The oldest recorded earthquake in South Africa is widely accepted (in several seismic catalogues) to have occurred on 07 April 1620. This earthquake was regarded as
having a Modified Mercalli Scale intensity of II-IV, corresponding to a Richter Scale Magnitude of ~4. An examination of the original sources on which the record of
this earthquake rests, reveals that it was based on a description of ‘two startling thunderclaps like cannon shots while ship was becalmed near Robben
Island’ by Augustin de Beaulieu, who was the head of a fleet of three ships which put in Table Bay in March–April 1620. A full excerpt of Beaulieu’s
account reveals that the thunderclaps took place in a short period of calm during an extended period of stormy weather, and that the observations were made on board
ship, so that no seismic ground vibration was felt. The Western Cape has a much lower incidence of lightning than the interior of South Africa, and the fact that the
thunderclaps were not accompanied by lightning is not unusual. Thus the simplest explanation of the thunderclaps is that they were the result of atmospheric phenomena,
and not a result of seismic activity, as interpreted by J.N. Theron in 1974. The events of 07 April 1620 should thus be removed from the catalogues of historical
seismicity in South Africa, making the slight shock felt in Cape Town in 1690, with a Modified Mercalli Scale intensity of III, the oldest recorded seismic tremor
in the history of South Africa.
In several catalogues of historical seismicity in South Africa,1,2,3 the oldest recorded earthquake
in South Africa is considered to have occurred in 1620,
on 07 April. This event was originally attributed to a seismic origin by Theron1 (1974), based on information from Edward
(1936). Theron1 summarised the observations related to this supposed earthquake as: ‘Two startling thunderclaps like cannon shots
while ship was becalmed
near Robben Island for several days’. He implicitly attributed the thunderclaps to a seismic origin, because the events occurred while the ship was
‘becalmed’ for several days. The underlying assumption behind this attribution, although not explicitly stated, was that thunderclaps do not occur in calm
weather, only during a storm; in the absence of other ships which could have set off cannons, the only other agency that could have produced these sounds was an
earthquake. Having deduced a seismic origin for the phenomena, Theron1 then assigned them to an intensity of III-IV on the Modified
Scale,5 which corresponds to a Richter Scale Magnitude of ~4. In the Modified Mercalli Scale, an intensity of III is
described as ‘Slight, like the
vibrations due to a passing lorry; felt by people at rest, especially on upper floors’, while an intensity of IV is described as ‘Moderate: felt by people
while walking; rocking of loose objects, including standing vehicles’5. Subsequent catalogues of southern African seismicity have
reproduced Theron’s1 observations and calculations, and the event of 07 April 1620 has become entrenched as the oldest recorded
seismic event in South
The information concerning the ‘earthquake’ of 07 April 1620 was obtained from Strangman4 (1936), who in turn gave a translated
excerpt from the
work of Augustin de Beaulieu6 (1666), published by Melchisedech Thévenot 29 years after Beaulieu’s death. Augustin de
was a French general, who, at the behest of merchants from Paris and his native Rouen, was placed in command, from 1619 to 1622, of a fleet of three ships – the
Montmorency, the Espérance and the Hermitage – which sailed to the East
Indies.4,7,8 This fleet, known as the ‘Fleet
of Montmorency’ put into Table Bay on 15 March 1620 and left a month later on 14 April6,9 (Figure 1). Beaulieu
had the following to say about his stay at
the Cape, and about the events of 07 April 16204,6,9:
Not a good platform for making seismic observations from – Augustin
de Beaulieu’s ‘Fleet of Montmorency’, which put into Table Bay in 1620. From an
anonymous 17th-century French engraving.
A tempest from the South South-East, which lasted until the 3rd of April , prevented me from weighing anchor. On that day, however, at 10 o’clock
in the morning, the wind having moderated and coming from the South-East, we set sail. But we had not made two leagues towards the open water of the Bay before we found
ourselves becalmed in a heavy sea from the South, with a tide running North, which threatened to drive us on to the island. We were therefore constrained to anchor about
a league from this island, which lay from us North one quarter North-East. We were in twenty fathom water, with bottom of muddy sand, but the swell from the South made us
roll prodigiously, and everything in the ship creaked and cracked.
