A strong and shallow earthquake registered by the EMSC as M6.5 hit Botswana, Africa at 17:40 UTC on April 3, 2017. The agency is reporting a depth of 22 km (13.6 miles). USGS is reporting M6.5 at a depth of 29 km (18 miles). Many smaller aftershocks have been recorded. This was the strongest quake to hit this region since serious seismic monitoring began in southern Africa about 70 years ago.
According to the USGS, the epicenter was located 132.9 km (82.6 miles) W of Moijabana (population 2 768) and 145.1 km (90.1 miles) SSW of Letlhakane (population 18 136), Botswana.
There are about 13 231 people living within 100 km (62 miles).
EMSC estimated there are 30 million people living in the felt area.
Many I felt it reports are coming from South Africa.
At 03:08 UTC today, a 5.2-magnitude earthquake hit 8 km (5 miles) south of the mining town of Stilfontein, South Africa. This is some 500 km (310 miles) S of the M6.5 epicenter.
Ian Saunders‚ a seismologist at the South Africa's Council for Geoscience‚ said today's earthquake in Botswana was a “serious” one.
“That is a big magnitude. We are currently assembling teams to be dispatched to Botswana. There are already teams heading to the earthquake zone from earlier in the day.” He said at this stage it was unknown if it was linked to the earthquake in South Africa. “We are currently awaiting reports of damage‚ injuries and possibly deaths.”
USGS issued a green alert for shaking-related fatalities and economic losses. There is a low likelihood of casualties and damage.
Overall, the population in this region resides in structures that are vulnerable to earthquake shaking, though some resistant structures exist.
Estimated population exposure to earthquake shaking
Selected cities exposed
Video bellow purportedly shows the shaking in Johannesburg, South Africa.
The Botswana earthquake of April 3, 2017, occurred in a region of southern Africa that has historically had a low level of earthquake activity. Moment-tensor calculations imply that the earthquake occurred as the result of slip on a northwest-trending fault centered in the lower-crust. This focal-mechanism is similar to those of earthquakes in the East African rift system, a diffuse zone of crustal extension that passes through eastern Africa from Djibouti and Eritrea on the north to Malawi and Mozambique on the south and that constitutes the boundary between the Africa plate on the west and the Somalia plate on the east. The mechanism, therefore, suggests that the April 3, 2017, earthquake occurred as the result of broad-scale regional tectonic stresses that are similar to those responsible for producing the East-African rift system. (USGS)
"It was the strongest quake to hit this region since serious seismic monitoring began in southern Africa about 70 years ago," UC Berkeley Seismology Lab said in a blog post.
"In contrast to its east and extreme north, the southern part of Africa is actually one of the oldest and most stable continental platforms on Earth. That is particularly true for Botswana, Namibia and the northern part of South Africa, where hardly any quakes were recorded in the last 70 years at all. Botswana had only two noteworthy quakes, one magnitude 5.8 event in the northwest of the country in 1952 and another in 2002 about 128 km (80 miles) southeast of Monday's temblor. That event registered with a magnitude of 4.5," they said.
As of early April 4, there are no reports of casualties or injuries.
According to USGS, the largest aftershock so far was M5.0 at 00:55 UTC on April 5, 2017.
According to seismologist Stephen Hicks of the University of Southampton, this earthquake is the largest to have struck mainland South Africa for over eleven years.
"The April 2017 Botswana event is classified as a normal faulting earthquake, yet its focal mechanism, which shows the orientation of extension, is approximately perpendicular to the East African rift. Therefore, a different geological structure, which may somehow be broadly related to the East African rift, may have been responsible for this earthquake," Hicks said.
"Earthquakes in Botswana are extremely rare. Given that this event has occurred over 1 000 km from the nearest tectonic plate boundary, we call these types of events 'intraplate earthquakes'. It is likely that the rupture occurred partly due to the gradual transfer of push and pull stresses from the East African Rift toward the more stable part of the continent. Occasionally, this stress is released along pre-existing weaknesses in Earth's crust as earthquakes. It is fundamentally the same reason why quakes occasionally occur in other stable regions such as the United Kingdom and the midwestern states of North America," he said.
Map showing earthquakes of magnitude 6.5 and greater that have occurred in Southern Africa since detailed records began (1900 onwards). Credit: USGS, Stephen Hicks, Google
Featured image credit: USGS