| In this paper, we relocated the aftershocks of October ,1982, M_L6.2 , Lulong earthquake and computed the focal mechanism. By this way we reveal the active tectonics feature of morphologic, kinematics and dynamics of Lulong Basin which locates on the blocks border in North China.In chapter 1, we re-processed the digital seismic data of the October 1982, M_L6.2 , Lulong earthquake. In total 391 records, we select 171 event records which can be precisely located, and 45 events were relocated by Hypoinverse program.The result of the relocation shows 5 seismic active faults which consists a reversal "F"-shaped seismic tectonics.Two NNE striking faults are truncated by a NWW striking fault. Two sets of the faults shows the conjugating state where are common in fragility faults. The NNE striking faults are feedthrough. The other two faults show a counterclockwise rotation fault set and they depart each other by 1km. Luanhe valley is a downfaulted basin surrounded by a series of faults. The seismic tectonics of Lulong earthquake is a strike tending fault assemblage with tensional fracture feature.In chapter 2, we computed the focal mechanism of each event by moment tensor inverse method and found that the focal mechanisms in different part of the Basin are different. The pressure axis inside the basin and which around the basin sometimes have an angle about 90 degrees. This illustrates the stress condition is not the same in different tectonic position.The statistics average value of dipping angel of T-axis and P-axis are both at about 20° . The dip angle of the maximum and the minimum press axis are low, intermediate axis is steep, that shows the actuating force is from horizontal direction.The region pressure axis is 74° NE, about in E-W direction, but it changes to 43° in the north of the basin. It is obvious that the stress field has rotated somewhere, it was caused by the movement of the small blocks. Lulong block is pushed and restricted by the Yanshan active block from north.The computed slip angel of double couple nodal planes is very small,-12.1° in average, it shows the aftershocks is mainly caused by striking fault but with a little tensor component. The dipping angel near the value of 60° or even higher. So we can also surpose the pressure axis is near horizontal.In chapter 3, we show the result of field investigates to the region geology and surface faults trace. We found that the fault determined by location is consisted with that by field investigated. Lulong fault is a branch stretch from Tangshan fault and also located in the northeast corner of Zhangjiakou-Bohai fault belt. It is an interjection part of two faults where strong earthquakes could breed. Tangshan fault is a strong seismic active tectonics. We know that an earthquake with M_L 7.8 occurred at Tangshan in 1976. So the activity of Tangshan fault must have important effect on Lulong region.We notice that two faults could be found on the surface and the other three are buried active tectonics. The five faults compose the seismic tectonics of Lulong earthquake.According to the geological investigation, F4 behave mostly as tensor fault like a "Z" sharp on the surface but F5 behave as a striking fault or have thrust feature ef. The hint the movement of northeast tectonics could not stretch completely because of the interdiction of northwest striking... |
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