The high-resolution 3D S-wave velocity structure in the shallow crust of Guangzhou—Foshan area based on short-period dense array
Guangzhou-Foshan area is located in the heartland of the Pearl River Delta economic zone.Three regional faults intersect each other and pass through this area.The fine 3D shallow S-wave velocity structure in Guangzhou-Foshan area is of great significance for urban planning and construction,earthquake disaster assessment,strong ground motion simulation of this area.In this study,we used the continuous waveform data recorded by 1104 short-period seismometers deployed in a dense seismic array in Guangzhou-Foshan area and calculated the cross-correlation functions between station pairs from the vertical component ambient noise data.39488 high-quality surface wave group velocity dispersion curves with a period of 0.1～5 s are further extracted.And then,the shallow crustal velocity structure in the depth range of 0.3～3 km is imaged by the direct surface-wave invert method based on ray tracing.The results show that there are significant velocity variations in the study area.The S-wave velocity structure in the Pearl River Delta is relatively complex,while it is relatively simple in the Guanghua basin.The low-speed anomalies in the study area are mainly located near the faults,at the same time in the falling plate of the faults.The eastern margin of Sanshui Basin in the Pearl River Delta shows a saddle shaped low-speed anomaly,which extends down to 2 km.The South and North boundaries of the low-speed body are basically consistent with the location of the basin controlling faults.There are two parallel high-speed anomalies in Guanghua basin,with a low-speed anomaly parallel to the basin tectonic strike in the middle.The overall velocity structure characteristics are consistent with the geological tectonic background of Guanghua basin as a compound syncline.The low-speed anomaly extends down to a depth of 1.4 km,which may suggest the maximum burial depth of the stratum involved in the syncline.Long strip-shaped low-speed anomaly is generally developed along the Guangzhou-Conghua fault,which is related to the sedimentary strata formed along the fault.The anomaly is divided into two sections in the shallowarea,indicating that the Guangzhou-Conghua fault may have segmental activity in history.The Yudai park is surrounded by high-speed anomalies,which extend upward to a distance of 1.3 km from the surface.Combined with the existing geological and geophysical data in the study area,it is speculated that the high-speed anomaly may be a reflection of early magma intrusion in the shallow crust.
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