ISSN 0016-8521, Geotectonics, 2019, Vol. 53, No. 5, pp. 601–616. © Pleiades Publishing, Inc., 2019.
Evaluation of Seismicity Triggering: Insights from the Coulomb Static
Stress Changes after the 30 August 1968 Dasht-e-Bayaz Earthquake
(Mw = 7.1), Eastern Iran1
S. Zareia, *, M. M. Khatibb, M. Zarec, and S. M. Mousavib
aPersian Gulf University, Faculty of Science, Department of Geophysics, Bushehr, P.C. 75169 Iran
bUniversity of Birjand, Faculty of Science, Department of Geology, Birjand, P.C. 9717434765 Iran
cInternational Institute of Earthquake Engineering and Seismology (IIEES), Tehran, P.C. 1953714453 Iran
Received October 16, 2017; revised March 24, 2018; accepted May 28, 2019
Abstract—In this research the Coulomb stress changes due to earthquake sequence that began in the 1936 to
1997 earthquakes in Eastern Iran and their triggering effect on the rupturing of adjacent faults were investi-
gated. Obtained results revealed a well triggering relation between main shocks and later events on the Dasht-
e-Bayaz and Abiz faults, respectively. The calculated stress maps indicate that positive and negative zones of
Coulomb stress changes with increasing lobes of 0.1‒1 bar are found in the off-faults tips, located at rupture
terminates while the decreasing Coulomb stress lobes lie in the high angle relative to the rupture plane or
relieve stress along the ruptures. Cross sections drawn respect to the source and received faults confirm the
results. Also, the stress perturbations resulted from successive earthquakes and the spatial patterns of the fol-
lowing earthquake distribution have a good consistency. This correlation shows that the population of sec-
ondary faults and subsequent earthquakes can be encouraged in the future by coseismic Coulomb stress
changes due to mainshock and background loading.
Keywords: earthquake sequence, triggering effect, Coulomb stress, Dasht-e-Bayaz Fault, Lut Block, Iran
The sequence of earthquakes during 30 years in the
NE Iran (e.g. Dasht-e-Bayaz and Zirkuh areas) rep-
resents a remarkable example for clustered large mag-
nitude seismicity worldwide [6, 8, 9, 17, 76]. Large
earthquake events may prevent or encourage failure on
adjacent faults or at distances more than a regional
fault network for times that the changes of stress play a
controlling role in this earthquake interplay .
Recently, the Coulomb stress changes and earth-
quake triggering effects have been investigated by several
authors [1, 4, 13, 22, 26, 39, 40, 47, 56, 61, 63, 64, 66].
Earthquake interplay is a basic character of seismicity
which may resulting to earthquake sequences, clustering
and aftershocks. One interplay criterion which guaran-
tees a deeper grasp of seismic event occurrence and
migration and seismic hazard assessment, normally
active regions following large earthquakes and a better
explanation of probable hazard, is Coulomb stress trans-
fer [18, 42, 50, 61, 65].
The main purpose of this research is to determine
the static Coulomb-stress changes after the damaging
large earthquakes (1936‒1997) based on the data of the
seismicity and the source faults in the Dasht-e-Bayaz
and Zirkuh areas. The interaction between this event
and the following earthquakes was also examined.
General Tectonic Characteristics
The oblique convergence between the Afro-Ara-
bian and Eurasian lithospheric plates has been con-
trolled the active deformation of Iran [31, 33], at a rate
of ~25 mmyr–1 . This convergence resulted to
shortening by distributed faulting in high mountain
ranges such as Zagros, Kopeh-Dagh and Alborz in the
southwestern and northern Iran, respectively (Fig. 1).
Relatively aseismic desert depressions separate these
deforming regions from each other. The Lut block is
located south of the Kopeh-Dagh and bordered by
large strike-slip faults to the east and west [52, 69, 79]
which concentrated an intracontinental deformation
due to convergence (Fig. 1).
A regional-scale shearing has been created due to
northward motion of Central Iran relative to western
Afghanistan in the eastern border of Iran plateau. This
1The article is published in the original.