MOHO DEPTH AND CRUSTAL STRUCTURE IN PENINSULAR ITALYAlessandro AmatoIstituto Nazionale di Geofisica e Vulcanologia

Neutrino Geoscience 2010

Talk outline

Italy: tectonic setting and deep structuresMoho depth through Receiver FunctionsCrustal structures Complexities and uncertaintiesFuture improvements: What can be done? Is it worth doing?

Evolution of the Mediterranean subduction and collision (courtesy of G. Rosenbaum)

300 km

AlgerianTyrrhenian

Ligurian

Alboran

Apennines

Evolution of the Mediterranean subduction and collision. Complex structures expected at LNGS

The LNGS is located in a very complex region:

-

Boundary between NAP

and central Apennines

- Extensional tectonics

About 56,000 earthquakes from 2005 to 2010 by the INGV seismic network

D’Agostino et al., 2010

GPS velocities in Italy

Reference: Eurasia

Strong improvement after 2003 (ongoing)

Coherent patterns

Clear trends: Extension across the ApenninesConvergence in NE Italy and Sicily (N-S)

LNGS located in an area of active extension across the Apennines

Rifted MarginContractional Shield & Platform

Paleozoic OrogenRift

ExtensionalArc

Forearc0

20

40

60

Km

Vp

6.4 6.6 6.8 7.0 7.2

Middle and Lower Crust --

Seismic evidence

From Rudnick & Fountain, 1995

Central Italyhas very different crustal characteristics at short

distance (see next slides)

Receiver Functions: why ?

Deep well data: few and shallow (< 7km)“Active” seismology: shallow commercial lines and very few deep seismic lines (CROP, DSS), 2D and with low resolution at depth. New lines unlikely, expensive

Receiver functions depend on seismic networks and teleseisms (M>6 at >30° distance, ~1/day)Great network improvement in Italy in last decadePossible “ad hoc” experiments (1-2 years)A lot of detailed studies in the last years in the world unraveled important processes (subduction fine structure, fluids transportation, etc.)

Seismic network in 1997 and 2007

1997 2007

De Luca et al. (2009)

Central Apennines seismic structure, SGI 2010, Pisa

Receiver Functions are time series made of Ps converted waves generated at interfaces at depth

RFs are obtained from seismic waveforms of teleseismic events

rotated in the radial

and

transverse

planes, through deconvolution of the

vertical component.

RFs reveal velocity jumps in the structure

Receiver functions: principles

A RF data-set

is made of hundreds of RFs binned as

a function of the back-azimuth direction of the incoming P-wave (i.e. all RF computed from events occurred in the same place are stacked to increase the S/N ratio.)

One RF computed via deconvolution of the Vertical seismogram from the horizontal one

Receiver functions: data

Data sets: radial and transverse RFs a simple crustal structure (left) and complex (right)

P diretta Ps-Moho Ps-Moho

Simple vs. doubled Moho

The ZK2000 technique allows us to retrieve Moho depth, crust is assumed homogeneous

Simple, well identified, shallow Moho Doubled (?) Moho in the belt

Zhu and Kanamori, JGR, 2000

Moho depth from teleseismic receiver functions

Receiver functions: application to Italy

Northern Apennines

Central Apennines

Southern Apennines

Piana Agostinetti and Amato (2009)

Receiver functions: application to Italy

Seismicity: transition from northern to central Apennines

Integration  of CSS and RF data for MOHO mappingR. Di Stefano, I. Bianchi, M.G. Ciaccio (in prep.)

La 

mappa 

e’

ottenuta 

dall’interpolazione 

su 

tre 

superfici 

(poligoni 

in 

figura) 

della 

profondità

della 

Moho 

ricavata 

da 

dati 

CSS 

e 

RF,   seguendo 

il 

metodo 

sviluppato 

da 

Waldhauser 

et 

al. 

1998, 

ed 

implementato 

per 

l’utilizzo 

delle 

RF. 

Le 

profondita’

della 

Moho 

ricavate 

dalle 

RF 

provengono 

da 

tre 

lavori: 

Geisller 

et 

al., 

2008, 

Lombardi 

et 

al., 

2008 

e 

Piana 

Agostinetti 

& Amato 2009 .

I 

risultati 

evidenziano 

le 

differenze 

di 

profondità

ai 

limiti 

di 

placca, sia in pianta che nei profili. Il 

vantaggio 

di 

interpolare 

su 

tre 

superfici 

permette 

la 

definizione 

delle 

zone 

di 

sovrapposizione 

delle 

moho 

appartenenti alle diverse placche.

Central Apennines seismic structure, SGI 2010, Pisa

• (z=22km) Low Vp suggests fluid filled volumes in the lower-crust;• (z=38km) Low Vp suggests an hydrated mantle nose (?);• (z=52km) High and Low Vp associated to the Adria lid and the Tyrrhenian hydrated upper mantle, respectively.

P-wave velocity perturbations of the crust and uppermost mantle in the central –

northern Apennines (tomography by Di Stefano et al., 2009).SKS simplified from Salimbeni et al. (2007) are mapped on the upper mantle layer

Di Stefano et al. (2009)

Vp anomalies in the crust and upper mantle in central Italy from seismic tomography (Di Stefano et al., 2009)

RF: what else do they tell us?

Details of the crustal and upper mantle structureFluid migration (?) in the continental subduction of northern ApenninesExamples from Apulia and Abruzzi

Importance of retrieving reliable estimates of Moho depth and crustal structure is demonstrated by these numbers:

Dye (2010)

Fluid migration from the slab in Northern Apennines is hypothesized from RF studies

Piana Agostinetti et al., in review on EPSL

Apulia foreland (Puglia 1 well): results from a RJMCMC inversion (Piana Agostinetti and Malinverno, 2010)

Two-layered Meso-Cenozoic Apulian Platform (limestones/evaporites?)LVs below (Permo-Trias) , thickness ~3-4 kmLVs in the lower crust (~20-24km)Layered lower crust (~24-30km)

~16 strati

MRVN

Amato et al., in prep.

Abruzzi (Teramo –

preliminary)

TERO (Teramo, not far from here)Preliminary from Amato et al. In prep.

Left: from Di Luzio et al. (2008)

Struttura della crosta al M. Conero

AOI –

M. ConeroPreliminary from Amato et al., in prep.

In this interpretation of CROP line, the UC is crystalline-Metamorphic. The “RF”

UC has low Vs

(Vp≈6km/s: granitic gneiss? Higher U,Th !)

From Finetti, 2005

High velocity shallow bodies from seismic tomography and RF:“mafic basement rocks”

(Chiarabba et al., 2010)

Map showing the instrumental seismicity of the past 28 years in central Apennines and the map location of the HV bodies in the upper crust.

Local earthquake data (ML<3.7) recorded by temporary (2003-2004) and permanent seismic stations belonging to the INGV and the Abruzzi regional network, for a total of 139 stations, to compute three-dimensional

Vp and Vp/Vs models

Abruzzi: Local Earthquakes Tomography and RF

Conclusions

The lithosphere structure around LNGS is very complex, strongly 3DA detailed Moho(s) depth map is available Current models are good but can be improved, particularly for middle and lower crustTeleseismic Receiver Functions are a powerful tool to unravel details of crust structure (and composition?)

Possible improvements

Detailed study of Central Apennines seismic stationsAnalyze extensively seismic station GIGS (2002-08)Ad hoc experiments(?)

• Better joint interpretation of Vp, Vs, etc. at various depths(incl. the HV bodies in the upper crust, and anisotropic patterns)

Thank you for your attention

Types of crust and typical P velocities for rock types (after Christensen and Mooney, 2005)