scholarly journals The 2008 and 2012 Moosiyan Earthquake Sequences: Rare Insights into the Role of Strike Slip and Thrust Faulting within the Simply Folded Belt (Iran)

2017 ◽  
Author(s):  
Stuart E. J. Nippress ◽  
Ross Heyburn ◽  
R. J. Walters
Keyword(s):  
Strike Slip ◽  
Thrust Faulting ◽  
Earthquake Sequences

Role of Strike-slip Faulting in the Evolution of the Chumphon Basin, Gulf of Thailand

2019 ◽  
Author(s):  
Sarawute Chantraprasert ◽  
Jakkree Kongchum ◽  
Natapol Kuenphan
Keyword(s):  
Strike Slip ◽  
Gulf Of Thailand

Source Investigation of the 2018 Lombok (Indonesia) Earthquake Sequences

2020 ◽  
Author(s):  
Dimas Salomo Januarianto Sianipar ◽  
Bor-Shouh Huang ◽  
Kuo-Fong Ma ◽  
Tio Azhar Prakoso Setiadi ◽  
Ming-Che Hsieh ◽  
...  
Keyword(s):  
Hazard Analysis ◽  
Thrust Faulting ◽  
The North ◽  
Banda Arc ◽  
Finite Fault ◽  
Source Mechanisms ◽  
Back Arc ◽  
Earthquake Sequences ◽  
Large Earthquakes ◽  
Lombok Island

<p>The western extension and deformation mechanism of Flores back-arc thrust in eastern Sunda-Banda Arc (Indonesia) are poorly investigated, and, thus, poorly constrained. From late July to August 2018, a sequence of large earthquakes (M6.4+) took place in the north of Lombok Island that marked the previously westernmost termination of the continuous zone of the back-arc thrusting. The 2018 Lombok earthquake sequences that began with Mw 6.4 (28 July 2018), and followed by Mw 6.9 (5 August 2018), and Mw 6.9 (19 August 2019) with massive subsequent aftershocks claimed on more than 500 casualties, nearly 500,000 people displaced and serious damages on Lombok Island. Here we relocate the aftershocks and perform the finite fault inversions of M6.4+ earthquake sequences constrained with teleseismic body and surface waves. Both refined hypocenters of aftershocks and rupture processes of large earthquakes provide detail kinematic descriptions of the source mechanisms of the sequences. The aftershocks distributions and slip model suggest that the earthquakes occurred on south-dipping low angle thrust faulting that striking to the east while it also activated aftershocks on surrounding complex shallow faulting with distinguishing distributions. The source inversions of large earthquakes over the entire of the western part of Flores back-arc thrust resulted as simple circular rupture propagations initiated from ~15 km depth for all events except the westernmost events (Mw 6.9 on 5 August 2019) that had a more complex rupture and initiated from shallower depth, and with slip distributed cross over the former identified westernmost termination of the Flores back-arc thrust. Our study suggests the further extension of back-arc thrusting and the possible structures revealed from the subsequence aftershocks. The source characterizations revealed in this study would be important for further seismic hazard analysis in this region.</p>

Interseismic stress field variations in Hjalli-Ölfus, SW Iceland

2020 ◽  
Author(s):  
Ingi Th. Bjarnason ◽  
Revathy M. Parameswaran ◽  
Bergthóra S. Thorbjarnardóttir
Keyword(s):  
Plate Boundary ◽  
Strike Slip ◽  
Seismogenic Zone ◽  
Plate Boundaries ◽  
Central Volcano ◽  
Seismic Zone ◽  
Stress Regime ◽  
Mid Atlantic Ridge ◽  
Spatio Temporal ◽  
Earthquake Sequences

