Recent Tectonic Processes Research Articles

GEOMORPHOLOGICAL INDICATORS OF SHEAR DISPLACEMENTS ON THE URUP ISLAND (GREAT KURIL RIDGE)

The Urup Island, located in the southern part of the Great Kuril ridge, is an interesting object of study because its relief is very contrasting and has a significant depth of vertical dissection. It was greatly influenced by the recent tectonic processes. Judging by the geological data, the island at the present stage is located in a shear stress field with the southeastern orientation of the axis of maximum compression. It can be explained by the subduction interaction of the Pacific and Sea of Okhotsk lithosphere plates at an acute angle of about 55°. Visual and automated decoding of satellite images and digital terrain models, and the analysis of the erosion network pattern made it possible to identify geomorphologic signs of shear displacements. These include the echeloned arrangement of lineaments as separation cracks in right-lateral shear zone in the area of the Rybnaya River and on the Skvoznyakovyj isthmus, where displacements of unidentified kinematics were previously revealed. The zones, which are oriented in the north-east direction and differ in the asymmetric pattern of the drainage network, were considered: within their limits, small tributaries are located on one side of the watercourse of the highest order as megatracks of separation. In the area of the epicenter of the earthquake of 1989, which occurred under the latitudinal horizontal stretching, a linear lowering of the relief with a feathery pattern of watercourses was recorded, interpreted as a morphostructure of stretching. Similar probably stretching zones, extending mainly along the azimuth of 130-140°, were recorded on the Pacific coast of the island. Their orientation, as well as the kinematics of probable shear displacements identified from the geomorphologic data, correlates with the general ideas about the stress-strain state of the Southern Kuriles, as well as the reconstruction of the main normal stress axes of the Kastricum Peninsula performed by us from the fracture measurements. All this prove that the suggested structural-geomorphologic interpretation of the Urup Island territory is quite reasonable. In general, our new data on the configuration and kinematics of probable active shear faults and extensional morphostructures complement the existing ideas about the latest deformations of the study area.

Active north-vergent thrusting in the northern Sicily continental margin in the frame of the quaternary evolution of the Sicilian collisional system

A three-stage evolution has characterized the Sicilian Fold and Thrust Belt (SFTB) during the last 15 My: two main thin-skinned shortening events involving mainly Meso-Cenozoic carbonate units, followed by thick-skinned thrusting involving Plio-Pleistocene deposits in the frontal area as well as the crystalline basement in the inner and deeper sector of the chain. We investigated the northern Sicily continental margin, by using differently-penetrative seismic reflection data and new field surveys, which revealed, both offshore and onshore, north-vergent compressional structures that affected the tectonic edifice during Quaternary time. These structures, correlated with the kinematic setting pointed out by seismicity and GPS measurements, could disclose an important change in distribution and orientation of deformation in the frame of the Africa-Europe convergence. Our hypothesis is that the most recent tectonic processes in the northern Sicily continental margin are representative of a jump of the deformation from the frontal area of the SFTB in the Sicily Channel to the inner sector in the Southern Tyrrhenian Sea. This study is in agreement with recent interpretations about a change in the subduction polarity in the central Mediterranean orogenic system, as a consequence of the ongoing collision of the African promontory with the thinned continental to oceanic sectors (Algerian and Tyrrhenian basins) of the European plate.The seismic activity associated with the north-vergent thrust could have implication for the assessment of the seismic risk in the Central Mediterranean and understanding of active structures in marine areas that could be responsible for tsunami hazard.

Local tectonic deformations measured by extensometer at the eastern foothills of the Alps at the Sopronbánfalva Geodynamic Observatory, Hungary

Abstract In Hungary, at the foot of the Eastern Alps, in the Sopronbánfalva Geodynamic Observatory (SGO), a quartz-tube extensometer has been used for recording the Earth’s tides and local tectonic deformations since 1991. The 27-year long strain record (1991–2017) shows a continuous compression of the rock with changing rate. The relations between the measured local deformation and present-day tectonics in the region of the observatory were investigated. The local strain rate variations were also compared with the temporal and spatial distribution as well as with the magnitudes of earthquakes occurred within 200 km from the observatory in two sectors around the azimuth of the extensometer (116°): 116°±15° and 296°±15°. Our investigations show that earthquakes can also influence the strain rate. Earthquakes to the west of SGO generally increase the compressive strain rate, while earthquakes in the Pannonian Basin, with some exceptions, have no significant effect on the local strain rate variations measured in the SGO. It has been found that the recorded compressive strain is in good accordance with the recent tectonic processes in the region of the SGO determined by Global Navigation Satellite System (GNSS) technology and geophysical measurements. From the results it can be concluded that the uplift of the Alps, tectonic processes in the East Alpine region and in the Pannonian Basin play the most important role in the changing local compressive strain rate.

