Velocity structure of upper-mantle transition zones beneath central eurasia from seismic inversion using genetic algorithms

Abstract

S U M M A R YWe present velocity constraints for the upper-mantle transition zones beneath Central Siberia based on observations of the 1982 RIFT Deep Seismic Sounding (DSS) profile. The data consist of seismic recordings of a nuclear explosion in north-western Siberia along a 2600 km long seismic profile extending from the Yamal Peninsula to Lake Baikal. We invert seismic data from the mantle transition zones using a non-linear inversion scheme using a genetic algorithm for optimization and the WKBJ method to compute the synthetic seismograms. A statistical error analysis using a graphbinning technique was performed to provide uncertainty values in the velocity models.Our best model for the upper-mantle velocity discontinuity near 410 km depth has a two-stage velocity-gradient structure, with velocities increasing from 8.70-9.25 km s-' over a depth range of 400-415 km, a gradient of 0.0433 s -', and from 9.25-9.60 km s-' over a depth range of 415-435 km, a gradient of 0.0175 SKI. This derived model is consistent with other seismological observations and mineral-physics models. The model for the velocity discontinuity near 660 km depth is simple, sharp and includes velocities increasing from 10.15 km s-l at 655 km depth to 10.70 km s-' at 660 km depth, a gradient of 0.055 s-'.

Deep Earth Structure - Transition Zone and Mantle Discontinuities

“…A thinned transition zone was shown in the Kurile-Kamchatka subduction zone by Petersen et al (1993a) and in southern California by Gurrola and Bernard Minster (1998). Relatively strong local variations of the transition zone thickness have been observed in Central Asia by Neves et al (1996) in nuclear explosion data, in Indonesia by Saita et al (2002), below the Philippines by Wright (2009) with wide-angle data, below the Philippine Sea by Suetsugu et al (2010), and at the Mariana slab by Tibi et al (2006) with ocean-bottom seismometers.…”

Crust and Lithospheric Structure - Active Source Studies of Crust and Lithospheric Structure

“…Similar experiments, known as deep seismic soundings (DSSs), were once common in Russia and India, but they usually did not use sufficient offsets to observe upper-mantle refractions, Pn (e.g., Kaila and Krishna, 1992). Wide-angle experiments with very long source-receiver offsets (>1000 km) have been used to image deep subcrustal lithospheric and asthenospheric structure (e.g., Gorman et al, 2002), particularly in the former Soviet Union in which peaceful nuclear explosions were sometimes available as sources (e.g., Morozova et al, 1999;Neves et al, 1996;Thybo and Perchuc, 1997).…”

Deep Earth Structure – Transition Zone and Mantle Discontinuities

“…Mechie et al (1993): Northern Eurasia; wideangle nuclear explosion; normal transition zone thickness. Neves et al (1996): North West Siberia and Lake Baikal; nuclear explosions; at the 410 a two-gradient structure between 400 and 435 km and a sharp 660. Saul et al (2000): India; receiver functions; 410 and 660 close to their average depths.…”