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The Tripoli, Libya, Earthquake of September 4, 1974: Implications for the active tectonics of the central Mediterranean
Author(s) -
Westaway Rob
Publication year - 1990
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/tc009i002p00231
Subject(s) - geology , seismology , tectonics , focal mechanism , seismotectonics , induced seismicity , slip (aerodynamics) , fault (geology) , physics , thermodynamics
Source parameters have been determined for the earthquake (M s 5.6) that occurred offshore of Tripoli, Libya, on September 4, 1974. One nodal plane of its focal mechanism has dip 37°, strike 297°, and rake −141°, indicating oblique normal faulting. This nodal plane is subparallel to many west‐northwest striking normal faults in the epicentral area and is most likely the fault plane, indicating a component of right‐lateral strike‐slip with slip vector azimuth N84°E. Inversion of long‐period teleseismic body waves indicates 12‐km centroid depth and 0.4 × 10 18 N m seismic moment. A much larger earthquake (M s 7.0) on April 19, 1935, that occurred in the same zone of active oblique normal faults ∼400 km farther southeast near Sirte probably involved similar slip sense. This zone, for which the name “Tunisia‐Libya seismic zone” appears appropriate, has overall northwest‐southeast extent ∼1000 km from northern Libya to between Tunisia and Sicily. It takes up a change in motion direction relative to stable Europe from west of north inside the African plate to between N30°E and N50°E in the Ionian Sea between Sicily, southernmost peninsular Italy, southwest Greece, and Libya. This suggested motion direction of Sicily relative to stable Europe agrees with independent estimates from fault slip rates and senses elsewhere in Italy.