Local earthquake tomography of the Erzincan Basin and the surrounding area in Turkey

H. Gökalp


In this study, selected travel time data from the aftershock series of the Erzincan earthquake (March, 1992,
Ms=6.8) were inverted simultaneously for both hypocenter locations and 3D Vp and Vs structure. The general
features of the 3D velocity structure of the upper crust of Erzincan Basin and the surrounding area, one of the
most tectonically and seismically active regions in Turkey were investigated. The data used for this purpose were
2215 P-wave and 547 S-wave arrival times from 350 local earthquakes recorded by temporary 15 short-period
seismograph stations. Thurbers simultaneous inversion method (1983) was applied to the arrival time data to
obtain a 3D velocity structure, and hypocentral locations. Both 3D heterogeneous P and S wave velocity variations
down to 12 km depth were obtained. The acquired tomographic images show that the 3D velocity structure
beneath the region is heterogeneous in that low velocity appears throughout the basin and at the southeastern
flank, and high velocities occur at south and east of the basin. The low velocities can be related to small and
large scale fractures, thus causing rocks to weaken over a long period of the active tectonic faulting process. The
ophiolitic rock units mostly occurring around the basin area are the possible reason for the high velocities. The
validity of 3D inversion results was tested by performing detailed resolution analysis. The test results confirm
the velocity anomalies obtained from inversion. Despite the small number of inverted S-wave arrivals, the obtained
3D S velocity model has similar anomalies with lower resolution than the 3D P-wave velocity model. Better
hypocenter locations were calculated using the 3D heterogeneous model obtained from tomographic inversion.


local earthquake tomography;Erzincan Basin;3D velocity structure

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DOI: https://doi.org/10.4401/ag-3052
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X