Seismotectonic aspects of the Markansu Valley, Tadjikstan, earthquake of August 11, 1974

Journal Article · Wed Oct 10 04:00:00 EDT 1979 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB084iB11p06157· OSTI ID:5858636

Jackson, J; Molnar, P; Patton, H; Fitch, T

The Markansu Valley earthquake of August 11, 1974, occurred in a structurally complex area of the northern Pamir. It was followed by more than 80 teleseismically recorded aftershocks, 13 with m/sub b/> or approx. =5.0. Fault plane solutions for the three largest aftershocks differ from one another and from the main shock and indicate both thrust and strike slip faulting. Geological mapping and aftershock locations suggest that the strike slip faulting occurred on both north and northwest trends. The region is one in which large northwest trending strike slip faults converge. To the north and south these faults are very clear topographic features. As they approach the northeastern Pamir, they become less distinct on the Landsat imagery, although they remain recognizable geologic features on the ground. The strike slip faults become less distinct toward their ends perhaps because the north-south motion is taken up progressively by east-west striking thrusts. It is not possible to fit orthogonal nodal planes to all of the observed first motions of the P waves from the main shock. This earthquake is located at the intersection of two inferred fault systems and appears to be a multiple rupture. The discrepant P wave first motions are all nodal in character. If faulting occurred on more than one fault plane during the main shock, then the apparent first motions in the nodal directions of the first rupture may be anomalous and actually belong to a rupture later than the first one. We are aware of one other similar occurrence: the 1967 Mudurnu, Turkey, earthquake, for which the few anomalous P wave first motions were also nodal and for which the fault plane solutions of the main shock and the largest aftershock are very different. The concentration of large earthquakes near the intersection of two systems is also observed in Iran. The seismic moment of the main shock of the Markansu Valley sequence is about 5 x 10/sup 26/ dyn cm.

• Research Organization: Department of Geodesy and Geophysics, Madingley Rise, Madingley Road, Cambridge, England CB3 0EZ, England
• OSTI ID: 5858636
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 84:B10; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580201* -- Geophysics-- Seismology & Tectonics-- (1980-1989)
ASIA
DEFORMATION
EARTH CRUST
EARTHQUAKES
GEOLOGIC FAULTS
GEOLOGIC STRUCTURES
PLATE TECTONICS
SEISMIC EVENTS
SEISMIC WAVES
SLIP
TECTONICS