The period from the middle Neoarchean period (Fuping movement 2600Ma) to the middle Neoproterozoic period in Shandong Province is the stage when the continental crust consolidated to form a stable block and developed to rigidity. In the early Sinian, the whole region was still in a stable uplift stage, and only the Yishu Strait area sank and accepted marine deposits. From the Late Sinian to the Early Cambrian, it accepted the epicontinental marine deposits in North China. The early Ordovician was a NE-trending fault, which made Yantai-Qingdao area land. In the Late Ordovician, Shandong was upgraded to the ancient land of North China, which lasted until the Early Carboniferous. During this period, under the influence of Caledonian tectonic movement, CAMBRIAN-Ordovician carbonate rocks experienced paleokarst, which is also a period when paleokarst generally developed in North China.

In the Late Carboniferous, the NE-trending ancient land appeared in Qingdao, while other areas in Shandong were still coastal areas and shallow seas in North China. In the early Permian, Qingdao-Yantai area was mountainous, while other areas were North China basin, which was deposited by land and sea, containing coal, detritus and carbonate rocks. Until the late Permian, it was still the North China basin and the ancient land, and the inland basin was fluvial and lacustrine deposits. In the early Triassic, Yantai-Jinan southeast was an ancient land, and other areas were the North China Basin. In the late Middle Triassic, it rose to the North China Plateau. Until the early Cretaceous, Shandong still belonged to the North China Plateau, but Qingdao and some Jiaozhou Bay became inland basins. In the Late Cretaceous, Shandong belonged to the North Jiangsu Basin and the North China Basin. In Paleogene, the northern Jiangsu basin shrank and the northern China basin expanded; In Neogene, the North China Basin was connected with the North Jiangsu Basin, forming a horseshoe-shaped offshore basin with fluvial and lacustrine deposits in the north-southwest-southeast area of Jinan.

In the early Pleistocene, Shandong was still a basin with river gravel deposits and freshwater lake facies deposits. In the late Pleistocene, Qingdao-Yantai-Jinan was an ancient land, and other areas were alternately deposited by land and sea.

Judging from the evolution process of the above geological environment, Taishan complex was deposited in Proterozoic, and igneous rocks were generated. Debris-carbonate rocks were widely developed from Cambrian to Middle Ordovician, and then rose to land, but paleokarst developed to late Carboniferous. Then subsidence and uplift occurred in Shandong area, resulting in the differentiation of ancient land basins, but shallow seas and coastal basins were widely distributed, and Yantai-Qingdao area became land for a long time.

At present, the landscape of Shandong Peninsula, which is mainly controlled by structural factors, is shown in Figure 4.

2. Stability analysis of crustal structure around Bohai Sea.

The earth has four layers: lithosphere, hydrosphere, atmosphere and biosphere. Lithosphere mainly refers to the outermost solid crust of the earth. How thick is the lithosphere and where is the interface? This kind of understanding develops with the deepening of people's understanding of the earth. 1909 found that there is an interface more than 50 kilometers underground in southern Europe, called Moho surface, which is also regarded as the bottom boundary of the crust. Below the Moho surface, it is considered as the mantle. The early crust is also divided into silicon-aluminum layer and silicon-magnesium layer. At 1925, between the bottom of sedimentary rock and Moho surface, an interface with obvious change of seismic wave velocity, called Conrad surface, was found as the boundary between silicon-aluminum layer and silicon-magnesium layer. In the past, the lower boundary of lithosphere was also set on Moho surface. Since the 1960s, a lot of geophysical exploration data have proved the analysis of B.Gutenberg (Birch, 1952) in the 1920s, and it is considered that there is a low-velocity seismic layer in the range of 100 ~ 200 km below the surface. In the past, it was thought that the crustal thickness of the Qinghai-Tibet Plateau (above Moho) was 60 kilometers, that of the plain area was 20-40 kilometers, and that of the ocean basin was only 5-8 kilometers. At the ridge, a large amount of mantle material upwelling. Later seismic wave velocity data show that there is something softer than the upper and lower rocks in the range of 60 ~ 250 km, and that is the asthenosphere. The upper limit of asthenosphere is the upper limit of low velocity layer, which is also an interface of upper mantle. At present, most scholars also regard it as the lower limit of the lithosphere. The thickness of asthenosphere is still inconclusive. There is a three-phase flow composed of solid, liquid and gas in the asthenosphere, which is closely related to the formation of mineral resources and the occurrence of geological disasters. The asthenosphere structure is shown in Figure 5 (Lu Yaoru, 1999).

