Lucas Schirbel , Marcelo Assumpção , Francisco António Pereira Neto , George Sand França
{"title":"Induced seismicity at the Laúca reservoir, Angola Craton: Focal mechanisms and implications for the stress field in Western Central Africa","authors":"Lucas Schirbel , Marcelo Assumpção , Francisco António Pereira Neto , George Sand França","doi":"10.1016/j.jafrearsci.2024.105327","DOIUrl":null,"url":null,"abstract":"<div><p>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 Hm<sup>3</sup>. 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 SH<sub>Max</sub> 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.</p></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2000,"publicationDate":"2024-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of African Earth Sciences","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S1464343X24001602","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"GEOSCIENCES, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
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.
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.