The Feasibilities and Limitations to Explore the Near-Surface Structure with Microtremor HVSR Method-- A Case in Baoding Area of Hebei Province, China

详细信息   

• 责任者：Wang Weijun (School of Earth and Space Science ; University of Science and Technology of China ; Hefei 230026 ; China) ; Chen Qifu
• 刊名：Chinese Journal of Geophysics
• 出版年：2011
• 卷期：54(7)
• 关键词：地震勘探 ; seismic exploration ; 噪声 ; noise ; 河北 ; Hebei Province
• 页码：p.1783-1797
• 图表：8 illus., 2 tables, 45 refs.
• 分类号：1600
• 出版序号：979
• issnNo：ISSN0001-5733
• isbnNo：CN11-2074/P

摘要

Near-surface structures exploration is an important way to deeply understand fault＇s nearsurface activities and seismic site effects in seismic hazard and risk analysis programs. In urban area, abundant noise often limits the application of traditional exploration methods. But new studies have shown that it is possible to use ambient noise to invert for near-surface structures. So we set up a profile with more than two hundred seismic noise observation sites to seek the feasibility of subsurface exploration with ambient noise. We used Horizontal to Vertical Spectral Ratio method （HVSR） to process noise data and the HVSR results show there exist peak frequencies with notable amplitude （≥2 ） along the profile which can be further delimited to three Zones A-C from west to east according to their peak frequency characteristics. The peak frequencies gradually drop easterly from 8 Hz to 0. 3 Hz excluding stations on rock without peak in Zone A, and have little fluctuation around 1.3 Hz in Zone B and have broad peak in Zone C. The broad peaks in Zone C might be composed of two peaks, one can be picked up in 0.8-1.0 Hz for many sites, and the other can be picked up reliably in 0.5-0.8 Hz only for a few sites. Using the peak frequency and soil thickness relationship appropriate for the velocity structures inverted from array data, the soil depth profile was converted directly from peak frequencies and was compared with two short seismic reflection profiles. The two derived soil interfaces in Zone C conform well to two reflection interfaces which belong to upper Pleistocene （Q3） layer （at about 100 m and 150 m respectively）. But the derived soil interface in Zone B severely deviates from reflection results, and further analysis has shown that the HVSR curve in Zone B may be seriously affected by topography, causing the peak frequency shifted from soil resonant frequency. The derived soil interface in Zone C slopes down easterly from 0 m to about 500 m depth but without further verifications. From HVSR and soil depth profiles, two normal faults in the middle of Zone A and the border between Zone A and B with significant vertical slip can be identified, but two other faults with small vertical slip canr t be discerned. The results of Baoding show that microtremor HVSR method can not only provide soil predominant frequency but also can provide a tool to explore near-surface interfaces which will help to find active faultsr shallow position and characteristics; while this method is limited by the fact that HVSR curves are liable to be affected by some environmental conditions such as wind, topography and near station transient sources.