<p>Western South Iceland Seismic Zone (SISZ) plate boundary lies adjacent to the Hengill central volcano. The sinistral SISZ connects the two arms of the divergent Mid-Atlantic Ridge (MAR) plate boundaries (Western and Eastern Volcanic Zones; WVZ, EVZ), while Hengill is a part of the WVZ. Seismicity in western SISZ, also known as the Hjalli-Ölfus region, closely interacts with the seismicity and magmatism in Hengill. For instance, the  4 June 1998 Mw 5.4 Hengill earthquake witnessed aftershocks that extended south to meet the Hjalli-Ölfus segment. This segment then hosted the Mw 5.1 Hjalli-Ölfus earthquake that occurred on 13 November 1998; elucidating the Hengill-Ölfus interaction. Relative relocations of earthquakes from July 1991 to December 1999 in Hjalli-Ölfus indicate that the seismogenic zone is predominant at 4-8 km depth, with 80% of the events occuring along an ~ENE-WSW trending seismic zone with lateral extension of ~12 km. The remaining occur along N-S faults, much like the observed norm of dextral faulting along the rest of the SISZ (e.g., 17 June 2000, 29 May 2008 earthquakes; Árnadottir et al., 2001; Brandsdottir et al., 2010). These relocated earthquake sequences were used to perform stress inversions within specified spatio-temporal grids. The results show that from 1994 to 1997, the western part of the Hjalli-Ölfus region exhibits an oblique normal stress regime, while the eastern part remains consistently strike-slip in nature. From mid-1997 to June 1998 western Hjalli-Ölfus shifts from an oblique normal to a strike-slip stress regime, while the eastern part maintains the strike-slip character of the SISZ. However, two months after the 4 June 1998 Hengill earthquake, the western part shifts back to an oblique normal regime, which loses a part of its normal-faulting tendency after the 13 November 1998 Hjalli-Ölfus earthquake. This variation in stress fields between two significant events on conjugately oriented prodominantly strike-slip faults is a clear example of these features influencing one another between seismic episodes. </p>

Geodynamic evolution of the Canadian Cordillera — progress and problems

1979 ◽  
Vol 16 (3) ◽  
pp. 770-791 ◽  
Author(s):  
J. W. H. Monger ◽  
R. A. Price
Keyword(s):  
Continental Margin ◽  
Middle Jurassic ◽  
Rocky Mountain ◽  
Ocean Basin ◽  
Strike Slip ◽  
Granitic Rocks ◽  
Canadian Cordillera ◽  
Thrust Faulting ◽  
Western Cordillera ◽  
Geophysical Surveys

The present geodynamic pattern of the Canadian Cordillera, the main features of which were probably established in Miocene time, involves a combination of right-hand strike-slip movements on transform faults along the continental margin, and, in the south and extreme north, convergence in subduction zones in which oceanic lithosphere moves beneath the continent, with consequent magmatism along the continental margin. In the southern Canadian Cordillera, geophysical surveys have outlined the subducting slab and the asthenospheric bulge that occurs beneath and behind the magmatic arc. They also show that there is now no root of thickened Precambrian continental crust beneath the tectonically shortened supracrustal strata in the southern parts of the Omineca Crystalline Belt and Rocky Mountain Belt.The Rocky Mountain, Omineca Crystalline, Intermontane, Coast Plutonic, and Insular Belts, the structural and physiographic provinces that dominate the present configuration of the Canadian Cordillera, were established with the initial uplift and the intrusion of granitic rocks in the Omineca Crystalline Belt in Middle and Late Jurassic time and in the Coast Plutonic Complex in Early Cretaceous time, and they dominated patterns of uplift, erosion and deposition through Cretaceous and Paleogene time. Their development may be due to compression with thrust faulting in the eastern Cordillera, and to magmatism that accompanied subduction and to accretion of an exotic terrane, Wrangellia, in the western Cordillera. Major right-lateral strike-slip faulting, which occurred well east of but sub-parallel with the continental margin during Late Cretaceous and Paleogene time, accompanied major tectonic shortening due to thrusting and folding in the Rocky Mountain Belt as well as the main subduction-related (?) magmatism in the Coast Plutonic Complex.The configuration of the western Cordillera prior to late Middle Jurassic time is enigmatic. Late Paleozoic and early Mesozoic volcanogenic strata form a complex collage of volcanic arcs and subduction complexes that was assembled mainly in the Mesozoic. The change in locus of deposition between Upper Triassic and Lower to Middle Jurassic volcanogenic assemblages, and the thrust faulting in the northern Cordillera may record emplacement of another exotic terrane, the Stikine block, in latest Triassic to Middle Jurassic time.The earliest stage in the evolution of the Cordilleran fold belt involved the protracted (1500 to 380 Ma) development of a northeasterly tapering sedimentary wedge that discordantly overlaps Precambrian structures of the cratonic basement. This miogeoclinal wedge may be a continental margin terrace wedge that was prograded into an ocean basin, but it has features that may be more indicative of progradation into a marginal basin in which there was intermittent volcanic activity, than into a stable expanding ocean basin of the Atlantic type.

