Geological mapping of the 1985 Chinese—British Tibetan (Xizang—Qinghai) Plateau Geotraverse route

1988 ◽  
Vol 327 (1594) ◽  
pp. 287-305 ◽  
Keyword(s):  
Strike Slip ◽  
Geological Mapping ◽  
Strike Slip Fault ◽  
Fault System ◽  
Late Triassic ◽  
Clastic Rocks ◽  
The North ◽  
Opposite Sequence ◽  
Geological Map ◽  
Qiangtang Terrane

The 1:500,000 coloured geological map of the traverse route combines observations from the Geotraverse, previous mapping, and interpretation of orbital images. The position of all localities visited by Geotraverse participants and basic geological data collected by them along the traverse route are shown on a set of maps originally drawn at 1:100,000 scale, reproduced on microfiche for this publication. More detailed mapping, beyond a single line of section, was achieved in five separate areas. The relationships between major rock units in these areas, and their significance, are outlined in this paper. Near Gyanco, (Lhasa Terrane) an ophiolite nappe, apparently connected with outcrops of ophiolites in the Banggong Suture about 100 km to the north, was under thrust by a discontinuous slice of Carboniferous—Permian clastic rocks and limestone, contrary to a previous report of the opposite sequence. At Amdo, a compressional left-lateral strike-slip fault zone has modified relationships along the Banggong Suture. Near Wuli, (northern Qiangtang Terrane) limited truncation of Triassic strata at the angular unconformity below Eocene redbeds demonstrates that most of the folding here is of Tertiary age. The map of the nearby Erdaogou region displays strong fold and thrust-shortening of the Eocene redbeds, evidence of significant crustal shortening after the India- Asia collision began. In the Xidatan-Kunlun Pass area, blocks of contrasting Permo—Triassic rocks are separated by east-trending faults. Some of these faults are ductile and of late Triassic — early Jurassic age, others are brittle and part of the Neogene—Quaternary Kunlun leftlateral strike-slip fault system. Some more significant remaining problems that geological mapping might help to solve are discussed briefly, including evidence for a possible additional ophiolitic suture within the Qiangtang Terrane.

The geometry of the North Anatolian transform fault in the Sea of Marmara and its temporal evolution: implications for the development of intracontinental transform faults

2014 ◽  
Vol 51 (3) ◽  
pp. 222-242 ◽  
Author(s):  
A.M. Celâl Şengör ◽  
Céline Grall ◽  
Caner İmren ◽  
Xavier Le Pichon ◽  
Naci Görür ◽  
...  
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Strike Slip ◽  
North Anatolian Fault ◽  
Strike Slip Fault ◽  
Fault System ◽  
Transform Fault ◽  
Sea Of Marmara ◽  
The North ◽  
Macro Scale

The North Anatolian Fault is a 1200 km long strike-slip fault system connecting the East Anatolian convergent area with the Hellenic subduction zone and, as such, represents an intracontinental transform fault. It began forming some 13–11 Ma ago within a keirogen, called the North Anatolian Shear Zone, which becomes wider from east to west. Its width is maximum at the latitude of the Sea of Marmara, where it is 100 km. The Marmara Basin is unique in containing part of an active strike-slip fault system in a submarine environment in which there has been active sedimentation in a Paratethyan context where stratigraphic resolution is higher than elsewhere in the Mediterranean. It is also surrounded by a long-civilised rim where historical records reach well into the second half of the first millennium BCE (before common era). In this study, we have used 210 multichannel seismic reflexion profiles, adding up to 6210 km profile length and high-resolution bathymetry and chirp profiles reported in the literature to map all the faults that are younger than the Oligocene. Within these faults, we have distinguished those that cut the surface and those that do not. Among the ones that do not cut the surface, we have further created a timetable of fault generation based on seismic sequence recognition. The results are surprising in that faults of all orientations contain subsets that are active and others that are inactive. This suggests that as the shear zone evolves, faults of all orientations become activated and deactivated in a manner that now seems almost haphazard, but a tendency is noticed to confine the overall movement to a zone that becomes narrower with time since the inception of the shear zone, i.e., the whole keirogen, at its full width. In basins, basin margins move outward with time, whereas highs maintain their faults free of sediment cover, making their dating difficult, but small perched basins on top of them in places make relative dating possible. In addition, these basins permit comparison of geological history of the highs with those of the neighbouring basins. The two westerly deeps within the Sea of Marmara seem inherited structures from the earlier Rhodope–Pontide fragment/Sakarya continent collision, but were much accentuated by the rise of the intervening highs during the shear evolution. When it is assumed that below 10 km depth the faults that now constitute the Marmara fault family might have widths approaching 4 km, the resulting picture resembles a large version of an amphibolite-grade shear zone fabric, an inference in agreement with the scale-independent structure of shear zones. We think that the North Anatolian Fault at depth has such a fabric not only on a meso, but also on a macro scale. Detection of such broad, vertical shear zones in Precambrian terrains may be one way to get a handle on relative plate motion directions during those remote times.

