de G. MÜLLER1, K.P. BONJER1, H. STÖCKL1, DUMITRU ENESCU2
1Institutul de Geofizica al Universitatii din Karlsruhe, Germania
2Centrul de Fizica Pamantului si seismologie, Bucuresti-Magurele
THE ROMANIAN EARTHQUAKE OF MARCH 4, 1977. RUPTURE PROCESS
INFERRED FROM FAULT-PLANE SOLUTION AND MULTIPLE-EVENT ANALYSIS
(Abstract)
The Romanian earthquake of March 4, 1977, was a multiple event, consisting of a foreshock and at least 3 main shocks. A fault-plane solution is given for the first main shock. It is of thrust type and similar to the solution for the earthquake of November 10, 1940. The locations of the main shocks relative to the foreshock are determined by the "master-event" technique. Rupture propagated mainly towards SW. The third main shock which was the strongest shock of the earthquake, occurred 19 sec after and at a horizontal distance of 62 km from the foreshock. This agrees well with the reported distribution of intensities and damages and with the aftershock distribution. P-wave polarities for the third main shock are opposite to those for the first and second main shock. This can be explained by (1) strong bending of the rupture surface, (2) reversal of the motion on the rupture plane due to a strongly inhomogeneous tectonic stress field or (3) abrupt termination of rupture producing strong stopping signals. The rupture plane dips about NW with a dip angle of 70°, and the apparent average rupture velocity is close to the S-wave velocity.