A variable resolution surface wave dispersion study of Eurasia, North Africa, and surrounding regions

Abstract

This paper presents the results of a large-scale study of surface wave dispersion performed across Eurasia and North Africa. Improvements were made to previous surface wave work by enlarging the study region, increasing path density, improving spatial resolution, and expanding the period range. This study expands the coverage area northwards and eastwards relative to a previous dispersion analysis, which covered only North Africa and the Middle East. We have significantly increased the number of seismograms examined and group velocity measurements made. We have now made good quality dispersion measurements for about 30,000 Rayleigh wave and 20,000 Love wave paths, and have incorporated measurements from several other researchers into the study. A conjugate gradient method was employed for the group velocity tomography, which improved the inversion from the previous study by adopting a variable smoothness. This technique allows us to go to higher resolution where the data allow without producing artifacts. The current results include both Love and Rayleigh wave inversions across the region for periods from 7 to 100 seconds at 1º resolution. Short period group velocities are sensitive to slow velocities associated with large sedimentary features such as the Caspian Sea, West Siberian Platform, Mediterranean Sea, Bay of Bengal, Tarim Basin, and Persian Gulf.Intermediate periods are sensitive to differences in crustal thickness, such as those between oceanic and continental crust or along orogenic zones and continental plateaus. At longer periods, fast velocities are consistently found beneath cratons while slow upper mantle velocities occur along rift systems, subduction zones, and collision zones such as the Tethys Belt. We have compared the group velocities at various periods with features such as sediment thickness, topographic height, crustal thickness, proximity to plate boundaries, lithospheric age and lithospheric thickness, and find significant correlations. We don't find any similar correlation between the longest period surface waves and hot spots.3

A top to bottom lithospheric study of Africa and Arabia

“…We use the latest updates of the group velocity maps of Pasyanos (2005). The inversion uses a 1˚ by 1˚ equal area grid, and a conjugate gradient method is used to solve for lateral variations in group velocity.…”

Crustal Structure of Iraq from Receiver Functions and Surface Wave Dispersion

“…Tomographic images of seismic structure of the Middle East have been estimated from Pn travel time tomography (Hearn and Ni, 1994;Al-Lazki et al, 2003, 2004, surface wave group velocity dispersion (e.g. Ritzwoller and Levshin, 1998;Pasyanos, 2005) and partitioned waveform inversion (Maggi and Priestley, 2005). These studies These previous seismic studies indicate that lithospheric structure in the northern Arabian Platform is variable, but strongly correlated with tectonics.…”

Lithospheric structure of the Arabian Shield from joint inversion of P- and S-wave receiver functions and dispersion velocities

“…The PRFs jointly inverted and SRFs obtained in task 1 with dispersion velocities measured on the Green's functions obtained in task 2 and with fundamental-mode, Rayleigh-wave, group and phase velocities borrowed from the tomographic studies of Pasyanos (2005) and Ekström et al (1997). Using he receiver functions and dispersion measurements, we produced joint inversion models for the broadband stations in Saudi Arabia.…”

“…Surface-wave dispersion velocities for the joint inversion were obtained from the independent surfacewave tomography study of Pasyanos (2005). The study measured quality fundamental-mode group velocities along 30,000 Rayleigh wave and 20,000 Love wave paths for periods between 7 and 100 s, and reported lateral variation in group-velocity across Eurasia and North Africa.…”