Seismic and geodetic response to crustal deformation in Krísuvík volcanic system, southwest Iceland

2020 ◽  
Author(s):  
Revathy M. Parameswaran ◽  
Ingi Th. Bjarnason ◽  
Freysteinn Sigmundsson
Keyword(s):  
Stress Field ◽  
Crustal Deformation ◽  
High Energy ◽  
Strike Slip ◽  
Normal Faults ◽  
Seismic Zone ◽  
The South ◽  
The West ◽  
Volcanic System ◽  
Geothermal Activity

<p>The Reykjanes Peninsula (RP) is a transtensional plate boundary in southwest Iceland that marks the transition of the Mid-Atlantic Ridge (MAR) from the offshore divergent Reykjanes Ridge (RR) in the west to the South Iceland Seismic Zone (SISZ) in the east. The seismicity here trends ~N80°E in central RP and bends to ~N45°E at its western tip as it joins RR. Seismic surveys, geodetic studies, and recent GPS-based kinematic models indicate that the seismic zone is a collection of strike-slip and normal faults (e.g., Keiding et al., 2008). Meanwhile, the tectonic processes in the region also manifest as NE-SW trending volcanic fissures and normal faults, and N-S oriented dextral faults (e.g., Clifton and Kattenhorn, 2006). The largest of these fissure and normal-fault systems in RP is the Krísuvík-Trölladyngja volcanic system, which is a high-energy geothermal zone. The seismicity here predominantly manifests RP’s transtentional tectonics; however, also hosts triggered events such as those following the 17 June 2000 Mw6.5 earthquake in the SISZ (Árnadottir et al., 2004) ~80 km east of Krísuvík. Stress inversions of microearthquakes from 1997-2006 in the RP indicate that the current stress state is mostly strike-slip with increased normal component to the west, indicating that the seismicity is driven by plate diverging motion (Keiding et al., 2009). However, the geothermal system in Krísuvík is a potential secondary source for triggered seismicity and deformation. This study uses seismic and geodetic data to evaluate the activity in the Krísuvík-Trölladyngja volcanic system. The seismic data is used to identify specific areas of focused activity and evaluate variations in the stress field associated with plate motion and/or geothermal activity over space and time. The data used, within the time period 2007-2016, was collected by the the South Icelandic Lowland (SIL) seismic network operated and managed by the Iceland Meterological Office (IMO). Furthermore, variations in seismicity are compared to crustal deformation observed with TerraSAR-X images from 2009-2019. Crustal changes in the Krísuvík area are quantified to develop a model for corresponding deformation sources. These changes are then correlated with the stress-field variations determined with seismic analysis.</p>

Rampart seismic zone of central Alaska

1983 ◽  
Vol 73 (3) ◽  
pp. 813-829
Author(s):  
P. Yi-Fa Huang ◽  
N. N. Biswas
Keyword(s):  
Main Shock ◽  
Fault Plane ◽  
B Value ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Lithospheric Plate ◽  
Normal Faults ◽  
Seismic Zone ◽  
The West ◽  
Fault Plane Solutions

abstract This paper describes the characteristics of the Rampart seismic zone by means of the aftershock sequence of the Rampart earthquake (ML = 6.8) which occurred in central Alaska on 29 October 1968. The magnitudes of the aftershocks ranged from about 1.6 to 4.4 which yielded a b value of 0.96 ± 0.09. The locations of the aftershocks outline a NNE-SSW trending aftershock zone about 50 km long which coincides with the offset of the Kaltag fault from the Victoria Creek fault. The rupture zone dips steeply (≈80°) to the west and extends from the surface to a depth of about 10 km. Fault plane solutions for a group of selected aftershocks, which occurred over a period of 22 days after the main shock, show simultaneous occurrences of strike-slip and normal faults. A comparison of the trends in seismicity between the neighboring areas shows that the Rampart seismic zone lies outside the area of underthrusting of the lithospheric plate in southcentral and central Alaska. The seismic zone outlined by the aftershock sequence appears to represent the formation of an intraplate fracture caused by regional northwest compression.

scholarly journals A New Way of Visualizing Iceland’s Crustal Deformation

Eos ◽  
2019 ◽  
Vol 100 ◽  
Author(s):  
Terri Cook
Keyword(s):  
Crustal Deformation ◽  
Active Volcano ◽  
Gps Data ◽  
Strain Rates ◽  
Seismic Zone ◽  
The South ◽  
Novel Method ◽  
South Iceland Seismic Zone ◽  
Rapid Deformation

