Preliminary definition of geophysical regions for the Middle East and North Africa

Abstract

The ability to calibrate seismic stations to improve the monitoring of the Comprehensive Test Ban Treaty is partially limited by the availability of seismic events with known locations and source properties. To confidently extrapolate from these events to aseismic regions, and to properly account for discontinuities in seismic properties requires accurate geophysical models. This paper lays out a preliminary, first-order, regionalization of the Middle East and North African (MENA) region. The model specifies boundaries and velocity structures based on the geology and tectonics of the region, previously published studies, and empirical data observations by the LLNL group. This model is a starting point and is expected to be improved and refined by comparisons with ongoing tomography efforts and the collection of new data. We anticipate that this model and its successors will prove useful as a background model in the process of forming station calibration maps based on intelligent interpolation techniques such as kriging. We also hope the model, as it improves and demonstrates some predictive power, will provide a reference model for broader CTBT research efforts in detection, location and discrimination as well as other aspects of earth science.

Preliminary Definition of Geophysical Regions in Western Eurasia

“…The first of these is MENA1.0 of Sweeney and Walter [1998] that has evolved to an updated MENA1.1 model ) which complements our study. WEA is defined in every 1° × 1° block though the layer parameters (thickness, velocity, density) are the same for blocks within the same region.…”

“…The WEA model is presented in 1° × 1° blocks and we consider that the seismic properties are uniform within each block. This is similar to the parameterization of Sweeney and Walter [1998] and is nominally chosen based on the nature of lateral variations in crustal structure and the lateral resolution of the seismic waves that will be calibrated. Large parts of western Eurasia are tectonically stable regions (e.g., Russian and Siberian platforms) and therefore the variations of crustal structure occur on length scales much larger than the 1°.…”

“…Each 1° × 1° block is parameterized by up to seven layers: one water layer, two sedimentary layers (consolidated and unconsolidated), three crustal layers (upper, middle and lower) and an upper mantle layer. This format follows the model format of Mooney et al [1998] and Sweeney and Walter [1998].…”

“…This region is defined by the TTZ to the north and east, the North sea to the northwest and the foreland basins related to the alpine orogeny to the south coinciding with Region 28 of Sweeney and Walter [1998]. Region 5 consists of several terrains including thin basins south of the TTZ and the orogenic belts of the Harz and the Jura mountains.…”

“…This approach is especially suitable for the analysis of large aseismic regions as it lets us extrapolate sparse calibration data, which lie within a similar geophysical region. The primary reasons for developing such a model is described in Sweeney and Walter [1998] and is briefly outlined here. First, using the three-dimensional seismic properties can improve our capability for seismic calibration.…”