Cyfeiriadau T. Nield, 'A quiverful of Welsh earthquakes', Country Quest (1985), 16-17. (Carwn ddiolch i Dafydd Guto am ddwyn yr erthygl hon i'm sylw.) 2 G. Neilson a P. W. Burton, A Brief History of the Seis- mological Observations in theBritishlsles, 1896-1960 (British Geol. Survey, Edinburgh, 1986). 3 Ibid. 4 S. van Rose, Earthquakes (HMSO, London, 1983), 17. 5 J. Erickson, Volcanoes and Earthquakes (Tab Books Inc, Blue Ridge Summit, 1988), 213-16. 6 Y Cymro, 24 Gorffennaf 1984. Graddfa ansoddol (tebyg i raddfa Mercalli) a ddefnyddir i gofnodi dwysedd daeargrynfeydd yw graddfa MSK. Mae'n raddfa a luniwyd yn gymharol ddiweddar gan S. Med- vedev, W. Sponheuer, a V. Kamik, gweler S.Medvedev et al., 'Neue sesmiche skola' [New seismic scale], yn W. Sponheuer (gol.), European Seismological Com- mission, 7th Symposium (1964), 69-76. 7 T. Turbitt et al., 'The North Wales earthquake of July 1984',J. geol. Soc. Lond., 142 (1985), 567-71; gweler yn arbennig t.569. 8 T. Turbitt (gol.), Global Seismology Report No.260. Catalogue of British Earthquakes recorded by the BGS seismograph network 1982, 1983, 1984 (British Geol. Survey, Edinburgh, 1985), 33-5. 9 T. Turbitt et al., op. cit. 10 Ibid. 11 N. Woodcock, 'Welsh Earthquakes', Geol. Today (1991), 143-4. 12 C. Davison, 'Earthquakes in Great Britain (1889- 1914)', Geol. J, 46 (1915), 357-74. 13 P. W. Burton a G. Nielson, Annual Catalogues of British earthquakes recorded on LOWNET (1967- 1978) (Seismological Bull. No.7, Institute of Geologi- cal Sciences, London, 1980). ° 14 T. Turbitt (gol.), op. cit. (1985), 11-32. 15 P. W. Burton a R. M. W. Musson, Global Seismology Report No. 271. A Provisional Catalogue of the Earth- quakes in Wales and the Marches (British Geol. Sur- vey, Edinburgh, 1986). 16 C. Davison 'On the Pembroke earthquakes of August 1892, and November, 1893', Quart. J. geol. Soc Lond., 53 (1897), 157-76. 17 Ibid., 'The Caernarvon earthquake of June 19th, 1903. and its accessory shocks', Quart. J. geol. Soc. Lond 60 (1904), 233-42. 18 Ibid. 'The Swansea earthquake of June 27th, 1906', Quart. J. geol. Soc. Lond., 63 (1907), 351-61. 19 N. Woodcock, op. cit. 20 Ibid. 21 E. L. James, 'Y Cyfandiroedd Symudol', Y Creu/Y Gwyddonydd, 16(2/3) (1978), 93-103.