Gravity anomaly recovered from satellite altimetry and its application

Gravity anomaly recovered from satellite altimetry and its application to
Xiaotao Chang1, Chuanyin Zhang1, Hanjiang Wen1 and Jiancheng Li2
Chinese Academy of Surveying and Mapping, Beijing, China
School of Geomatics, Wuhan University, Wuhan, China
High precision full resolution ocean gravity anomaly is obtained in this paper with the
combination of global gravity field models and satellite altimetry waveform retracking gravity
anomaly. Global gravity field models used in the research are EGM96 and GGM02C, where
coefficients of order/degree 2-180 are from EGM96 model and coefficients of order/degree
181-360 are from GGM02C model. And those beyond order/degree 360 are from the results
of altimetry waveform retracking. Based on the spherical harmonic expression of the gravity
field, as an application of physical geodesy to the geodynamics, ocean floor topography and
tectonic detection, and the geophysics researches in the deep earth are investigated and
analyzed in the paper.
The author analyzes the relationship between the gravity anomaly and its correction
items and computes the order components of the gravity anomaly, and then discusses the
possibility of replacing gravity anomaly corrections with spectral components of the gravity
anomaly. At the same time, the effect of ocean floor on the gravity anomaly is calculated and
its distribution in the full resolution gravity anomaly spectrum is detected in the paper. And
then methods to calculate the thickness of the crust/lithosphere from gravity anomaly are
investigated. On this base, the lower mantle, upper mantle, and crust components of the full
resolution gravity anomaly spectrum are analyzed, and the geodynamics background and
mechanism in the ocean areas of east China are studied. The evidence shows gravity anomaly
of order 2-6 in the ocean areas of east China is mainly due to lower mantle mass distribution,
and the difference between the continent and the ocean is not obvious in the lower mantle.
The dynamical imbalance of upper mantle affects the topography equilibrium obviously,
which is a decisive factor for the crustal movement and hydrostatical balance between the
crust and the upper mantle. The gravity anomaly in the upper mantle is an embodiment of
geopotential imbalance, and the dynamical imbalance from the geopotential imbalance is the
source of the global dynamics activities, which changes the lithosphere structure through
mantle circulation. Gravity anomaly of order 7-60 in the ocean areas of east China is mainly
due to upper mantle mass distribution. The gravity anomaly duo to the upper mantle is
obvious near the volcanic arc. The mantle circulation is under the control of the rising flow,
and the mantle flow with high density is from the deep earth of the ocean side. So the rising
mechanism of the mantle is not from the influence of gravity-induced rising flow stress field
of the continent mantle, but from the collision pressure between plates, which makes the
ocean mantle rise from the deep part. The basic stress characteristic of the trench-arc-basin
system shows the back-arc is a stress diffusion area, the island arc is a stress convergence strip,
and the trench is a stress diffusion strip. The magma from the deep ocean mantle rushes up
into the upper mantle, resulting in violent geodynamic process, which accounts for the violent
volcanic actions near the boundary between the ocean and continent mantle.