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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)