A novel method of calculating strain rates from GPS data shows the South Iceland Seismic Zone is experiencing rapid deformation, including inflation near the island’s most active volcano.

scholarly journals Sedimentology and sequence stratigraphy of paralic and shallow marine Upper Jurassic sandstones in the northern Danish Central Graben

2003 ◽  
Vol 1 ◽  
pp. 367-402 ◽  
Author(s):  
Peter N. Johannessen
Keyword(s):  
Sea Level ◽  
Upper Jurassic ◽  
High Energy ◽  
Salt Dome ◽  
The South ◽  
The West ◽  
Relative Sea Level ◽  
Shallow Marine ◽  
The North ◽  
Plateau Area

Paralic and shallow marine sandstones were deposited in the Danish Central Graben during Late Jurassic rifting when half-grabens were developed and the overall eustatic sea level rose. During the Kimmeridgian, an extensive plateau area consisting of the Heno Plateau and the Gertrud Plateau was situated between two highs, the Mandal High to the north, and the combined Inge and Mads Highs to the west. These highs were land areas situated on either side of the plateaus and supplied sand to the Gertrud and Heno Plateaus. Two graben areas, the Feda and Tail End Grabens, flanked the plateau area to the west and east, respectively. The regressive–transgressive succession consists of intensely bioturbated shoreface sandstones, 25–75 m thick. Two widespread unconformities (SB1, SB2) are recognised on the plateaus, forming the base of sequence 1 and sequence 2, respectively. These unconformities were created by a fall in relative sea level during which rivers may have eroded older shoreface sands and transported sediment across the Heno and Gertrud Plateaus, resulting in the accumulation of shoreface sandstones farther out in the Feda and Tail End Grabens, on the south-east Heno Plateau and in the Salt Dome Province. During subsequent transgression, fluvial sediments were reworked by high-energy shoreface processes on the Heno and Gertrud Plateaus, leaving only a lag of granules and pebbles on the marine transgressive surfaces of erosion (MTSE1, MTSE2). The sequence boundary SB1 can be traced to the south-east Heno Plateau and the Salt Dome Province, where it is marked by sharp-based shoreface sandstones. During low sea level, erosion occurred in the southern part of the Feda Graben, which formed part of the Gertrud and Heno Plateaus, and sedimentation occurred in the Norwegian part of the Feda Graben farther to the north. During subsequent transgression, the southern part of the Feda Graben began to subside, and a succession of backstepping back-barrier and shoreface sediments, 90 m thick, was deposited. In the deep Tail End and Feda Grabens and the Salt Dome Province, sequence boundary SB2 is developed as a conformity, indicating that there was not a significant fall in relative sea level in these grabens, probably as a result of high subsidence rates. Backstepping lower shoreface sandstones overlie SB2 and show a gradual fining-upwards to offshore claystones that are referred to the Farsund Formation. On the plateaus, backstepping shoreface sandstones of sequence 2 are abruptly overlain by offshore claystones, indicating a sudden deepening and associated cessation of sand supply, probably caused by drowning of the sediment source areas on the Mandal, Inge and Mads Highs. During the Volgian, the Gertrud Plateau began to subside and became a graben. During the Late Kimmeridgian – Ryazanian, a long-term relative sea-level rise resulted in deposition of a thick succession of offshore claystones forming highstand and transgressive systems tracts on the Heno Plateau, and in the Gertrud, Feda and Tail End Grabens.

Spatial variation in the present-day stress field and tectonic regime of Northeast Tibet from moment tensor solutions of local earthquake data

2020 ◽  
Vol 221 (1) ◽  
pp. 478-491 ◽  
Author(s):  
Zhengyang Pan ◽  
Jiankun He ◽  
Zhigang Shao
Keyword(s):  
Stress Field ◽  
Compressive Stress ◽  
Moment Tensor ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Qilian Mountains ◽  
Compression Axis ◽  
The South ◽  
Maximum Compression ◽  
Stress Orientation

