大地震に対する山岳地形の応答を地形条件が支配することを解明（Topography Controls How Mountains Respond to Large Earthquakes）

2026-08-11 中国科学院（CAS）

中国科学院地球環境研究所の研究チームは、ニュージーランドのアルパイン断層で1717年に発生した巨大地震（Mw8超）の影響を解析し、山地侵食に対する地震の影響を左右する主要因が地形であることを明らかにした。研究では、Mapourika湖とParinga湖の堆積物に記録された地震サイクルを、炭素・窒素同位体や分子バイオマーカーなどの地球化学指標と地形解析を組み合わせて調査した。その結果、急峻で斜面と河川の連結性が高いMapourika流域では、深層地すべりによって深部土壌や基盤岩が大量に湖へ運ばれた。一方、比較的緩やかなParinga流域では表層土壌の侵食が卓越した。さらに、Paringaでは地震後に侵食源が高標高の表層土壌から低標高の深部土壌へ変化したのに対し、Mapourikaでは地震前後で侵食様式に大きな変化は見られなかった。これらの結果は、地形条件が地震後の侵食過程や土砂・有機炭素輸送を規定し、景観進化や地球規模の炭素循環の理解に重要であることを示している。

Study authors Jamie Howarth and Sean Fitzsimons collect a sediment core from Lake Paringa, New Zealand, for reconstructing the erosion history following large earthquakes. (Credit: Adelaine Moody)

＜関連情報＞

地形条件が、大地震に対する侵食の反応を左右する
Topographic regime controls the response of erosion to large earthquakes

Jin Wang;Jamie D. Howarth;Zhangdong Jin;Erin L. McClymont;Alexander L. Densmore;Sean J. Fitzsimons;Thomas Croissant;Darren R. Gröcke;Martin D. West;Erin L. Harvey;Mark H. Garnett;Chao Zhu;Robert G. Hilton
Geology Published:July 28, 2026
DOI:https://doi.org/10.1130/G54785.1

Physical erosion can impact the carbon cycle over a range of time scales. In mountains, widespread landslide-triggering events can remove significant quantities of soil from landscapes, yet isolating the spatial pattern and processes of erosion is difficult. Here we reconstruct the impacts of a great earthquake (M_w >8.0) on two lake sedimentary systems in New Zealand and use a combination of geochemical proxies to explore organic matter provenance and soil erosion. The two catchments differ notably in their geomorphic properties, with the median slope of the Lake Mapourika catchment of 47° (+11°/−18°) versus 39° (+9°/−13°) in the Lake Paringa catchment. Carbon and nitrogen isotopes, n-alkane abundance, and n-alkane hydrogen isotopes show that in the steeper Lake Mapourika catchment, landslides from the earthquake mobilized aged soil organic matter and rock-derived organic carbon by deep erosion. Rock organic carbon erosion increased from 15% (+14%/−10%) to 24% (+13%/−13%) in the Lake Mapourika catchment following the earthquake. By comparing the slopes, sediment connectivity, and stream power indices, we show that in the steeper Lake Mapourika catchment, erosion mobilized deeper soil and more bedrock than in Lake Paringa throughout the record, implying that bedrock landslides remained a key process both during and after the earthquake. Thus, we find that even along the same fault zone and under similar climatic, geological, and ecological conditions, topography strongly controls physical erosion as well as its response to widespread landsliding events.