摘要
运用变分原理,我们得到了最小地震波辐射能量约束准则并用于研究震源的物理过程.通过研究1995年ML4.1河北沙城地震序列主震和余震的动力学过程,可知主震和余震震源的动态破裂过程明显不同;ML4.1主震的破裂速度与瑞利波速相近,约为剪切波速度的0.89倍;而28个余震的破裂速度远远小于剪切波速度,大约是剪切波速度的0.05到0.55倍.根据裂纹扩展模型,计算得到其余震的地震波辐射效率多在10%以下,这也说明了余震的地震效率较低.我们认为余震震源的动态破裂过程应与断层内部新生裂纹的扩展有关,而非简单的岩体间的相对滑动.余震震源的动态破裂传播与破裂能占主导地位的小地震有关.这些小震所带来的破裂能也导致了断层的进一步扩展.在对该地震序列的研究中,我们发现主震与余震的震源破裂过程在能量分配上有着本质的区别.因此当地震断层尺度相当小时,破裂能的贡献不能忽略,它的大小将显著地影响地震波辐射能的大小.
From variational principle, we have derived the minimum radiation energy criterion （MREC）, and use it in the earthquake source dynamics study. For the 1995 ML 4. 1 Shaeheng Heibei earthquake sequence, we come to the conclusion that the dynamic rupture processes of main shock and aftershocks are totally different： the rupture speed of the ML 4. 1 main shock is about 0.89 of shear wave speed, closing to the Rayleigh wave speed, while the rupture speeds of the remained 28 aftershocks range from 0.05 to 0.55 of shear wave speed, which is much smaller than shear wave speed. In addition, based on the circular crack extending model, we also calculate the seismic radiation efficiencies for this earthquake sequence, and the results indicate that, for most aftershocks, the radiation efficieneies are less than 10%, inferring a low seismic efficiency. In our study, we suggest that the dynamic rupture processes of these aftershocks could be related to the crack （sub-fault） extension inside the main fault, rather than the simple momentum of the moving block, which has been commonly assumed in the fault frictional motion if an overshoot occurs during earthquake rupture. The local stress concentrations inside the fault after main shock may play an important role in sustaining the crack extension. Therefore, the fracturing process associated with the crack extension for the aftershock becomes a main energy dissipation mechanism. Compared with the ML 4.1 main shock, we also find that there exists an essential difference in the earthquake energy partition for the aftershock source dynamics. In other words, the fracture energy dissipation could not be ignored in the source parameter estimation for the earthquake faulting, especially for small earthquakes. Otherwise, the radiated seismic energy could be overestimated or underestimated.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2008年第6期1797-1803,共7页
Chinese Journal of Geophysics
基金
中国地震局地壳应力研究所中央级公益性科研院所基本科研专项(ZDJ2007-1)
中国科学院百人计划和国家基金委(40574022)资助
关键词
错动过头
分数应力降
裂纹扩展
地震波辐射能
破裂能
最小能量约束准则
Overshoot, Partial stress drop, Crack extending, Seismic radiation energy, Fracture energy, Minimum radiated energy constraint （MREC）