SUMMARY Focal mechanism solutions and their predicted stress pattern can be used to investigate tectonic deformation in seismically active zones and contribute to understanding and constraining the kinematic patterns of the outward growth and uplift of the Tibetan Plateau. Herein, we determined the focal mechanisms of 398 earthquakes in Northeast Tibet recorded by the China National Seismic Network (CNSN) by using the cut-and-paste method. The results show that the earthquakes predominately exhibited thrust and strike-slip faulting mechanisms with very few normal events. We then combined the derived focal mechanisms with global centroid moment tensor (GCMT) catalogue solutions and previously published solutions to predict the regional distribution of the stress field through a damped linear inversion. The inversion results show that most of region is dominated by a thrust faulting regime. From the southern East Kunlun fault in the west to the northern Qilian Mountains along the Altyn Tagh fault (ATF), the maximum compression axis rotates slightly clockwise; farther to the south of the Haiyuan fault in the east, there is an evident clockwise rotation of the maximum compression axis, especially at the eastern end of the Haiyuan fault. In the Qilian Mountains, the axis of the compressive stress orientation approximately trends NE–SW, which does not markedly differ from the direction of India–Eurasia convergence, emphasizing the importance of the compressive stress in reflecting the remote effects of this continental collision. The overall spatial pattern of the principal stress axes is closely consistent with the GPS-derived horizontal surface velocity. A comparison of the stress and strain rate fields demonstrated that the orientations of the crustal stress axes and the surface strain axes were almost identical, which indicates that a diffuse model is more suitable for describing the tectonic characteristics of Northeast Tibet. Additionally, the compressive stress orientation rotated to ENE–WSW in the northern Qilian Mountains along the ATF and to ENE–WSW or E–W along the eastern part of the Haiyuan fault and its adjacent area to the south, highlighting the occurrence of strain partitioning along large left-lateral strike-slip faults or the lateral variation of crustal strength across these faults. Combining geodetic, geological and seismological results, we suggest that a hybrid model incorporating both the diffuse model associated with shortening and thickening of the upper crust and the asthenospheric flow model accounting for the low-velocity zone in the middle-lower crust may reflect the primary mode of crustal deformation in Northeast Tibet.

Strain partitioning around an indenter during oroclinal bending: kinematics of the Circum-Moesian fault system of the Carpatho-Balkanides

2021 ◽  
Author(s):  
Nemanja Krstekanic ◽  
Liviu Matenco ◽  
Uros Stojadinovic ◽  
Ernst Willingshofer ◽  
Marinko Toljić ◽  
...  
Keyword(s):  
Large Scale ◽  
Strike Slip ◽  
Fault System ◽  
Normal Faults ◽  
Strain Partitioning ◽  
The South ◽  
The Carpathians ◽  
The North ◽  
Moesian Platform ◽  
Parallel Extension

<p>The Carpatho-Balkanides of south-eastern Europe is a double 180° curved orogenic system. It is comprised of a foreland-convex orocline, situated in the north and east and a backarc-convex orocline situated in the south and west. The southern orocline of the Carpatho-Balkanides orogen formed during the Cretaceous closure of the Alpine Tethys Ocean and collision of the Dacia mega-unit with the Moesian Platform. Following the main orogen-building processes, the Carpathians subduction and Miocene slab retreat in the West and East Carpathians have driven the formation of the backarc-convex oroclinal bending in the south and west. The orocline formed during clockwise rotation of the Dacia mega-unit and coeval docking against the Moesian indenter. This oroclinal bending was associated with a Paleocene-Eocene orogen-parallel extension that exhumed the Danubian nappes of the South Carpathians and with a large late Oligocene – middle Miocene Circum-Moesian fault system that affected the orogenic system surrounding the Moesian Platform along its southern, western and northern margins. This fault system is composed of various segments that have different and contrasting types of kinematics, which often formed coevally, indicating a large degree of strain partitioning during oroclinal bending. It includes the curved Cerna and Timok faults that cumulate up to 100 km of dextral offset, the lower offset Sokobanja-Zvonce and Rtanj-Pirot dextral strike-slip faults, associated with orogen parallel extension that controls numerous intra-montane basins and thrusting of the western Balkans units over the Moesian Platform. We have performed a field structural study in order to understand the mechanisms of deformation transfer and strain partitioning around the Moesian indenter during oroclinal bending by focusing on kinematics and geometry of large-scale faults within the Circum-Moesian fault system.</p><p>Our structural analysis shows that the major strike-slip faults are composed of multi-strand geometries associated with significant strain partitioning within tens to hundreds of metres wide deformation zones. Kinematics of the Circum-Moesian fault system changes from transtensional in the north, where the formation of numerous basins is controlled by the Cerna or Timok faults, to strike-slip and transpression in the south, where transcurrent offsets are gradually transferred to thrusting in the Balkanides. The characteristic feature of the whole system is splaying of major faults to facilitate movements around the Moesian indenter. Splaying towards the east connects the Circum-Moesian fault system with deformation observed in the Getic Depression in front of the South Carpathians, while in the south-west the Sokobanja-Zvonce and Rtanj-Pirot faults splay off the Timok Fault. These two faults are connected by coeval E-W oriented normal faults that control several intra-montane basins and accommodate orogen-parallel extension. We infer that all these deformations are driven by the roll-back of the Carpathians slab that exerts a northward pull on the upper Dacia plate in the Serbian Carpathians. However, the variability in deformation styles is controlled by geometry of the Moesian indenter and the distance to Moesia, as the rotation and northward displacements increase gradually to the north and west.</p>

