Induced seismicity at the Laúca reservoir, Angola Craton: Focal mechanisms and implications for the stress field in Western Central Africa

IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Journal of African Earth Sciences Pub Date : 2024-06-26 DOI:10.1016/j.jafrearsci.2024.105327
Lucas Schirbel , Marcelo Assumpção , Francisco António Pereira Neto , George Sand França
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Abstract

We present the first case of reservoir induced seismicity (RIS) ever reported in the Angola Craton, Laúca reservoir. Impoundment of the reservoir began in late 2017 and seismicity started in March 2018 shortly after the water level reached 86 m. Earthquakes continued to be recorded in the following years, with 287 events detected between March/2018 and April/2024. The largest event had magnitude 3.0 ML. The dam is 156 m tall, and the total reservoir volume is 5,044.85 Hm3. The reservoir area is monitored by two stations, LAUC and ZERO. Seismic data is of high quality, with sharp P- and S-wave arrivals at both stations. We derive a half-space velocity model for the lake area using a composite Wadati diagram and minimization of travel time residuals and locate 90 events with arrivals at both stations. S-to-P converted phases at the surface were used to help constrain hypocentral depths and epicentral locations. We use waveform modeling to determine focal mechanisms for ten events using the program FMNEAR, and invert for the local stress field. We find the faulting regime in the area to be strike-slip and SHMax oriented roughly NE-SW. We compare our results to the broader stress field in western Central Africa and find them to be in agreement with nearby stress determinations from focal mechanisms in the Congo Basin. Our results make an important contribution to the state of knowledge of the stress field in western Central Africa, which can be taken into consideration in future geodynamic models of the Nubian plate as more data is gathered and help further our understanding of stress sources in this region.

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安哥拉克拉通劳卡储层的诱发地震:焦点机制及其对非洲中西部应力场的影响
我们介绍了安哥拉克拉通地区劳卡水库首次报告的水库诱发地震(RIS)案例。水库于 2017 年末开始蓄水,2018 年 3 月水位达到 86 米后不久便开始发生地震。最大的一次地震震级为 3.0 ML。大坝高 156 米,水库总容积为 5,044.85 立方米。库区由两个监测站(LAUC 和 ZERO)进行监测。地震数据质量很高,两个站点都有尖锐的 P 波和 S 波到达。我们利用综合瓦达蒂图和移动时间残差最小化推导出湖区的半空间速度模型,并确定了 90 个到达两个站点的事件。地表的 S-P 转换相位被用来帮助确定低中心深度和震中位置。我们利用波形建模,使用 FMNEAR 程序确定了 10 个事件的病灶机制,并对当地应力场进行了反演。我们发现该地区的断层机制为走向滑动,SHMax 走向大致为东北-西南。我们将我们的结果与中非西部更广泛的应力场进行了比较,发现它们与刚果盆地焦点机制的附近应力测定结果一致。我们的研究结果对了解中非西部的应力场做出了重要贡献,随着更多数据的收集,努比亚板块未来的地球动力学模型可以考虑这些数据,并有助于我们进一步了解该地区的应力源。
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来源期刊
Journal of African Earth Sciences
Journal of African Earth Sciences 地学-地球科学综合
CiteScore
4.70
自引率
4.30%
发文量
240
审稿时长
12 months
期刊介绍: The Journal of African Earth Sciences sees itself as the prime geological journal for all aspects of the Earth Sciences about the African plate. Papers dealing with peripheral areas are welcome if they demonstrate a tight link with Africa. The Journal publishes high quality, peer-reviewed scientific papers. It is devoted primarily to research papers but short communications relating to new developments of broad interest, reviews and book reviews will also be considered. Papers must have international appeal and should present work of more regional than local significance and dealing with well identified and justified scientific questions. Specialised technical papers, analytical or exploration reports must be avoided. Papers on applied geology should preferably be linked to such core disciplines and must be addressed to a more general geoscientific audience.
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