Abstract
On the 3rd of April 2017, an earthquake of moment magnitude 6.5 occurred near Moiyabana in central Botswana. This paper is aimed at studying the spatial distribution of the foreshock and aftershock sequences associated with the Moiyabana earthquake. The foreshocks and aftershocks data used were from the Botswana Geoscience Institute (BGI) and the Seisan software was used to analyze the foreshock and aftershock events. The analyses revealed nine epicenter locations of foreshocks which are spread out across the country and most of them are located in the central and southern parts of Botswana, while the aftershocks are clustered around the mainshock. Although five of the nine foreshocks occurred far from the boundaries of major tectonic units, the other four occurred near key features such as the Zoetfontein, Lecha and Chobe faults. The spatial distribution of aftershocks indicates that the stress released by the mainshock, re-activated the planes of weakness in the vicinity of the mainshock and farther away from the mainshock. Hence, this affected the Zoetfontein fault, the boundary between Passarge basin and Magondi belt and the boundary between the Kaapvaal craton and Limpopo mobile belt. The aftershocks also show a northwest-southeast trend, which probably indicates the rupture plane; and mainly lie within the Limpopo mobile belt that is sandwiched between the Kaapvaal craton to the south and Zimbabwe craton to the north. Furthermore, the aftershocks concentration to the south reveals a close relation in demarcating the boundary of the Kaapvaal craton and the Limpopo mobile belt.
Highlights
An earthquake or tremor is the sudden movement of the ground caused by the rapid release of energy that has accumulated along fault zones in the earth’s crust [1]
The main aim of this study is to use data recorded by the Network of Autonomously Recording Seismographs (NARS) project to understand the spatial distribution of epicentres of foreshocks and aftershocks associated with the Moiyabana earthquake that occurred in central Botswana on the 3rd April 2017
The NARS database was searched for seismic events starting with the month of 1st December 2016 through to 2nd April 2017 to identify possible foreshock events for a period of 4 months associated with the Moiyabana earthquake that occurred in central Botswana on the 3rd April 2017
Summary
An earthquake or tremor is the sudden movement of the ground caused by the rapid release of energy that has accumulated along fault zones in the earth’s crust [1]. Seismologists have adopted two widely used scales, which are the Richter scale and Mercalli scale, to measure the energy released by an earthquake [1]. According to [3], the largest earthquakes occur in a seismic cycle in which the interseismic stage makes up most of the cycle and steady motion occurs away from the fault, but the fault is “locked”. There is the preseismic stage that can be associated with foreshocks (small earthquakes). The mainshock (large earthquake) marks the coseismic phase during which rapid motion on the fault generates seismic waves [3]. Earthquakes are thought to trigger aftershocks either from the dynamic effects of their radiated seismic waves or the resulting permanent static stress changes [4]
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