3D stratigraphic and structural synthesis of the Dannemarie basin (Upper Rhine Graben)

2005 ◽  
Vol 176 (5) ◽  
pp. 433-442 ◽  
Author(s):  
Christian Le Carlier de Veslud ◽  
Olivier Bourgeois ◽  
Marc Diraison ◽  
Mary Ford
Keyword(s):  
Fault Zone ◽  
Normal Faults ◽  
Upper Rhine Graben ◽  
Fault Propagation ◽  
The South ◽  
The West ◽  
Vosges Mountains ◽  
Rhine Graben ◽  
Western Border ◽  
Upper Rhine

Abstract The Dannemarie basin is the southwesternmost depocentre of the Upper Rhine Graben, which belongs to the West-European Tertiary rift system. It is bounded to the west by the Vosges mountains, to the south by the folded Jura belt and to the east by the Mulhouse block. The rifting reached its maximum activity during the Priabonian and early Rupelian (35-31 Ma). In the framework of the GeoFrance 3D project “Fossé rhénan”, a 3D geometrical model of the Dannemarie basin was built in the gOcad 3D modeler. It incorporates the BRGM well database and geological maps, and 40 seismic cross-sections. These data are used to study the structure and geological history of the area. Seismic data have been converted from time to depth using a 1D time-to-depth polynomial law deduced from the analysis of the Bellemagny borehole. The Dannemarie basin is bounded to the west by the Vosges fault zone and to the east by the Illfurth fault zone. On both borders, basin subsidence was controlled by normal faults and associated syn-rift flexures. The minimum throw on the Vosges fault zone is about 1400 m to the north of the model, decreasing to the south, where it is replaced by a syn-rift flexure. On the Illfurth fault zone, subsidence is accommodated by faults (with about 1000 m throw) and by a flexure (about 300 m). Stratigraphic data indicate that these flexures were active during Priabonian and early Rupelian extension. These monoclinal flexures are interpreted as fault-propagation folds that developed above upward propagating normal faults in the basement. As displacement accumulates, the fault propagates upwards and cuts the overlying fold. Similar fault-fold geometries have been described on the western border of the Rhine graben, close to Colmar and in other extensional tectonic contexts. In the Colmar area, the Vosges fault zone cuts through the basin margin fold, while further south along the western border of the Dannemarie basin, displacement on the fault decreases and subsidence is accommodated on a major flexure. Flexure locations correspond to gravimetric discontinuities attributed to Variscan structures, suggesting reactivation of deep structures during rifting. The Illfurth fault zone displays upwardly divergent fault geometries that resemble “flower structures”. The data can be interpreted as follows, either that (a) the Illfurth fault zone accommodated a minor sinistral strike-slip component due to a post-Miocene NW-SE compressive regional stress field or (b) these faults developed in association with the fault propagation folds.

General Geology

1995 ◽  
Author(s):  
K. O. Emery ◽  
David Neev
Keyword(s):  
Red Sea ◽  
Dead Sea ◽  
Strike Slip ◽  
The South ◽  
The West ◽  
The North ◽  
Central Segment ◽  
Crystalline Crust ◽  
Major Fault ◽  
The Dead

