EVALUATION STRESS FIELD AND TECTONIC REGIME IN MID-EASTERN IRAQ-WESTERN IRAN FROM THE INVERSION OF MOMENT TENSOR FOCAL MECHANISM DATA

  • Hasanain jasim mohammed Department of Seismology, Iraqi Meteorological Organization and Seismology, Baghdad, Iraq
  • Ali M. Al-Rahim Department of Geology, College of Science, University of Baghdad. Baghdad, Iraq
Keywords: Focal mechanism solutions, Moment stress axes, Stress inversion, Stress regimes

Abstract

The estimation of the stress-field direction from focal mechanism of an earthquake is a pertinent tool to understand crustal mechanics and earthquake habit. The main aim of this study is to infer the stress pattern of the mid-eastern Iraq - western Iran region. The study area is situated between latitudes 33.59°–34.93°N and longitudes 45.44°–46.39°E. Active stressed inversions of 102 moment tensor focal mechanisms data were used to rating the present day stress field. These data are subdivided into four regional subsets (circles) as a function of their geographical location and tectonic setting. The regional principal stress axes (σ1, σ2, and σ3) were inferred using right dihedron and rotational optimization methods by the formal stress inversion method. The results showed that there are spatial differences in the tectonic stress field, proportionate with fault orientations and faulting mechanisms. Thus, five stress regime categories are presented for the study area. It turns out that the prevailing tectonic systems are thrust faulting (50.98 %), strike-slip faulting (29.40 %), and unknown or oblique faulting (13.70 %); while the rest of the tectonic systems are less present thrust with strike-slip faulting (4.90 %), and normal with strike-slip faulting (0.98 %). The orientation of the maximum horizontal stress has a general directional trend towards NW-SE and NE-SW with local deviations related to the main predominant geological structures. Quality stress classifications were determined for the four groups’ areas and were of B and C quality. The local extensional tectonic environment between strike-slip fault systems possibly it's the reason there are some normal faults. Finally, we note that the spatial differences of the tectonic regime and the stress field are compatible with the neotectonic stress field that is identified from focal mechanism data.

Published
2020-07-28