High resolution local Moho determination using gravity inversion: A case study in Sri Lanka

The seismic data incorporated in global Moho models are sparse and therefore the interpolation of global Moho depths on a local area may give unrealistic results, especially in regions without adequate seismic information. Gravity inversion is a useful tool that can be used to determine Moho depths in the mentioned regions. This paper describes an interactive way of local Moho depth determination using the gravity inversion method constrained with available seismic data. Before applying inversion algorithms, the Bouguer gravity data is filtered in various stages that reduce the potential bias usually expected in Moho depth determination using gravity methods with constant density contrast assumption. A test area with reliable seismic data is used to validate the results of Moho computation, and subsequently the same computation procedure is applied to the Sri Lankan region. The results of the test area are in better agreement with seismically determined Moho depths than those obtained by global Moho models. In the Sri Lankan region, Moho determination reveals a fairly uniform thin crust of average thickness around 20. km. The overall result suggests that our gravity inversion method is robust and may be suitable for local Moho determination in virgin regions, especially those without sufficient seismic data.Department of Land Surveying and Geo-Informatic

An improved geometric lunar figure from Chang’E-1 and SELENE laser altimetry

This study calibrates the footprint positions of 8.5 million Chang'E-1 and 8.8 million SELENE laser altimetry measurements against accurately known lunar laser reflector locations. The resulting datasets are used to estimate triaxial, biaxial and spherical models of the lunar figure based on the two datasets individually. The equatorial semi-major, minor and polar axes of the Chang'E-1 and SELENE solutions differ by 143 m, 3 m and 49 m respectively. The differences between their geometric centers and the lunar center of mass along the three axes are 186 m, 3 m, and 52 m. The complete laser altimetry datasets from the two missions reveal a lunar figure that is more spherical than previously thought. Furthermore, the Chang'E-1 and SELENE solutions are in better agreement with each other than either is with the ULCN 2005 lunar figure.Department of Land Surveying and Geo-Informatic