H. Fuenzalida et al., MECHANISM OF THE 1992 ERZINCAN EARTHQUAKE AND ITS AFTERSHOCKS, TECTONICS OF THE ERZINCAN BASIN AND DECOUPLING ON THE NORTH ANATOLIAN FAULT, Geophysical journal international, 129(1), 1997, pp. 1-28
The 1992 March 13 Erzincan earthquake (M(s) = 6.8) affected the Erzinc
an Basin on the eastern part of the North Anatolian Fault (NAF). This
event occurred on the eastern tip of a westward-propagating series of
major North Anatolian earthquakes between 1939 and 1967 (Ambraseys 197
0). It is located within a key region of eastern Anatolia, which displ
ays both expulsion of the Anatolian block towards the west and regiona
l N-S convergence due to the Arabian-Eurasian collision (Philip et al.
1989). A reinterpretation of the tectonics of the Erzincan Basin is m
ade from field information and the analysis of satellite images. A mod
el explaining the development of the basin is proposed. It combines a
pull-apart on the NAF with the effect of two compressional wedges. One
is formed by the Northeast Anatolian fault (NEAF) and the NAF; the ot
her, around Pulumur, is limited by the Ovacik Fault (OF) and the NAF.
Both E-W extension and N-S compression occur according to this model.
Normal faulting on the southwestern border and extension-related Quate
rnary rhyolitic volcanic domes along the northeastern boundary of the
basin support the proposed E-W extension. The block limiting the south
ern side of the basin is uplifted and displaced left-laterally along t
he OF, suggesting southward growth of the basin. A kinematic model of
the 1992 Erzincan earthquake combines aftershock field information, ne
otectonic observations, satellite image interpretation and body-wavefo
rm inversion. The complex earthquake rupture starts on the NAF and pro
pagates bilaterally, Westward rupture propagation progresses along the
northern border of the basin. Eastward propagation is shifted on a se
gment of the NAF south of the Euphrates, and ends within the Pulumur w
edge. Both branches are connected by a system of normal faults. The ma
in focal mechanism is strike-slip with a slight normal component (phi
= 122 degrees; delta = 63 degrees; lambda = - 164 degrees). The strong
est aftershock mechanism is compatible with N-S compression within the
Pulumur wedge. Aftershock mechanisms and stress-tenser analyses give
detailed insight into the earthquake sequence. The 1992 Erzincan earth
quake is located between two segments of the NAF that suffered large d
estructive earthquakes in the past. The 1939 earthquake (M(s) = 8.2) r
uptured 370 km west of Erzincan. The last major earthquake east of the
Erzincan Basin occurred in 1784, rupturing a segment of at least 75 k
m length. This area has displayed a seismic gap since then. The mechan
ism of the main shock and the absence of aftershock activity east of T
anyeri indicate decoupling between the 1992 event and the 1784 gap. Af
tershocks within the Pulumur wedge suggest that the probability of the
occurrence of a future earthquake is higher on the OF than in the 178
4 earthquake gap.