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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS011 Poster presentation 2178
Determination of minimum 1-D velocity model for north west Iran region,
using simultaneous inversion of local earthquake travel times.
Mr. Esmaeil Bayramnejad
Institute of Geophysics University of Tehran
Earthquakes travel times inversion for determination of velocity structure of crust is one of the most
important objectives in seismology. In simultaneous inversion method, the parameters of earthquakes
and velocity model are determined initially and are improved in inversion steps.In this study, we used
more than 22000 calculated travel times for first arrivals of 6000 earthquakes occurred in north west
Iran region (bounded 36N-40N & 44E-50E) to estimate P wave velocities and thickness of crust in this
region. We used this information to determine several initial models. At first we selected 181
earthquakes with magnitudes 4 or above that were well located. Then, we used the simultaneous
inversion method to obtain the best initial and final improved model. The obtained model tested again
with travel times of 2940 earthquakes with magnitudes greater than 2.5 in six independent sets. The
results were in good agreement, specially for depths deeper than 8 km. The results show two low
velocity shallow layers with thickness of 3 km and 2 km and with corresponding average velocity of 4.8
and 5.4 km/s for P wave. Also, a sharp change of velocity was detected in depth 23 km, where the P
wave velocity increase from 6.1 km/s to 6.6 km/s. The depth of Moho was obtained to be 45 km while
the P wave velocity in upper mantle was evaluated to be 8.0 km/s.
Keywords: velocity model, simultaneous inversion, travel times