**3.2. Triggered by the early Jurassic earthquake activities of the Talas-Ferghana strike-slip fault (TFSSF)**

#### *3.2.1. Soft-sediment deformation structures at the southeast end of TFSSF*

**Figure 3.** Sand volcano, liquefied dune, sand sheet, liquefied deformation of sand bed, triggered by May 12, 2008 Wenchuan earthquake (photographed by Li Haibing). (A) Sand volcano in the terraces of Mingjiang river; (B) liquefied sand sheets in the terraces of Mingjiang river; (C) a higher liquefied sand mounds in the Yingxiu-Beichuan fault zone; (D) liquefied sand dunes distributed in the lineal arrangement and parallel with the fault trend of the Yingxiu-Beichuan; (E) a liquefied sand and gravel mound, the gravels have been carried over the top of mound; (F) collapse sink resulted from liquefaction; (G) linear arrangement of the collapse sinks, diameter of collapse sinks are about 80–90 cm, the orientation

is also parallel to the Yingxiu-Beichuan fault, showing the orange colour dot line.

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Talas-Ferghana strike-slip fault has been active since the Mesozoic, but the initial time of strike-slip is still in dispute [42–44]. The Wuqia pull-apart basin of the Lower Jurassic was controlled by this huge fault (**Figure 5a**), with NW-trending, which is located at the southeast end of the significant Talas-Ferghana fault, SW Tianshan. Soft-sediment deformations were preserved in sandstone layers at top of the Lower Jurassic Kangsu Formation, and three earthquake-induced deformation sequences have been recognised within 10 m thickness of sandstones deposited in the lacustrine environment (**Figure 5b**). They are included as load cast, ball-and-pillow, droplet, cusps, homogeneous layer, and liquefied unconformity.

Load casts and ball-and-pillow are the main types of deformation in the third layer of SSDSs in the Kangsu formation. The parental sand layer providing load casts to subside is 80-cmthick laminated siltstone and consists of limonite debris, feldspar, quartz and muscovite. The

**Figure 4.** Sketch tectonic model of the Longmen Mountain and Sichuan Basin (modified from [47]), showing the main fault belts and 5.12 earthquake hypocentral locations and SSDS triggered by this earthquake. F1, Maoxian-Wenchuan Fault; F2, Yingxiu-Beichuan Fault; F3, Anxian-Guanxian Fault.

**Figure 5.** Geological sketch map (a) and stratigraphic column (b) showing the Wuqia Basin, southwest Tianshan Mts., Xinjiang (modified from [20, 47, 48]), and location of the SSDS in the Kangsu Formation in Jurassic. I, II and III presented the three layers of seismic events and composed a paleo-earthquake episode. The star marks the positions of these layers.

**Figure 6.** Soft-sediment deformation structures in the Kangsu Formation, Wuqia Basin, Southwest Tianshan Mountains. (A) Load cast and ball-and-pillow in the third layer of seismic event; a, b and c represent orders of load cast structures

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and-pillow (oblate ellipsoid body). (B) Load cast showing syncline-like laminated layers resulted from subsidence of sand beds. (C and D) Long section morphology of droplet and upward cusps in the first layer of seismic event; arrows

shows the intact stereo configuration of ball-

displays spindle, concentric laminae in ball-and-pillow. a4

submerged. a3

mark the directions of liquefying movement.

grain sizes range from 0.01 to 0.05 mm, with minor less than 0.5–0.1 mm, displaying distinct feature of seasonal lacustrine lamination (**Figure 6A** and **B**). The deformation structures resulted from the static pressure of the unconsolidated silt beds that were destroyed while Soft Sediment Deformation Structures Triggered by the Earthquakes: Response to the High… http://dx.doi.org/10.5772/intechopen.72941 111

**Figure 6.** Soft-sediment deformation structures in the Kangsu Formation, Wuqia Basin, Southwest Tianshan Mountains. (A) Load cast and ball-and-pillow in the third layer of seismic event; a, b and c represent orders of load cast structures submerged. a3 displays spindle, concentric laminae in ball-and-pillow. a4 shows the intact stereo configuration of balland-pillow (oblate ellipsoid body). (B) Load cast showing syncline-like laminated layers resulted from subsidence of sand beds. (C and D) Long section morphology of droplet and upward cusps in the first layer of seismic event; arrows mark the directions of liquefying movement.

grain sizes range from 0.01 to 0.05 mm, with minor less than 0.5–0.1 mm, displaying distinct feature of seasonal lacustrine lamination (**Figure 6A** and **B**). The deformation structures resulted from the static pressure of the unconsolidated silt beds that were destroyed while

**Figure 5.** Geological sketch map (a) and stratigraphic column (b) showing the Wuqia Basin, southwest Tianshan Mts., Xinjiang (modified from [20, 47, 48]), and location of the SSDS in the Kangsu Formation in Jurassic. I, II and III presented the three layers of seismic events and composed a paleo-earthquake episode. The star marks the positions of these layers.

