocos‐Caribbean. This means that 80 per cent of the plate motion along the Cocos‐North America plate margin is expressed as thrust-faulting earthquakes, as compared to the velocity given by global plate motion models. In contrast, only about 10 per cent of the Cocos‐Caribbean relative motion is translated into thrusting events. Similar results are obtained when a 102-yr earthquake database is used. We suggest that differences in strain rate and percentage of plate motion are due to differences in the behaviour of the overriding plate and/or the Central America forearc sliver being detached from the Caribbean Plate and being incorporated into the Cocos Plate.

Results of the VLBI experiments conducted with Syowa Station, Antarctica

The first successful geodetic Very Long Baseline Interferometry (VLBI) observations to Antarctica were made on baselines from Syowa Station (Antarctica) to Tidbinbilla (Australia) and to Kashima (Japan) in January 1990. Regular geodetic experiments started in 1998 with the installation of a permanent VLBI terminal at Syowa Station. These observations are conducted at the standard geodetic VLBI frequencies of 2.3 and 8.4 GHz, S- and X-Bands. In the first year, the 11-m multipurpose antenna at Syowa Station observed together with the 26-m radio telescope of the University of Tasmania in Australia and the 26-m radio telescope of the Hartebeesthoek Radio Astronomy Observatory in South Africa. From 1999, the experiments were expanded to also include the O’Higgins Station in Antarctica, Fortaleza in Brazil and Kokee on Hawaii. From 1999 until the end of 2003, 25 observing sessions have been reduced and analyzed using the CALC/SOLVE geodetic VLBI data reduction package. The results show that the horizontal baseline of Syowa-Hobart is increasing at the rate of 57.0±1.9 mm/year. The baseline Syowa-Hartebeesthoek is also increasing, but at the lower rate of 9.8±1.9 mm/year. The VLBI result of 2.0±3.1 mm/year and the GPS result of −1.9±0.7 mm/year for the Syowa-O’Higgins horizontal baseline support the hypothesis of one rigid Antarctic plate without intra-plate deformation, which is consistent with the NNR-NUVEL-1A global plate motion model. The location of the Euler pole of the Antarctic plate by VLBI is estimated as 59.7°S and 62.6°E with a rotation rate of 0.190 deg/Myr, while that by GPS in our study is estimated as 60.6°S and 42.2°E with a rotation rate of 0.221 deg/Myr. These pole positions are slightly different to that implied by the NNR-NUVEL-1A model of 63.0°S and 64.2°E with a rotation rate of 0.238 deg/Myr. VLBI observations over a longer time span may resolve small discrepancy of current plate motion from the NNR-NUVEL-1A model. The consistency of the VLBI coordinates with the GPS coordinates at Syowa Station, after correction for the local tie vector components between the two reference markers, is also discussed.

Instantaneous global plate motion model from 12 years of continuous GPS observations

We estimate a global plate motion model for 17 major and minor tectonic plates solely on the basis of analysis of data from 106 globally distributed continuous GPS stations, spanning the period from January 1991 to July 2003. Site positions estimated from 24‐hour segments of data are aligned day‐by‐day to the International GPS Service (IGS) realization of the ITRF2000 reference frame using a similarity transformation, thereby ensuring that the ITRF2000 no‐net‐rotation condition is preserved. Linear velocities of a carefully selected set of stations are estimated from the position time series, along with annual and semiannual fluctuations and position offsets due to GPS instrument changes. A white noise plus flicker noise model is applied to estimate realistic uncertainties for the site velocities, which are then propagated into the derived plate motion model parameters. We also examine the vertical velocities in the site selection process. At the Scripps Orbit and Permanent Array Center we have implemented a procedure whereby the plate motion model is updated on a regular (monthly) basis to improve its precision and reliability as new data become available and as a baseline against which anomalous motions can be detected.

Active deformation in the Mediterranean from Gibraltar to Anatolia inferred from numerical modeling and geodetic and seismological data

From Gibraltar to Anatolia, the active tectonics in the Mediterranean is studied by means of an integrated approach based on geophysical, geodetic, and seismological methodologies. The aim of this study is to gain a deep insight into the kinematics and dynamics of the crustal and lithospheric processes affecting the Mediterranean. Major tectonic processes, such as continental collision and subduction, characterize this region, which marks a broad transition zone between the African/Arabian and Eurasian plates. A thin‐shell finite element approach allows us to simulate the deformation pattern in the Mediterranean, from 10°W to 40°E and from 30° to 50°N. The global plate motion model NUVEL‐1A is used to account for the convergence, while the relative velocities of the overriding and subduction plates are obtained from another family of models. These models simulate the effects of the negatively buoyant density contrasts of the subducted lithosphere on the horizontal velocity at the surface. A systematic comparison between model results and the seismic strain rates obtained from the National Earthquake Information Center catalog, the geodetic velocity field and strain resulting from GPS, satellite laser ranging, and very long baseline interferometry analyses and the World Stress Map, indicate that Africa/Arabia versus Eurasia convergence and subduction in the Aegean Sea and Calabrian Arc are the major tectonic mechanisms controlling the deformation style in the Mediterranean. It is shown that in order to carry into coincidence the modeled and the seismic strain rate patterns and the geodetically retrieved strain rate tensors, a deep subduction in the Aegean Arc must be included in the modeling.

