大地水準面（Geoid），是在物理上最靠近真實地球形狀的重力等位面，而地球的表面有超過百分之七十的面積，被海水所覆蓋，海水是為流體的一種，會趨向於最低位能的高度以達到最穩定的狀態，故在理想狀態下，海平面高度會直接被視為大地水準面的量值。在本篇文章中，使用了三組接續的測高衛星資料：Topex/Poseidon、Jason-1和Jason-2，來觀測規模約在9的地震，所造成的海平面高度變化，依此條件選擇了三個地震來做分析：2004年12月的蘇門答臘地震、2010年2月的智利大地震及2011年3月的日本東北地震。我們使用的海平高度資料，為沿著衛星軌道測得的真實值，以保持資料的高解析度和準確性，並以此資料將地震造成的同震（Coseismic）衰減和震後（Postseismic）回復的海平面變化分開比較，發現有超過雜訊干擾範圍外的可信數值，出現在結果之上，我們接著將此資料與 GRACE（Gravity Recovery and Climate Experiment）衛星所計算出來的大地水準面之值及套用 EOF（Empirical Orthogonal Function）分析出來的結果做比較，發現這些數值有決定性的差異，以此比較量可引導更多的其他未來研究。;The geoid is the gravitational equipotential surface that is closest to the shape of the real earth. Sea water, being fluid, flows to a lowest gravitational state such that the mean sea surface conforms to the geoid, while the dynamic height departure between them are caused by tides, winds, ocean currents, and other dynamic or even anthropogenic effects. Here we use the sea surface height data, from altimetry satellites of Topex/Poseidon, Jason-1 and Jason-2 to detect possible geoid changes due to three recent large earthquakes, namely the Sumatra-Andaman event of December 26 in 2004, Chile event of February 27 in 2010 and the Tohoku-Oki event of March 11 in 2011. Instead of applying directly the gridded sea surface height data processed by AVISO, we download the “along-track” altimetric data in the respective regions to take advantage of their detailed information content and higher resolutions. With the data, we constructed for 1-year each the pre- and post-seismic sea surface height maps in order to detect the coseismic geoid changes, and analyzing longer time series for postseismic phenomena. We found moderate geoid change signals that are above the noise level. We compared them with the observed geoid change from the GRACE (Gravity Recovery and Climate Experiment) satellite data and then conduct EOF (Empirical Orthogonal Function) analysis. The comparison is encouraging and promises further studies.
