Classical focal mechanism techniques for body waves
- 72 Downloads
The initial motion of primary body waves and polarization directions of secondary body waves have been applied successfully to the study of the mechanism operating at the earthquake focus. Equal area plots of these body wave characteristics resulted in radiation patterns that were compared to patterns due to theoretical focal mechanism sources. Such an approach indicated that a double couple force is the source mechanism operating at earthquake foci. This can be physically represented by faulting at the focus. This seems likely because of the relation between earthquakes and fault motion in shallow earthquakes. The possibility of other mechanisms operating in deep focus earthquakes has not been ruled out.
The technique of solving for fault plane orientation/motion in equal area plots ofP-wave first motion andS-wave polarization, has been a powerful tool in areas where fault motions cannot be directly observed in studying tectonics. Such an approach has been used to test the theory of global tectonics. This approach has resulted in the confirmation of the suggested mechanics of plate motion, and the results of plate motion, such as spreading of the sea floor from mid-oceanic ridges and underthrusting of lithospheric plates at the sites of oceanic trenches.
KeywordsTrench Fault Plane Focal Mechanism Plate Motion Body Wave
Unable to display preview. Download preview PDF.
- Byerly, P.: 1926, ‘The Montana Earthquake of June 28, 1925 G.M.C.T.’,Bull. Seism. Soc. Am. 16, 209–263.Google Scholar
- Bath, M.: 1961, ‘Polarization of Transverse Seismic Waves’,J. Geophys. Res. 4, 106–123.Google Scholar
- Hamilton, R. M. and Muffler, L. J. P.: 1972, ‘Microearthquakes at the Geysers Geothermal Area, California’,J. Geophys. Res. 77, 2081–2086.Google Scholar
- Hodgson, J. H.: 1957, ‘Nature of Faulting in Large Earthquakes’,Geol. Soc. Am. Bull. 68, 611–644.Google Scholar
- Hodgson, J. H. and Storey, R. S.: 1953, ‘Tables Extending Byerlys Fault Plane Technique to Earthquakes of any Focal Depth’,Bull. Seism. Soc. Am. 43, 49–62.Google Scholar
- Hodgson, J. H., and Allen, J. F. J.: 1954, ‘Tables of Extended Distances forPkP andPcP’,Publ. Dominion Obs. Ottawa 16, 327–348.Google Scholar
- Hodgson, J. H., Allen, J. F. J., and Cock, J. I.: 1956, ‘Tables of Extended Distances forS, SS, andsS’,Publ. Dominion Obs. Ottawa 18, 85–100.Google Scholar
- Honda, H.: 1934, ‘On theScS Waves and the Rigidity of the Earth's Core’,Geophys. Mag. 8, 165–177.Google Scholar
- Isacks, B., Sykes, L. R., and Oliver, J.: 1969, ‘Focal Mechanisms of Deep and Shallow Earthquakes in the Tonga-Kermadec Region and the Tectonics of Island Arcs’,Geol. Soc. Am. Bull. 80, 1443–1470.Google Scholar
- Nakano, H.: 1923, ‘Notes on the Nature of the Forces Which Give Rise to the Earthquake Motions’,Cent. Meteor. Obs. Japan Seism. Bull. 1, 92–120.Google Scholar
- Nuttli, O. and Whitmore, J. D.: 1962, ‘On the Determination of the Polarization Angle of theS-Wave’,Bull. Seism. Soc. Am. 52, 95–107.Google Scholar
- Reid, H. F.: 1910.The California Earthquake of April 18, 1906, Report of the State Earthquake Investigation Committee 11, Car. Inst. of Wash. Publ. 87.Google Scholar
- Sbar, M. L., Rynn, J. M. W., Gumper, F. J., and Lahr, J. C.: 1970, ‘An Earthquake Sequence and Focal Mechanism Solution, Lake Hopatcong, Northern New Jersey’,Bull. Seism. Soc. Am. 60, 1231–1244.Google Scholar
- Spencer, E. W.: 1969.Introduction to the Structure of the Earth, McGraw-Hill Co., New York, p. 572.Google Scholar
- Stauder, W.: 1962, ‘The Focal Mechanism of Earthquakes’,Advances in Geophysics 9, 1–76.Google Scholar
- Stauder, W., and Bollinger, G. A.: 1966, ‘The Focal Mechanism of the Alaska Earthquake of March 28, 1964, and of its Aftershock Sequence’,J. Geophys. Res. 71, 5283–5296.Google Scholar
- Willmore, P. L. and Hodgson, J. H.: 1955, ‘Charts for Measuring Azimuth and Distance and for Tracing Seismic Rays through the Earth’,Publ. Dominion Obs. Ottawa 16, 405–414.Google Scholar
- Wilson, J. T.: 1965, ‘A New Class of Faults and their Bearing on Continental Drift’,Nature 207, 343–347.Google Scholar