Sedimentary basin structure of the Bohai Bay from teleseismic receiver functions

We calculated P wave receiver functions using 895 teleseismic events from September 2006 to September 2009 recorded by 70 temporary stations located in the Bohai Bay basin.We found that it is difficult to identify the P to S converted phases from the Moho discontinuity.The first few seconds after the direct P arrival are mainly controlled by the sedimentary structure response which includes the Ps phase generated by the bottom of the basin and its multiple reverberations in the basin.Based on these characteristics, we used the neighborhood algorithm to invert the data and try to find the best basin velocity model that produces the best fit between the theoretical receiver functions and observed ones in the least-squares sense.The results show that there is a series of depressions and uplifts orienting in the NNE direction in the Bohai Bay basin.The sedimentary depth in the Jizhong Depression is about 3-6 km.There are several secondary depressions and uplifts alternating in the NNE or NE direction in the Jizhong depression.The thickest sedimentary layer is located in the eastern Jizhong depression.The above shows the characteristics of a half rift valley (rift valley)-half horst (horst) structure.The ratio of the P velocity to S velocity in the uplifts is larger than that in the depressions, which may be caused by the lack of the Paleogene stratum in the uplifts.The proximity of geothermal fields to the high v_P/v_S ratio depressions shows a close relationship between the high temperatures of the stratum and the large v_P/v_S ratios .The average of S velocity of the sedimentary in the uplift is smaller than that in the depression, and the thicker sedimentary area always has a higher average S velocity.These characteristics show a relationship between thick sedimentary and high average S velocity.It may be because that the thicker sedimentary area has a thicker Paleogene stratum and the S velocity of the Paleogene stratum is much higher than that of the Neogene and Quaternary stratums.The sedimentary structure provides a base to determine crustal structure beneath the Bohai Bay basin.