Project plan and research progress on geodynamic models of earthquakes and strong seismic hazards in boundary zone of the Ordos active block
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摘要: 鄂尔多斯地块及其周缘地区的地震动力学和强震危险性研究，是检验和发展活动地块理论的理想场所。近年来，伴随青藏高原动力学研究视角的不断扩大，逐渐成为国内外新的地学研究热点。项目以“丝绸之路”经济带东端、我国重点强震危险区之一的鄂尔多斯活动地块为研究对象，构建活动地块及边界带三维深浅结构和构造变形模式，建立适用于板块内部的强震孕育动力学模型，完善大陆强震孕育和发生的活动地块理论，研发具有物理意义的时间相关强震预测理论模型，提出地震危险性理论预测技术规程。我国科学家20世纪末提出的大陆强震受控于活动地块的理论，为中国大陆强震危险地点预测提供了重要理论指导，但是如何将该理论更好地应用于实际的强震危险性预测研究中，还需要进一步深入研究活动地块运动和变形如何控制边界带强震的孕育和发生过程。选择鄂尔多斯活动块为研究的目标区，重点开展以下几个方面的研究内容：地块边界带断裂活动习性与强震复发行为；地块及周缘现今三维地壳运动与应变分配；地块及边界带深部结构与深-浅构造耦合；活动地块理论完善与边界带强震危险性研究。项目执行两年来，在几个方面均取得了进展和初步成果，建立了主要边界带断裂强震复发行为模式，获得了地块及周缘不同类型现今三维地壳运动状态，建立了关键区域地块边界带深-浅构造耦合构造模型，开展了边界带强震危险性研究。Abstract: The Ordos active block and its surrounding areas are ideal to examine and develop the active block theory on geodynamics and seismic hazards. In recent years, research on geodynamics of the Tibetan Plateau has become a new hotspot in geoscience both at home and abroad. This project will target on the Ordos active block and its boundary belts （a key seismic hazard area in continental China）, which located on the east end of the Silk Road economic belt, establish the three-dimensional structural models of deep and shallow structures, build the regional geodynamic models of strong earthquake preparation processes inside the plate, improve the active block theory of strong continental earthquake preparation and occurrence, to develop a time-dependent strong earthquake prediction model with physical significance, and propose a technical regulation of earthquake prediction. The active block theory, which has been proposed by Chinese scientists at the end of 20th century, has suggested that the continental strong earthquakes mainly occurred on the active block. The theory provides important guidance for predicting the strong-earthquake-occurring locations in China. However, further work is necessary to apply it into practice, including research on how the block movement and structural deformation of active blocks control the preparation and occurrence of strong earthquakes on the boundary zones. Therefore, we focus on the Ordos active block to carry out the following research contents, including the behaviors of fault activity and strong earthquake recurrence of the block boundary zones, the 3D crustal movement and strain partitioning of the Ordos block and its surrounding areas, the structural coupling between deep and shallow structures of the Ordos block and its boundary zone, and the perfection of active block theory and research on the strong earthquake hazard on the boundary zones. In the last two years after starting the project, some preliminary results have been achieved. We have built a model to study the strong earthquake recurrence behaviors, obtained different patterns of 3D crustal movements in the Ordos block and its surrounding areas, built a coupling model between deep and shallows structure in the key regions, and conducted research on strong earthquakes hazard.
