Here, we present the source mechanism and rupture process for the destructive 24 January 2020 Mw 6.7 Doğanyol–Sivrice earthquake at the East Anatolian Fault Zone (EAFZ, Turkey), obtained from ...seismological waveform analysis and space geodetic observations. Multi-data analyses and modelling in the present study provide fundamental data and strong constraints for retrieving complex source mechanism of an earthquake and its spatiotemporal slip characteristics along the ruptured segment of fault. The acquired slip model of this earthquake reveals heterogeneous slip distribution along strike N244°E of the fault plane dipping NW (68°) with duration of the source time function (STF) and low stress drop value (Δσ) of ~25 s and ~6 bars, respectively. Back-projection analysis validates fault length (L) stretching along strike for a distance of ~75 km and supports predominant south-westerly bilateral rupture propagation with a variable rupture velocity (Vr) of ~2.3–3.4 km/s along with two main patches, presumably a sequence of two asperities being ruptured following the surface trace of the EAFZ. The distribution of aftershocks based on the analysis of two months long data consistently confirms spreading of seismicity along the ruptured fault. The evaluation of Interferometric Synthetic Aperture Radar (InSAR) data reveals that left-lateral co-seismic slip and significant deformation extends for ~20 km on either side of the fault with evident post-seismic displacement. Yet, no significant vertical offsets were observed as GNSS stations detected only horizontal motions. Coda-wave analysis as an independent tool also confirms moment magnitude of Mw 6.7. Our results highlight a case of a damaging earthquake and enhance our understanding of earthquake mechanics, continental deformation and augmented earthquake risk on the EAFZ.
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•Source model and slip history for the largest magnitude earthquake on the EAFZ are obtained.•Bilateral rupture contributed to directivity and the pattern of strong shaking.•Slow rupture speed on discrete patches of the EAFZ down to ~20 km depth is obtained.•No significant vertical offsets sensed as GNSS stations exposed horizontal motions.•Aftershocks extends for ~75 km along strike of N244°E, and co-seismic displacements ~20 km on either side of the fault.
Analyzing subduction initiation is key for understanding the coupling between plate tectonics and the underlying mantle. Here we focus on suprasubduction zone (SSZ) ophiolites and how their formation ...links to intraoceanic subduction initiation in an absolute plate motion frame. SSZ ophiolites form the majority of exposed oceanic lithosphere fragments and are widely recognized to have formed during intraoceanic subduction initiation. Structural, petrological, geochemical, and plate kinematic constraints on their kinematic evolution show that SSZ crust forms at fore‐arc spreading centers at the expense of a mantle wedge, thereby flattening the nascent slab. This leads to the typical inverted pressure gradients found in metamorphic soles that form at the subduction plate contact below and during SSZ crust crystallization. Former spreading centers are preserved in forearcs when subduction initiates along transform faults or off‐ridge oceanic detachments. We show how these are reactivated when subduction initiates in the absolute plate motion direction of the inverting weakness zone. Upon inception of slab pull due to, e.g., eclogitization, the sole is separated from the slab, remains welded to the thinned overriding plate lithosphere, and can become intruded by mafic dikes upon asthenospheric influx into the mantle wedge. We propound that most ophiolites thus formed under special geodynamic circumstances and may not be representative of normal oceanic crust. Our study highlights how far‐field geodynamic processes and absolute plate motions may force intraoceanic subduction initiation as key toward advancing our understanding of the entire plate tectonic cycle.