During the calm, I went to inspect the island. […] When I wanted to return on board a violent storm from the South-East suddenly broke upon us. It came over the
Bay from the land and swept so furiously between the mainland and the island that we - ourselves and one of the boats of the Vice-Admiral which had also been ashore -
were forced to seek shelter on the island, where we passed a very bad night. There was scarcely any wood, not enough to enable us to dry our clothes, which had become
thoroughly soaked in our attempt to force our way back to the ship through the storm. The next day, however, at dawn, we went aboard, where I was told that they had had
no wind at all, only complete calm, a circumstance which had troubled them greatly, as they could not conceive why we had remained all night on the island.
Tuesday, the 7th April, found us at the same anchorage, for lack of wind, though the rolling was still exceeding great. At break of day there was a startling
thunder-clap, followed immediately by another, which burst as though they had been cannon-shots, without any rumbling in the air as is usual with thunder. We feared a
storm was coming, but the calm continued to the next day, when, about 2 o’clock in the afternoon, there came a gentle breeze from the West, which made me resolve
to re-enter the Bay. Drizzling mists, however, so thick that we could scarcely see from one end of the ship to the other, overtook us, and I had to give orders for the
drum to be beaten and the trumpets to be sounded, so that the other ships might be guided by the noise of these instruments. Groping our way with the sounding-line, we
returned to our former anchorage, having previously noted that the head of the Bay lay South-East of us.
It is clear from the above account that no seismic shock was actually felt. The observers were located on a ship, and merely heard two loud thunderclaps, during a lull in
an extended period of stormy weather. Lightning strikes are much less common in the Western Cape than in the interior of the country (the coastal Western Cape has 0.1 to
1 strikes per km2, compared to >10 strikes per km2 in Gauteng, southern Mpumalanga and north-western
KwaZulu-Natal).10,11 In the
period from 30 March to 14 April 2011, the Western Cape had between 0 and 2000 lightning strikes per day, compared to the South African national average of between 75
and 153 000 lightning strikes per day.11 So the crew of Beaulieu’s ships may have been startled by the sound of the
thunderclap, without having
seen lightning, or heard the normal rumbling in the air associated with thunder. But this is not unusual, and cannot be used to argue for a seismic origin. The
tenuousness of the claim for a seismic origin1 is further exacerbated by the fact that the observations of the two thunderclaps were
made on board ship in
twenty fathoms of water, and not on terra firma, and hence no ground vibration was felt.
Although there are techniques to compress and speed up instrumentally recorded seismic signals to make them audible,12 modern seismic
instruments do not
capture sounds in the audible range, and most accounts of earthquake sounds are anecdotal. Historical records of past earthquakes in the Cape Town area indicate that
these earthquakes were accompanied by sounds like distant thunder, but very much louder, and by low subterraneous
rumblings.13,14 It should be borne in mind
that in the original description by Beaulieu,4,6 the sounds were recorded as two ‘thunderclaps’ in a
matter-of-fact way, with no indication that
there was anything mysterious or unusual about them, and the author should be taken at his word. Thus the most reasonable and uncomplicated explanation, in accordance
with the principle of Occam’s razor, is that the thunderclaps were merely atmospheric phenomena, and not seismic ones.
Aside from lightning-induced thunderclaps, there are other possible, although less likely, explanations for the atmospheric sounds that were heard by Beaulieu’s
crew on 07 April 1620. These possibilities include sounds generated by rainfall-induced landslides, and widely reported phenomena called ’skyquakes’.
Gunshot-like sounds were heard during the initiation of flood-induced landslides at Chilinda in the Nyika Plateau of Malawi on 23 April 1960, and during the December
1991 landslide at Punta Delgada, Madeira.15 ‘Skyquakes’ is the name given to the increasingly commonly reported phenomenon
of mysterious booming
sounds that are recorded in the atmosphere from many localities around the world; the commonest explanation for these is that they represent sonic booms generated by
meteorites or fireballs entering or exploding in the atmosphere.16,17
The discreditation of the events recorded on 07 April 1620 as being the result of an ‘earthquake’ means that the slight shock felt in Cape Town in 1690,
with a Modified Mercalli Scale intensity of III,1,3 is now the oldest recorded seismic tremor in the history of
South Africa. The field of historical
seismology relies on historical records of earthquakes and their effects in order to assess seismic hazards in particular regions.18 The
historical record of
South African earthquakes has been shortened by 70 years, which is unfortunate, but in the process a false report of a seismic phenomenon has been removed from the
history of the seismicity of the region around Cape Town, which is one of the hotspots for natural seismicity in southern Africa.
