crustal structure in southern tyrrhenian sea from seismic

32 GNGTS TRIESTE 18-20 nov 2013

R. de Franco, G. Caielli, G. Biella, G. Boniolo,

A. Corsi, A. Morrone, A. Tento, G. Tango

C. Ranero, V. Sallares, M. Prada

I. Grevemeyer

N. Zitellini

Crustal structure in southern Tyrrhenian sea from seismic processing of HG-MEDOC WARR line.

Istituto Scienze Marine, ISMAR-CNR,

Bologna, Italy

Istituto per la Dinamica dei Processi

Ambientali, IDPA-CNR, Milan, Italy

Barcelona Center for Subsurface

Imaging, ICM-CSIC, Barcelona, Spain

GEOMAR Helmholtz Centre for Ocean

Research, Kiel, Germany

http://www.utm.csic.es/



AIMS of the Presentation

•Framework: MEDOC project (MEDiterràneo OCcidental) is a Spain-Germany-Italy cooperation project for the exploration of the crustal structures of the Balearic, Ligurian and Tyrrhenian basins. •A new procedure of static corrections for Wide-Angle Reflection/Refraction (WARR) Data •Data Processing of HG-WARR MEDOC Line •New results on the crustal structure in southern Tyrrhenian sea a contribution to the study of the processes of formation of rifted continental margins.



THE MEDOC PROJECT

MEDOC project acquired a total of 17 (2800 km) MCS (Multi-Channel Seismic Reflection) lines

and 5 WARR (Wide-Angle-Reflection/Refraction) profiles using OBS, OBH and land-stations

installed in Corsica and Sardinia.

A B

C D

E F

G H M

N

Co

rnag

lia T

erra

ce

Sard

inia

Mar

gin

H G Magnaghi

Smt Vavilov

Smt

Marsili Smt

Flavio Gioia Smt

Cam

pan

ian

Ter

race

Cam

pan

ian

Mar

gin



MEDOC HG LINE: EXPERIMENTAL LAYOUT

WIDE ANGLE REFLECTION\REFRACTION SEISMIC DATA

H G

5 OBS (UTM-CSIC) AND 25 OBH (Geomar) TYRRHENIAN

SEA FLOOR 5 LAND STATIONS (IDPA-CNR) SARDINIA-CORSICA MARGIN

Vessel Sarmiento de Gamboa (CSIC) MCS data & WARR Shooting

Vessel Urania (ISMAR-CNR) OBS-OBH deployment WARR-Data



WARR DATA

DATA ACQUISITION & PROCESSING

Data Filtering Butterworth Band Pass 4-15 hz (signal signature 7-8 hz)

Spectral Analysis

First arrivals Picking

Common receiver gather data construction (navigation, shoting files)

WARR Static correction

Refraction Velocity analysis

PmP picking & depth conversion

Panel LMO

WARR Data

MOHO Refracted wave

PmP Phases

Pn Phases

MCS Data

MCS and WARR seismic data were acquired shooting twice the same lines using different devices, geometry and acquisition parameters

MCS data were acquired in common shot gather from 3450 m streamer (276 ch), shot spacing 50 m, fold 35, source 9 G-II airguns 3040 inch3

WARR data were acquired in common receiver gather from OBH, OBS, in-land Stations; 90 s shoting interval, ~220 m shot spacing, source two arrays of 6 G-II airguns, 4600 inch3.

Panel NMO

Pn Imaging depth conversion



MOTIVATIONS TO DEVELOP A PROCEDURE FOR WARR STATIC CORRECTIONS

WARR STATIC CORRECTIONS

•In the standard WARR interpretation procedures (Trial&error method or traveltime inversion&Tomography) it is difficult to assign the correct seismic phases to the observed arrivals on profiles. •In the signal processing procedures detection and stacking routines are applied to the traces in order to enhance and focusing Pg, Pn and PmP phases and to obtain simplified transforms of the wave field and then to construct crustal (with different scales) images.



PROCESSING PROPOSED GLOBAL WARR STATIC CORRECTION

i=i-th Source j=j-th Receiver Ti

Obs=Observed Travel times Ti

Smooth=Smoothed Travel times HBatsmt =Smoothed bathymetry

VS= Sea velocity VCbas=Crustal Basement velocity

Vbasin=Basin Velocity

Morphology Basin

Morphology Bottom Sea

)0(

)0(

iRE S

iRE S

iObs

iSm ooth

iRE S

DT

DT

TTDT

Cb a sS

iBa tsm t

iL

Cb a s

jBa tsm tj

L

iL

jL

i jL

V

1

V

1HDT ;

V

HDT

DTDTDT

SHOT/RECEIVER CORRECTION (long wavelength effect of

bathymetry)

RESIDUAL CORRECTION (short wavelength effect of

the top of crustal basement)

