Seismic data obtained from an about 210km long Baiyan‐Jianghong deep seismic sounding profile, which was completed in the Leiqiong area in 1984 and 1985, were processed by means of finite difference tomography, time term inversion and 2‐D dynamic ray tracing methods. And 2‐D inhomogeneous crustal structure images along the Baiyan‐Jianghong seismic line were determined. The results show that the crustal thickness in northern Hainan province and Leizhou Peninsula is about 25~26km. In northern Hainan Island embossment of the southern part of Qiongzhou Channel, the average crustal velocity is about 6.16km·s–1 and 5.70km·s–1 in the Leiqiong Depression area of northern segment of Qiongzhou Channel. The crustal velocity is particularly low and especially obvious in lower crust where it is only about 6.3~6.5km·s–1. The crystalline basement presents a velocity gradient belt, the thickness of which is about 2~4km and the velocity is approximately 5.5~6.0km·s–1. Moho, the velocities of which on its two sides are 6.5km·s–1 and 8.05km·s–1 respectively, shows one‐order velocity discontinuity, and there is no obvious crust‐mantle transitional zone to be found. Because the Baiyan‐Jianghong seismic line lies in the Leiqiong Depression area with basalt covering of the Pleistocene Period, it is suggested that the thinner crust and lower velocity in this area mainly reflect the multi‐erupting of volcanic magma from the Cenozoic till the late Quaternary as well as the underplating and delaminating of hot mantle to the crustal bottom which are interrelated with the crust being still in a comparatively hot state.

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We compute the gravitational radiation of the supermassive binary black hole OJ287. By fitting the data of its recent seven outbursts, we obtain the orbital motion up to 3.5PN (Post-Newtonian) order, the energy and angular momentum fluxes and the waveform up to the 2PN. It is found that the 1PN term of the energy flux, has an opposite sign to the Newtonian flux, and the 2PN term has an opposite sign to the 1PN one. The same pattern is also found for the angular momentum fluxes. The total flux is reduced by 30.8% on average from the Newtonian flux for OJ287, resulting in a smaller orbital decay rate than that of 2.5PN calculation. Consisting with this, it is checked that, in the sequence of non-dissipative PN forces, each term of i th order (dissipative or non-dissipative) has a sign opposite to the (i − 1) th order. The origin of this characteristic is traced to the appearance of the non-diagonal metric component g0i in PN approximation. This feature will have profound impact on estimation of gravitational waves from binary systems.

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