General Adjustment of the Fundamental Gravity Network in Mexico, Preliminary Results.

Abstract:

The fundamental gravity network in Mexico is currently a set of 661 stations distributed in the country to serve as an absolute reference to local relative surveys. The National Institute of Statistics and Geography maintains a program that continuously adds new observations to the network thus increasing the robustness of its structure. This activity has led us to identification of stations with time-variable g value as well as stations with a systematic difference to the official IGSN71 solution.

Following an approach to assemble in a single data set all the available observations, collected from the early 1960’s to 2014, we make an effort to create a simultaneous adjustment of nearly 6600 relative ties by a generalized least squares scheme. At this time, a careful review of the conditions in which the surveys were made is the main challenge so as to assign proper weight to each observation. So far the first execution of the adjustment delivers a result that compares well to the IGSN71 solution (with a standard deviation of 0.171 mGal) and the time variations computed for some points are being verified against known effects of local or regional geodynamics.