scholarly journals Revealing the earthquake history during the last 200 ka on a large submarine strike-slip fault: The Yusuf Fault System (Alboran Sea)

2020 ◽  
Author(s):  
Hector Perea ◽  
Eulàlia Gràcia ◽  
Stefanie Almeida ◽  
Laura Gómez de la Peña ◽  
Sara Martínez-Loriente ◽  
...  
Keyword(s):  
Complex Structure ◽  
Strike Slip ◽  
Strike Slip Fault ◽  
Fault System ◽  
Alboran Sea ◽  
North African ◽  
The South ◽  
Active Structures ◽  
The North ◽  
Alborán Sea

<p>The NW-SE convergence (4-5 mm/yr) between the African and Eurasian plates controls the present-day crustal deformation in the Alboran Sea (westernmost Mediterranean). Although seismic activity is mainly characterized by low to moderate magnitude events, large and destructive earthquakes (I > IX) have occurred in this region (i.e., 1522 Almeria, 1790 Oran, 1910 Adra, 1994 and 2004 Al-Hoceima or 2016 Al-Idrissi earthquakes). The identification and the seismogenic characterization of the active structures in the Alboran Sea using ultra high-resolution (UHR) geophysical data is essential to evaluate better the exposure of the South Iberian Peninsula and North African coasts to related natural hazards (i.e., large earthquakes and related tsunamis and triggered landslides). During the SHAKE cruise, the Asterx and Idefx AUVs (Ifremer, france) were used to acquire UHR bathymetric (1m grid) and seismic (cm vertical resolution) data across the main active faults systems in the Alboran Sea with the aim to carry out sub-aqueous paleoseismological studies. One of the studied active structures has been the Yusuf Fault System (YFS), a dextral strike-slip system that is one of the largest structures in the Alboran Sea and a lithospheric boundary between different crustal domains: the East Alboran Basin to the north and the North African Margin to the south. It trends WNW-ESE, is ~150 km-long and can be divided into two main segments (W and E), producing the formation of a pull-apart basin where both overlap. The analysis of the UHR geophysical dataset reveals that in the imaged area this system is a complex structure composed by an array of strike-slip faults. Most of them reach up and offset the seafloor and the upper Pleistocene to Holocene sedimentary units. The results of the on-fault paleoseismological analyses reveal that the YFS may have generated at least 8 earthquakes in recent times. Although a detailed on-site geochronology is not available, a regional chronostratigraphic correlation have allowed estimating that the events have occurred during the last 200 ka, then providing an average recurrence interval of 27.5 ka. The estimated average vertical offset is about 0.64 m while the vertical slip-rate would be around 0.03 mm/yr. However, this value needs to be considered as a minimum since YFS is predominantly a strike-slip fault and the lateral slip will be much larger than the vertical one. According to different empirical relationships, the YFS could produce earthquakes above magnitude M<sub>w </sub>7.0. Finally, our results demonstrate that detailed geomorphological, active tectonic and paleoseismological studies are essential to reveal the present-day activity and to characterize the seismic behavior of the YFS, with crucial implications for seismic (and tsunami) hazard assessment in the surrounding coastal areas.</p>

Analyses des contraintes par méthodes graphiques dans une zone de coulissage : exemple de la région de Matapédia, Gaspésie, Appalaches du Québec

1993 ◽  
Vol 30 (3) ◽  
pp. 591-602 ◽  
Author(s):  
Claude Trudel ◽  
Michel Malo
Keyword(s):  
Cross Sections ◽  
Shear Zones ◽  
Strike Slip ◽  
Geological Mapping ◽  
Fault System ◽  
Upper Ordovician ◽  
The North ◽  
Principal Compressive Stress ◽  
Ground Faults ◽  
Dextral Strike Slip

The north-northeast trending Sellarsville and Rafting Ground faults are southeasterly directed Acadian (Devonian) thrusts in the Québec Appalachians. They are located at the western end of the Grand Pabos fault system, a dextral strike-slip fault system that transects Upper Ordovician to Lower Devonian sedimentary rocks in the southern Gaspé Peninsula. The structural analysis of mesoscopic brittle and brittle–ductile shear zones by graphical methods was used to determine the stress field related to these two faults. The attitude of slip lines was calculated when the slickenside striations were not observed on the movement plane. Conjugate faults, Arthaud's method, and Angelier and Mechler's method were used to determine the paleostress. The maximum principal compressive stress σ1, always subhorizontal and striking west-northwest – east-southeast, is perpendicular to the Sellarsville and Rafting Ground faults and was probably the cause of the thrusting motion along the faults. North-northeast-trending regional folds and cleavage could also be related to this same stress. Geological mapping and structural cross sections confirm the southeasterly directed thrust motions, which are well integrated in the Grand Pabos fault system. Sellarsville and Rafting Ground faults with the Restigouche fault may represent a leading contractional imbricate fan in a dextral strike-slip system. [Journal Translation]

Is the North Altyn fault part of a strike-slip duplex along the Altyn Tagh fault system?

