The 2020 Mw 6.0 Jiashi Earthquake: A Fold Earthquake Event in the Southern Tian Shan, Northwest China

2020 ◽  
Author(s):  
Yuan Yao ◽  
Shaoyan Wen ◽  
Tao Li ◽  
Chisheng Wang
Keyword(s):  
Seismic Reflection ◽  
Fault Plane ◽  
Leading Edge ◽  
Northwest China ◽  
Coseismic Deformation ◽  
Slip Angle ◽  
Integrated Analysis ◽  
Seismogenic Structure ◽  
Seismic Reflection Profiles ◽  
Tian Shan

Abstract The complexity of the coseismic rupture process of active thrust faults and the limitation of the 3D geometry of the fault plane play important roles in seismic risk assessment. The 2020 Mw 6.0 Jiashi earthquake is an example of seismic events that have occurred in the Kepingtage fold-and-thrust belt (FTB) in the southern Tian Shan belt. Integrated analysis of surface geology, topography, and seismic reflection profiles has delineated the surface and subsurface geometries of the Keping thrust fault (KPT). Combined with the focal mechanism, seismic reflection profiles, and Interferometric Synthetic Aperture Radar coseismic deformation, we are able to reveal the seismogenic structure of this earthquake. The Jiashi event was mainly a horizontal compression deformation; the sliding distribution was concentrated at a depth of 4–6 km, and the fault-slip angle was ∼15°. Our results show that the seismogenic structure of the Jiashi event was the KPT at the leading edge of the Kepingtage FTB. The fault plane is separated at depth by a horizontal detachment, with an upper (∼30°) and lower (∼15°) ramp. The coseismic rupture of the Jiashi event was constrained within the lower ramp. This event is a good example that readily explains why the Kepingtage FTB is characterized by moderate-magnitude (Mw 6.0–6.5) events.

scholarly journals Structural controls on earthquake rupture revealed by the 2020 Mw 6.0 Jiashi earthquake (Kepingtag belt, SW Tian Shan, China)

2021 ◽  
Author(s):  
Siyu Wang ◽  
Edwin Nissen ◽  
Timothy Craig ◽  
Eric Bergman ◽  
Léa Pousse-Beltran
Keyword(s):  
Cross Sections ◽  
Surface Deformation ◽  
Coseismic Deformation ◽  
Southern Chinese ◽  
Pattern Length ◽  
Waveform Modelling ◽  
Thrust Sheets ◽  
Dip Angle ◽  
Seismic Reflection Profiles ◽  
Tian Shan

The Kepingtag (Kalpin) fold-and-thrust belt of the southern Chinese Tian Shan is characterized by active shortening and intense seismic activity. Geological cross-sections and seismic reflection profiles suggest thin-skinned, northward-dipping thrust sheets detached in an Upper Cambrian décollement. The January 19 2020 Mw 6.0 Jiashi earthquake provides an opportunity to investigate how coseismic deformation is accommodated in this structural setting. Coseismic surface deformation resolved with Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) is centered on the back limb of the frontal Kepingtag anticline. Elastic dislocation modelling suggests that the causative fault is located at ~7 km depth and dips ~7° northward, consistent with the inferred position of the décollement. The narrow slip pattern (length ~37 km but width only ~9 km) implies that there is a strong structural or lithological control on the rupture extent, with up-dip slip propagation possibly halted by an abrupt change in dip angle where the Kepingtag thrust is inferred to branch off the décollement. A depth discrepancy between mainshock slip constrained by InSAR and teleseismic waveform modelling (~7 km) and well-relocated aftershocks (~10-20 km) may imply that sediments above the décollement are velocity strengthening. We also relocate 148 regional events from 1977 to 2020 to characterize the broader distribution of seismicity across the Kepingtag belt. The calibrated hypocenters combined with previous teleseismic waveform models show that thrust and reverse faulting earthquakes cluster at relatively shallow depths of ~7-15 km but include abundant out-of-sequence events both north and south of the frontal Kepingtag fault.

scholarly journals Spatial Relationships between Pockmarks and Sub-Seabed Gas in Fjordic Settings: Evidence from Loch Linnhe, West Scotland

Geosciences ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 283
Author(s):  
Allan Audsley ◽  
Tom Bradwell ◽  
John Howe ◽  
John Baxter
Keyword(s):  
Water Column ◽  
Seismic Reflection ◽  
Hot Spot ◽  
Geophysical Data ◽  
Spatial Relationships ◽  
Hydrocarbon Gases ◽  
Offshore Industry ◽  
Seismic Reflection Profiles ◽  
Spot Analysis ◽  
Sedimentary Carbon

Sub-seabed gas is commonly associated with seabed depressions known as pockmarks—the main venting sites for hydrocarbon gases to enter the water column. Sub-seabed gas accumulations are characterized by acoustically turbid or opaque zones in seismic reflection profiles, taking the form of gas blankets, curtains or plumes. How the migration of sub-seabed gas relates to the origin and distribution of pockmarks in nearshore and fjordic settings is not well understood. Using marine geophysical data from Loch Linnhe, a Scottish fjord, we show that shallow sub-seabed gas occurs predominantly within glaciomarine facies either as widespread blankets in basins or as isolated pockets. We use geospatial ‘hot-spot’ analysis conducted in ArcGIS to identify clusters of pockmarks and acoustic (sub-seabed) profile interpretation to identify the depth to gas front across the fjord. By combining these analyses, we find that the gas below most pockmarks in Loch Linnhe is between 1.4 m and 20 m deep. We anticipate that this work will help to understand the fate and mobility of sedimentary carbon in fjordic (marine) settings and advise offshore industry on the potential hazards posed by pockmarked seafloor regions even in nearshore settings.

scholarly journals Inverted Basins by Africa–Eurasia Convergence at the Southern Back-Arc Tyrrhenian Basin

Geosciences ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 117
Author(s):  
Maria Filomena Loreto ◽  
Camilla Palmiotto ◽  
Filippo Muccini ◽  
Valentina Ferrante ◽  
Nevio Zitellini
Keyword(s):  
Seismic Reflection ◽  
Magnetic Data ◽  
Normal Faults ◽  
Sedimentary Sequence ◽  
Initiation Zone ◽  
Arc Setting ◽  
Seismic Reflection Profiles ◽  
Back Arc ◽  
Flower Structures ◽  
Tyrrhenian Basin

The southern part of Tyrrhenian back-arc basin (NW Sicily), formed due to the rifting and spreading processes in back-arc setting, is currently undergoing contractional tectonics. The analysis of seismic reflection profiles integrated with bathymetry, magnetic data and seismicity allowed us to map a widespread contractional tectonics structures, such as positive flower structures, anticlines and inverted normal faults, which deform the sedimentary sequence of the intra-slope basins. Two main tectonic phases have been recognised: (i) a Pliocene extensional phase, active during the opening of the Vavilov Basin, which was responsible for the formation of elongated basins bounded by faulted continental blocks and controlled by the tear of subducting lithosphere; (ii) a contractional phase related to the Africa-Eurasia convergence coeval with the opening of the Marsili Basin during the Quaternary time. The lithospheric tear occurred along the Drepano paleo-STEP (Subduction-Transform-Edge-Propagator) fault, where the upwelling of mantle, intruding the continental crust, formed a ridge. Since Pliocene, most of the contractional deformation has been focused along this ridge, becoming a good candidate for a future subduction initiation zone.

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