Key Points:
Metamorphic soles exhume by changing mantle wedge shape during fore‐arc spreading
Subduction initiates in absolute plate motion direction of nascent trench
Anchoring of advancing slab generates fore‐arc extension at subduction initiation
Induced earthquakes and ground displacements were seldom reported in relation to gas injection or extraction. The Hutubi underground gas storage (HUGS) facility is the largest one in China and is ...also a unique case with both earthquakes and ground displacements detected during multiple cycles of injection and extraction since 9 June 2013. Unlike previous studies with a primarily seismological focus, here, we conducted quantitative analysis on the geomechanics of seismicity induced by the HUGS through developing a hydrogeologic framework, which systematically integrated geodetic, geophysical and geological data. First, we measured horizontal ground extension and shortening on the order of cm in response to gas injection and extraction of the HUGS at depth using a local GPS network, which was not reported in other regions with induced seismicity. Second, we synthesized a variety of data, including seismic reflection profiles, a newly acquired local velocity model, rock physics measurements, well drilling and logging data, to build up a 2D geomechanical model for the HUGS. Third, based on fully-coupled poroelasticity, we proposed two methods to optimize the permeability of the upper aquifers as well as the reservoir porosity and permeability with constraints from well level, GPS and well pressure data. Numerical simulations using the calibrated 2D model revealed that the horizontal extension due to the reservoir dilation is larger than ground uplift. The observed seismicity on faults without hydraulic connections to the gas repository was probably induced by the poroelastic effect of reservoir dilation. Our study provided a prototype scheme for detecting and characterizing the geomechanical behavior of cyclic fluid injection and extraction in a deep reservoir, which would be applicable to other UGS facilities.
•Ground extension due to gas injection-extraction was first observed by GPS.•A hydrogeologic framework was built for geomechanical analysis of induced events.•The reservoir porosity and permeability were optimized using pressure and GPS data.•Fully-coupled poroelastic modeling reveals larger ground extension than uplift.•The seismicity was probably induced by the poroelastic effect of reservoir dilation.
The Pieniny Geodynamic Test Field is situated in the middle of the region between the Inner and Outer Carpathians. Geodynamic research conducted in the past in the Pieniny Klippen Belt (PKB) region ...were suggestive of neotectonic activity. The goal of the investigation was to determine whether the nearby structures, the Podhale Flysh (FP) and the Magura Nappe (MN), are affected by neotectonic activity in the PKB. The goal of the study was to ascertain the velocity and direction of motion of stations situated close to the Pieniny Geodynamic Test Field’s 3 main structures. Twelve GNSS stations, including 6 in the PKB, 3 in the MN, and 3 in the FP, make up the Pieniny Geodynamic Test Field. Three GNSS sites in the Tatra Mountains (TM) complete the entire geodynamic test field. The satellite observations made between 2004 and 2020 (excluding the year 2005 due to lack of observation) were investigated to identify the horizontal movements. Using the IGb14 reference system, the station’s positions and velocities were calculated. First, daily sessions were used to process the horizontal coordinates of the points for an average observation epoch in a given year. Sixteen measurement epochs were included in the long-time solution. Based on the horizontal velocity residues in the north–south and east–west directions, the station’s movement was calculated. The collected results were compared to information from the EUREF Permanent GNSS Network (EUREF) and to the findings of prior research on the tectonic activity of the PKB. The results of horizontal displacements calculated using GNSS measurements in the area of the PKB and nearby structures—the MN and the FP are presented and analyzed in this article.
The infiltration of fluids into porous media frequently presents anomalous features, in which the fluid front displacement varies in time with an exponent ν different from the expected Fickean value ...of 1/2. A variety of transport models in fractal media predict the anomalies in this process and in related diffusion problems, but the associated exponents are non universal, i.e they depend not only on the fractal dimensions Df but also on other geometric properties. Here we study the horizontal infiltration in layered porous media where the matrices of higher conductivity have fractal distributions (Df<1) of lower conductivity inclusions. When the conductivity contrast is high, this process exhibits universal superdiffusive infiltration with ν=1/1+Df. This result is first demonstrated for inclusion patterns modeled by Cantor sets, but we argue that it extends to any fractal distributions of the inclusions under the condition of no spatial anisotropy in the rescaling of the observation size. Randomized versions of the Cantor sets are presented as possible realizations of disordered fractal patterns and confirm the universal relation. By considering properties of typical granular media and various soils, numerical calculations indicate that this universal superdiffusive infiltration could be observed in physically realizable laboratory and field settings.
•A model of pressure driven infiltration into horizontal layered media is developed.•Distributions of low conductivity layers (inclusions) in the media are fractal.•Infiltration is superdiffusive with exponent depending only on the fractal dimension.•The same results are applicable to regular or random fractal organizations.•The superdiffusive behavior is realizable in field and laboratory settings.
