This is a presentation I gave at the University of Washington in Dec 2011 that gives an overview of my Ph.D thesis work at a relatively early stage (includes updated references). It lays out the objective of my thesis, and presents three different "views" of the Hellenic subduction zone, using three complimentary seismic imaging methods: 1) Teleseismic migration, 2) Receiver functions, and 3) Local tomography.

1. Seismic imaging of the western Hellenic
subduc6on zone: A link between slab buoyancy,
differen6al rollback, and upper-plate deforma6on?
F D Pearce1, S Rondenay2, H Zhang1, J L Olive3, and L Royden1
1 Dept. of Earth, Atmospheric, and
Planetary Sciences, MIT
2 University of Bergen, Norway
3 MIT / Woods Hole Oceanographic
Ins6tute Joint Program
Frederick D. Pearce

2. Suckale et al., GJI 2009 (a[er McClusky et al., JGR 2000)
Mo6va6on
Frederick D. Pearce

3. SS
NS
CTF
GPS veloci6es from
McClusky et al., 2000
31 mm/yr
What drives the different slip rates between the northern and
southern segments of the western Hellenic subduc6on zone?
AE
Mo6va6on
Frederick D. Pearce

4. Objec6ve
Seismic constraints on geometry of upper and lower
plates along the western Hellenic subduc6on zone
Royden and Papanikolaou, 2011
• Oceanic lithosphere subducted
beneath southern Greece?
• Con6nental lithosphere subducted
beneath northern Greece?
• Evidence of faster trench retreat
along southern Greece
• 3-D geometry of mantle wedge
Frederick D. Pearce

5. Outline
I. Background
II. Methods
III. Data
IV. Results
V. Discussion
VI. Conclusions
Frederick D. Pearce

6. Geology
Burchfiel, Personal Communica6on Frederick D. Pearce

7. Finea et al., CROP Project 2005
Surface Seismics
12 km
28 km
Frederick D. Pearce

8. Methods
2D Teleseismic Migra6on
3D Receiver Func6ons
hdp://garnero.asu.edu
Shear-Wave Spliang
Local (DD) Tomography
Ps
Sharp Boundaries Volumetric Proper6es
Zhang and Thurber, 2003
Frederick D. Pearce

9. Data
SS
NS
CTF
AE
Frederick D. Pearce

10. SL SL
XSL (km)
Oceanic
Crust
Teleseismic Migra6on
Δβ from backscadered modes
-5% (red) to 5% (blue)
* 8-10 km thick LVL interpreted as subducted oceanic crust
* Overriding Moho between 30-40 km depth is sharp, con6nuous
* Evidence for basal accre6on of subducted sediments
* Deepest subducted crust approximately 7-10 mya
Z (km)
See final image in
Pearce et al.,
JGR (2012)
Frederick D. Pearce

11. Δβ from backscadered modes
-5% (red) to 5% (blue)
* ~20 km thick LVL interpreted as subducted con6nental crust
* Overriding Moho between 35-45 km depth is discon6nuous
* Evidence for accre6on of ~10 km of sediments into thrust belt
* Deepest subducted crust approximately 20-25 mya
NL
Z (km)
XNL (km)
Con6nental
Crust
Teleseismic Migra6on
NL
Frederick D. Pearce
See final image in
Pearce et al.,
JGR (2012)

12. * 20-25 km of addi6onal sinking of the southern segment rela6ve to the
northern segment
* Translates into ~70 km of differen6al trench retreat between the two
segments, which roughly aligns two trenches & Mohos
X
X (km)
X (km)
Teleseismic Migra6on
Frederick D. Pearce
See final figure in
Pearce et al.,
JGR (2012)

13. 3D RF: SL
Depth (km)
XST (km)
A
B
C
A
B
C
Only
P S
Frederick D. Pearce
See final images in
Pearce MIT Ph.D.
Thesis (2014)

14. 3D RF: NL
Depth (km)
XST (km)
A
B
C
A
B
C
Frederick D. Pearce
See final images in
Pearce MIT Ph.D.
Thesis (2014)

15. Y (km)
Depth (km) A
B
C
A
B C SL NL
* Shallower, sharp Moho beneath SL versus deeper, irregular Moho beneath NL
* Undula6ng (discon6nuous?) Moho separates two domains beneath central Greece
3-D RF Imaging
Frederick D. Pearce
See final images in
Pearce MIT Ph.D.
Thesis (2014)

16. 3-D RF Imaging
Overriding Moho Slab Moho
0 200 400
−100
0
100
200
300
20
25
30
35
40
45
0 200 400
−100
0
100
200
300
40
60
80
100
X (km) X (km)
Y (km)
km km
S S
X
Y
Frederick D. Pearce
See final maps in
Pearce MIT Ph.D.
Thesis (2014)

17. * In forearc, high-velocity, shallow-dipping slab overlain by low-
velocity mountain belt, which retreat seaward from NL to SL
* In backarc, low-velocity mantle wedge overlain by high-veloci6es
beneath extended crust, which advance seaward from NL to SL
0 100 200 300 400 500 600
−300
−200
−100
0
100
200
300
400
X [km]
Y[km]
Local (DD) Tomography
S S
Frederick D. Pearce

18. X [km]
Z [km]
NL
SL
CG
0 200 400 600
−400
−300
−200
−100
0
100
200
300
400
X [km]
Y[km]
NL
CG
SL
X [km]
Local (DD) Tomography
Frederick D. Pearce

19. Anisotropic signature of slab retreat
continental
lithosphere
oceanic
lithosphere
Olive et al., EPSL (2014) Frederick D. Pearce

20. Depth
50-100 km
100-150 km
> 150 km
Discussion: Intermediate Depth EQs
Frederick D. Pearce
See final figure in
Pearce et al.,
JGR (2012)

21. Warren et al., EPSL 2008
Discussion: Con6nental Subduc6on
Frederick D. Pearce

22. Conclusions
Teleseismic migra6on images show
* oceanic crust beneath southern segment (SS)
* con6nental crust beneath northern segment (NS)
* SS slab has retreated ~70 km more than NS slab
3-D RF and local tomographic images show
* A progressive seaward migra6on of slab, mantle
wedge, and thrust belt from NS to SS
* Thicker overriding plate along NS compared to SS
* Corridor of undula6ng Moho trending roughly N-S
delineates edge of thinned Aegean lithosphere
Frederick D. Pearce