The Dead Sea occupies a linear down-dropped region between two roughly parallel faults along the central segment of the major northsouth- trending crustal rift that extends about 1,100 km from the Red Sea through the Gulf of Elath to Turkey. This rift or geosuture separates the Arabian crustal sub-plate on the east from the Sinai one on the west. An origin as early as Precambrian is possible (Bender, 1974; Zilberfarb, 1978). Crystalline crust along the north-south trough of the Sinai sub-plate is about 40 km thick in contrast with a thickness of half as much above ridges along both flanks (Ginsburg and Gvirtzman, 1979). Toward the north the ridges appear to converge (Neev, Greenfield, and Hall, 1985). Since the Miocene period the Arabian plate has moved north about 105 km relative to the Sinai plate. This sort of crustal movement along either side of a rift is termed strike-slip faulting. One result of it was the opening of the Red Sea relative to the Gulf of Suez. The Dead Sea graben, a down-dropped block between two roughly parallel faults, occupies the central segment of the long crustal rift. The boundary between these is rather sharp along the east shore of the sea (Frieslander and Ben-Avraham, 1989). Actual post-Miocene movement was along not just a single major fault but was distributed among numerous sub-parallel faults that form a 100-km-wide belt in which movements were transferred from one fault to another (Eyal et al., 1981; Gilat and Honigstein, 1981). Recent movements have occurred along the south segment of the north-south-trending Arava fault south of the Amazyahu transverse fault (Zak and Freund, 1966). These strike-slip movements probably did not continue after Miocene along the main East fault of the Dead Sea, which is the north extension of the Arava wrench fault. In contrast, recent movements have been present along the north-northeast- trending Jordan or Dead Sea fault (Ben-Menahem et al., 1977, fig. 1). The movements extend south from east of Jericho in the north along the base of the west submarine slope of the sea and the elongate salt diapir of Mount Sedom as far as the Amazyahu fault in the south.

Role of dextral strike slip faulting in the distribution of Aegean extension since Miocene times inferred from receiver function analysis

2020 ◽  
Author(s):  
Agathe Faucher ◽  
Christel Tiberi ◽  
Frédéric Gueydan ◽  
Alexandrine Gesret
Keyword(s):  
Receiver Function ◽  
Function Analysis ◽  
Receiver Functions ◽  
Strike Slip ◽  
Point Of View ◽  
Normal Faults ◽  
The South ◽  
Crustal Thinning ◽  
Dextral Strike Slip

<p>Aegean plate is marked since Eocene by widespread NE-SW extension induced by the African slab roll-back. In Miocene times, E-W shortening created by the westward Anatolian extrusion overlays the extension, with the formation of Miocene dextral strike slip faults in addition to normal faults. We propose to quantify the role of large dextral strike slip faults in accommodating Aegean extension, using receiver functions to image Moho geometry.</p><p>Aegean extension is particularly evidenced by a topographic difference between the emerged continental Greece and the submerged Cyclades. In this study we characterize the associated Moho geometry with a particular focus on the transition between these two domains. From a geological point of view, the transition between continental Greece and the Cyclades is marked by two dextral strike slip faults: the Pelagonian fault (onshore) and the South Evvia fault (offshore). Our objective is also to show a potential Moho signature of these strike slip faults.  We processed receiver functions (RF) from the MEDUSA stations located in Attic and Evvia.</p><p>Our results show that the Moho is deeper beneath continental Greece (~27km) than beneath the Cyclades (~25km). A detailed azimuthal study of RF distribution shows a flat Moho underneath Continental Greece. The crustal thickness is also almost constant inside the Cyclades, as already suggested by previous studies. However, the transition between the Cyclades and Continental Greece is not continuous. These two crustal blocks are separated by the Pelagonian and the South Evvia strike slip faults in a narrow transition zone (~75km). In this zone (South Evvia/Attica), dip and strike of the Moho vary and suggest a crustal signature of the strike slip structures observed at the surface. These strike slip faults therefore accommodate in a narrow zone the inferred variations in crustal thicknesses between the Cyclades and Continental Greece.</p><p>Our data show that differences in topography between Continental Greece and the Cyclades are isostatically compensated, reflecting various amount of crustal thinning larger in the Cyclades than in Continental Greece. Inside these two crustal blocks, we imaged a flat Moho, suggesting a wide rift extension process associated with the formation of numerous Miocene and Plio-Quaternary basins.  The dextral strike slip faults at the edges of the continental blocks (Continental Greece and Cyclades) accommodated the inferred variations in the amount of crustal thinning, suggesting that they act as continental transfer zones at crustal-scale during Miocene Aegean Extension.</p>

Crustal deformation measured by GPS in the South Iceland Seismic Zone due to two large earthquakes in June 2000

2001 ◽  
Vol 28 (21) ◽  
pp. 4031-4033 ◽  
Author(s):  
Thóra Árnadóttir ◽  
Sigrún Hreinsdóttir ◽  
Gunnar Gudmundsson ◽  
Páll Einarsson ◽  
Michael Heinert ◽  
...  
Keyword(s):  
Crustal Deformation ◽  
Seismic Zone ◽  
The South ◽  
South Iceland Seismic Zone ◽  
Large Earthquakes
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