Moment tensor and stress inversion for an active fault system in west part of Lut-Block, Iran

Authors

1 M.Sc. Student, Department of Earth Physics, Institute of Geophysics, University of Tehran, Ira

2 Associate Professor, Department of Earth Physics, Institute of Geophysics, University of Tehran, Iran

Abstract

Iran is one of the most tectonically active regions on the Alpine-Himalayan earthquake belt. Eastern Iran, nowadays, is one of the most active regions of the country. The occurrence of several destructive earthquakes during the past 50 years provides the evidence for the seismic activity in this region. The earthquakes are mostly concentrated around the Lut-block. There are strike-slip fault systems with nearly north-south strike, east and west of the Lut-block. The fault system located in the west part of the Lut-block includes Tabas, Nayband, Lakarkuh, Gowk and Sabzevaran faults. This system is of great importance since it has generated destructive earthquakes such as Dasht-e-Bayaz. Since understanding the focal mechanism of the fault responsible for earthquake is one of the most important parameters, the accuracy to calculate the focal mechanism is extremely vital. Therefore, we have calculated focal mechanisms of the 34 recent earthquakes happened on this system using full moment tensor inversion. The waveform data from 8 broad-band stations, operated by International Institute of Earthquake Engineering and Seismology (IIEES), was used in this study. Appling ISOLated Asperities (ISOLA) package for the full moment tensor inversion using the local and regional data enables us to achieve a higher accuracy in determined focal mechanisms, in comparison with other methods which use teleseismic data. As the magnitude of these events are all smaller than 5.5 (the biggest one equals 5.2), it was not possible to obtain the focal mechanism of almost all of these events through CMT solutions using teleseismic data. The obtained focal mechanisms show that the main mechanism of the Nayband-Gowk-Sabzevaran system is right-lateral strike-slip with a reverse component. The trends of the three main stress axes were also calculated using the 32 focal mechanisms and the stress inversion technique. The results show that the second stress axis (σ2) is nearly vertical, which is one of the characteristics of the strike-slip regimes.

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Berberian, M., Jackson, J., Fielding, E., Parsons, B., Priestley, K., Qorashi, M., Talebian, M., Walker, R., Wright, T. and Baker, C., 2001, The 1999 March 14 Fandoqa earthquake (Mw= 6.6) in Kerman province, southeast Iran: re-rupture of the 1981Sirch earthquake fault, triggering of slip on adjacent thrusts and the active tectonics of the Gowk fault zone, Geophys. J. Int., 146, 371-398.
Bott, M. H. P., 1959, The mechanics of oblique slip faulting, Geol. Mag., 96, 109-117.
Bouchon, M., 1981, A simple method to calculate Green’s functions for elastic layered media, Bull. Seismo. Soc. Am., 71, 959-971.
Dziewonski, A. M., Chou, T. A. and Woodhouse, J. H., 1981, Determination of earthquake source parameters from waveform data for studies of global and regional seismicity, J. Geophys. Res., 86, 2825-52.
Henry, C., Woodhouse, J. H. and Das, S., 2002, Stability of earthquake moment tensor inversions: effect of the double-couple constraint, Tectonophysics, 356, 115-124.
Hessami, K., Jamali, F. and Tabassi, H., 2003, Major active faults of Iran, scale 1:25,000,000, Ministry of Science, Research and Technology, International Institute of Earthquake Engineering and Seismology.
Kanamori, H. and Given, J. W., 1981, Use of long period surface waves for rapid determination of earthquake source parameters, Phys. Earth Planet. Inter., 27, 8-31.
Kikuchi, M. and Kanamori, H., 1991, Inversion of complex body waves-III, Bull. Seismol. Soc. Am., 81, 2335-2350.
McCaffrey, R., 1992, Oblique plate convergence, slip vectors, andforearc deformation, J. geophys. Res., 97, 8905-8915.
Michael, A. J., 1984, Determination of stress from slip data, faults and folds, J. Geophys. Res., 89, 11517-11526.
Michael, A. J., 1987, Use of focal mechanisms to determine stress: a control study, J. Geophys. Res., 92, 357-368.
Sokos, E. and Zahradnik, J., 2008, ISOLA a Fortran code and a Matlab GUI to perform multiple-point source inversion of seismic data, Computers and Geosciences, 34, 967-977.
Strelitz, R. A., 1978, Moment tensor inversions and source models, Geophys. J. Roy. Astron. Soc., 52, 359-64.
Walker, R. and Jackson, J., 2002, Offset and evolution of the Gowk fault, S. E. Iran: a major intra-continental strike-slip system, Journal of Structural Geology, 24, 1677-1698.
Walker, R., Jackson, J. and Baker, C., 2004, Active faulting and seismicity of the Dasht-e-Bayaz region, eastern Iran, Geophys. J. Int., 157, 265-282.
Zahradnik, J., Jansky, J. and Papatsimpa, K., 2001, Focal mechanisms of weak earthquakes from amplitude spectra and polarities, Pure appl. Geophys., 158, 647-665.
Zahradnik, J., Jansky, J. and Plicka, V., 2008, Detailed waveform inversion for moment tensors of M∼ 4 events: examples from the Corinth Gulf, Greece, Bull. Seismol. Soc. Am., 98, 2756-2771.
Zahradnik, J., Serpetsidaki, A., Sokos, E. and Tselentis, G. A., 2005, Iterative deconvolution of regional waveforms and double-event interpretation of 2003 Lefkada earthquake, Greece, Bull. Seismol. Soc. Am., 95,159-172.