Earthquakes triggered by the subsurface undrained response to reservoir-impoundment at Irapé, Brazil

IF 3.2 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Haris Raza, George Sand França, Eveline Sayão, Victor Vilarrasa
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Abstract

Abstract. The necessity to reduce carbon emissions to mitigate climate change is accelerating the transition from fossil fuels to renewable energy sources. Specifically, hydropower, in particular, has emerged as a prominent and safe renewable energy source but entails reservoir-triggered seismicity (RTS). This phenomenon causes significant challenges for safe reservoir management. Irapé, in Brazil, is a prominent RTS site where seismicity surged after reservoir filling, with a maximum event of magnitude 3.0 in May 2006, just six months after the start of reservoir impoundment. Despite more than a decade has passed since the seismicity occurred, the factors governing these earthquakes and their connection to subsurface rock properties remain poorly understood. Here, we attempt to understand the potential causes of RTS at Irapé dam, which is the highest dam in Brazil with 208 m, and the second highest in South America. Permeability and porosity measurements of cylindrical cores from hard and intact rock samples, which have been extracted near the RTS zone, by pitting 10 cm from the surface, reveal a low-permeability rock. Porosity values range from 6.340 to 14.734 %. Only 3 out of the 11 tested samples present permeability higher than the lowest measurable value of the apparatus (0.002 mD), with the highest permeability being 0.0098 mD. The undrained response of the low-permeability rock placed below the reservoir results in an instantaneous increase in pore pressure and poroelastic stress changes due to elastic compression, which brings potential faults located below the reservoir closer to failure conditions. According to our analytical calculations, the increase in 136 m of the reservoir-water level caused a 0.54 MPa pore pressure buildup at the depth of the Magnitude 3.0 earthquake, i.e., 3.88 km, resulting in an increase of 0.82 MPa in the vertical effective stress and a decrease of 0.34 MPa in the horizontal effective stress. These changes resulted in an increase in the deviatoric stress that led to fault destabilization, causing the RTS. The laboratory measurements and analytical calculations corroborate the hypothesis that the initial seismic activity was induced by the undrained subsurface response to the reservoir loading at Irapé.
巴西伊拉佩水库蓄水的地下排水反应引发的地震
摘要减少碳排放以减缓气候变化的必要性正在加速从化石燃料向可再生能源的过渡。具体而言,水力发电已成为一种重要而安全的可再生能源,但会引起水库触发地震 (RTS)。这种现象给水库的安全管理带来了巨大挑战。巴西的 Irapé 是一个突出的 RTS 地点,水库蓄水后地震频发,2006 年 5 月,即水库蓄水开始后仅 6 个月,就发生了 3.0 级的最大地震。尽管地震发生已经过去了十多年,但人们对这些地震的影响因素及其与地下岩石性质的关系仍然知之甚少。在此,我们试图了解伊拉佩大坝 RTS 的潜在原因,该大坝是巴西最高的大坝(208 米),也是南美洲第二高的大坝。在 RTS 区域附近,通过在距离地表 10 厘米处打洞,从坚硬完整的岩石样本中提取圆柱形岩芯,对其渗透性和孔隙度进行测量,结果显示岩石的渗透性很低。孔隙度值从 6.340 % 到 14.734 % 不等。在 11 个测试样本中,只有 3 个样本的渗透率高于仪器的最低测量值(0.002 mD),最高渗透率为 0.0098 mD。位于储层下方的低渗透性岩石的不排水反应导致孔隙压力瞬间增加,弹性压缩引起孔弹性应力变化,从而使位于储层下方的潜在断层更接近破坏条件。根据我们的分析计算,储层水位增加 136 米导致 3.0 级地震深度(即 3.88 千米)的孔隙压力增加 0.54 兆帕,从而使垂直有效应力增加 0.82 兆帕,水平有效应力减少 0.34 兆帕。这些变化导致偏差应力增加,从而导致断层失稳,引发 RTS。实验室测量结果和分析计算结果证实了这一假设,即最初的地震活动是由地下未排水对伊拉佩储油层加载的反应引起的。
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来源期刊
Solid Earth
Solid Earth GEOCHEMISTRY & GEOPHYSICS-
CiteScore
6.90
自引率
8.80%
发文量
78
审稿时长
4.5 months
期刊介绍: Solid Earth (SE) is a not-for-profit journal that publishes multidisciplinary research on the composition, structure, dynamics of the Earth from the surface to the deep interior at all spatial and temporal scales. The journal invites contributions encompassing observational, experimental, and theoretical investigations in the form of short communications, research articles, method articles, review articles, and discussion and commentaries on all aspects of the solid Earth (for details see manuscript types). Being interdisciplinary in scope, SE covers the following disciplines: geochemistry, mineralogy, petrology, volcanology; geodesy and gravity; geodynamics: numerical and analogue modeling of geoprocesses; geoelectrics and electromagnetics; geomagnetism; geomorphology, morphotectonics, and paleoseismology; rock physics; seismics and seismology; critical zone science (Earth''s permeable near-surface layer); stratigraphy, sedimentology, and palaeontology; rock deformation, structural geology, and tectonics.
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