Geology ◽  
2000 ◽  
Vol 28 (3) ◽  
pp. 255 ◽  
Author(s):  
Eric Cowgill ◽  
An Yin ◽  
Wang Xiao Feng ◽  
Zhang Qing
Keyword(s):  
Strike Slip ◽  
Fault System ◽  
Altyn Tagh Fault ◽  
The North ◽  
Altyn Tagh

Inversion of regional surface-wave spectra for source parameters of aftershocks from the 1992 Petrolia earthquake sequence

1995 ◽  
Vol 85 (3) ◽  
pp. 705-715
Author(s):  
Mark Andrew Tinker ◽  
Susan L. Beck
Keyword(s):  
Surface Wave ◽  
Focal Mechanism ◽  
Source Parameters ◽  
Strike Slip ◽  
Earthquake Sequence ◽  
Fault System ◽  
Accretionary Wedge ◽  
Wave Spectra ◽  
The North ◽  
Gorda Plate

Abstract Regional distance surface waves are used to study the source parameters for moderate-size aftershocks of the 25 April 1992 Petrolia earthquake sequence. The Cascadia subduction zone had been relatively seismically inactive until the onset of the mainshock (Ms = 7.1). This underthrusting event establishes that the southern end of the North America-Gorda plate boundary is seismogenic. It was followed by two separate and distinct large aftershocks (Ms = 6.6 for both) occurring at 07:41 and 11:41 on 26 April, as well as thousands of other small aftershocks. Many of the aftershocks following the second large aftershock had magnitudes in the range of 4.0 to 5.5. Using intermediate-period surface-wave spectra, we estimate focal mechanisms and depths for one foreshock and six of the larger aftershocks (Md = 4.0 to 5.5). These seven events can be separated into two groups based on temporal, spatial, and principal stress orientation characteristics. Within two days of the mainshock, four aftershocks (Md = 4 to 5) occurred within 4 hr of each other that were located offshore and along the Mendocino fault. These four aftershocks comprise one group. They are shallow, thrust events with northeast-trending P axes. We interpret these aftershocks to represent internal compression within the North American accretionary prism as a result of Gorda plate subduction. The other three events compose the second group. The shallow, strike-slip mechanism determined for the 8 March foreshock (Md = 5.3) may reflect the right-lateral strike-slip motion associated with the interaction between the northern terminus of the San Andreas fault system and the eastern terminus of the Mendocino fault. The 10 May aftershock (Md = 4.1), located on the coast and north of the Mendocino triple junction, has a thrust fault focal mechanism. This event is shallow and probably occurred within the accretionary wedge on an imbricate thrust. A normal fault focal mechanism is obtained for the 5 June aftershock (Md = 4.8), located offshore and just north of the Mendocino fault. This event exhibits a large component of normal motion, representing internal failure within a rebounding accretionary wedge. These two aftershocks and the foreshock have dissimilar locations in space and time, but they do share a north-northwest oriented P axis.

Secondary faulting near the terminus of a seismogenic strike-slip fault: Aftershocks of the 1976 Guatemala earthquake

1979 ◽  
Vol 69 (2) ◽  
pp. 427-444
Author(s):  
C. J. Langer ◽  
G. A. Bollinger
Keyword(s):  
Focal Mechanism ◽  
Linear Trend ◽  
Strike Slip ◽  
Strike Slip Fault ◽  
Aftershock Activity ◽  
Focal Mechanism Solutions ◽  
The North ◽  
Composite Focal Mechanism ◽  
Theoretical Pattern ◽  
Main Fault

abstract Aftershocks of the February 4, 1976 Guatemalan earthquake (Ms = 7.5) were monitored by a network of portable seismographs from February 9 to February 27. Although seismic data were obtained all along the 230-km surface rupture of the causal Motagua fault, the field program was designed to concentrate on the aftershock activity at the western terminus of the fault. Data from that locale revealed several linear or near-linear trends of aftershock epicenters that splay to the southwest away from the western end of the main fault. These trends correlate spatially with mapped surface lineaments and, to some degree, with ground breakage patterns near Guatemala City. The observed splay pattern of aftershocks and the normal-faulting mode of the splay earthquakes determined from composite focal mechanism solutions, may be explained by a theoretical pattern of stress trajectories at the terminus of a strike-slip fault. Composite focal mechanism solutions for aftershocks located on or near the surface break of the Motagua fault, to the north and east of the linear trend splay area, agree with the mapped surface movements, i.e., left-lateral strike-slip.

Sign in / Sign up

Export Citation Format

Share Document