The Complex Love Numbers of Long-Period Zonal Tides Retrieved From Global GPS Displacements: Applications for Determining Mantle Anelasticity

Long-period zonal tidal Love numbers are more sensitive to lower-mantle anelasticity (which is difficult to determine even from laboratory); however, the Love numbers of the zonal tides have not been adequately determined. In this study, we use the optimal sequence estimation method with the Global Positioning System (GPS) displacements to estimate the complex Love numbers of the long-period zonal tides. For the first time, we retrieve the complex Love numbers h(20) and l(20) for the Msm, Msf, SN, Mstm, Mtm, Msqm, and Mqm tides from the Up- and North-components of the global GPS displacements; we also re-estimate the same complex Love numbers for the Mm (monthly) and Mf (fortnightly) tides with a higher precision. Based on the robust estimated h(20) and l(20) values for the nine zonal tides, we inverse their corresponding mantle anelastic parameters f(r) and f(i), respectively. We finally obtain that the material-dependent parameter alpha for the lower mantle is 0.189 +/- 0.07, and find that the 18.6-year nodal tide and the Chandler wobble, as well as the long-period zonal tides, can be represented by a single absorption band. Our estimates for f(r), f(i), and alpha can be further used to construct attenuation and velocity models of the Earth's interior.

Automated summary

In this study, complex Love numbers of long-period zonal tides were estimated for the first time using the optimal sequence estimation method with GPS displacements. The results allow for the determination of lower mantle anelastic parameters and material-dependent parameters, and can be used to construct attenuation and velocity models of the Earth's interior.