Geometric form of Haiyuan fault zone in the crustal interior and dynamics implications

Introduction The deep faults in the crust have direct relation to the occurrence of earthquakes and the dis-tribution of active seismic zones, so the researches on the geometric form and physical parametersof deep crustal faults are always an important problem in seismology. The researches are not onlysignificant to knowledge the deep tectonic background of strong earthquake and seismogenicmechanism, but also play a very important role in earthquake hazard estimation and earthquakeprevent…

Geometric form of Haiyuan fault zone in the crustal interior and dynamics implications

The deep seismic reflection data on profile HY2 are reprocessed by the method of simultaneous inversion of veloc-ity distribution and interface position. By the travel-time inversion with the data of the diving wave Pg and faultplane reflection wave, we determine the geometric form and velocity of Haiyuan fault zone interior and surroundingrock down to 10 km depth. The measured data show that the amplitudes have strong attenuation in the range of stakenumber 37～39 km, suggesting the fault zone has considerable width in the crustal interior. The results of this paperindicate that to the north of the fault zone the crystalline basement interface upheaves gradually from southwest tonortheast and becomes shallow gradually towards northeast, and that to the south of the fault zone, within the basinbetween Xihua and Nanhua mountains, the folded basement becomes shallow gradually towards southwest. Theobliquity of the fault zone is about 70° above the 3 km depth, about 60° in the range of the 3～10 km depths. From theresults of this paper and other various citations, we believe that Haiyuan fault zone is in steep state from the Earth'ssurface to the depth of 10 km.