TY - JOUR
T1 - High frequency seismic waves and slab structures beneath Italy
AU - Sun, Daoyuan
AU - Miller, Meghan S.
AU - Piana Agostinetti, Nicola
AU - Asimow, Paul D.
AU - Li, Dunzhu
PY - 2014/4/1
Y1 - 2014/4/1
N2 - 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% V p 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.
AB - 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% V p 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.
KW - High frequency waves
KW - Slab beneath Italy
KW - Small-scale heterogeneities
UR - http://www.scopus.com/inward/record.url?scp=84894054563&partnerID=8YFLogxK
U2 - 10.1016/j.epsl.2014.01.034
DO - 10.1016/j.epsl.2014.01.034
M3 - Article
SN - 0012-821X
VL - 391
SP - 212
EP - 223
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
ER -