On 6 February 2023, two large earthquakes with magnitude 7.8 and 7.6 rocked south-central Türkiye and northwestern Syria. At the time of writing, the death toll exceeded 50,000 in Türkiye and 7200 in ...Syria. The epicenter of the first mainshock was located ∼15 km east of the east Anatolian fault (EAF), the second large earthquake (9 hr later) initiated ∼90 km to the north on the east-west-trending Sürgü fault. Aftershocks delineate fault lengths of ∼350 and ∼170 km, respectively. Using satellite and seismic data for first-order analyses of surface-fault offsets, space-time rupture evolution, and recorded ground motions, our study sheds light on the reasons for the extensive destruction. The first event ruptured the EAF bilaterally, lasted for ∼80 s, and created surface fault offsets of over 6 m. The second event also ruptured bilaterally with a duration of ∼35 s and more than 7 m surface offsets. Horizontal ground accelerations reached locally up to 2g in the first mainshock; severe and widespread shaking occurred in the Hatay-Antakia area with values near 0.5g. Both earthquakes are characterized by directivity effects and abrupt rupture cessation generating stopping phases that contributed to strong seismic radiation. Shaking was further aggravated locally by site-amplification effects.
Landslides pose threats to the safety and property of people living in mountainous areas like Hong Kong. Dependence of landslide travel distance on initial conditions and travel routes has broad ...implications for assessing the landslide risks. In this study, the controlling topographic and geologic factors for travel distances of open hillslope landslides and channelized debris flows are examined based on the Enhanced Natural Terrain Landslide Inventory (ENTLI) in Hong Kong with 11,622 records during the period of 1984–2013. The mean values of the horizontal travel distances of open hillslope landslides and channelized debris flows are 24.1 and 86.3 m, respectively. Correlations combining horizontal travel distances, volumes and fall heights of open hillslope landslides have been derived. The horizontal travel distances (L) and fall heights (H) are closely related for both types of landslides. The use of the L/H ratio alone as a representation of natural terrain landslide mobility is not suggested. Because of the entrainment of loose materials, the travel distances of channelized debris flows are enlarged significantly on colluvium lands (with mean value of 142.6 m), compared with those on weathered mantles (with mean value of 74.2 m).
•The frequency distribution of the landslide travel distances in Hong Kong is established.•The relationship between horizontal travel distance and slope gradient is discussed.•The effects of bedrock type and surficial materials on landslides are evaluated.
SUMMARY
Northwestern South America is a plate boundary zone where the Nazca, Caribbean and South American plates interact to produce a wide area of active continental deformation from the Gulf of ...Guayaquil (latitude 3°S) to Venezuela. Previous studies have identified a ∼2000-km-long continental sliver, referred as the North Andean Sliver (NAS), squeezed between the Nazca, Caribbean and South American plates and escaping at ∼1 cm yr−1 northeastward with respect to South America. Subduction of the Nazca Plate beneath the NAS has produced a sequence of large and great earthquakes during the 20th century along the coast of Ecuador and Colombia. Large crustal earthquakes up to magnitude 7.7 have been documented along the proposed eastern boundary of the NAS. However, active tectonics data, historical and recent earthquakes all indicate active fault systems within the NAS, possibly resulting from the interaction of several tectonic blocks. Here, we derive an extensive horizontal velocity field using continuous and episodic GNSS data from 1994 to 2019.9, covering northern Peru, Ecuador, Colombia, Panama and Venezuela. We model the GNSS velocity field using a kinematic elastic block approach that simultaneously solves for rigid tectonic block rotations and interseismic coupling along the subduction interfaces and along major crustal faults. In contrast to previous results that considered a single rigid NAS, our dense GNSS velocity field demonstrates that the NAS undergoes significant internal deformation and cannot be modelled as single rigid block. We find that block kinematics in the northern Andes are well described by the rotation of 6 tectonic blocks, showing increasing eastward motion from south to north. The Eastern boundary of the sliver is defined by a right-lateral transpressive fault system accommodating 5.6–17 mm yr−1 of motion. Fragmentation of the NAS occurs through several fault systems