Using observations of the YRY2 borehole shear strainmeter,we studied maximum shear strain orientation of the earth’s torsional oscillation excited by two Sumatra earthquake occurred on December 26,2004 and March 28,2005. Firstly, we did insitu calibration for the data of borehole shear strainmeter and then detected the torsional oscillations. It is found that fundamental torsional modes 0T11~0T18 were very obvious and variation trend of the two earthquakes’ amplitude were in agreement with each others,and variations of maximum shear strain orientations with time of fundamental torsional modes
0T11~0T18 of the two Sumatra earthquakes are small. Through the comparison,we found that the Dvalue of the mean measured value with theoretical anticipation value was only 2°. On the one hand,it comfirmed the theoretical model, on the other hand it also comfirmed that this observation was reliable.
A numerical simulation was made to examine the influence of outliers on CHAMP gravity field recovery. It shows that the model accuracy from least square ( LS) estimation is wholly decreased even if with only one large outlier occurs, and there is a large bias in geoid heights in the large area around the location where the outlier exists. In order to overcome this problem, robust estimation is intruduced into the CHAMP gravity field recovery and its influence function of errors is also given.For one month CHAMP rapid science orbit(RSO) and accelerometer data from GFZ with randomly added to simulated outliers from 5 to 100
m 2s -2 two 60×60 degree gravity field models were solved by LS and robust estimation individually and compared with other models such as EIGENCG03C,EIGEN2. The results show that the robust solution can efficiently control the influence of the outliers. ROCHAMP model is obviously more accurate than LSCHAMP one, and more accurate than EGM96, EIGEN1S, and EIGEN2 at the same degree and order.