Landslides types controlled by tectonics-induced evolution of valley slopes (Northern Apennines, Italy)

This paper investigates the role played by geomorphological and tectonic processes affecting a portion of an active mountain belt in causing the occurrence of different types of landslides developed in flysch bedrock. The adopted multidisciplinary approach (geomorphology, geology and geophysics) allowed to recognize in a portion of the Northern Apennines of Italy different types of landslides that developed in response to slope dynamics, in turn dependent on broader regional-scale tectonic processes. Sedimentary bed attitude, local tectonic discontinuities and lithology only partially influenced the type of landslides, which have been deeply affected by the activity of regional-scale antiform that controlled the hillslope geomorphic evolution in different ways. The growth of this structure and the tilting of its forelimb produced gently dipping slopes that approached the threshold angle that can cause the occurrence of (mainly) translational rockslides. Conversely, high-angle normal faulting parallel to the antiform axis (related to a later stage of activity of the antiform itself) strongly controlled the stream network evolution and caused the watercourses to deeply incise portions of their valleys. This incision produced younger steep valley slopes and caused the development of complex landslides (roto-translational slides-earth/debris flow). The results of the integrated study presented in this paper allowed to distinguish two main types of landslides whose development reflects the events that led to the geomorphological and geological evolution of the area. In this perspective, within the study area, landslides can be regarded and used as indicators of broader-scale recent tectonic processes.

On the relationship between recent tectonic processes and mud volcanism by the example of Mt. Karabetov, Taman Peninsula

The results of studying the near-surface and deep structure of the mud volcano of Mt. Karabetov are presented. Based on direct observations in a specially dug trench and in the natural outcrops, together with the analysis of the structural morphological data, the structural kinematic characteristics are obtained for the fault zone associated with a mud volcano. The displacements of recent soil and overburden, as well as the topographic manifestations testify to the recent high level of mobility of the fault, whereas the natural structural parageneses suggest the primarily tectonic nature of the displacements, which is determined by the regional stress field.

The role of recent tectonics and hydrological processes in the evolution of recurring landslides on the Danube's high bank in Dunaföldvár, Hungary

There are high loess banks prone to landslide along the River Danube in Hungary. One of these is the high loess bank in Dunaföldvár, where several landslides occurred in the last decades. Quantitative relationships between the movements of the high loess bank and the variation of the water level of the River Danube, the ground water table, precipitation and temperature are investigated by two borehole tiltmeters and a vertical borehole extensometer. The twelve-year long observation from 2002 to 2014 made it possible to distinguish between the high bank movements due to slow recent tectonic and geomorphologic processes and the short-period (from hours to months) movements caused by hydrometeorological effects. The results revealed that besides geomorphologic processes recent tectonics can play an important role in the recurrence of landslides in the area. In the investigated period the total tilt of the high bank was 162μrad in the SSE direction according to the geomorphologic and recent tectonic processes in the surroundings of Dunaföldvár. Investigations of the relationships between the high bank movements and the water level of the River Danube, ground water table changes and the precipitation revealed that the tilt magnitudes caused by the ground water table variations are two orders of magnitude greater than the tilts caused by the water level regime of the river and the direct effect of the precipitation on the high bank tilts can be disregarded.

Influence of recent depositional and tectonic controls on marine gas hydrates in Trujillo Basin, Peru Margin

Abstract The development of bottom simulating reflectors (BSRs) and the gas hydrate stability zone (GHSZ) in continental margins is related to recent depositional and tectonic processes. This interrelation is important for understanding the potential resource of gas hydrate deposits. The purpose of this study is to understand the influence of such activity on the marine gas hydrate system of the seaward extension of the Trujillo Basin, Peru Margin. Here, we analyze near-seafloor heat flow probe data, high-resolution multichannel seismic (MCS) profiles, swath bathymetry and ocean floor observation system (OFOS) images. Based on our results, we identify three main physiographical subregions in the study area: (1) an area with turbidites, continuous BSRs and low-to-moderate near-seafloor heat flow (7–33 mW/m2), (2) an area with sediment waves of turbidity origin, a mix of continuous and patchy BSRs, and moderate near-seafloor heat flow (26–39 mW/m2), (3) an area with extensional faulting, patchy BSRs and moderate-to-high near-seafloor heat flow (52–110 mW/m2). We conclude that sediment flow processes are the result of recent depositional controls, and faulting is the result of recent tectonic activity. Near-seafloor heat flow around chemoherms is moderate. Estimates of BSR-derived heat flow show differences to near-seafloor heat flow. This difference points to advection of fluids occurring at the seafloor. Alive Calyptogena and tube worms were observed in these venting zones. Based on our analysis, we conclude that: (1) recent depositional processes control the development of continuous BSRs and may restrict heat transfer through the GHSZ in the form of fluid venting at the seafloor, (2) recent tectonic processes control the development of patchy BSRs and allow heat transfer through the GHSZ along faults, which is manifested as fluid venting at the seafloor.