The temperature gradient below Moho surface is 12℃/km, and the temperature of Moho surface is about 500 ~ 700℃. The open system on the asthenosphere is exposed to the seabed. According to the study of magma eruption in Hawaii and other places, the temperature of basalt from deep underground reaches 1200 ~ 1300℃. Primary magma is formed at 50 ~ 200 km, which is the active position of asthenosphere. The asthenosphere is the birthplace of large-scale magmatic activities, and the global submarine expansion movement shows the role of the asthenosphere. The heat of the asthenosphere comes from the transformation of radioactive elements, as well as from the thermal diffusion, thermal convection and heat conduction of the mantle. The matter in the asthenosphere comes from the water and volatile matter differentiated from the lower mantle, and also from the bottom of the orogenic belt, that is, the internal erosion of the lithosphere boundary by the asthenosphere, which makes the lithosphere eroded and melted and become a part of the asthenosphere. The thickness of eroded and melted lithospheric objects is estimated to be several hundred kilometers, and the lithosphere drifts on the asthenosphere in a state of high temperature melting, which is the mechanism of lithospheric plate movement. According to the principle of balance, mountains and thick lithosphere will sink more into the asthenosphere (similar to Archimedes principle). In this way, the inner interface between asthenosphere and lithosphere will inevitably melt and erode. The interaction between lithosphere and asthenosphere makes the flow field of gas-liquid-solid three-phase flow constantly change, and the seabed expansion and volcanic eruption lead to the constant change of asthenosphere and lithosphere, forming a balanced-unbalanced-balanced-unbalanced circulation state, which leads to a series of active geological processes and changes in hydrogeological conditions.

The main mineral components in the asthenosphere are olivine, plagioclase, clinopyroxene and garnet. The lithosphere produces different minerals at different depths and pressures. The continental lithosphere is thicker than the oceanic lithosphere, averaging 120km. Continental basaltic magma is mainly formed in the asthenosphere of 100 ~ 150 km.

The interface between the lower asthenosphere and the lower mantle has not yet been determined. The upper mantle viscosity is1020 ~1021MPa s (mccon-nell, 1968), and the lower mantle viscosity is estimated to be 1022 ~ 1028. The differentiation of the lower mantle provides water and volatiles for the asthenosphere, which leads to low viscosity and increased fluidity of the asthenosphere. On the other hand, the matter in the asthenosphere can also sink into the lower mantle, which is divided into metal sulfides and oxides, and the composition of magnesium and nickel at the bottom increases. Due to the uneven accumulation of deep heavy materials during the evolution of the earth, the lower mantle is also the source of deposit elements. The ferromagnesium silicate minerals in the lower mantle gradually changed from sparse stacking structure to dense stacking structure, and high-pressure oxides such as MgO, FeO and SiO2 _ 2 were generated. The upward migration of these components closely affects the rock changes of carbonate rocks, such as dolomitization and silicification (Niu Wen Yuan,1981; Linwood, 198 1).

Fig. 4 Geomorphology Diagram of Shandong Peninsula Urban Agglomeration Area (provided by Shandong Provincial Department of Land and Resources)

Fig. 5 Schematic diagram of asthenosphere structure (according to Lu Yaoru, 1999)

In the orogenic belt where mountains collide with plates, because the lithosphere sinks deeply into the asthenosphere, the three-phase flow (solid, liquid and gas) in the asthenosphere is blocked. Under high temperature and high pressure, the interior of the lithosphere is eroded, and some of it is solid flow, which increases the viscosity and also produces internal adsorption to the adjacent areas. Internal proliferation increases the thickness of the earth's crust, which correspondingly causes the immersion of the earth's crust, resulting in settlement and subsidence. This three-phase flow is an important reason for structural changes and crustal rise and fall, and it is also the birthplace of volcanic eruptions, earthquakes and other disasters.

