(1) uplift structure

This is a structure formed by a wide range of lifting movements. The area can reach hundreds of square kilometers or more. There is little difference within the structure, but the movement of the nucleus is usually the largest. Such structures are often accompanied by fault structures, or compensatory grabens are formed in the core or Hebei. Others form monoclinic uplift (Figure 10-4). For example, Ordos Plateau in China is a typical arched uplift structure (Figure 10-5).

(2) Depression structure

The structure formed by long-term downward movement in a large area is opposite to the direction of large-scale uplift. This structure is mainly identified by analyzing the Neogene-Quaternary sedimentary thickness isoline of the plain (or basin) or the paleotopography fluctuation buried above the strata. According to the variation of sedimentary thickness in most plains (or basins), the edge of such structures is sometimes accompanied by faults on both sides, sometimes without faults on one side, or controlled by a series of faults. The sedimentary thickness varies greatly in the vertical direction of the fault, and the basement is uneven. Some sediments along the fault side are very thick. According to the new sedimentary thickness change controlled by the basement fault in the plain (or basin), a series of secondary concavities and convexities can be divided (Figure 10-6).

Figure 10-4 Schematic Diagram of Large Area Arch Structure

(Quoted from Beijing Institute of Geology, Regional Geology of China, 1963)

(a) Simple arched uplift; (b) Inclined or monoclinic fault block uplift; (c) The edge of the arch uplift is accompanied by fracture; (d) block uplift; (e) and (f) compensatory graben; (g) undulated uplift

Figure 10-5 schematic diagram of Ordos arch uplift

(Quoted from Beijing Institute of Geology, Regional Geology of China, 1963)

1-neotectonic movement amplitude; 2- Deep faults and speculation in Neotectonic period; 3- Faults and speculation in Neotectonic period; 4- a basin with relative depression in the uplift part; 5- The epicenter of a strong earthquake

Figure 10-6 Common Neotectonic Depression and Settlement Center in Plain (great basin)

(a) uniform depressions; Graben depression; Asymmetric depression; (d) Composite depression (including secondary concave and convex), in which the thickness change of Neogene-Quaternary sediments filled reflects the characteristics of the depression. The arrow indicates the subsidence center of N→Q, F is the fault, and the diagonal line is the pre-Neogene (Neogene) stratum.

(3) Fault block structure

Fault block structure refers to the geomorphological structure form of basins and ridges that alternate with neotectonic movement. Compared with large-scale uplift, two adjacent fault blocks in fault block structure have obvious differences in topographic height and sedimentation. Most of this structure is developed on the basis of the old fault block structure. According to the height and sedimentary differences of adjacent fault blocks, there are two basic types of fault block structures:

1. Strong difference fault block structure

The landform height and sedimentary conditions of two adjacent fault blocks are very different, and the displacement of the fault blocks is very large (Figure 10-7a). Qilian Mountain in China is a typical structure of this type. There are planation planes in different periods of the peak uplift; Or different heights after the planation plane breaks in the same period. Thick or extremely thick Quaternary sediments are accumulated in intermountain basins and piedmont. Fault cliffs or fault line landforms can be seen everywhere.

2. Weak difference fault block structure

The displacement of two adjacent fault blocks is small, and the movement amplitude is small, but volcanic activity, hot springs and earthquakes often occur along the fault zone (Figure 10-7b), indicating that the activity of fault blocks mainly has the characteristics of "fault structure". For example, in the southwest of Xiaoxing 'anling, the landform is not obvious, but the Quaternary sandy volcanic group, Wudalianchi volcanic group, Jianshan volcanic group and Erguangshan volcanic group develop along the fault direction.

Figure 10-7 Schematic Diagram of Fault Block Structure

(Quoted from Beijing Institute of Geology, Regional Geology of China, 1963)

(a) Differential fault block structure; (b) fracture structure

(4) Compressive folds and fault structures

In Neogene and Quaternary sedimentary basins, a series of small-scale compressional folds and reverse faults often appear at the edge of the basin due to the compression during the Neotectonic period in the mountains (Figure 10-8).

Figure 10-8 compressive fold structure

(Quoted from Beijing Institute of Geology, Regional Geology of China, 1963)

(5) Active faults

1. The concept of active fault

Scholars at home and abroad have given many definitions of the concept of active fault. These definitions all emphasize the modern and modern activity of active faults, but they are different in the specific time limit of active faults. To sum up, these definitions can be divided into the following opinions: ① 1 ten thousand years, that is, since Holocene; ② Since the Late Quaternary; ③ Since the Quaternary; (4) There is no need to give rigid rules, and some time attributes should be added to active faults if necessary, such as since Neogene, Quaternary and Holocene. Considering the particularity of long-term tectonic movement and Quaternary crustal movement (strong climate change, strong crustal movement, accompanying glacier balance, water balance change and the resulting mantle flow, etc. Chinese scholars define the time limit of active faults as Quaternary, that is, active faults that have been active since Quaternary, are currently active or intermittently active, and have potential for future activities are called active faults.

Active faults can leave a variety of signs of activity, which can be manifested not only in geology and geomorphology, but also in earthquake activity, and also cause geophysical and geochemical anomalies. Through these marks, we can understand the active process and trend of active faults. With the diversification of research methods and the enrichment of data, the research on active faults is gradually developing from qualitative research to quantitative research. The related contents are more and more extensive, including not only important theoretical problems in geology, seismology and geodynamics, but also many practical problems such as large-scale engineering facilities city construction, earthquake risk zoning and earthquake prediction, which makes the study of active faults a very attractive research field in geosciences.

2. Main active faults in China.

Active faults are extremely developed in China (Figure 10-9). With the north-south belt as the boundary, a series of nearly east-west faults and NWW-NW, Nee-NE thrust-slip giant active fault zones are formed in the west, and small near-SN- trending normal faults or strike-slip normal faults are developed. The displacement rate of faults in the west is mostly above 6 mm/a, and the east is characterized by NNE-NE strike-slip normal faults or the combination of normal strike-slip faults and NWW-NW strike-slip faults. The displacement rate of the eastern fault is below 5 mm/a, and the active faults in the southeast coastal continental margin gradually change from NNE to NE-Nee from Taiwan Province Province to Fujian and Guangdong, and the earthquake magnitude tends to decrease in this direction. The faults are mainly left-handed strike-slip normal faults, and the NW-trending faults with yokes are mostly normal faults or normal strike-slip faults, but they are small in scale and do not extend far.