**4.1. Understanding the history of fault activities**

fissures. The fissures are filled with dark siliceous chert rock. A carbonate sand volcano also remains, which is shaped just like a small volcano with a crater (**Figure 13c**). It has a diameter of 110 cm and a thickness of about 30 cm. And a thin layer of black siliceous rock is built up in the centre of the depression. There are also at least three (possibly five) radial

Loop beddings are ductile deformation structures, which consist of lacustrine finely laminated sediments and are induced by extension stress, presented as loops or chains (**Figure 13d**), and the adjacent layers are undeformed. In the Wumishan Formation of the Mesoproterozoic near Yongding River Valley, they are formed in a deep-water carbonate platform setting and suffered the horizontal shear stress. Loop beddings can be also formed in epicontinental seas and a low energy environment below the wave base of marine settings [66, 72, 76]. It is a result of stretching from unlithified to progressively lithified laminated sediments in response to successive minor seismic shocks, ultimately related to the slow movement of extensional faults [74, 75].

The strong intrastratal folds occur in the upper part of the Zhuanghuwa section and Yongding River Valley and are about 10–20 cm thick. They are deposited in a very shallow-water depositional environment indicated by the mud cracks and ripple marks beneath this deformed layer. Plate-spine breccias are widely observed in lamellose or ribbon stripped layers of the Mesoproterozoic in the North China craton. These deformations are formed when the incomplete consolidated laminated layers experience continued compression and completely crack along the axial plane of folds. **Figure 12f** is a superimposed deformation structure of the intrastratal fold and plate-spine breccias, which are formed on two wings of folds, and the top of the fold layer without erosion looks like clouds and is covered by undeformed laminated layers. The formation mechanism of plate-spine breccias may be seismic activities [60]. Ettensohn et al. called the intense folds accordion-like folds, which are induced by earthquakes [34].

The Yanliao taphrogenic trough is a NE-trending rifting basin in the northern part of North China Craton and is open to the north [63–65]. The Shijiazhuang-Lingyuan Fault Belt (>800 km long) is the main fault belt with the NE-trending (**Figure 12B**), which is extended along the axial part of the Yan-Liao Aulacogen, activated during the early Mesoproterozoic in an extension tectonic environment [63]. The observed SSDSs are mainly distributed approximately less than 20 km from the fault in vertical distances. Identified SSDSs include intrastratal faults, liquefaction sand veins, liquefaction carbonate mounds and volcanos along the paleo-active fault belts. The SSDS layers have been interbedded by the many undeform layers. And some of them have the abnormal geochemical records such as Re, Os, Ir and other rare elements in black silty mudstones or shale of Chuanlinggou Formation that give a clue that volcanic and seismic events existed [77]. The liquefaction carbonate mounds and sand volcanos in the Mesoproterozoic have similar features which induced by the recent Wenchuan earthquake

*3.4.2. SSDSs triggered by the paleo-activity of the Shijiazhuang-Lingyuan Fault Belt*

fissures exposed, which are filled with dark siliceous material.

*3.4.1.3. Intense intrastratal folds and plate-spine breccias*

*3.4.1.2. Loop bedding*

122 Tectonics - Problems of Regional Settings

The typical cases of seismites at different times in China reveal the sequence of paleo-earthquake events, and the activities of seismogenic faults can help us understand the dynamics of tectonic developments in different regions.

Seismites research may provide geo-history evidences for active seismic fault belts. The vertical sequences of paleo-earthquakes (seismites) are separated by undeformed sedimentary layers. They will provide a history of gradual and abrupt changes of the tectonic development and evolution in a particular region and regular patterns of seismicity of this region. Correlation of the paleo-earthquake activity sequences will help us to know spatial and temporal characteristics of paleo-seismic events in the main tectonic movement. This will provide important supplementary evidences of the impulsive and cyclicity of tectonism of the main tectonic movement. And they can also provide evidences for the tectonic records during a period from 102 to 106 yr (The white paper resulting from a workshop held at Denver Colorado, 2002), which is a difficult issue in the frontier research of structural geology and tectonic science. Paleo-earthquake events will build a link between orogenesis, high-frequency tectonism (in basin-mountain system) and a seismic activity.
