地震和爆炸的P波层析成像——第二部分:由时频地震图得到的2004年苏门答腊-安达曼地震的断层破裂特征(英文)

Tomography of Seismic P-Waves from Earthquakes and Explosions —Part Ⅱ:Morphology of Faulting of the 2004 Sumatra-Andaman Earthquake from Spectral Seismograms

本文分析了2004年12月26日苏门答腊-安达曼地震的宽频带地震图。目的是通过不同频率成分的子事件的发生时间了解断层的破裂过程。具体分析的是由相应宽频带地震记录得到的P波的时频地震图。分析结果说明,在S波到达前的时窗内发生了最大辐射强度的相应频率低于1 Hz的15次较大子事件,但在同样的时窗内,还发生了最大辐射强度的频率更高的数百次小事件,形成了准连续的次声频率的蜂鸣声,在远至8 000 km的距离上都还能观测到。由于高频波在射线传播路径上存在较强的吸收,因而可以断定,地震期间有一大部分的地震能量是以蜂鸣声的形式被释放了。

The paper is concerned with the analysis of broadband seismograms of the Sumatra-Andaman earthquake of 26 December 2004. The purpose of the analysis is to recognize the morphology of the faulting process in terms of the time of occurrence and of the frequency content of subevents. The analysis is based on spectral seismograms of P-waves, obtained from the corresponding broadband recordings. It is found that 15 major subevents with maximum radiation intensity at frequencies lower than about 1 Hz occurred during the time window prior to the arrival of the major S-wave. In the same time window however hundreds of subevents took place with maximum radiation intensity at higher frequencies, producing a quasi-continuous ＂humming＂ at infrasonic frequencies observable at distances of the order of 8 000 km. In view of the strong absorption of the high frequency waves during the propagation along the ray path, it may be concluded that the ＂humming＂ reflects a substantial portion of the seismic energy released during the earthquake.