| 从地震折射和反射剖面结果讨论唐山地震成因 |
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| 引用本文： | 曾融生,陆涵行,丁志峰.从地震折射和反射剖面结果讨论唐山地震成因[J].地球物理学报,1988,31(4):383-398. |
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| 作者姓名： | 曾融生 陆涵行 丁志峰 |
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| 作者单位： | 国家地震局地球物理研究所 北京 |
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| 摘 要： | 通过唐山震中的地震测深以及深反射剖面,揭示了唐山震源区的浅部及深部构造图象,它与以往的推测很不相同。 唐山东面的开平向斜属中生代构造,探测的结果表明,向斜轴是一近于直立的地壳断裂。唐山地震时的水平地形变主要是由开平地壳断裂的位移引起的,它是北北东-南南西向右旋走滑断裂。开平地壳断裂西面的陡河断层是一自地表向南东方向下插的正断层,断层倾角为26°,延伸至5km深处。陡河正断层刚好插到唐山市震中区的正下方。唐山地震时的垂直地形变主要是由陡河正断层的滑动引起的。 野鸡坨-丰台断层通过震源区的西部边缘,断层以西的第四纪沉积层,在过去一百万年间曾经沿北北东方向水平滑移15km,表明它也是一个右旋的走滑断层。但是它在近代数百年间并无地震活动,唐山地震时该断层的滑动亦不明显。 开平地壳断裂和陡河正断层在唐山地震时同时滑动,说明地震的作用力除区域水平构造力外,地壳上方还存在一个附加的引张力。在开平断裂处,上部地壳的反射面倾角杂乱,而且在它的正下方,莫霍界面明显错断,因此,地幔顶部的热物质可能自开平地壳断裂中上升。热物质产生的热应力在地壳上方可表现为张应力,而在地壳下方却表现为压应力,这与反射地震剖面图的现象相符合。开平地壳断裂中热物质的上升对地震的产生有
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| 关 键 词： | 反射剖面 地震成因 唐山 |
| 收稿时间： | 1987-05-14 |
SEISMIC REFRACTION AND REFLECTION PROFILINGS ACROSS TANGSHAN EPICENTRAL REGION AND THEIR IMPLICATION TO SEISMOGENIC PROCESSES |
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| ZENG RONG-SHENG LU HAN-XING DING ZHI-FENG.SEISMIC REFRACTION AND REFLECTION PROFILINGS ACROSS TANGSHAN EPICENTRAL REGION AND THEIR IMPLICATION TO SEISMOGENIC PROCESSES[J].Chinese Journal of Geophysics,1988,31(4):383-398. |
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| Authors: | ZENG RONG-SHENG LU HAN-XING DING ZHI-FENG |
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| Affiliation: | Institute of Geophysics, State Seismological Bureau |
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| Abstract: | Seismic refraction and reflection profilings across Tangshan epicentral region have depicted a clear picture of the crustal structure in this area, where a large earthquake of magnitude 7.8 occurred in 1976.A paleozoic syncline of Kaiping, located just east of Tangshan city is a nearly vertical right lateral strike-slip fault, broken throughout the whole crust. This fault has been activated in recent time. Its horizontal displacement with. NNE direction accounts for the horizontal surficial strain during the occurrence of Tangshan earthquake. The western flank of Kaiping syncline is associated with Douhe fault a normal fault striking NNE and dipping southeas-twards to a depth of about 5 km, with a dipping angle of 26°. The Douhe normal fault extends right over the epicentral region of Tangshan City. The vertical surficial strain during the great earthquake is produced by the displacement of this normal fault. The focal depth of both the main shock and the aftershocks are about 5-22 km. The deformation at this depth-range revealed from the reflection profile is different from that in the upper 5 km medium of this region. An analysis of the thermodynamic properties in the deep crustal medium has shown that transition layers consisting of alternating "brittle" and "ductile" material may prevail at the seat of earthquakes.The simultaneous occurrence of the horizontal displacement of the Kaiping Crustal Break and the movement of Douhe normal fault requires that an extensional force should exist in addition to the regional horizontal compression prevailing in North China Plain. The chaotic dipping of reflections in the upper crust and a prominent offset of 3-5 km of Moho discontinuity highly suggest that the migration of hot material from the uppermost mantle to the crust may occur in Kaiping crustal break. The thermal stress of a hot crustal channel can produce an extensional stress in the upper crust and a compressional stress in the lower crust. It explains the seismic reflection profile pretty well. The migration of hot material in Kaiping Crustal Break has two effects on the occurrence of the earthquake: it produces additional extension in the upper crust which activates the motion of Douhe normal fault, and also softens the material in Kaiping crustal break so that his strike slip fault becomes easier for moving. |
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| Keywords: | Reflection profiling Seismogenic process Tangshan of China |
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