High frequency seismic waves and slab structures beneath Italy

Author(s)

Daoyuan Sun, Meghan S. Miller, Nicola Piana Agostinetti, Paul D. Asimow, Dunzhu Li

Abstract

Tomographic images indicate a complicated subducted slab structure

beneath the central Mediterranean where gaps in fast velocity anomalies

in the upper mantle are interpreted as slab tears. The detailed shape

and location of these tears are important for kinematic reconstructions

and understanding the evolution of the subduction system. However,

tomographic images, which are produced by smoothed, damped inversions,

will underestimate the sharpness of the structures. Here, we use the

records from the Italian National Seismic Network (IV) to study the

detailed slab structure. The waveform records for stations in Calabria

show large amplitude, high frequency (f>5 Hz) late arrivals with long

coda after a relatively low-frequency onset for both P and S waves. In

contrast, the stations in the southern and central Apennines lack such

high frequency arrivals, which correlate spatially with the central

Apennines slab window inferred from tomography and receiver function

studies. Thus, studying the high frequency arrivals provides an

effective way to investigate the structure of slab and detect possible

slab tears. The observed high frequency arrivals in the southern Italy

are the strongest for events from 300 km depth and greater whose

hypocenters are located within the slab inferred from fast P-wave

velocity perturbations. This characteristic behavior agrees with

previous studies from other tectonic regions, suggesting the high

frequency energy is generated by small scale heterogeneities within the

slab which act as scatterers. Furthermore, using a 2-D finite difference

(FD) code, we calculate synthetic seismograms to search for the scale,

shape and velocity perturbations of the heterogeneities that may explain

features observed in the data. Our preferred model of the slab

heterogeneities beneath the Tyrrhenian Sea has laminar structure

parallel to the slab dip and can be described by a von

Kármán function with a down-dip correlation length of 10

km and 0.5 km in thickness with ∼2.5% Vp fluctuations

within the slab. This suggests that the heterogeneities are inherited

from the melt shear bands formed during the original formation of the

oceanic lithosphere near the mid-ocean ridge.

Organisation(s)

Department of Geology

External organisation(s)

University of Southern California, Dublin Institute for Advanced Studies, California Institute of Technology (Caltech)

Journal

Earth and Planetary Science Letters

Volume

391

Pages

212-223

No. of pages

12

ISSN

0012-821X

DOI

https://doi.org/10.1016/j.epsl.2014.01.034

Publication date

04-2014

Peer reviewed

Yes

Austrian Fields of Science 2012

105102 General geophysics

Keywords

ASJC Scopus subject areas

Geochemistry and Petrology, Geophysics, Earth and Planetary Sciences (miscellaneous), Space and Planetary Science

Portal url

https://ucrisportal.univie.ac.at/en/publications/4ba0f582-3e3c-420e-aa84-20114b2b395a