INVERSION OF RAYLEIGH WAVES GROUP VELOCITY TO SHEAR WAVE VELOCITY STRUCTURE FOR THE NORTH-WEST OF IRAN

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DAVODIAN R.; MOTAGHI K.; SOBOUTI F.; RAHIMI H.; GHODS A.

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Journal: Journal of the Earth and Space Physics Year:2017 | Volume:43 | Issue:1 Page(s): 1-13

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Title

INVERSION OF RAYLEIGH WAVES GROUP VELOCITY TO SHEAR WAVE VELOCITY STRUCTURE FOR THE NORTH-WEST OF IRAN

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Keywords

CRUSTQ3

RAYLEIGH WAVESQ3

NON-LINEAR INVERSIONQ1

DISPERSION CURVEQ1

HEDGEHOGQ1

Abstract

Shear wave structure has been determined using data from a temporary network of 23 broadband stations in the north west of Iran. Waveforms have been used from 230 tele-seismic and regional earthquakes to obtain inter station DISPERSION CURVEs of group velocity of the RAYLEIGH WAVES. Events in the epicentral distance range of 250 to 3000 km with magnitudes 3.0≤ Mw ≤ 7 were also used. The individual DISPERSION CURVEs of group velocity of the RAYLEIGH WAVES for each source-station path were calculated; Then via double-station method we calculated 20 DISPERSION CURVEs for inter station paths. The group velocities are available in the range of 6-48 sec; in general it is only possible to resolve the parameters of upper mantle and CRUST. We divided the study area to 5 regions, and then we calculated the average DISPERSION CURVE in each region. These curves were used to determine shear wave structure in each region via non-linear HEDGEHOG inversion method. We need the initial velocity model to start the NON-LINEAR INVERSION process, therefore initial model was calculated via linear inversion method. In addition, the obtained velocity models show that CRUSTal thickness in these 5 regions varies between 40 and 56 km. Also the boundary between upper and lower CRUST changes between 12 and 28 km. The results from the non-linear HEDGEHOG inversion as applied to derived DISPERSION CURVEs show a CRUSTal thickness of approximately 40 km in the west part of study area, 56 km in the middle of the area and 43 km in the western coast of Caspian Sea. Based on the obtained results the Moho depth varies from 56 km to 40 km when you move from the middle of the study area to western coast of the Caspian Sea. We propose that under thrusting of Caspian Sea basement beneath the Talesh Mountains impresses Moho depth in Talesh zone. But no geological observation proves the under thrusting of Caspian Sea basement beneath the Talesh Mountains, therefore we cannot be certain about this proposal. On other hand, Talesh zone is located in passive continental margin of the Caspian Sea; these kinds of margins have complicated structure. We can assume that the observed results in Talesh zone have been created by passive continental margin of the Caspian Sea. Also we observed a low velocity anomaly in the range of 12-22 km depths beneath the Sahand volcano. We derived attenuation effects of south Caspian basin when periods are longer than 32 seconds of fundamental mode RAYLEIGH WAVES propagating across the south Caspian Basin. We also used 20 events along the Apsheron Sill and calculated the DISPERSION CURVEs of these events at our stations. We collected 172 waveforms from the used events and found only 31 fundamental mode waveforms of RAYLEIGH WAVES. In other waveforms energy of fundamental mode was diffused and we cannot specify any trend for dispersion. The South Caspian Basin contains one of the thickest sedimentary deposits in the world. In the South Caspian Basin, based on Priestley et.al. (2001), attenuation of surface waves is largely controlled by sediments in the basin. Therefore we guess that our observations about attenuation of the RAYLEIGH WAVES are related to sediments in this basin.

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APA: Copy

DAVODIAN, R., MOTAGHI, K., SOBOUTI, F., RAHIMI, H., & GHODS, A.. (2017). INVERSION OF RAYLEIGH WAVES GROUP VELOCITY TO SHEAR WAVE VELOCITY STRUCTURE FOR THE NORTH-WEST OF IRAN. JOURNAL OF THE EARTH AND SPACE PHYSICS, 43(1 ), 1-13. SID. https://sid.ir/paper/80371/en

Vancouver: Copy

DAVODIAN R., MOTAGHI K., SOBOUTI F., RAHIMI H., GHODS A.. INVERSION OF RAYLEIGH WAVES GROUP VELOCITY TO SHEAR WAVE VELOCITY STRUCTURE FOR THE NORTH-WEST OF IRAN. JOURNAL OF THE EARTH AND SPACE PHYSICS[Internet]. 2017;43(1 ):1-13. Available from: https://sid.ir/paper/80371/en

IEEE: Copy

R. DAVODIAN, K. MOTAGHI, F. SOBOUTI, H. RAHIMI, and A. GHODS, “INVERSION OF RAYLEIGH WAVES GROUP VELOCITY TO SHEAR WAVE VELOCITY STRUCTURE FOR THE NORTH-WEST OF IRAN,” JOURNAL OF THE EARTH AND SPACE PHYSICS, vol. 43, no. 1 , pp. 1–13, 2017, [Online]. Available: https://sid.ir/paper/80371/en

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