+

Shot-ith

Rec-jth

Crustal Basement

HiBatsmt

HjBatsmt

Crustal Basement

DTiRES(>0)

DTiRES(<0)

VS

VCbas

VBasin



RESIDUAL STATIC CORRECTION: PROCEDURE

PROCESSING

0 10 20 30 40 50 60 70 802

2.5

3

3.5

4NPsmoot=50 Itsmt=13 Psmt=3.7276e-005

0 10 20 30 40 50 60 70 80-0.5

0

0.5Chi 4.2404

0 10 20 30 40 50 60 70 80-0.5

0

0.5

0 10 20 30 40 50 60 70 80-6

-4

-2

0

2x 10

-4

SMOOTHING PICKING LINE PICKING LINE

SECOND DERIVATIVE

RESIDUALS Sea CORRECTION

Offset [km]

Offset [km]

Tim

e [s

] Ti

me

[s]

Der

ivat

ive

Tim

e [s

]

APPLY RESIDUAL STATIC CORRECTION DTRES

YES

Derivative check

TiSmooth

D2<=0

NO

STARTING SMOOTHING Ti

Obs Corrected for smoothed bathymetry

PROCEDURE

APPLY LONG WAVE LENGHT STATIC

CORRECTION DTL

CH

AN

GE

SMO

OTH

ING

PA

RA

MET

ERS



THEORY PROPOSED GLOBAL WARR STATIC CORRECTION:CRITICAL REFRACTION SYNTHETIC EXAMPLE

Refr

Cbas-1

3

Refr

Basin-1

2

Refr

S-1

1

i

Batsmt

i

Basin

i

Basin

i

Bat

i

Batsmt

i

Bat

Cbas

3

Basin

2i

Basin

Cbas

3

S

1i

Bat

Cbas

3

S

1i

Batsmt

Basin

2j

Basin3

Cbas

j

Basin

j

BatsmtRefr

Refr

ijij

Refr

V

Vsinθ;

V

Vsinθ;

V

Vsinθ

HHh

HHh

:and

receiver th-jj andsource th-iiWhere

.V

)cos(θ

V

)cos(θh

V

)cos(θ

V

)cos(θh

V

)cos(θ

V

)cos(θH

V

)cos(θh)cos(θ

V

)hH(2H

V

XT

In the hypothesis of local planar interfaces near the source and receiver (approximation for low angle <5 -10 ) , the critical refracted travel time is:

HiBat

hiBasin

HjBat

HRefr

J-th Receiver

i-th Shot Xij

HiBatsmt

hiBat

Travel-time terms including long wavelength effects due to the smoothed bathymetry at the sources and local time-term at the receiver. It can be approximated with a smoothed travel-time.

Time term (early times) including short wavelength effects due to local variations of the bathymetry or to the horst-like morphology of the top of crustal basement below the sources

Time term (delay times) including short wavelength effects due to the presence of the basins or to the graben-like morphology of the top of crustal basement below the sources



Ri f r

Cbas1-3

Ri f r

B asi n1-2

Ri f r

S1-1

Cbas

3

B asi n

2iB asi n

iB atsm t

iRE S

Cbas

3

S

1iB at

iB atsm t

iRE S

iObs

iS m ooth

iRE S

V

Vsinθ;

V

Vsinθ;

V

Vsinθ

V

)cos(θ

V

)cos(θH-H0)(DT

V

)cos(θ

V

)cos(θH-H0)(DT

TTDT

THEORY PROPOSED GLOBAL WARR STATIC CORRECTION:CRITICAL REFRACTION SYNTHETIC EXAMPLE

hiBat=Hi

Batsmt-HiBat

hiBasin=Hi

Basin-HiBatsmt

hiBasin

hiBat



CONCLUSION: RESULTS REMARK RESIDUALS COMPARISON MCS-WARR

•Estimate of WARR Static correction is robust and consistent •It is possible to obtain a “raw morphology” of the top of the crustal basement in

TWT ONLY from WARR data static processing!!!???



RESULTS EXAMPLE STATIC APPLICATION

Offset (km)

Reduced T

ime V

red=

8km

/sO

ffset

(s)

20 40 60 80 100 120 140 160

0

1

2

3

4

5

6

7

8

9

10

Reduced T

ime V

red=

8km

/sO

ffset

(s)

Offset (km)

20 40 60 80 100 120 140 160

0

1

2

3

4

5

6

7

8

9

10

Pmp



Trace number

T-x

/8 [

s]

OBS 95

V=7.9769 To=3.8119

1150 1200 1250 1300 1350 1400 1450 1500 1550 1600

0

2

4

6

8

10

12

PROCESSING Pn PHASES Linear move-out

Pn



PROCESSING Pn PHASES Linear move-out

Trace number

T-x

/8 [

s]

OBH 90

V=8.0563 To=4.2904

V=7.9794 To=3.7981

900 1000 1100 1200 1300 1400 1500 1600

0

1

2

3

4

5

6

7

8

Pn

Pn



RESULTS Pn IMAGING AND VELOCITY ANALYSIS

17 km

10 km

22 km

E W

Vavilov Seamount

Magnaghi Seamount

8.1 8.1

8 7.9 7.8 7.7 7.8 7.7 7.7 7.8

7.9 8

7.9 8 8.1 8.2

Vavilov Magnaghi



PROCESSING PmP PHASES

Pmp

E W

Vavilov Magnaghi



PROCESSING PmP PHASES NMO

? ?

