宜蘭平原蘊藏著豐富的地熱資源，了解淺部地下構造有助於地熱資源的開發與應用。重力測勘常被用於推求地下密度分布，進而探討地下構造。本研究彙整已有之海陸重力資料及新增實測重力資料，繪製出宜蘭平原的布蓋重力異常圖。利用重力訊號分離方法，分離出不同深度所反映的重力異常，進行研究區域構造之定性分析，探討宜蘭平原主要構造分布。定量分析則參考此研究區域之震測、地質與地物資料，模擬宜蘭平原南北向之淺部二維密度構造，由模型與剩餘重力圖之間的異同，探討宜蘭平原的淺部地下構造。 本研究之重力異常顯示，宜蘭平原北部多為逆衝斷層，位於平原南部之濁水斷層為限界斷層。三星斷層與重力異常分布關連性較低，可能因該區域地層密度差異較小。宜蘭平原南部之負重力異常，可能與斷層活動有關。同時，本研究在蘭陽溪及羅東地區深度二到五公里處發現正重力異常，反映有高密度物質存在，與磁力測量結果比較，認為可能為火成岩體入侵所至。;The Ilan geothermal field is the largest known productive geothermal area in Taiwan, and the distribution of geothermal reservoirs are related to the pattern of shallow structure. Using gravity analyses are well suited to investigate the reliable subsurface density structure. First, we combine with land and marine gravity data to obtain gravity anomaly. We use the filter based on the relationship between gravity anomalies and the depth of source to analysis gravity data. Second, we obtained two-dimensional density structure referred to north-south seismic profile. In our study, residual gravity anomalies show that most of the faults in the north part of the Ilan Plain are reverse fault. The Choshui Fault is the boundary fault between the Hsuehshan Range and the Central Range. The pattern of SanShin fault is not clear, but the negative gravity anomaly was found in south part of the Ilan Plain might relate to the activity structure. Furthermore, there is a positive gravity anomaly beneath the Lanyang River, comparing with the magnetic result, we propose intrusive igneous rocks exist beneath the Ilan Plain.
