Spatial and Temporal Stress Changes in the Aftershock Sequence Following the Nov. 12, 2017 Sarpol-e Zahab Earthquake

Document Type : Seismology and Engineering Seismology


International Institute of Earthquake Engineering and Seismology (IIEES)


A devastating earthquake with moment magnitude of 7.3 hit Sarpol-e Zahab in the Zagros on November 12, 2017. An intense aftershock sequence was recorded by the permanent and dense temporary seismic networks, which installed rapidly in the epicentral region. The focal mechanisms of the November 2017 aftershocks were gathered (for about 50 events) and derived (for about 10 events) from P-wave polarities and/or waveform modeling, show predominantly thrust movements. The transpressional stress regime in the region is suggested as the driving force for the earthquakes. The temporal variation of the principal stress directions analyzed by subsequent stress inversion in several time intervals following the Nov. 2017 mainshocks. In addition, the spatial stress variations were studied implementing the stress tensor inversion in different clusters of events. These results suggest that the 2017 mainshock ruptures caused both spatial and temporal stress perturbations that continued in time showing a specific character, which was not observed before in the Zagros region.


Hauksson, E. (1994) State of stress from focal mechanisms before and after the (1992) Landers earthquake sequence. Bulletin of the Seismological Society of America , 84(3), 917-934.
Hardebeck, J. and Hauksson, E. (2001) Stress orientations obtained from earthquake focal mechanisms: what are appropriate uncertainty estimates? Bulletin of the Seismological Society of America , 91(2), 250-262.
Ickrath, M., Bohnhoff, M., Bulut, F., and Dresen, G. (2013) Stress rotation and recovery in conjunction with the 1999 Izmit MW 7.4 earthquake. Geophysical Journal International, 196, 951-956.
Hasegawa, A., Yoshida, K., and Okada, T. (2011) Nearly complete stress drop in the 2011 MW 9.0 off the Pacific coast of Tohoku Earthquake. Earth, Planet and Space, 63, 703-707.
Hardebeck, J. (2012) Coseismic and postseismic stress rotations due to great subduction zone earthquakes. Geophysical Research Letters, 39, L21313, doi: 10.1029/2012GL053438.
Hensch, M., Lund, B., Arnadottir, T., and Brandsdottir, B. (2015) Temporal stress changes associated with the 2008 May 29MW 6 earthquake doublet in the western South Iceland Seismic Zone. Geophysical Journal International, 204(1), 544-554. doi:10.1093/gji/ggv465.
Jackson, J. and McKenzie, D. (1984) The active tectonics of the Alpine-Himalayan belt between western Turkey and Pakistan. Geophys. J. R. Astr. Soc., 77, 185-265.
Walpersdorf, A., Hatzfeld, D., Nankali, H., Tavakoli, F., and Nilforoushan, F. (2006) Difference in the GPS deformation pattern of north and central Zagros (Iran). Geophysical Journal International, 167, 1077-1088.
Vernant, P., Nilforoushan, F., Hatzfeld, D., Abbassi, M., Vigny, C., Masson, F., Nankali, H., Martinod, J., Ashtiani, A., Bayer, R., Tavakoli, F., and Chery, J. (2004) Contemporary crustal deformation and plate kinematics in middle east constrained by GPS measurements in Iran and Northern Oman. Geophysical Journal International, 157, 381-398.
Madanipour, S., Ehlers, T.A., Yassaghi, A., Rezaeian, M., Enkelmann, E., and Bahroudi, A. (2013) Synchronous deformation on orogenic plateau margins: Insights from the Arabia-Eurasia collision. Tectonophysics, 608, 440-451.
Snoke, J.A., Munsey, J.W., Teague, A.C., and Bollinger, G.A. (1984) A program for focal mechanism determination by combined use of polarity and SV-P amplitude ratio data. Earthquake Notes, 55(3), 15.
Waldhauser, F. and Ellsworth, W.L. (2000) A double-difference earthquake location algorithm: Method and application to the northern Hayward fault. Bulletin of the Seismological Society of America , 90, 1353-1368.
Kagan, Y.Y. (2002) Double-couple earthquake focal mechanism: random rotation and display. Geophysical Journal International, 163, 1065-1072.
International Seismological Centre (2016) On-line Bulletin,, Thatcham, United Kingdom.
Lund, B. and Slunga, R. (1999) Stress tensor inversion using detailed microearthquake information and stability constraints: Application to Olfus in southwest Iceland. Journal of Geophysical Research, 104(B7), 14947-14964.
Gephart, J.W. and Forsyth, D.W. (1984) An improved method for determining the regional stress tensor using earthquake focal mechanism data: application to the San Fernando Earthquake sequence. Journal of Geophysical Research, 89, 9305-9320.
Lund, B. and Townend, J. (2007) Calculating horizontal stress orientations with full or partial knowledge of the tectonic stress tensor. Geophysical Journal Internationa l , 170, 1328-1335, doi:10.1111/j.1365-246X.2007.03468.x.
National Earthquake Information Center (NEIC) U.S. Geological Survey,
Global CMT Catalog Search. Global Centroid Moment Tensor Catalog,
Institut De Physique Du Globe De Paris,