Appendix 19        

9/56 YEAR CYCLE: CAPE PROVINCE EARTHQUAKES

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Appendix for the paper 9/56 year Cycles: Earthquakes & Volcanoes.

 

Geological Survey of South Africa, Seismology Unit gave a comprehensive listing of earthquakes to 1971 in the southwestern Cape Province of South Africa. Of the total 44 earthquakes presented for the period 1800 to 1971, 21 appeared in the 12 months beginning June 15 of those years in the 9/56 year grid shown in Table A (significant at p < .001). Problems arose in regard to the listing's suitability for appraisal and the result may be spurious. Some events were only entered once, yet they clearly involved several notable earthquakes (eg: 4-12 December 1809; June 2 1811; October 7, 1969; April 4 1970; April 15 1970; September 19 1970). These cases were assumed to be just one quake, because this was the only viable approach.

 

Table A     9/56 YEAR CYCLE: SOUTH AFRICAN QUAKES 1800 - 1971
Year commencing June 15
  Sq
32		 Sq
41		 Sq 
50		 Sq
03		 Sq 
12		 Sq
21		     Sq
48
                  1808
    1801 1810
***		 1819 1828 1837 1846 1855 1864
1839  1848 1857 1866 1875  1884 1893  1902 1911
**		 1920
***
1895  1904

1913

 1922

1931

 1940

1949

 1958 1967

1976
1951 1960

1969
******

 1978

1987

 1996 2005      

The 56 year sequences are each separated by 9 years.
Years in bold contained major South African quakes in the 12 months commencing June 15 of those years in the table.
Source of Raw Data: Geological Survey of South Africa, Seismology Unit

 

SOUTHWESTERN CAPE PROVINCE EARTHQUAKES: 1800 TO 1971
Date Effects Intensity Mag
4-12 Dec 1809 Three strong quakes, second most violent on 4th. Another 4 tremors from 5th to 12th, some strong VI-VIII 6.1
26 Dec 1810 Genadendal III 3.5-4
7 Jan 1811 Not given II-III ± 3.8
2 Jun 1811 Two loud shocks. Location not given VII 5.5-6
19 Jun 1811 Not given V 4.8
24 Jun 1819 Piketberg III ± 4
14 Apr 1826 Not given III ± 4
Early in 1826 Saldanha Bay VI? ± 5?
11 Nov 1835 Not given V 4.8
14 Aug 1857 Cape Town IV ± 4.5
28 May 1902 Not given IV-V 4.8
6 Jul 1911 Oudtshoorn III-IV ± 4
20 Feb 1912 Koffiefontein. Felt all over South Africa. VIII ± 6
13 Aug 1920 Not given IV 4.5
4 Dec 1920 Cape Town, George, Port Elizabeth.  IV 6.2
19 Feb 1921 Vanrhynsdorp V 4.8
9 Oct 1921 Tulbagh VI ± 5.0
1924 Slight tremble only felt locally III ± 4
11-13 Aug 1926 Series of tremors at Darling III-IV? ± 4?
18 Nov 1932 Cape Town VI ± 5?
19 Aug 1937 Darling IV ± 4.5
1940? Wolseley IV ± 4.5
23 Oct 1941 West of Bitterfontein V 4.8
24 Aug 1944 Beaufort West II-III 3
27 Feb 1947 Two very noticeable earth tremors felt at Cape Columbine and Paternoster. V 4.8
19 Nov 1950 Cape Town III 4.2
26 Feb 1952 Swellendam III 4.2
20 Sep 1957 Cape Town III 4.2
30 Sep 1957 Cape Town III 4.2
29 Aug 1960 Boland & Cape Town IV-V 4.3-4.8
27 Aug 1963 Western Cape VI 5.0
18 Sep 1963 Karoopoort-Ceres IV-V 4.3-4.8
21 Feb 1964 Peninsula IV 4.3
28 Sep 1965 Oudtshoorn IV 4.3
1 Mar 1966 Peninsula IV 4.3
12 Sep 1969 Western Cape IV-V 5.4
29 Sep 1969 Western Cape VIII-IX 6.3
1 Oct 1969 Tulbagh III? 4.2
6 Oct 1969 Sea Point III? 4.2
7 Oct 1969 to 13 Apr 1970 Tulbagh/Ceres area 10 tremors were felt on 4 Mar 1970; at Ceres at 01:00 a readning of 4 Richter Scale. III-IV ± 4.2
14 Apr 1970 Ceres/Tulbagh. Western Cape VII 5.7
15 Apr 1970 to 19 Sep 1971 According to newspapers very few tremors of great magnitude.    
19 Sep 1971 Ceres-Tulbagh-Porterville IV ± 4
28 Sep 1971 Southwestern Cape Province IV-V 4.8
Events presented in bold occurred in the 12 months beginning June 15 of those years in Table A.
Source: Geological Survey of South Africa, Seismology Unit.
Theron, J.H., 1974, The earthquake of 29 September 1969 in the southwestern Cape Province, South Africa. Seismologic Series 4, Geological Survey, p. 12-18.
Fernandez, L.M., & Guzman, J.A., 1979, Seismic history of Southern Africa. Seismologic Series 9, Geological Survey, 38 pp.