EOF???????GRACE????????????е?????????仯

????GRACE??????????????????300 km???????????????????????????0??5°????????????????????仯???????t????????????????????????????з????????????????????????????仯???????????????????????????????????δ???????t???????????????????????????????????????仯????????????????????????С????????????????????????????У????????????????????仯??????????????????????????????????GRACE???????????????????????????????????????????????????????????GRACE????????????????????????У?????t?????????????????????з?????????????????????????M??w8.8???????????????????????????????????С???M??w8.6?????????????????????????M??w8.6~8.8????п??????????????

COSEISMIC GRAVITY SIGNALS DETECTION FROM GRACE RESULTS BY EOF METHOD

The EOF method was used to extract coseismic gravity signals from GRACE monthly gravity field data. Because the GRACE satellites can't sensor the gravity changes due to vertical displacement of the Earth's surface, the gravity disturbance is used as the target signal. First, the temporal gravity disturbances at the grid points, with 0.5° resolution, on the Earth’s surface were calculated according to the GRACE monthly gravity field results, in which the 300 km fan??filter was used. And then the EOF method was applied to these temporal gravity disturbances to obtain the coseismic signals. The results show that the coseismic signals due to the recent 3 huge earthquakes, i.e. occurred in Sumatra, Chile and Japan, were successfully extracted, whereas the coseismic signals due to the Wenchuan earthquake, with relatively smaller magnitude, was not extracted because the signals are inundated by other signals and the error of GRACE data. In order to obtain the knowledge of how large an earthquake whose coseismic signal can be extracted from GRACE data should be, a simulation study was carried out by adding a known signal which was calculated in terms of the focal parameters of the Wenchuan earthquake according to dislocation theory, but with different magnitude. The simulation shows that the coseismic signal can be extracted when the magnitude reaches to ??M??w8.8 or larger; it is difficult to be extracted when the magnitude is smaller than
????M??w8.6;?? and it is possible to be extracted when the magnitude is between ??M??w8.6 and ??M??w8.8.