Source parameters of four strong earthquakes in Bulgaria and Portugal at the beginning of the 20th century |
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| Authors: | S Dineva J Batllo D Mihaylov T van Eck |
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| Institution: | (1) Department of Earth Sciences, University of Western Ontario, 1151 Richmond St., London, Ontario, Canada, N6A 5B7;(2) Dept. Matematica Aplicada I, UPC, Av. Diagonal 647, E-08028, Barcelona, Spain;(3) Dept. Geodinamica i Geofisica, UB, c. Marti Franques s/n, E-08028 Barcelona, Spain;(4) Geophysical Institute Bulgarian Academy of Sciences, Acad. G. Bonchev St. block 3, 1113 Sofia, Bulgaria;(5) Seismology Division, Royal Netherlands Meteorological Institute, P.O. Box 201, 3730 AE De Bilt, The Netherlands |
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| Abstract: | Using original seismograph records and bulletin data we re-determined theorigin time, location, seismic moment (M0) and magnitudes(MS and Mw) for four earthquakes in the beginning of the20th century. These are two strong earthquakes April 4, 1904 nearKrupnik, Bulgaria (Mw = 6.8, MS = 7.2 respectively), the April 231909 earthquake near Benavente, Portugal (MS = 6.3), and the June14, 1913 earthquake near Gorna Orjahovitza, Bulgaria (MS = 6.3).Twenty-nine traces from original records have been analysed, a largenumber of original station bulletins have been consulted and a consistentmethodology for analysing these early 20th century instrumentalinformation is presented.In spite of a thorough effort in re-assembling and quality control of theoriginal data, large inaccuracies remain in the improved instrumentalepicentre locations and origin times. The seismic moment estimates weobtained (2.3 1018  M0 3.9 1019Nm) are the first ever determined for these events. The magnitudeestimates (6.3 MS 7.2 and 6.2 Mw 7.0) are robust and systematically lower than most of previousestimates for all earthquakes (Gutenberg and Richter, 1954; Christoskovand Grigorova, 1968; Karnik, 1969). For the largest Krupnik event ourestimates agree with those of Abe and Noguchi (1983b) and Pacheco andSykes (1992). The studied earthquakes all occur in moderately seismicactive regions, therefore our results may have significant consequences forhazard estimates in those regions. |
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| Keywords: | Bulgaria early 20th century magnitudes mechanical seismographs Portugal seismic moment seismogram digitising source parameters |
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