PICTURES and CEVICHE: controlled source seismic experiments to probe the
relationship between subduction zone slip and geologic structure in Chile
Anne Tréhu (Oregon State University) and Nathan Bangs (Un. Texas Institute for Geophysics)
In late 2016 and early 2017, the R/V Marcus Langseth will be on the continental margin of Chile
for two NSF-funded projects to explore crustal velocity, seismic reflectivity and margin structure
for comparison with geodetically-determined interseismic creep and with the distribution of slip
during large plate boundary earthquakes (Figure 1). These projects represent examples of the
use of controlled source seismic data to complement continuous observatory geodetic and
seismic observations in order to study subduction zone earthquakes. Controlled source seismic
experiments provide critical data for understanding subduction (see the white paper by
Shillington et al.), and any SZO should include a controlled source component for highresolution characterization of the subsurface geologic structure. The PICTURES and CEVICHE
projects will provide an excellent basis for potential complementary SZO projects along the
South American margin and data to test innovative new analysis approaches. Lessons learned
will be applicable to future SZO experiments.
PICTURES (Pisagua/Iquique Crustal Tomography to Understand the Region of the Earthquake
Source) is a collaborative effort between the Oregon State University, GEOMAR and the Un. Of
Chile to image crustal structure in the region of the 2014 Pisagua/Iquique earthquake. The
Pisagua/Iquique earthquake was exceptional in having a long and well-recorded foreshock
sequence and a remarkable correlation between seismicity and the gravity field, suggesting
strong structural control on megathrust slip. Moreover, it only ruptured half of a seismic gap that
last ruptured in a very large event in 1877, heightening concerns about a future event in this
region. PICTURES is the first of two planned cruises to image 3D crustal structure and focuses
on the region that ruptured in 2014; phase 2, on the R/V Sonne, will focus on the unruptured gap.
Seismic sources from the R/V Marcus Langseth will be recorded on 69 ocean-bottom
seismometers (50 from the US OBSIP and 19 from GEOMAR) and on onshore seismometers of
the Chilean National Seismic and IPOC seismic networks as well as on the R/V Langseth MCS
streamer. In addition to obtaining data to develop a 3D velocity model of the source region, two
longr profiles along and across the subduction zone will be acquired to characterize the incoming
plate structure and an apparent change in structure between the remaining gap and the region that
ruptured in 2014.
CEVICHE (Crustal Experiment from Valdivia to Illapel to Characterize Huge Earthquakes) is an
MCS experiment that spans the source region of the 2015 Illapel and 2010 Maule earthquakes,
and the northern half of the great 1960 Valdivia earthquake. The objective of this project is to
image changes in plate boundary reflectivity for comparison with the slip distribution during
these recent large earthquakes and with variations in interseismic locking and post-seismic
afterslip behavior as determined geodetically. MCS data will be acquired with the 15-km long
streamer on the R/V Marcus Langseth along the continental slope and shelf and just seaward of
the deformation front. A number of dip lines across the forearc will also be acquired. Although
the placement of the dip lines is shown schematically on Figure 1C, locations will be fine-tuned
during the cruise in response to results from the strike profile along the shelf.
1
68°W
PA C I F I C
OC E A N
30°S
Caldera
Isla Grande de Atacama
Isla Chañaral
Islas Choros - Damas
!
Valparaíso
!
!
38°S
CHILE
!
ARGENTINA
!(
!
! !
!! !
!!
42°S
Marine Protected Area
52°W
Iquique
!
38°S
Ocean Depth Contour
56°W
La Rinconada
34°S
Territorial Waters (12 nmi)
60°W
BOLIVIA
!(
Seismic Transect
Exclusive Economic Zone
64°W
18°S
72°W
22°S
76°W
26°S
GEOMAR OBS Location
!.
80°W
22°S
Scripps OBS Location
!(
A
84°W
26°S
LEGEND
88°W
30°S
18°S
92°W
34°S
Figure 1. Maps showning the general location (A) and
planned experimental geometries (B,C).
96°W 92°W 88°W 84°W 80°W 76°W 72°W 68°W 64°W 60°W 56°W 52°W 48°W
PICTURES (Pisagua/Iquique Crustal Tomography to
Understand the Region of the Earthquake Source)
77°W
30°S
31°S
32°S
38°S
39°S
43°S
22°S
44°S
70°W
Gulf of Ancud
Lafken Mapu-Lahual
!
!
!
!
Chiloé Island
Gulf of Corcovado
Guafo Island
100 50 0
79°W
78°W
Bosque Fósil de Punta Pelluco
Pullinque
Islotes de Punihuil
!
!
Putemún
Chiloé
!!
!
100 Kilometers
77°W
76°W
75°W
74°W
41°S
!(
1000 m
3000 m
71°W
40°S
!
!(
40 Kilometers
72°W
m
73°W
42°S
!(
ARGENTINA
Fiordo ComauSan Ignacio de Huinay
43°S
!(
400
0
2000 m
100 m
!(
Bahía TicToc-Golfo
de Corcovado
Tic-Toc
44°S
!(
1000 m
2000 m
3000 m
73°W
0
CHILE
!(
!.
4000 m
5000 m6000 m
40 20
33°S
33°S
19°S
!.
34°S
35°S
36°S
20°S
37°S
!(
!.
PA C I F I C
OCEAN
!(
!(
!(.
21°S
m
7000 m
6000 m
5000 m
0
400
21°S
!(
!(
!(
!.(
Península de Hualpén
!
Southern
Survey
38°S
!.
Iquique
!(
!(
!.(
Las Cruces
Islotes Lobería y Lobería Iglesia
de Piedra de Cobquecura
!
39°S
!.
0m
!(
!(
!(
Valparaíso
Rocas de Constitución
!
40°S
4!( 0
0
!.(
!(
!(
22°S
20°S
!(
!.
!(
69°W
100 m
!(
!(
!(
!(
!(
!(
!.
!(
!(
!(
!(
70°W
Bosque de Calabacillo
de Navidad
41°S
!(
!(
!(
!(
(!!.
!(
!(
!(
!(
!(
!(
!(
!.
!(
!(
(!.
PA C I F I C
OCEAN
!
42°S
!(
Northern
Survey
71°W
34°S
Central
Survey
32°S
18°S
19°S
!(
72°W
C
4000 m
CHILE
!(
73°W
1000 m2000 m
4000 m 3000 m
6000 m5000 m
18°S
PERU
74°W
35°S
Punta Coles
75°W
5000 m
30°S
B
76°W
36°S
70°W
37°S
71°W
31°S
72°W
CEVICHE (Crustal Experiment from Valdivia to Ilapel
to Characterize Huge Earthquakes)
Pitipalena-Añihué
72°W
71°W
70°W
69°W