The 2015–2017 Pamir Earthquake Sequence: Fore-, Main-, and Aftershocks,
Seismotectonics, Fault Interaction, and Fluid Processes
Lothar Ratschbacher
Geologie, Technische Universität Bergakademie Freiberg, 09599 Freiberg, Germany, Geologie, Technische Universität Bergakademie Freiberg, 09599 Freiberg, Germany, Geologie, Technische Universität Bergakademie Freiberg, 09599 Freiberg, Germany
Author ProfileSanaa Reuter
Geologie, Technische Universität Bergakademie Freiberg, 09599 Freiberg, Germany, Geologie, Technische Universität Bergakademie Freiberg, 09599 Freiberg, Germany, Geologie, Technische Universität Bergakademie Freiberg, 09599 Freiberg, Germany
Author ProfileAbstract
A sequence of three strong (M W 7.2, 6.4, 6.6) earthquakes struck the
Pamir of Central Asia in 2015–2017. With a local seismic network, we
recorded the succession of the fore-, main-, and aftershock sequences at
local distances with good azimuthal coverage. We located 11,784 seismic
events and determined 33 earthquake moment tensors. The seismicity
delineates the tectonic structures of the Pamir in unprecedented detail,
i.e., the thrusts that absorb shortening along the Pamir’s thrust front,
and the strike-slip and normal faults that dissect the Pamir Plateau
into a westward extruding block and a northward advancing block.
Ruptures on the kinematically dissimilar faults were activated
subsequently from the initial M W 7.2 Sarez event at times and distances
that follow a diffusion equation. All mainshock areas but the initial
one exhibited foreshock activity, which was not modulated by the
occurrence of the earlier earthquakes. Modeling of the static Coulomb
stress changes indicates that aftershock triggering occurred over
distances of ≤90 km on favorably oriented faults. The third event in the
sequence, the M W 6.6 Muji earthquake, ruptured despite its repeated
stabilization through stress transfer in the order of -10 kPa. To
explain the accumulation of M W > 6 earthquakes, we reason
that the initial mainshock may have increased nearby fault permeability,
and facilitated fluid migration into the mature fault zones, eventually
triggering the later large earthquakes.