2023-07-19 スイス連邦工科大学ローザンヌ校(EPFL)
◆地下水注入は地熱エネルギー抽出に不可欠であり、そのリサーチは地震引き起こしの物理的メカニズムを理解するために重要です。地下4〜6キロメートルの地熱井戸は地震リスクがあり、スイスのHaute-Sorneでは地熱発電所計画に反対がありました。水圧刺激により岩の透水性が増す一方で地震を引き起こす可能性もあるため、慎重に研究が行われています。
◆彼らは特に流体注入終了後に発生する地震に注目し、遅延地震の新たなメカニズムを解明しました。研究結果はエンジニアに地震リスクの軽減に役立ち、地熱エネルギーの活用によるエネルギーシステムの脱炭素化を推進する重要な一歩となっています。
＜関連情報＞
- https://actu.epfl.ch/news/scientists-gain-insight-into-geothermal-technology/
- https://royalsocietypublishing.org/doi/10.1098/rspa.2022.0810
遅発性地震誘発のメカニズムとしての注入後の地震すべり Post-injection aseismic slip as a mechanism for the delayed triggering of seismicity
Alexis Sáez and Brice Lecampion
Proceedings of the Royal Society A Published:24 May 2023
DOI:https://doi.org/10.1098/rspa.2022.0810
Abstract
Injection-induced aseismic slip plays an important role in a broad range of human-made and natural systems, from the exploitation of geo-resources to the understanding of earthquakes. Recent studies have shed light on how aseismic slip propagates in response to continuous fluid injections. Yet much less is known about the response of faults after the injection of fluids has stopped. In this work, we investigate via a hydro-mechanical model the propagation and ultimate arrest of aseismic slip during the so-called post-injection stage. We show that after shut-in, fault slip propagates in pulse-like mode. The conditions that control the propagation as a pulse and notably when and where the ruptures arrest are fully established. In particular, critically stressed faults can host rupture pulses that propagate for several orders of magnitude the injection duration and reach up to nearly double the size of the ruptures at the moment of shut-in. We consequently argue that the persistent stressing of increasingly larger rock volumes caused by post-injection aseismic slip is a plausible mechanism for the triggering of post-injection seismicity—a critical issue in the geo-energy industry. Our physical model shows quantitative agreement with field observations of documented cases of post-injection induced seismicity.
