Background seismicity and seismic monitoring in the Lai Chau reservoir area

Abstract

Reservoir-triggered seismic activity depends not only on the technical characteristics of the future reservoir (filling volume, the height of water column) but also on the seismo-tectonics and the natural seismic processes occurring in the area before construction of an artificial reservoir. Passive seismic monitoring was realised near Lai Chau (Vietnam) before the impoundment started. It allowed exploration of the natural seismicity in the area of the future dam. Locations of seismic events several months prior to the reservoir impoundment were observed with ten stations installed in the reservoir vicinity. Events were mainly located near the dam along the Da river headwaters fault. However, only four stations were available for the entire period before the impoundment. Despite the network limitations, completeness of seismic catalogue and b value were determined and may be used as a baseline for analysis of the seismicity in this area after impoundment. The magnitude completeness level is significantly smaller than in the broader seismogenic zones covering an area of the dam. The b value differs from the results obtained for regional seismicity of Northeastern Vietnam. The capability of the local network for moment tensor inversion was estimated with the use of synthetic data tests. Test results provided the requirements for the station number according to azimuthal coverage of the network to obtain the reliable full moment tensor (MT) solution. Preliminary analysis of the seismic activity after Lai Chau reservoir impoundment indicates some changes in activity related to the impoundment and reservoir exploitation.

Reservoir-Triggered Earthquakes Around the Atatürk Dam (Southeastern Turkey)

“…Shallow focal depths (<10 km) are also revealed in the study of Irmak et al (2020). Shallow hypocenters are often found for seismicity induced or triggered by reservoir loading in other regions (Simpson et al, 1988;Lizurek et al, 2019;Ruiz-Barajas et al, 2019) and they can be linked to the significant damage in the vicinity of the AR in 2017 and 2018. As previously indicated in the study of Irmak et al (2020) most of the epicenters are located close to the Samsat town and mapped along the Samsat fault, which has been known but not considered as an active fault in Turkey's current faults map (Emre et al, 2018).…”

Overview of the Characteristics of Reservoir-triggered Seismic Activity at Some Hydropower Reservoirs in Vietnam

“…Triggered earthquakes in Hoa Binh and Son La areas are associated with deep fault systems and limestone geological structures, while in Song Tranh 2 area, triggered earthquakes occur mainly on gneiss rock, associated with faults grad II (Table 2) Nguyen et al 1996;Le et al 2012;Cao et al 2016;Dinh Dinh). et al 2017;Lizurek et al 2019).…”

“…Five short-period seismic stations were installed around the reservoir, and operated from 1990 to 1995, these seismic stations detected ~400 earthquakes of magnitude M=2.0-4.0 (Dinh et al 2017); (2) The Song Tranh 2 hydropower was constructed in Vu Gia -Thu Bon river basin, the reservoir was fully impounded in October 2010, soon after that earthquakes started occurring. Since then, over 3.000 earthquakes of magnitude M ≥ 1.0 have been recorded, the largest event of magnitude M = 4.7 occurred on November 15, 2012 Gahalaut et al 2016;Thai et al 2017;Lizurek et al 2019). Ten seismic stations have been installed and operated around the reservoir since September 2013.…”

“…The distance between stations is about 5 to 15 km; (3) The largest triggered earthquake of magnitude of 4.4 occurred in the Son La hydropower reservoir on July 19, 2014, after the reservoir was fully impounded in April 2012 (Le et al 2012;Cao et al 2016). Currently, around the Son La reservoir exists a seismic network comprising 6 stations which monitor earthquakes in the region (Dinh et al 2017;Lizurek et al 2019).…”

Slow slip-driven seismic signature triggered by water-reservoir impoundment

“…To conduct this analysis, we launched a seismic monitoring campaign, during which we recorded more than 7000 earthquakes with magnitudes ranging from −0.6 to 3.6 in the ST2 region from August 2013 to June 2017 (see Methods for details). This experiment is one of three projects targeting AWR impoundment seismicity in the ST2, Lai Chau, and Hue regions of Vietnam (23). The ST2 Reservoir's volume is 740 million cubic meters, and the water level varies from 140 to 175 m. The seismic activity in the reservoir region began in 2011, soon after the reservoir was filled.…”