Rayleigh wave group velocity dispersion across Northern Africa, Southern Europe and the Middle East

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THis report presents preliminary results from a large scale study of surface wave group velocity dispersion throughout Northern Africa, the Mediterranean, Southern Europe and the Middle East. Our goal is to better define the 3D lithospheric shear-wave velocity structure within this region by improving the resolution of global surface wave tomographic studies. We hope to accomplish this goal by incorporating regional data at relatively short periods (less than 40 sec), into the regionalization of lateral velocity variation. Due to the sparse distributions of stations and earthquakes throughout the region (Figure 1) we have relied on data recorded at both teleseismic ... continued below

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13 p.

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McNamara, D. E. & Walter, W. R. July 15, 1997.

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THis report presents preliminary results from a large scale study of surface wave group velocity dispersion throughout Northern Africa, the Mediterranean, Southern Europe and the Middle East. Our goal is to better define the 3D lithospheric shear-wave velocity structure within this region by improving the resolution of global surface wave tomographic studies. We hope to accomplish this goal by incorporating regional data at relatively short periods (less than 40 sec), into the regionalization of lateral velocity variation. Due to the sparse distributions of stations and earthquakes throughout the region (Figure 1) we have relied on data recorded at both teleseismic and regions; distances. Also, to date we have concentrated on Rayleigh wave group velocity measurements since valuable measurements can be made without knowledge of the source. In order to obtain Rayleigh wave group velocity throughout the region, vertical component teleseismic and regional seismograms were gathered from broadband, 3-component, digital MEDNET, GEOSCOPE and IRIS stations plus the portable PASSCAL deployment in Saudi Arabia. Figure 1 shows the distribution of earthquakes (black circles) and broadband digital seismic stations (white triangles) throughout southern Europe, the middle east and northern Africa used in this study. The most seismicly active regions of northern Africa are the Atlas mountains of Morocco and Algeria as well as the Red Sea region to the east. Significant seismicity also occurs in the Mediterranean, southern Europe and throughout the high mountains and plateaus of the middle-east. To date, over 1300 seismograms have been analyzed to determine the individual group velocities of 10-150 second Rayleigh waves. Travel times, for each period, are then inverted in a back projection tomographic method in order to determine the lateral group velocity variation throughout the region. These results are preliminary, however, Rayleigh wave group velocity maps for a range of periods (10-95 sec) are presented and initial interpretations are discussed. Significant lateral group velocity variation is apparent at all periods. In general, shorted periods (10-45 sec) are sensitive to crustal structure as seen by the relatively low velocities associated with large sedimentary features (eastern Arabian shield, Persian Gulf, Eastern Mediterranean, Caspian Sea). At longer periods (50-95 sec), Rayleigh waves are most sensitive to topography on the Moho and upper mantle shear-wave velocity structure. This is observed in the group velocity maps as low velocities associated with features such as the Zagros Mountains, Iranian Plateau and the Red Sea. Analysis will eventually be expanded to include Love wave group and phase velocity. Knowledge of the lateral variation of group velocity and phase velocity will allow us to invert for shear velocity at each grid point. A detailed regionalization of shear-wave velocity will potentially lower the threshold for Ms determinations and improve event location capabilities throughout the region. Better Ms estimates and locations will improve our ability to reliably monitor the Comprehensive Test Ban Treaty (CTBT).

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13 p.

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OSTI as DE98052176

Other: FDE: PDF; PL:

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  • Research symposium on monitoring a comprehensive test ban treaty, Orlando, FL (United States), 23-25 Sep 1997

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  • Other: DE98052176
  • Report No.: UCRL-JC--128102
  • Report No.: CONF-970967--
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 611845
  • Archival Resource Key: ark:/67531/metadc696152

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  • July 15, 1997

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  • Aug. 14, 2015, 8:43 a.m.

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  • April 10, 2017, 1:29 p.m.

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McNamara, D. E. & Walter, W. R. Rayleigh wave group velocity dispersion across Northern Africa, Southern Europe and the Middle East, article, July 15, 1997; California. (digital.library.unt.edu/ark:/67531/metadc696152/: accessed September 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.