I am grateful for comments made by two anonymous reviewers, which helped to improve the paper.
I declare that I have no financial or personal relationships which may have inappropriately influenced me in writing this paper.
1. Theron JN. The seismic history of the southwestern Cape Province. In: The earthquake of 29 September 1969 in the southwestern Cape Province, South Africa.
Seismological Series, Geological Survey of South Africa. 1974;4:12–18.
2. Fernández LM, Guzmán JA. Seismic history of southern Africa. Seismological Series, Geological Survey of South Africa. 1979;9:1–38.
3. Brandt MBC, Bejaichund M, Kgaswane EM, Hattingh E, Roblin DL. Seismic history of South Africa. Seismological Series of the Council for Geoscience, Pretoria.
4. Strangman E. Early French callers at the Cape. Cape Town, Johannesburg: Juta & Co.; 1936.
5. Holmes A. Principles of physical geology. 2nd ed. London: Thomas Nelson and Sons;1965.
6. Beaulieu A de. Relation de l’estat present du commerce des Hollandais et des Portugais dans les Indes orientales: Mémoires du Voyage aux Indes Orientales
du Général Beaulieu dressés par luy-mesme [Relation of the present state of commerce of the Hollanders and Portuguese in the East Indies: Memoirs of
the voyage to the East Indies by General Beaulieu, as written by himself]. In: Thévenot M, editor. Relations de divers Voyages curieux [Accounts of diverse curious
voyages]. Volume II. Paris: Sebastien Mabre-Cramoisy, 1666; p. 1–128. French.
7. Guérin E. Relations anciennes de voyageurs célèbres: Augustin de Beaulieau, sa navigation aux Indes Orientales, 1619–1622 [Old accounts of
celebrated voyagers: Augustin de Beaulieu, his navigation to the East Indies, 1619–1622]. Paris: Hachette; 1905. French.
8. Gunn GC. The first globalization: The Eurasian exchange, 1500–1800. Lanham, MD: Rowman and Littlefield; 2003.
9. Harris J. The expedition of Commodore Beaulieu to the East Indies. In: Navigantium et Itinerantium Bibliotheca [Library of voyages and itineraries]. Volume 1.
London: T. Woodward, A. Ward and S. Birt, 1745; p. 728–731.
10. De Wet P. How to deal with a million bolts a month. Mail & Guardian 2011 January 28–February 3;20–21.
11. South African Weather Services [homepage on the Internet]. No date [cited 2011 Oct 25]. Available from:
12. Frantti GE, Leverault LA. Auditory discrimination of seismic signals from earthquakes and explosions. Bull Seismol Soc Am. 1965;55:1–25.
13. Von Buchenroder WL. An account of the earthquakes which occurred at the Cape of Good Hope, during the month of December, 1809; with a meteorological table, from the
4th to the 27th; and an appendix containing notices of shocks which have occurred at various other periods. South African Quarterly Journal. 1829–1830;1(1)
14. Master S. The 4th December 1809 Cape Town (South Africa) earthquake and attendant phenomena – a bicentennial perspective. Paper presented at: International
Association of Seismology and Physics of the Earth’s Interior (IASPEI) General Assembly 2009: Abstracts; 2009 Jan 10–16; Cape Town, South Africa.
15. Master S, Duane MJ. The Nyika Plateau Structure (Malawi, Central Africa) rediscovered: Not an astrobleme. Paper presented at: 29th Lunar & Planetary Science
Conference. Lunar & Planetary Science XXIX; 1998 March 16–20; Houston, TX, USA. Houston, TX: Lunar and Planetary Institute; 1998. Abstract No. 1057 (CD-ROM).
16. Global Disaster Watch. Mystery booms/skyquakes [homepage on the Internet]. No date [cited 2012 May 05]. Available from:
17. Griffith M. Mysterious explosion and daylight fireball in Nevada, California skies (+video) [homepage on the Internet]. c2012
[cited 2012 May 05]. Available from:
18. Reicherter K, Michetti AM, Silva Barroso PG. Palaeoseismology: Historical and prehistorical records of earthquake ground effects for seismic hazard assessment. The
Geological Society, London, Special Publications. 2009;316:1–10.