1. ---------------------------------
EUSTACY FEEDBACK COUPLING TO SEISMOGENIC BEHAVIOR OF THE NORTHERN PERU SUBDUCTION ZONE
Location of the studied area
LOCATION
This figure shows the location of the studied area.
It covers the Andean forearc along the Peru subduction from the border between Ecuador and Peru at about 3°30’ South to about 7°South Latitude to the South.
In this region the Nazca plate underthrusts the South American plate at a rate of 8 cm/yr, the convergence between the two plates being perpendicular to the trench axis.
Along this segment of the Andean subduction, the decollement is known to be flat dipping less than 10° to the East.
DATA CONSIDERED
This map shows the data considered in this work.
From East to West it includes:
(1) the Tablazos along the coastal plain shown by these yellow patches.
(2) the seismic profiles provided by PERUPETRO as shown by red and thin grey lines. These profiles extend across the continental margin and shelf.
(3) More to the West we took advantage of the EM12 bathymetry from the ANDINAUT cruise of the L’Atalante that covers the middle and the lower slope between 4 and 6,000 m water depth. These data cover also the trench axis and part of the subducting Nazca plate.
Both seismic records and bathymetry document seaward dipping low angle detachments penetrating deep into the continental basement of the margin.
These detachments document a tectonic segmentation allowing us to identify the Talara, Paita, and the Sechura segments from North to South.
Onshore coastal landforms were dated using cosmonuclides.
These data document a tectonic segmentation including the Cabo Blanco segment to the North and the Paita-Illesca segment to the South.
A significant result of this work is to show that no clear tectonic correlation exists between the onshore and continental margin segmentations
decollement is flat
Data considered in this work
The tablazos (light yellow) along the coastal plain
The seismic profiles (red and grey lines) from Perupetro
(3) EM12 bathymetry acquired during the Andinaut cruise

2. DISTRIBUTION OF PERMANENT DEFORMATION ALONG THE NORTHERN
PERU FOREARC FOR THE PAST 200 KYR:
Long-term SUBSIDENCE characterizes the continental margin as the
effect of Subduction erosion working at depth.
Along the coastal plain (tablazo) PERMANENT TOPOGRAPHY is created
through a long-lived sequence of MAJOR EARTHQUAKES.
The neutral line between uplift and subsidence is located ~10 km seaward from
The coast line

3. Tectonic evolution of the middle slope area during the past 400 kyr
(After Bourgois et al., Geology 1993)
critical angle of
gravity stability
Sechura detachment
A catastrophic debris avalanche occurred at 13.8 ± 2.7 ka
producing a destructive tsunami (von Huene et al., JGR 1989)

4. tablazo (i.e. the uplifted paleo shelf) in the Paita area
paleo-island
tablazo (i.e. the uplifted paleo shelf) in the Paita area
140 ± 13 ka
Paleozoic basement
tablazo

5. Tablazo
Normal fault
Eocene
Paleozoic basement
Tablazo

6. EAST OF DIVIDE : flat Mancora tablazo dipping gently to the
Taime Fm and paleo shoreline
DIVIDE
EAST OF DIVIDE : flat Mancora
tablazo dipping gently to the
South from 280 to 150 m.
WEST OF DIVIDE : steep and
rough hill slope down to the
coast line.

7. CLIFF N01, N02 61.4 ± 7.2 ka El Nuro Mb 160 ± 12 ka Golf Course Mb
NNE
SSE
CLIFF N01, N02
61.4 ± 7.2 ka
(10Be exposure age**)
El Nuro Mb 160 ± 12 ka
(OSL* dating )
Golf Course Mb
Carrizo Mb
*OSL = Optically stimulated luminescence
** Cosmic rays exposure dating
Eocene
unconformity

8. Cliff, N02, 61.4±7.2 ka
notch
Rock fall
El Nuro Mb

9. EAST OF DIVIDE : flat Mancora tablazo dipping gently to the
Cabo Blanco profile
DIVIDE
EAST OF DIVIDE : flat Mancora
tablazo dipping gently to the
South from 280 to 150 m.
WEST OF DIVIDE : steep and
rough hill slope down to the
coast line.

10. Casehardened sandstone
wave cut notch
The cliff hides the notch
From view
beach gravel
Casehardened sandstone
cliff
wave cut notch
beach gravel
8.6 ± 0.5 m between notches

11. 6 ± 0.5 m between notches
notch
beach gravel
cliff
notch
beach gravel

12. N ± 1.8 ka
N ± 2.4 ka
(B)
(A)
(A) Transect from the Mancora tablazo to the coastline, note the steep and rough geomorphic signature west of the divide.
(B) Elevation versus distance diagram of coseismic terraces: 16 terraces were identified
Vertical resolution using two GPS TRIMBLE 4600 LS receivers is ~0.5 m.

13. The uplift rate : 10 and 12 mm.yr-1 for the past 20-25 kyr
Uplift rate reconstruction along the Cabo blanco segment from geomorphic markers dated using in-situ produced 10Be
The uplift rate : 10 and 12 mm.yr-1 for the past kyr
Lower panel : sea level past estimates
Upper panel : tectonic uplift reconstruction

14. LOCATION OF N10 AND N12 SAMPLES
ALONG THE PAITA-ILLESCA SEGMENT
N10
N12

15. uplift history for samples N10 and N12 collected along
Paita-Illesca segment
Decelarating uplift rate
at both sites
Uplift tectonic phases
Roughly match
sea level rise during
isotope stage 6
to substage 5e
Past sea level
estimates
from SPECMAP
We favor the issue assuming that Illesca (N12) evolved similar
to Paita (N10).
Uplift rates from mm.yr-1 (N10) and 10.7 mm.yr-1 (N12).

16. Paita-Illesca segment
Cabo Blanco segment
Paita-Illesca segment ?
N05
N10
N07
N12
Term. I
Term. II
At sites N10 and N12 uplift
tectonic matches sea level rise
from Termination II
At Cabo Blanco uplift matches
sea level rise from Termination I

17. WE INFER THAT EUSTACY EXERTS IMPORTANT FEEDBACK COUPLING
TO SEISMOGENIC BEHAVIOR OF THE NORTH PERU SUBDUCTION ZONE.
(B) During the eustatic sea level rise, pore pressure increases along the subduction channel that weakens the previouly locked zone along the plate interface contributing the locked zone to enter a long-lived sequence of major earthquakes
(A) During sea level fall, pore fluid pressure diminishes along the subduction channel inducing a possible seaward migration of the locked zone.
Bourgois, J., et al., (2007), J. Geophys. Res.,112, doi: /2006JB00449.

18. two main tectonic phases during main stages of sea level rise.
During the past 200 kyr the shore line migrated to the west through
two main tectonic phases during main stages of sea level rise.
first tectonic phase 125 and 150 ka at Paita-Illesca segment
second tectonic phase past kyr at Cabo Blanco.
It is related to a sequence of major earthquakes
200 ka
100 ka
PRESENT
WE INFER THAT EUSTACY EXERTS IMPORTANT FEEDBACK COUPLING
TO SEISMOGENIC BEHAVIOR OF THE NORTH PERU SUBDUCTION ZONE.