The Moho depth around Bohai Sea has little change (Tian Depei, 2005), and the Moho depth in Shandong Peninsula is about 30km, indicating that the three-phase flow active zone in the crust in this area is shallow. See Figure 6 for Moho isobath around Bohai Sea.

See Figure 7 for the distribution of structural zones around Bohai Sea.

3. Analysis of crustal structure and crustal stability in Shandong Peninsula urban agglomeration area.

The last section outlined the evolution of geological environment and tectonic movement in Shandong. It should be emphasized that the influence of Yanshan Movement in Shandong is also remarkable. After Cretaceous, basin-land changes have taken place, and many fault structures have been inherited and developed, resulting in new structural characteristics. The Tan-Lu fault zone is the most important active fault zone for Shandong Province, especially for the peninsula urban agglomeration.

The Tancheng-Lujiang fault zone is a fault zone between Tancheng and Lujiang, and it is a giant fault zone in the eastern continental margin of China, with a general direction of NNE and a total length of more than 2,400 kilometers. The fault zone spans Hebei-Hei Block in Northeast China, North China Plate and Dabie Mountain-Sulu Structural Belt, and has different evolutionary histories. Its formation and evolution are closely related to sedimentary lithofacies, paleogeographic environment, magmatism, metal minerals and oil and gas fields in eastern China since Mesozoic. The Tancheng-Lujiang fault zone occurred in the process of splicing the North China plate and the South China plate at the end of Indosinian, and the fault zone is mainly characterized by sinistral ductile shear deformation of the middle and lower crust. Yanshan period is its main active period.

Fig. 6 contour map of Moho depth around Bohai Sea (according to Tian Depei, 2005)

Fig. 7 Distribution map of active tectonic zones around Bohai Sea (according to Tian Depei, 2005)

The Tanlu fault zone actually starts from the north bank of the Yangtze River in Wuxue, Hubei (formerly known as Guangji), passes through Susong, Buried Hill, Lujiang and Jiashan in Anhui, Sihong and Suqian in Jiangsu, Tancheng, Yishui and Weifang in Shandong, passes through Bohai Bay, passes through three northeastern provinces, and reaches Xunke in Heilongjiang, and enters Russian territory. The Tanlu fault zone can be divided into three sections: the northern section is characterized by branch faults, including Dunhua-Mishan fault, Yilan-Yitong fault, Dongxunke fault and Sunwu fault in Songliao Plain; The middle section is Yishu fault, which consists of four roughly parallel main faults (Figure 8); In the southern section, Jiashan-Lujiang fault and Wuhe-Hefei fault constitute the east-west main faults.

The middle section of the Tan-Lu fault zone consists of four roughly parallel main faults, which are Changyi-Dadian fault zone, Anqiu-Juxian fault zone, Yishui-Tangtou fault zone and Tang Wu-Gegou fault zone in turn from east to west. The paleostress value σ 1-σ 3 of the Tan-Lu fault zone measured by predecessors is 29. 1 ~ 176.3 MPa. The paleostress value of ductile deformation in the Tanlu fault zone and its adjacent area is 40. 35 ~ 1 18.83 MPa. σ 1-σ 3 of other famous active fault zones at home and abroad is 20 ~ 150 MPa (USA, France, Australia, Scotland, etc. (Wang Xiaofeng, 2002).

The Tan-Lu fault zone is mainly brittle fracture or brittle deformation after ordinary ductile deformation in the early stage (before Yanshanian) (after Yanshanian). The values of tectonic principal stress at different stages of rock deformation in the Tan-Lu fault zone are estimated to be 565,438+0.3 ~ 65,438+092.8 MPa and the compressive strength is 87. 6 ~240.7MPa。 The principal stress direction σ 1 of the ductile deformation of the Tan-Lu fault zone is shown in table 1.

In addition to the influence of the Tancheng-Lujiang fault zone, the whole Shandong Province is influenced by the secondary structural units, such as Huabei Depression, Luxi Uplift, Ludong Uplift and Jiaonan-Weihai Orogenic Belt.

