Preliminary Definition of Geophysical Regions in Western Eurasia

Abstract

We present a regionalized crustal model of Western Eurasia, WEA. The model is constructed using results from published studies and maps of geological and geophysical parameters in this region, and was developed in conjunction with the updated regionalization of Middle East and North Africa by Walter et al. [2000]. As this is the first realization of our Eurasian modeling effort, we have limited ourselves to only twelve broad regions. Particular attention has been given to identifying the boundaries for each region. The main use of this model will be to assist in monitoring the Comprehensive Nuclear Test Ban Treaty (CTBT). Specifically, this model will help us to calibrate and predict the travel time and amplitudes of various regional seismic phases and to locate events accurately. Our model based approach allows us to readily calibrate both the seismic and the aseismic parts of western Eurasia. Each region is specified by an onedimensional model of compressional and shear velocities, densities and layer thicknesses.Further improvements to this model will involve, but not be limited to, increasing the spatial coverage toward the east and west of Eurasia, identify sub-regions based on their distinct physical properties and the use of new and improved body wave and surface wave datasets. In the future, we expect to use this model and its successors to be the baseline model for calibration techniques, e.g., kriging, to improve our capability to detect, locate and discriminate different seismic events in Eurasia.2

MENA 1.1 - An Updated Geophysical Regionalization of the Middle East and North Africa

“…There were several changes planned for the MENA1.1 update to the MENA1.0 model, including changes required to match with a new Western Eurasia (WEA) model being developed. In summary the five main reasons for this update are to: 1) Fixing a few small errors in MENA1.0 2) Improving MENA1.0 periphery regions (regions 1 and 17-28) 3) Provide seamless transition to a new WEA model (Bhattacharyya et al, 2000). 4) Subdividing regions that stand out in surface wave tomography studies.…”

“…Part of the motivation for improving these regions came from the need to match the Western Eurasia (WEA) geophysical regionalization being done by Bhattacharyya et al (2000). In particular we wanted the boundaries and velocity models of the two regionalizations to match exactly so that there would be a seamless transition between the two.…”

“…To ensure this we revised the boundaries of the northern tier of regions (20, 21, 23, 26, 27 and 28) in MENA1.0 to both improve their definition and to match boundaries in WEA. We slightly modified the velocity model of region 28 to be consistent with Bhattacharyya et al (2000), and supplied the velocity models of the other northern tier regions to Joydeep Bhattacharyya for inclusion in the WEA regionalization. Finally we added the southern most portion of the Urals as a new region 29.…”

“…Pasyanos et al, 2000;Ritsema and van Heijst, 2000). In particular the ocean rift systems show up prominently in these studies as slow regions and we have decided to separate rift regions out as region 1A.…”

“…Not unexpectedly, regional surface-wave tomography (e.g. Pasyanos et al, 2000;Ritsema and van Heijst, 2000) shows the active ridges in the Indian ocean as slow. We used bathymetry and seismicity as criteria to separate the oceanic ridges as model 1A.…”