Seismic response to recent tectonic processes in the Banda Arc region

Abstract Internal structure and recent tectonics of the geologically complex Banda Arc region (latitude 1–9°S, longitude 124–135°E) have been studied by means of the analysis of global seismological data. Relocated hypocentral determinations of the International Seismological Center (EHB data) and fault plane solutions of the Global Centroid Moment Tensor Project have been used together with previously published information on regional geology and dynamics. The analysis considered earthquakes in the lithospheric wedges above subducting slabs and earthquakes in the uppermost portions of the Wadati–Benioff zones (focal depth

Crustal structure and signatures of recent tectonism as influenced by ancient terranes in the western United States

The amalgamation of crustal blocks that composes the western cordillera of North America has a long history of deformation across a broad zone. Investigations spanning a range of scales in the region have sought to unravel details of its structure and evolution. By sampling the entire western portion of the United States, the deployment of the Transportable Array component of the EarthScope USArray provides broadband seismic data to study crustal structure across much of this deforming region. Receiver functions recorded across the western United States provide insight into the thickness of the crust and how it varies between tectonic provinces. The thickness of the crust varies from 50 km beneath the Rocky Mountains in Colorado and Wyoming. Distinct crustal structures characterize the Basin and Range, Snake River Plain, the Sierra Nevada, and the active Cascade volcanic arc, suggesting that the recent tectonic processes that affected the region have shaped the crustal structure. In addition, characteristics of the crust appear to relate to the boundaries of, and structures within, the terranes that formed North America. Patterns of crustal thickness across an expansive region presented here allow for the crustal response to specific tectonic processes to be determined while still imaging small-scale structures that can be more difficult to identify in a continental-scale study. This provides a context for previous and future detailed studies to understand how observed crustal structures relate to the evolution of western North America.

Analyzing Spatial Autocorrelation for the Hypsometric Integral to Discriminate Neotectonics and Lithologies Using DEMs and GIS

This investigation documents the sensitivity of the hypsometric integral (HI) and its relationship to neotectonics and lithology. We used digital elevation models (DEMs) of 30 and 90 m spatial resolution from the Shuttle Radar Topographic Mission (SRTM) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) to calculate HI values in the Hindu Kush and its vicinity (Northwest Pakistan and Northeast Afghanistan). We used an analysis grid of regular squares of different sizes to calculate maximum, minimum, and mean elevations. The spatial distributions of HI do not show clear spatial patterns and correlation with mean elevation or relief amplitude. We applied spatial pattern analysis using Local Indices of Spatial Autocorrelation (LISA) to measure the degree to which our HI distribution was clustered, dispersed, or randomized. LISA analysis shows that the data are autocorrelated because of high positive z-scores. Hot spots (clusters with high HI values) are consistent with tectonic uplift and show a strong correlation with the different structural domains in the region. Cold spots represent recent sedimentation close to faults and coincide with shallow earthquake clusters in the region. The HI values do not show any correlation with relative topographic position or lithology. Analysis of HI distribution shows that they are robust and independent of digital elevation model (DEM) resolution but are strongly scale dependent. The LISA technique allows the extraction of clusters of the HI that reveal recent tectonic processes; otherwise it is difficult to interpret the high variability of HI values. The scale dependency of the HI may reflect the varying importance of drainage network and hillslope processes.

A case study comparing landscape metrics to geologic and seismic data from the Ischia Island (Southern Italy)

In this paper, a high-resolution digital elevation model (DEM) of the Ischia Island has been created, and a digital terrain analysis has been carried out to identify of morphostructural elements of this landscape. Ischia is an active volcano located in the Western sector of the Gulf of Naples that is characterized by historical and recent volcano-tectonic activity. The local kinematics is unclear, and so identification of tectonic lineaments might elucidate recent tectonic processes. We identify morphostructural features using geomorphic parameters derived from analysis of the high-resolution DEM. Successively, the comparison with known geologic features provides validation of the extracted morphotectonic data. We found that one of the main directions of the morphostructural lineaments extracted is consistent with the regional NE–SW extensional stress field; moreover, the lineaments on the northern flank of Mt. Epomeo are strictly correlated with the mapped faults that have a history of strong and moderate earthquakes. The technique implemented for this study area allowed us to identify new original morphostructural lineaments in a reproducible way that may be useful for investigating various landscapes where field survey is not possible. Indeed, the extracted lineaments represent potential active faults near the northern coast of the Ischia Island, where both seismicity and intense urbanization delineate a high seismic risk.