4. Overview of seismic activity

To sum up, the Tancheng-Lujiang fault zone was still active in Holocene, concentrated in Shang Ling, Juxian County to Sunpai, Sihong County, with a total length of about 200km, in which the F5 fault suffered an earthquake of magnitude 8 at 1668, and the modern fault modes are compression and right-lateral strike-slip. The Tang Wu-Gegou fault zone and Yishui-Tangtou fault zone in the west branch of the Tanlu fault zone also have evidence of late Pleistocene activity, which are dextral strike-slip; A large number of late Cenozoic basalts erupted between Yishui and Weifang. In southwestern Shandong, Mengshan fault zone and Cangni fault zone were also active in the late Pleistocene.

Fig. 8 Structural map of the middle section of the Tan-Lu fault zone (according to Guo, 1985)

Table 1 principal compressive stress direction σ 1

(According to Wang Xiaofeng, 2002)

The formation of a series of basins in Shandong Peninsula is closely related to the structure and fault zone activity. Most basins, such as Yiyuan Basin, Linqu Basin, Juxian Basin and Huangxian Basin, had tectonic activities in the early Pleistocene, but gradually weakened, and some remained active in the Holocene, such as Juxian Basin.

From the regional earthquake analysis, apart from the Tan-Lu fault zone, there are also the South Yellow Sea seismic tectonic belt and the Yanshan-Bohai seismic tectonic belt, which are closely related to the crustal stability and earthquakes in the urban agglomeration area of Shandong Peninsula.

The South Yellow Sea seismic belt is mainly controlled by NW-NNE and NW-NNW active faults of Quaternary. The earthquake zone of magnitude 7 and 8 is located at the intersection of two sets of faults, and the earthquake zone of magnitude 6 is located in a certain part of the structural zone.

Yanshan-Bohai seismic tectonic belt is mainly embodied in Bohai-Weihai strong earthquake belt and Zhucheng-Huimin medium-strong earthquake belt. The former is controlled by NW-trending and NWW-trending fault zones, which is a new active fault zone developed since Neogene, crossing the Tancheng-Lujiang fault zone in the middle of Bohai Sea, and is a strong earthquake-prone zone with high intensity and high frequency. The latter benefits from the control of the Dudu fault and the Shuang Shan-Li Jiazhuang fault zone, and Linqu once happened.

Study on Geological Ecological Environment and Sustainable Development in Shandong Peninsula Urban Agglomeration Area

Magnitude earthquake. The focal depth of the Shandong Peninsula earthquake is shown in Figure 9.

Fig. 9 Distribution map of focal depth of modern earthquakes in Shandong Peninsula urban agglomeration and its vicinity (1970 ~ 2005. 12) (Seismological Bureau of Shandong Province)

5. Exploration of earthquake law in Shandong Peninsula urban agglomeration area.

Zoning and clustering of (1) earthquakes

According to the observation records from 1480 to 2005, the earthquakes with M ≥ 4.7 in Shandong Peninsula were obviously affected by the active fault zone, showing a banded feature. Strong earthquakes occurred at the intersection of large structures, which inherited and developed in clusters. See figure 10 for the epicenter distribution and structure analysis of earthquakes with magnitude of 4.7 or above in Shandong Peninsula urban agglomeration area.

Figure 10 distribution map of the epicentre of the Shandong Peninsula urban agglomeration and its adjacent areas (1480 ~ 2005)

According to the relevant earthquake monitoring data, the earthquakes of 1480 to 2005 in Tanlu fault zone and Shandong Peninsula with Ms > 5 and Ms > 6 are shown in Table 2 and Table 3.

Table 2 episodic activities of earthquakes with M ≥ 5 along the Tan-Lu fault zone (1480 ~ 2005)

Table 3 Relationship between Shandong Peninsula Urban Agglomeration and Its Adjacent Areas and Episodic Activities of North China Earthquake

(2) Earthquake comprehensive situation

The comprehensive earthquake situation of Shandong Peninsula is shown in figure 1 1, which shows that the whole peninsula is in an area with earthquake fissure degree above VII, and the highest is VIII. Parts of Juxian, Rizhao, Wulian, Zhucheng and Anqiu are located within ⅸ, and the proportion of ⅷ area is also high.

Figure 1 1 Comprehensive Isoseismic Map of Shandong Peninsula Urban Agglomeration Area (according to the Seismological Bureau of Shandong Province)