汶川地震区平通镇断层围陷波探测

EXPLORATION OF FAULT ZONE TRAPPED WAVES AT PINGTONG TOWN IN WENCHUAN EARTHQUAKE REGION

平通镇位于汶川8.0级地震断层带上,地表破坏十分严重。该断层围陷波测线横跨断层,以地震探槽为大致中点,沿NW-SE方向两端延伸,测线长约400m。观测结果表明,在汶川8.0级地震的新破裂带中可以观测到断层围陷波,反映了断层带内外的介质在物理性质上有较大的差异。该测线记录的断层围陷波优势频率大约为3～4Hz。探槽附近的台站断层围陷波较强,初步推测,该地段地壳内断层的宽度有200多米。另外,从一些地震记录上可以看出,以探槽为界,两侧波形差异十分明显,S波到时错位也很明显。地壳内波形明显差异的部位与考察看到的地表隆起边界位置一致。

Pingtong Town locates just over the fractured zone of the Wenchuan Ms8.0 earthquake and the damage at the surface is very serious. The observational line with its middle point at an earthquake exploration trough crosses the fractured zone, and stretches in NW-SE direction, whose total length is about 400 m. The observational results show that the fault zone trapped waves from the fractured zone of Wenchuan Ms 8.0 earthquake were observed. That indicates that there is a great difference in physical property between the media inside and outside the fault zone. The predominant frequency of the fault zone trapped waves is about 3 -4 Hz. It is stronger near the exploration trough The width of the fault zone in the crust in this region is estimated to be 200 m. Furthermore, some records it can be seen that the waveforms between the two sides of the trough are quite different and the arrival times of the S waves are also different. The sudden variation point of the waveforms is consistent with the boundary of the uplift at the surface.