Crustal dynamics and active fault mechanics during subduction erosion. Application of frictional wedge analysis on to the North Chilean Forearc

The forearc region of the non-accreting South American Plate margin in northern Chile is characterised by subduction erosion and regional uplift. Neotectonic deformation structures reflect simultaneous extensional and contractional fault kinematics. In the outer forearc, where the brittle crust directly overlies the subducting Nazca Plate, the stress regime changes from extension in the upper part to compression at the base of the forearc wedge as seen in neotectonic surface structures and seismic data. In the inner forearc, surface structures indicate a compressional stress regime also affecting the western rim of the magmatic arc. This stress regime is limited to a brittle crustal wedge segment which overlies the ductile part of the inner forearc lithosphere. The shape of the two brittle forearc wedges at the leading edge of the South American Plate is controlled by exogenetic surface processes, internal deformation processes, contemporaneous basal tectonic erosion and underplating. Mechanical parameter sets controlling and reflecting the recent tectonic processes and geometrical wedge segmentation within the forearc system are evaluated and applied to general frictional wedge models. The states of stress within the crustal wedges are controlled by spatial variations of the basal mechanical parameters in the down-dip direction of the forearc wedge base. The new models illustrate the fundamental kinematics and dynamic processes of ‘Coulomb-type’ basal tectonic erosion and mass transfer modes along active non-accretive convergent margins. The frictional wedge models explain the dynamics of the simultaneous and contrary deformation processes affecting the forearc crust at the North Chilean convergent margin shaped by active basal tectonic erosion.

Some peculiarities of the secular variation of the geomagnetic field in the Carpathians

The secular variation (SV) of the geomagnetic field is studied in the Western Carpathians and Eastern (Transcarpathian) Carpathians. Possible influences of other geophysical fields on the SV behaviour have been studied. The analysis is based on geomagnetic data from the interval 1979–1984. Comparisons are made with gravitational field anomalies and with recent vertical movements of the Earth's crust on Deep Seismic Sounding (DSS) profiles No. II. and VI. Connections between recent tectonic processes and the morphology of the SV field are evident in the region studied.

The ties between recent crustal movements and fault tectonics in the Caraptho-Balkan region

To identify the faults controlling the intensity of recent tectonic processes in the region and to study their geometry and dynamics, one of the variants of the statistical method was used-trend analysis. The map of recent vertical crustal movements in the Carpatho-Balkan region (1:2.000.000) published in Budapest in 1979 was used as initial data for establishing these faults.

Regional upper mantle S-velocity models from phase velocities of great-circle Rayleigh waves

Summary A linear inversion approach is used to interpret a wide set of great-circle Rayleigh wave phase velocities in terms of regionalized Earth models. In a first step ‘pure-path’ fundamental Rayleigh wave phase velocities are estimated by linear regression from great-circle measurements of phase velocity in the period range 150-300 s, using both published and new observations. For these data a method based on the deviations of observed eigenfrequencies from those for a spherically averaged model of the Earth, is used after subtraction of the effect of ellipticity in the range of geometrical optics. A regionalization of the Earth is fixed a priori, models of variation of structure with depth being sought for each region; this regionalization is based on a variation with age, both for oceans and continents. Four regions are distinguished: (1) ‘young ocean’ regions (age less than 30 Myr), (2) ‘old ocean’ regions (age greater than 30 Myr), (3) ‘shield and platform’ regions and (4) ‘tectonic’ regions. In a second step, the ‘pure-path’ phase velocity curves are then interpreted in terms of S-wave velocity models by a linear inversion scheme. The resolution of the data with regard to surface structure is discussed, and care has been taken to constrain continental and oceanic crustal structures in the starting models. In the upper 250 km, the well-known strong difference between oceanic and continental structures clearly appears in the resulting models. In the depth range 300-450 km, no resolvable differences appear between the ‘shield and platform’ and ‘old ocean’ models; yet, slight differences between the ‘young ocean’ and the ‘old ocean’ models are indicated. Also for the ‘tectonic’ region, which includes both subduction zones and mountainous areas, the model contains a 2 per cent higher velocity zone between 300 and 450 km depth. The results are in agreement with independent regional studies and lead to the conclusion that deep lateral S-velocity variations are related to recent tectonic processes.