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Key words:
- active block /
- block boundary zones /
- earthquake dynamics /
- seismic hazard /
- Ordos block
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图 5 鄂尔多斯北缘断裂分布（下）及古地震活动特征（上）
Figure 5. Active fault distributions（lower）and Paleoearthquake characteristics（upper）in the northern margin of Ordos active block
图 7 鄂尔多斯及周缘GPS台站分布
Figure 7. Distributions of GPS stations in and around the Ordos active block
图 8 鄂尔多斯及周缘水准网分布
Figure 8. Distributions of leveling lines in and around the Ordos active block
图 9 跨六盘山断裂带连续GPS台站分布
（a）黄色图框为已确定的长剖面踏勘位置； （b、c）为台站场地照片
Figure 9. Distributions of continuous GPS stations across the Liupanshan fault zone
（a）the identified location of GPS profile is shown in yellow； （b）and（c）are station pictures
图 10 鄂尔多斯地块及周缘地区的水平运动速度场
Figure 10. Horizontal velocity fields in and around the Ordos active block
图 11 鄂尔多斯地块及周缘地区垂直运动速度场
Figure 11. Vertical velocity fields in and around the Ordos active block
图 12 鄂尔多斯活动地块及周缘基线长度（a）和三角网主应变（b）变化
（a）中数值代表基线变化率（正值为伸长，负值为缩短）
Figure 12. Changes of baseline length（a）and main strain（b）in and around the Ordos active block
The values in the（a）represent rates of change for baseline（the positive values are elongated，whereas the negative values are shortened）
图 13 鄂尔多斯周边地震台站分布
红色三角为区域固定台站；深绿色线段为块体边界
Figure 13. Distributions of seismic stations in and around the Ordos active block
The regional fixed stations are shown in the red triangle，the block boundaries are shown in the dark green line
图 15 鄂尔多斯地块周缘地区流动地震台阵测点分布图
实心三角代表已搜集数据的台站，空心三角为待搜集数据的台站
Figure 15. Distributions of mobile seismic array survey points in and around the Ordos active block
Stations that have been collected data are shown in the solid triangles，whereas in the hollow triangles
图 17 鄂尔多斯西北缘速度间断面结构[46]
图D中白线对应图A、B和C的剖面位置，剖面上黑色圆点间隔距离为1°，蓝色三角形为本文所用台站，台站周围的 红色点为Moho转换点位置，灰色实线为该区域断层分布，HTG：河套断陷盆地，YCG：银川断陷盆地，HL：贺兰山， YBL：雅布赖山，HHF：黄河断裂，ZWPF：卓子山西麓断裂，DBF：磴口—本井断裂
Figure 17. Structures of velocity discontinuity in the northwestern margin of the Ordos active block[46]
Locations of the three profiles in the figures A，B，and C are indicated in figure D，the black dots on the profiles are spaced one degree apart. The blue triangles are the stations used in this paper，the red dots around the stations are the Moho transfer points. The locations of the faults are shown in the solid gray lines. HTG：Hetao Basin，YCG：Yinchuan Basin，HL： Helan Shan，YBL：Yabrai Shan，HHF：Huanghe fault，ZWPF：Zhuozi fault，DBF：Dengkou-Benjing fault
图 18 定位前后地震事件分布及深度变化
(a)定位前地震事件分布图；(b)定位后地震事件分布图；(c)定位前地震深度分布图；(d)定位后地震深度分布图
Figure 18. Spatial and depth distribution characteristics of earthquake events before and after earthquake location
The spatial distributions of earthquake events before (a) and after (b) earthquake location；the depth distributions of earthquake events before (c) and after (d) earthquake location
图 19 运城盆地地区流动地震台阵和大地电磁阵列探测台站分布
蓝色空心三角为新布设流动地震观测台站，蓝色和绿色实心三角为已有流动和固定地震台站， 红色和绿色圆圈为新布设和已有大地电磁测深测点
Figure 19. Distributions of mobile seismic arrays and magnetotelluric array detection stations in and around the Yuncheng Basin
The new mobile seismic observation stations are shown in the blue hollow triangles；the existing mobile and fixed seismic stations are shown in the blue and green solid triangles；the new and existing magnetotelluric array detection stations are shown in the red and green circles
图 20 鄂尔多斯西南缘三维断裂结构模型（俯视图）
不同颜色的小球代表不同的地表活动断裂， 不同颜色代表不同断裂在地下的断裂面
Figure 20. 3-D fault model of the southwestern margin of the Ordos active block（top view）
The colored spheres represent different active faults on the surface，the different colors represent subsurface fault geometries of different active faults
图 21 不同各向异性条件下断层上地震的破裂过程模拟（改自文献 [51]）
（a）介质各向异性不均匀条件下破裂传播过程； （b）各向异性的不均匀性导致地震位错分布不对称； （c）PGA分布非对称性
Figure 21. Simulations of earthquake rupture processes under different anisotropic conditions（Modified from the reference [51]）
（a）the propagation process of earthquake rupture under different anisotropic conditions； （b）anisotropy leads to asymmetric distribution of earthquake offsets； （c）asymmetric distribution of the PGA
图 22 地块-断层运动学模型获得的海原—六盘山断层运动学参数
（a）走向滑动速率； （b）倾向滑动速率； （c）耦合系数和； （d）滑移亏损速率
Figure 22. Kinematic parameters of Haiyuan-Liupanshan fault zone obtained from block-fault kinematic model
（a）slip-rate along strike； （b）slip-rate along downdip； （c）the cumulative coupling coefficient； （d）the rate of slip deficit
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