Seismic waveform tomography of the central and eastern Mediterranean upper mantle

Nienke Blom,Andreas Fichtner,Alexey Gokhberg

doi:10.5194/se-11-669-2020

Nienke Blom, Andreas Fichtner + Show 1 more

Open Access

https://doi.org/10.5194/se-11-669-2020

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Abstract

Abstract. We present a seismic waveform tomography of the upper mantle beneath the central and eastern Mediterranean down to the mantle transition zone. Our methodology incorporates in a consistent manner the information from body and multimode surface waves, source effects, frequency dependence, wavefront healing, anisotropy and attenuation. This allows us to jointly image multiple parameters of the crust and upper mantle. Based on the data from ∼ 17 000 unique source–receiver pairs, gathered from 80 earthquakes, we image radially anisotropic S velocity, P velocity and density. We use a multi-scale approach in which the longest periods (100–150 s) are inverted first, broadening to a period band of 28–150 s. Thanks to a strategy that combines long-period signals and a separation of body and surface wave signals, we are able to image down to the mantle transition zone in most of the model domain. Our model shows considerable detail in especially the northern part of the domain, where data coverage is very dense, and displays a number of clear and coherent high-velocity structures across the domain that can be linked to episodes of current and past subduction. These include the Hellenic subduction zone, the Cyprus subduction zone and high-velocity anomalies beneath the Italian peninsula and the Dinarides. This model is able to explain data from new events that were not included in the inversion.

Highlights

Since the late 1970s (Dziewonski et al, 1977; Aki et al, 1977), seismic tomography has been emerging as the primary method for imaging the Earth’s interior from the kilometre to the global scale
On regional to continental scales, the 3-D images can help to decipher the tectonic situation and history of an area by linking the surface observations to structures deeper in the mantle: high-velocity structures have been associated with subduction since the earliest days of seismic tomography
Computationally more expensive than ray-based tomography methods, the advantage of waveform tomography lies in its ability to make use of all and any part of seismograms that has a sufficient signal-to-noise ratio, allowing for a more complete extraction of all information that is carried by seismic waves

Summary

Introduction

Since the late 1970s (Dziewonski et al, 1977; Aki et al, 1977), seismic tomography has been emerging as the primary method for imaging the Earth’s interior from the kilometre to the global scale. On regional to continental scales, the 3-D images can help to decipher the tectonic situation and history of an area by linking the surface observations to structures deeper in the mantle: high-velocity structures have been associated with subduction since the earliest days of seismic tomography. The Mediterranean in particular is an area that has attracted much attention from the beginning – not in the least because of its strong seismicity and good data coverage. Classical ray tomography has been applied numerous times to study this area, both using body and surface waves Classical ray tomography has been applied numerous times to study this area, both using body and surface waves (e.g. Spakman et al, 1988; Piromallo and Morelli, 1997, 2003; Amaru, 2007; Biryol et al, 2011; Koulakov et al, 2015; Portner et al, 2018; Snieder, 1988; Zielhuis and Nolet, 1994; Marone et al, 2004; Schivardi and Morelli, 2009; Salaün et al, 2012; Legendre et al, 2012)

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