with slip rates of 2–4 mm yr−1. Slow reverse motion is found across the sub-Andean domain in Ecuador and northern Peru at 2–4 mm yr−1, marking a transitional area between the NAS and stable South America. In contrast, such a transitional sub-Andean domain does not exist in Colombia and western Venezuela. At the northwestern corner of Colombia, fast (∼15 mm yr−1) eastward motion of the Panama block with respect to the NAS results in arc-continent collision. We propose that the Uramita fault and Eastern Panama Deformed Zone define the current Panama/NAS boundary, accommodating 6 and 15 mm yr−1 of relative motion, respectively. A fraction of the Panama motion appears to transfer northeastward throughout the San Jacinto fold belt and as far east as longitude ∼75°W. Along the Caribbean coast, our model confirms, slow active subduction at ∼4.5 mm yr−1 along the South Caribbean Deformed Belt offshore northern Colombia and a relatively uniform rate of ∼1–2 mm yr−1 offshore northern Venezuela. Along the Nazca/NAS subduction interface, interseismic coupling shows a first-order correlations between highly locked patches and large past earthquake ruptures. These patches are separated by narrow zones of low/partial coupling where aseismic transients are observed. Compared to previous studies, our interseismic coupling model highlights the presence of deep coupling down to 70 km in Ecuador.
We performed a numerical study to understand the dynamical mechanisms of back-arc basin formation induced by slab rollback. To this end, we used two-dimensional numerical models of an integrated ...plate–mantle convection system with 410- and 660-km phase transitions. Retrograde slab migration occurs when the slab stagnates in the transition zone or when the deep section of the slab is vertical. In both cases, slab rollback occurs because the deep slab section obstructs the descending motion of the shallow slab section with an inclination. Buoyancy of the 660-km phase boundary acts as the obstructing force in the case of stagnant slab formation, and an anchoring force against the horizontal motion works similarly in the case of vertical slabs. To balance the horizontal component of the obstructing force, a suction force at the plate boundary pulls the overriding plate toward the ocean. Back-arc spreading is produced by means of slab rollback when the overriding plate with a weak area is fixed to the model boundary. The back-arc deformation becomes compressional when the overriding plate is freely movable despite trench retreat, because the wedge mantle flow viscously drags the overriding plate toward the trench. This implies that forces tending to actuate the overriding plate away from the trench are necessary to generate back-arc extension even when trench retreat is generated by slab rollback.
► We performed numerical simulations of slab rollback with back-arc basin formation. ► Obstruction of the shallow slab motion by the deep section drives the rollback. ► Stagnant slab formation and vertical slab anchoring generate the obstructing force. ► Wedge mantle flow strongly drags a movable overriding plate toward the trench. ► Mobility of the overriding plate influences back-arc deformation.
Geodetic GNSS observations at 43 sites well distributed over the Southern Patagonian Icefield region yield site velocities with a mean accuracy of 1 mm/a and 6 mm/a for the horizontal and vertical ...components, respectively. These velocities are analyzed to reveal the magnitudes and patterns of vertical and horizontal present-day crustal deformation as well as their primary driving processes. The observed vertical velocities confirm a rapid uplift, with rates peaking at 41 mm/a, causally related to glacial-isostatic adjustment (GIA). They yield now an unambiguous preference between two competing GIA models. Remaining discrepancies between the preferred model and our observations point toward an effective upper mantle viscosity even lower than 1.6⋅1018 Pas and effects of lateral rheological heterogeneities. An analysis of the horizontal strain and strain-rate fields reveals some complex superposition, with compression dominating in the west and extension in the east. This deformation field suggests significant contributions from three processes: GIA, a western interseismic tectonic deformation field related to plate subduction, and an extensional strain-rate field related to active Patagonian slab window tectonics.
•Crustal deformation at the Southern Patagonian Icefield observed at 43 GNSS sites.•Glacial-isostatic adjustment generates crustal uplift of up to 4 cm per year.•Plate collision and the Patagonian slab window contribute also to horizontal strain.
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