**Figure 4.** Sketch tectonic model of the Longmen Mountain and Sichuan Basin (modified from [47]), showing the main fault belts and 5.12 earthquake hypocentral locations and SSDS triggered by this earthquake. F1, Maoxian-Wenchuan

Fault; F2, Yingxiu-Beichuan Fault; F3, Anxian-Guanxian Fault.

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shaking, and gravity differentiation took place and sands or silts (the denser material) sank into the underlying (less dense) mud beds to form load-cast structures that evolved into 'balland-pillow structures' or pseudonodules [28, 32, 35].

Droplets and cusp anticlines occurred in the first event layer, about 60-cm-thick sandstone layer, of the Kangsu formation. Droplets and cusp anticlines resulted from strongly liquidised sandstone grains migrated vertically up and down during earthquake [45]. Seventeen intensively-distributed droplets can be seen within a distance of 170 cm along the sandstone layer (**Figure 6C** and **D**). They are revealed as cylinders and drops, with elongated U-type synclines in vertical cross sections and wavy laminates, presenting the trace of liquefaction flowing. Directions of axial planes of syncline-shaped laminae in each droplet are out of order, upright, oblique and curve, suggesting that downward displacement of sand grains is random and without sliding of sand bodies on slope. Cusp anticlines are similar to diapirs in configuration of structures but different to diapiric structures. The diapiric structure refers to the underlying liquefied sand bed puncture into overlying soft sediments, while cusps are the result of liquefaction sands migrated upwards within liquefied sand layer with corn-shape body and without distinct xenolith in nucleus (**Figure 6C** and **D**). Droplets and cusp anticlines are formed under the duel effects by liquefaction and gravity. Groups of droplets resulting from superimposition of droplets and cusp anticlines resulting from upward movement of liquefying sandstone constitute multilayer complex deformation layers, which are generally explained to be triggered by earthquakes.

### *3.2.2. The activity of Talas-Ferghana strike-slip fault during the late early Jurassic*

Three deformation layers of the Kangsu formation in the Lower Jurassic in Wuqia Basin had differences of deformation mechanisms (**Figure 5b**). The first deformation layer was characterised by droplet and cusp structures resulted from vertical liquefied displacement; the second was mainly homogeneous layers of liquefied sands and local unconformity and the third was mainly load casts and ball-and-pillow resulted from the effects of gravity and seismic shaking. Therefore, three seismic events suggest that the Talas-Ferghana strike-slip fault zone occurred due to at least three times large-scale active events during the late early Jurassic, with the different paleo-stresses imposed on soft sediments and made them deformed. According to the recorded data of liquefaction of sand layers by modern earthquakes and previous earthquakes [20, 30, 46], the SSDS were 45 to 50 km away from the Talas-Ferghana fault, and Ms 6.5–7 of the paleo-earthquake magnitudes were estimated.

early Palaeozoic is the main period of development, especially in the central parts of the basin. During the first tectonic cycle, which is from the latest Neoproterozoic to the Middle Devonian, two unconformities that are Silurian/Upper Ordovician and Upper Devonian-Carboniferous/pre-Upper Devonian unconformity were formed during the middle and late Caledonian tectonic movements [49–53]. The properties of main faults changed from the normal faulting to reverse faulting during the middle Caledonian movement. The paleo-tectonic activities of this area are key issues and remain enigmatic for understanding the basin recon-

**Figure 7.** Schematic map of the structural units of the Tarim Basin, showing the location of deep drilling wells in Tazhong

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uplift and Manjiaer depression, in which various SSDSs of the Ordovician and Silurian are observed.

From the Ordovician to Silurian, the sedimentation (**Figure 8**) took place in a marine basin facies, shelf-and-platform (**Figure 8b**) and tidal-flat facies (**Figure 8a**) depositional environment in the Tazhong Uplift and the Manjiaer Depression. Various millimetre-, centimetre- and metre-scale soft-sediment deformation structures (SSDSs) have been identified in the Upper Ordovician and Lower-Middle Silurian from deep drilling cores in the Tazhong Uplift and the Manjiaer Depression (**Figure 7**). They include liquefied sand veins, liquefaction-induced breccia, boudinage-like structures, load and diapir- or flame-like structures, dish and mixed-layer structures, hydroplastic convolutions and seismic unconformities (**Figure 8**). They were commonly mistaken for worm traces, mud cracks or storm deposits since they have abrupt contacts with the surrounding sedimentary rock (according to the

structions and hydrocarbon explorations.

geological well reports).

## **3.3. Triggered by the early Palaeozoic activities of interior faults of the Tarim Basin**
