Data Services Newsletter

Volume 20 : No 3 : Winter 2018

Botswana Seismological Network (BX)

Inspired by recommendations from a plethora of previous local and regional seismic studies, the Government of Botswana through the Department of Geological Survey or DGS (now the Botswana Geoscience Institute or BGI) embarked on the implementation of a national development project (NDP) entitled the “Botswana Seismological Network” (BSN). The BSN project was launched during the period between 2000 and 2001, and involved the installation of a network of seven accelerographic stations distributed across the Okavango delta region (ODR) in northwestern Botswana that is the most seismically active area in Botswana. The network was deployed for long-term monitoring of seismic activity of northwestern Botswana to improve our understanding of the causes of earthquakes in the area and enable better assessment of the distribution, frequency, and severity of seismic-related hazards and risks throughout the northwestern part of Botswana. Thus, the BSN stations were installed mainly as an earthquake risk management tool for improving our knowledge of the seismotectonics and seismic hazard potential of Botswana particularly in the ODR in order to build the nation’s resilience to earthquakes. In addition to seismic hazard mapping, the data from the BSN stations can also be used in various other seismological applications such as mapping tomographic, attenuation and anisotropic structures of the crust and uppermost mantle beneath northeastern Botswana and investigation of processes involved in the on-going incipient rifting across the Okavango rift zone. The DGS collaborated with the University of Botswana’s Physics Department (UBPD) in the acquisition, installation and maintenance of the BSN equipment. Hence as of 2011, the BSN comprised a total of nine seismic stations of which two stations were contributed by the UBPD while seven stations were provided by the DGS (Table 1).

Table 1: List of the BSN stations as of October 2011. Stations in the index range 1–7 were operated by the Department of Geological Survey, while the stations indexed 8 and 9 were operated by the University of Botswana. All the station sites were equipped with digital broadband, three-component EpiSensor Kinemetrics K-2 accelerometers equipped with GPS receiver timing, Altus K2 recorders and removable hard disks.
1 TOT1 20.377°S 22.965°E 940m Toteng Operational DGS
2 SVT1 18.582°S 24.072°E 940m SavutiI Operational DGS
3 MTP1 20.230°S 24.099°E 936m Motopi Operational DGS
4 MWG1 19.630°S 23.820°E 962m Mawana Operational DGS
5 KBH1 20.702°S 23.051°E 1042m Kgwebe Operational DGS
6 TSD1 18.707°S 21.713°E 1045m Tsodilo Operational DGS
7 QNG1 19.525°S 21.208°E 1050m Qangwa Operational DGS
8 UBOT 20.540°S 22.740°E 957m Bothatogo Operational UB
9 ORC1 19.900°S 23.520°E 955m ORC Not working UB

The BSN accelerometric stations reached the end of their lifetime of operation around 2015, and were consequently de-installed from the field sites in 2016. Due to the high level of seismicity in the ODR, there is a need for the re-establishment of a dense network of seismic sensors for monitoring micro-earthquakes in the Ngamiland region.

Currently (as of November 2018), the BSN stations have been revitalized through the deployment of a countrywide state-of-the-art network of 21 autonomously recording broadband, three-component and high-sensitivity seismographic stations (Table 2 and Figure 1). The network was installed through a collaborative project between the BGI and the Netherlands based University of Twente (UT) and the Utrecht University (UU), called the 2013-2018 Network of Autonomously Recording Seismographs Botswana or NARS-Botswana. The NARS network utilized a combination of the Streckeisen STS-2 and Nanometrics Trillium 120 seismometers (Table 2). The scientific purpose of the NARS-Botswana project was to map the seismological structure of the crust and mantle beneath Botswana using seismic signals generated by earthquakes from all over the world. At the end of the NARS-Botswana project in April 2018, ownership of the modern seismic stations was transferred to the BGI to reconstitute the BSN earthquake monitoring system.