scholarly journals Superposition of two kinematically distinct extensional phases in southern Death Valley: Implications for extensional tectonics

Geosphere ◽  
2021 ◽  
Author(s):  
Z.D. Fleming ◽  
T.L. Pavlis ◽  
S. Canalda
Keyword(s):  
Early Period ◽  
Rock Avalanche ◽  
Strike Slip ◽  
Death Valley ◽  
Normal Faults ◽  
Geologic Mapping ◽  
The North ◽  
Transcurrent Deformation ◽  
Two Phases

Geologic mapping in southern Death Valley, California, demonstrates Mesozoic contractional structures overprinted by two phases of Neogene extension and contemporaneous strike-slip deformation. The Mesozoic folding is most evident in the middle unit of the Noonday Formation, and these folds are cut by a complex array of Neogene faults. The oldest identified Neogene faults primarily displace Neoproterozoic units as young as the Johnnie Formation. However, in the northernmost portion of the map area, they displace rocks as young as the Stirling Quartzite. Such faults are seen in the northern Ibex Hills and con­sist of currently low- to moderate-angle, E-NE– dipping normal faults, which are folded about a SW-NE–trending axis. We interpret these low-angle faults as the product of an early, NE-SW extension related to kinematically similar deformation recognized to the south of the study area. The folding of the faults postdates at least some of the extension, indicating a component of syn-exten­sional shortening that is probably strike-slip related. Approximately EW-striking sinistral faults are mapped in the northern Saddlepeak Hills. However, these faults are kinematically incompatible with the folding of the low-angle faults, suggesting that folding is related to the younger, NW-SE extension seen in the Death Valley region. Other faults in the map area include NW- and NE-striking, high-angle normal faults that crosscut the currently low-angle faults. Also, a major N-S–striking, oblique-slip fault bounds the eastern flank of the Ibex Hills with slickenlines showing rakes of <30°, which together with the map pattern, suggests dextral-oblique movement along the east front of the range. The exact timing of the normal faulting in the map area is hampered by the lack of geochronology in the region. However, based on the map relationships, we find that the older extensional phase predates an angular unconformity between a volcanic and/or sedimentary succession assumed to be 12–14 Ma based on correlations to dated rocks in the Owlshead Mountains and overlying rock-avalanche deposits with associated sedimentary rocks that we correlate to deposits in the Amargosa Chaos to the north, dated at 11–10 Ma. The mechanism behind the folding of the northern Ibex Hills, including the low- angle faults, is not entirely clear. However, transcurrent systems have been proposed to explain extension-parallel folding in many extensional terranes, and the geometry of the Ibex Hills is consistent with these models. Collectively, the field data support an old hypothesis by Troxel et al. (1992) that an early period of SW-NE extension is prominent in the southern Death Valley region. The younger NW-SE extension has been well documented just to the north in the Black Mountains, but the potential role of this earlier extension is unknown given the complexity of the younger deformation. In any case, the recognition of earlier SW-NE extension in the up-dip position of the Black Mountains detachment system indicates important questions remain on how that system should be reconstructed. Collectively, our observations provide insight into the stratigraphy of the Ibex Pass basin and its relationship to the extensional history of the region. It also highlights the role of transcurrent deformation in an area that has transitioned from extension to transtension.

scholarly journals Classification of Zagros earthquakes based on focal mechanism

2021 ◽  
Vol 51 (3) ◽  
pp. 265-275
Author(s):  
Mehdi Nouri DELOUEI ◽  
Mohammad-Reza GHEITANCHI
Keyword(s):  
Focal Mechanism ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Nodal Plane ◽  
Iranian Plateau ◽  
Populated Region ◽  
Compression Type ◽  
Selection Of

The Zagros suture zone is seismically active region in Iranian plateau. This region is of high importance in terms of seismicity, since it is a vast and populated region and in recent years the earthquakes with high intensities have frequently occurred and have caused extensive destruction and heavy human loss. The study of the focal mechanism is very important in understanding the seismotectonic characteristics. Focal mechanisms of Zagros were collected over a period of 20 years and they were classified by FMC software. Seven groups were considered for the type of faulting and Zagros was divided into three zones. For each zone, the frequency percentage of each group of faults was determined. The most of faulting are of the reverse and compression type with the strike-slip component. Finally, the role of nodal plane selection in determining the type of faulting was discussed and it was found that the selection of each nodal plane in determining the type of faulting has the same result.

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