Updated absolute gravity rate of change associated with glacial isostatic adjustment in Southeast Alaska and its utilization for rheological parameter estimation

In Southeast Alaska (SE-AK), rapid ground uplift of up to 3 cm/yr has been observed associated with post-Little Ice Age glacial isostatic adjustment (GIA). Geodetic techniques such as global navigation satellite system (GNSS) and absolute gravimetry have been applied to monitor GIA since the last 1990s. Rheological parameters for SE-AK were determined from dense GNSS array data in earlier studies. However, the absolute gravity rate of change observed in SE-AK was inconsistent with the ground uplift rate, mainly because few gravity measurements from 2006 to 2008 resulted in imprecise gravity variation rates. Therefore, we collected absolute gravity data at six gravity points in SE-AK every June in 2012, 2013, and 2015, and updated the gravity variation rate by reprocessing the absolute gravity data collected from 2006 to 2015. We found that the updated gravity variation rate at the six gravity points ranged from −2.05 to −4.40 μGal/yr, and its standard deviation was smaller than that reported in the earlier study by up to 88 %. We also estimated the rheological parameters under the assumption of the incompressible Earth to explain the updated gravity variation rate, and their optimal values were determined to be 55 km and 1.2×10¹⁹ Pa s for lithospheric thickness and upper mantle viscosity, respectively. These optimal values are consistent with those independently obtained from GNSS observations, and this fact indicates that absolute gravimetry can be one of the most effective methods in determining sub-surface structural parameters associated with GIA accurately. Moreover, we utilized the gravity variation rates for estimating the ratio of gravity variation to vertical ground deformation at the six gravity points in SE-AK. The viscous ratio values were obtained as −0.168 and −0.171 μGal/mm from the observed data and the calculated result, respectively. These ratios are greater (in absolute) than those for other GIA regions (−0.15 to −0.16 μGal/mm in Antarctica and Fennoscandia), because glaciers in SE-AK have melted more recently than in other regions

Absolute Gravity Measurements and Gravity Changes at Syowa Station, Antarctica

第3回極域科学シンポジウム/第32回極域地学シンポジウム 11月29日（木） 統計数理研究所 ３階セミナー

第53次日本南極地域観測隊で新設した重力基準点

第53 次日本南極地域観測隊では，昭和基地の国際絶対重力基準点（IAGBN（A）点）およびラングホブデの露岩で絶対重力測定と相対重力測定を行った．これに伴い，昭和基地に2点，ラングホブデに5点の重力基準点を新たに設置した．本稿では，新設した各重力基準点の位置および重力値を含む詳細情報を記載する．Absolute and relative gravity measurements were carried out at International Absolute Gravity Basement Network (IAGBN (A)) site #0417 at Syowa Station and at outcrops at Langhovde during the summer operation of the 53rd Japanese Antarctic Research Expedition (JARE-53). Two new gravity reference sites were established at Syowa Station and five at Langhovde. We present detailed data for the new sites, including location coordinates and gravity values

Brief overview of the absolute gravity measurement conducted in JARE53

第3回極域科学シンポジウム/第32回極域地学シンポジウム 11月30日（金） 国立極地研究所 ３階ラウン

Absolute gravity observation at the Antarctic Continent with the portable absolute gravimeter A10

第3回極域科学シンポジウム/第32回極域地学シンポジウム 11月29日（木） 統計数理研究所 ３階セミナー