The 2013-2018 NARS-Botswana project has provided a large quantity of continuous record of high quality seismic waveform data from earthquakes in Botswana and from all over the world. The analysis of the seismograms is providing a better definition of the local seismicity of Botswana to improve our understanding of the causes of the earthquakes in the region. The seismicity information also provides a base for earthquake disaster risk reduction research involving assessment of the potential for future damaging earthquakes to contribute in the minimization of loss of human life, property damage, and social and economic disruption attributable to earthquakes in the country. Furthermore, the NARS waveform database will be used for an array of other seismological studies, including tomographic inversion for the three-dimensional structure of the crust and upper mantle under Botswana for guiding area selection for mineral exploration, and development of local 1-D models to enable accurate locations of earthquakes to be determined.

With the modern seismological observatory of the BSN in place, the BGI is currently working on the establishment of a Botswana Seismological Research Center (BSRC). The BSRC will serve as a center of excellence dedicated to undertaking fundamental research in seismology for building a nation that is earthquake hazard conscious and earthquake-resilient in public safety within the built environment and economic development in order to avoid earthquake disasters and minimize loss of human life, property damage, and social and economic disruption due to earthquakes in Botswana. The stages of the BSRC project will involve benchmarking with the best earthquake research and seismic data dissemination organizations in the world, including, among others, the Incorporated Research Institutions for Seismology (IRIS) Data Management Center (DMC). Following a fruitful BGI meeting with the Director of IRIS Data Services Dr Tim Ahern in Gaborone recently, the Consortium supports the BGI’s decision to establish the BSRC and has offered to host BGI team for the planned benchmarking visit to Seattle in the January–February 2019 period that will include BGI staff training provided by the DMC as part of the benchmarking exercise. In addition, IRIS has donated a powerful computer system to serve as an Sc3 workstation. The BSN has already been provided with the network code BX as assigned by the International Federation of Digital Seismograph Networks (FDSN), and so IRIS will work with the BGI in making the BSN part of the Federated Data Centre System in line with plans by IRIS to incorporate about 6 data centers especially in the East African Rift System region to enable long-term collaborative seismological research of common interest.

Table 2: Tabulated specification list of the current BSN stations
Station code Location name Sensor Latitude Longitude Altitude (Meters)
SKOMA Sekoma Trillium 120p 24.51535°S 23.93279°E 980
LKGWB Lokgwabe Trillium 120p 24.11352°S 21.78230°E 1153
KOOLE Kole Trillium 120p 22.99307°S 20.19555°E 1313
XAUDM Xaudum STS-2 18.53956°S 21.33822°E 1060
SLIND Selinda Trillium 120p 18.62089°S 23.50048°E 961
KSANE Kasane Trillium 120p 17.80017°S 25.16189°E 1006
QNGWA Qangwa Trillium 120p 19.52957°S 21.17400°E 1094
KHWEE Khwee Trillium 120p 21.94641°S 25.44691°E 1083
CKGRV Central Kalahari Game Reserve Trillium 120p 21.40355°S 23.77177°E 1005
GRTLG Groot Laagt STS-2 21.36192°S 21.21571°E 1198
KGCAE Kacgae Trillium 120p 22.85382°S 22.20679°E 1153
KDWAN Kaudwane Trillium 120p 23.38039°S 24.66079°E 1038
PHEPN Phepeng Trillium 120p 25.47553°S 22.85729°E 1030
GMARE Gumare STS-2 19.38931°S 22.16246°E 985
BTLPN Bottlepan STS-2 18.78417°S 25.19601°E 1035
PHDHD Phuduhudu STS-2 20.19568°S 24.53719°E 956
BROLN Borolong Trillium 120p 21.09968°S 27.33424°E 1047
SOOWA Sowa Trillium 120p 20.56285°S 26.21785°E 941
MREMI Moremi Trillium 120p 22.56967°S 27.44682°E 911
LPHEP Lephepe Trillium 120p 23.36303°S 25.85961°E 1020
MAKGR Mmakgori Trillium 120p 25.81185°S 24.80085°E 1158

Figure 1
Figure 1: Map showing the distribution of the BSN stations (triangles) across Botswana (Table 2). These stations were initially installed within the framework of the NARS-Botswana project.

by Motsamai Kwadiba , Onkgopotse Ntibinyane and Puso Akanyang (Botswana Geoscience Institute)

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