Pmp

E W

Vavilov Magnaghi




? ? ? ?

E W

Vavilov Magnaghi




Pmp Pmp

E W

Vavilov Magnaghi




Pmp

E W

Vavilov Magnaghi

Pmp



RESULTS PmP LACK

PmP LACK

Vavilov Magnaghi

EGT ’86 Southern Segment - Egger, 1992

Tirreno ’71 - Biella et al. , 2007



PMP LACK: WHY? THE TRANSITIONAL HIGH GRADIENT HYPOTHESIS

NO TRANSITIONAL MODEL TRANSITIONAL HIGH GRADIENT MODEL

8km/s 7 6 5 4 3 2 8km/s 7 6 5 4 3 2

PmP Triplications Pre-critical PmP

Pn Pn

shots

OBS

OBH



Baronie Smt. Magnaghi Smt. Vavilov Smt.Flavio Gioia Smt.

DISTANCE (km)

RESULTS COMPARISON WARR RESULTS VS MCS DATA

(MCS MEDOC Data; Prada et al. EGU 2012, submitted JGR)



CRUSTAL VELOCITY ANALYSIS Vavilov Magnaghi

Reduced travel-time method

Velocity isolines are the envelope for

Vred=cost of traveltime at offset xx/2

Deep structure of the Tyrrhenian basin from 2-D joint refraction and reflection travel-

time tomography of wide angle seismic data

M Prada, V Sallares, CR Ranero, M Guzman, N Zitellini, I Grevemeyer, R de Franco

EGU 2012 General Assemby, also summitted JGR


http://scholar.google.com/citations?view_op=view_citation&hl=it&user=jIwPdCoAAAAJ&sortby=pubdate&citation_for_view=jIwPdCoAAAAJ:OU6Ihb5iCvQC






RESULTS: CRUSTAL VELOCITY DOMAINS

Sardinian Margin

Campanian Terrace

Campanian Margin

Magnaghi Vavilov Basin

Vavilov

~0.5 km/s

Cornaglia Terrace

Magnaghi



CONCLUSIONS: CRUSTAL STRUCTURE

MANTLE

Vavilov Smt Magnaghi Smt Baronie Smt Flavio Gioia Smt

Cornaglia Terrace Campanian Terrace Sardinian Margin Campanian Margin

Magnaghi-Vavilov Basin

Max 6-9 cm/y - min 2.5-5.5 cm/y

Continental Crust

Continental Crust

Mantel Exhumation

Central Tyrrhenian basin evolution: 1) Eastward continental crust extension 2) Back-arc spreading due to campanian-ionian crustal roll-back with generation of oceanic-like crust

followed by mantle exhumation with intrusions of later magmatic episodes. 3) Considering Magnaghi-Vavilov basin was emplaced in ~1.6-1.9 My (Sartori et al. 2004) we can

estimate a spreading rate of about 6-9 cm/y. 4) Alternatively, considering the maximum temporal interval for the emplacement of the basin

(Gortani ridge ~4 My, Magnaghi 2.7-3 My, Vavilov smt ~0.1/0.4-2.4 My ; Kastens et al. 1998, Sartori et al. 2004, Doglioni et al. 2004) the minimum spreading rate should be about 2.5-5.5 cm/y

The minimum crustal thickness is ~7 km, it is observed in correspondence of the depocenter of the Magnaghi-Vavilov basin. The minimum depth mantle is ~10 km.

The PmP lack is observed between the eastern limit of Cornaglia Terrace and western limit of Campanian Terrace. In this area (~125 25 km) the crustal velocity and gradients indicate rock mantle constitution of the crustal basement due to mantle exhumation.

The crustal structure is slightly asymmetric with different dips of Moho for Sardinian and Campanian domains and maximum Moho depth respectively of ~22 km and ~17 km.

Both domains show velocities and gradients typical of continental crust. The Campanian domain presents a lesser crustal thickness (~5 km) and generally a higher mean velocity (~ 0.5 km/s).

Cornaglia Terrace and Campanian Terrace domains show a crustal velocity structure of a continental crust type contaminated by mantel intrusions, quite a “oceanic crust type” for Campanian Terrace.


crustal structure in southern tyrrhenian sea from seismic

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