Crustal seismic structure of the eastern Mediterranean: evidence from broadband seismology

Abstract

Understanding the crustal structure of the Anatolian Plate has important implications for its formation and evolution, including the extent to which its high elevation is maintained isostatically. However, previous receiver function studies of Anatolian Moho depths return results differing by <21km. H-K stacking is used routinely to infer crustal thickness and Vp/Vs ratio from teleseismic receiver functions, assuming the largest amplitude P-to-S conversions beneath the seismograph station are generated by a sharp velocity contrast at the Moho. However, synthetic seismogram analysis demonstrates that H-K results are strongly dependent on the choice of stacking input parameters.

To address this issue of parameter sensitivity, an H-K approach is developed in which cluster analysis selects a final solution from 1000 results, each calculated using randomly selected input parameters via bootstrapping. When the Moho is sharp, H-K results cluster tightly and the method is reliable; in areas of more complex crustal structure, H-K analysis is often unreliable.

The new crustal model for the Eastern Mediterranean (ANATOLIA-HK21) provides fresh insight into Anatolian crustal structure and topography. While the crust thins from ~45km below the uplifted Eastern Anatolian Plateau to ~25km below lower-lying western Anatolia, Moho depth is generally correlated poorly with elevation. Residual topography calculations confirm the requirement for a mantle contribution to Anatolian Plateau uplift, with localised asthenospheric upwellings in response to slab break-off and/or lithospheric dripping/delamination example candidate driving mechanisms.

In the absence of good-quality H-K results on Cyprus, Rayleigh wave group velocity inversions place new constraints on the island's crustal structure. Resulting tomographic images reveal high velocities at short periods directly beneath the surface expression of the Troodos Ophiolite; anomaly amplitudes decrease at longer periods (from +30% at 8s to +5% at 14s) and shift northeastward, corroborating studies that consider the ophiolite a mid-to-upper crustal feature.