中国西北黄土地区地震崩滑的分布与宏观影响因素
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摘要
在中国黄土高原划分了9个震害区,分析研究了中国西北黄土地区地震崩滑的分布与宏观影响因素。研究结果认为,位于六盘山西侧、会宁以东的第4区地震崩滑最发育;可以产生黄土地震崩滑的最大震中距或区域最大面积都与震级有关;影响黄土地区地震崩滑敏感性的宏观因素包括活动地质构造、地震断层、地层、地形、水文条件、地震强度等。坡度>2°的黄土斜坡就有可能发生地震滑坡,高烈度可以削弱或消除微地形对地震滑坡的影响。与现代地形具有相似性的埋藏地形、高达黏土层或砂层的地下水位、新黄土地层等,可加重地震滑坡的发育;而一定位置的下更新统砾岩层、老黄土等则可起到抗滑作用。中国西北黄土地区产生地震崩落、滑移的最低震级分别为4、5级,或地震烈度5度。在第4震害区,烈度6～7度就可能产生明显的地震崩滑;10度以上可形成较大面积的崩滑群;7(1/2)、8级以上的地震可分别产生滑陷、流滑。多因素组合对滑坡的影响可能不同于单因素,但比单因素更重要。
The 9 seismic hazard regions in the loess plateau of China are divided. The 4th region of it, locating on west of Liupan Mountain and east of Huining, is the region of the most serious seismic landslides in the loess plateau of China. Both the largest epicentral distance and the largest area in which the loess seismic landslides can occur have something to do with seismic magnitudes. The macroscopic factors influencing sensitivity of seismic loess landslides include geological structure, seismic fault, stratum, topography, hydrological condition, seismic intensity etc. The loess slope whose gradient>2° can occur seismic landslides, but the small topography in high intensity region cannot decide occurrence of seismic landslides. Higher comparability between the embedding topography and the present one, the water table high to the clay or the sand stratum, and the new loess stratum can aggravate occurrence of loess seismic landslides. The conglomerate (Q_p~1) and the old loess stratum on some location have function of skid resistance. In the loess region of Northwest China, the smallest magnitudes at which the seismic avalanche or slippage can occur individually are MS 4, 5 (about intensity 5). In the 4th seismic hazard region, the earthquakes with intensity 6~7 can obviously occur landslides, the ones with intensity 10 can occur landslides group with larger area; and the ones with MS 7.5, 8 can individually occur subsiding landslide and flowing landslide. The combination effect of multi-factors can be different with any single factor, and the former is more important than the latter.
The 9 seismic hazard regions in the loess plateau of China are divided. The 4th region of it, locating on west of Liupan Mountain and east of Huining, is the region of the most serious seismic landslides in the loess plateau of China. Both the largest epicentral distance and the largest area in which the loess seismic landslides can occur have something to do with seismic magnitudes. The macroscopic factors influencing sensitivity of seismic loess landslides include geological structure, seismic fault, stratum, topography, hydrological condition, seismic intensity etc. The loess slope whose gradient>2° can occur seismic landslides, but the small topography in high intensity region cannot decide occurrence of seismic landslides. Higher comparability between the embedding topography and the present one, the water table high to the clay or the sand stratum, and the new loess stratum can aggravate occurrence of loess seismic landslides. The conglomerate (Q_p~1) and the old loess stratum on some location have function of skid resistance. In the loess region of Northwest China, the smallest magnitudes at which the seismic avalanche or slippage can occur individually are MS 4, 5 (about intensity 5). In the 4th seismic hazard region, the earthquakes with intensity 6~7 can obviously occur landslides, the ones with intensity 10 can occur landslides group with larger area; and the ones with MS 7.5, 8 can individually occur subsiding landslide and flowing landslide. The combination effect of multi-factors can be different with any single factor, and the former is more important than the latter.
引文
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[5]国家地震局兰州地震研究所,宁夏回族自治区地震队.1920年海原大地震[M].北京:地震出版社,1980.
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[11]David K Keefer.Landslides caused by earthquakes[J].Geological Society of America Bulletin,1984,95(4):406-421.
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