Motion of the Philippine Sea plate consistent with the NUVEL-1A model

Summary We determine Euler vectors for 12 plates, including the Philippine Sea plate (PH), relative to the fixed Pacific plate (PA) by inverting the earthquake slip vectors along the boundaries of the Philippine Sea plate, GPS observed velocities, and 1122 data from the NUVEL-1 and the NUVEL-1A global plate motion model, respectively. This analysis thus also yields Euler vectors for the Philippine Sea plate relative to adjacent plates. Our results are consistent with observed data and can satisfy the geological and geophysical constraints along the Caroline (CR)–PH and PA–CR boundaries. The results also give insight into internal deformation of the Philippine Sea plate. The area enclosed by the Ryukyu Trench–Nankai Trough, Izu–Bonin Trench and GPS stations S102, S063 and Okino Torishima moves uniformly as a rigid plate, but the areas near the Philippine Trench, Mariana Trough and Yap–Palau Trench have obvious deformation.

The Investigations on Crustal Deformation in China under ITRF97 Plate Model using Data of “Crustal Movement Observation Network in China”

AbstractBesides setting up the global plate motion models based on the International Terrestrial Reference Frame ITRF97, we establish the latest sub plate models in China based on velocity fields of 79 GPS base network sites set up by 'Crustal Movement Observation Network of China'. In comparison with NNR‐NUVEL1A geological model, our model presents the present‐time crustal deformation at the span of years. As the background velocity field, the Eurasia model based on the ITRF97 velocity fields are recommended to investigate present time tectonic deformation in China rather than NNR‐NUVEL1A.

Present-day crustal deformation in China relative to ITRF97 kinematic plate model

A global plate motion model is established based on the ITRF97 velocity fields and geological model NUVEL1. Sub-plate models are estimated by using the velocity fields derived from 45 global positioning system (GPS) sites under the ITRF97 reference frame in China. Comparisons between space geodesy and geological models are given. It is found that the Euler vector of the AFRC–EURA pair has an obvious discrepancy between space geodetic and geological models. The motion patterns of tectonic blocks in China predicted by GPS are consistent with those of geological data on the whole.

Present-day spreading motion of the mid-Atlantic ridge

Over a long period of time, the spreading rate of the mid-Atlantic ridge has been ascertained by the geological age of the magnetic stripe laid out on either side of the mid-ocean ridge in conjunction with the annals of the magnetic reversal history. Is the mid-Atlantic ridge still spreading today? How fast is it moving or are there any changes? All these questions remain unsolved. Based on the newest ITRF2000 velocity field published by the International Earth Rotation Service (IERS), the contemporary global plate motion model ITRF2000VEL is constructed, independent of any plate model hypothesis. Solutions for relative Euler’s vectors of plate pairs as North America-Eurasia, North America-Africa and South America-Africa are obtained, implying current spreading rates of the mid-Atlantic ridge. Comparing them with results from the NNR-NUVEL1A model displays the present-day motion characteristics of the mid-Atlantic ridge that the mid-ridge of the South Atlantic, whose spreading is slowing down, spreads faster than the North Atlantic, whose spreading is speeding up.

Determination of Euler parameters of Philippine Sea plate and the inferences

Euler vectors of 12 plates, including Philippine Sea plate (PH), relative to a randomly fixed Pacific plate(PA) were determined by inverting the 1122 data from NUVEL-1 global plate motion model, earthquake slip vectors along Philippine Sea plate boundary, and GPS observed velocities. Euler vectors of Philippine Sea plate relative to adjacent plates are also gained. Our results are well consistent with observed data and can satisfy the geological and geophysical constraints along the Caroline(CR)-PH and PA-CR boundaries. Deformation of Philippine Sea plate is also discussed by using the plate motion Euler parameters.

Comment on “A new intracontinental transcurrent structure: the Central Anatolian Fault Zone, Turkey” by A. Koçyiğit and A. Beyhan

Koçyiğit and Beyhan have described the Central Anatolian Fault Zone (CAFZ), as a >700 km long active strike–slip fault zone in Turkey. If their interpretation is correct, then several major Turkish cities are vulnerable to a significant earthquake hazard which was previously unsuspected, and the existing close agreement between observed slip rates on major strike–slip faults in Turkey and predictions from global plate motion models is spurious. Whether the CAFZ is real, or based on mistaken interpretations of diverse evidence, is thus a matter of some importance. The aim of this comment is to describe difficulties which arise over the published interpretation of the CAFZ, with the aim of encouraging either a retraction or a more thorough presentation of the available evidence in support of the existence of a major active fault zone in the required position. Three main difficulties are discussed in detail. First, strands of the CAFZ have been interpreted in many localities where previous detailed studies have either found no evidence of faulting or have reported ancient faults which have been described as no longer active. Second, many other features which previous studies have explained satisfactorily are reinterpreted as consequences of active strike–slip faulting. Finally, no observational evidence is presented for the slip rate or the timing of the start of the alleged present phase of slip on the CAFZ. The suggestion that it has slipped by 24 km during this present phase of activity is inadequately documented and conflicts with other evidence.