--------------------------------- EUSTACY FEEDBACK COUPLING TO SEISMOGENIC BEHAVIOR OF THE NORTHERN PERU SUBDUCTION ZONE Location of the studied area LOCATION.

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--------------------------------- 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

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

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)

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

Tablazo Normal fault Eocene Paleozoic basement Tablazo

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.

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

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

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.

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

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

N05 8.1 ± 1.8 ka N07 20.4 ± 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.

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 20-25 kyr Lower panel : sea level past estimates Upper panel : tectonic uplift reconstruction

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

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 16.9-20.7 mm.yr-1 (N10) and 10.7 mm.yr-1 (N12).

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

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:10.1029/2006JB00449.

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 20-23 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.