鲜水河断裂带上特征地震的初步研究
PRELIMINARY STUDY OF CHARACTERISTIC EARTHQUAKES IN THE XIANSHUIHE FAULT ZONE
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摘要: 特征地震是大地震原地重复的重要表现形式.现有资料的初步研究表明,鲜水河断裂带上大地震属特征地震模式,其地震破裂长度、同震位错量以及断层错动方式,在原地保持较长时间的一致性.由于大地震屡屡在原地重复发生,沿断裂特定地段累积位错分布与一次地震的位错相一致,从而导致断层滑动速率的同步变化.本文以1973年炉霍地震为例,研究了鲜水河断裂的特征地震现象.该段的地震活动属特征地震模式,不服从古登堡-里克特的线性震级频度关系.特征地震不仅对断错地貌、滑动速率有重要的影响,由于这种地震模式是以特定震级的大地震为主导,几乎没有中等震级地震发生,这对地震活动性研究也具有重要的意义.Abstract: The characteristic earthquake is a main manifestation of large earthquakes repeated in the same place. The present information suggests that large earthquakes on the Xianshuihe fault may follow the characteristic earthquake model,for which the uniformity of earthquake fault length,coseismic displacement and fault slip pattern all remain for a relatively long time. The cumulative dislocation distribution at a given section along the fault shows variation consistent with the displacement by a single earthquake because of reccurrence of the events at the same place,and thus causing synchronous variations of slip rates. Taking the coseismic fracture segment of the Luhuo earthquake of 1973 as an example,this paper discusses the phenomena of the characteristic earthquake at the Xianshuihe fault. The seismicity of this segment does not follow the linear frequency-magnitude relationship described by Gutenberg and Richter because it is controlled by the characteristic earthquake model. This model not only has great influence on fault produced landforms and fault slip rates,but also has great significance in the research on seismic activity since it implies that characteristic events dominate earthquake recurrence and the lack of moderate-magnitude events.