3D seismic tomography in Ecuador

3D seismic tomography and seismotectonics of the Ecuadorian margin
inferred from the 2016 Mw 7.8 Pedernales aftershock sequence
Sergio Leon-Rios et al. | 26.09.2019
GEOPHYISICAL INSTITUTE (GPI)
KIT – University of the State of Baden-Wuerttemberg and
National Laboratory of the Helmholtz Association
www.kit.edu

The 2016 Pedernales earthquake
−82˚
−80˚
−78˚
2˚
% ISC
100
80
60
40
Slow
Slip
Event
Repeating
earthquakes
Swarm
episodes
−10
−20
−30
−40
1979 Mw8.2
−50
2˚
Ecuador - Colombia border
46 mm / yr
20
0
Coseismic
slip contour
Nazca Plate
1958 Mw7.7
1906 Mw8.8
Esmeraldas
2016 SSE
2016 Mw7.8
0˚
1942 Mw7.8
Pedernales
0˚
Carnegie Ridge
−10
−20
−30
−40
−50
Bahia
1998 Mw7.1
Caraquez
−2˚
La Plata
Island
2010 & 2013 SSE
North
Andean
Sliver
−2˚
South American
Plate
−82˚
−80˚
−78˚
Context 2D 3D Discussion Conclusion
Sergio Leon-Rios et al. – GPI 26.09.2019 2/16

Emergency network
Large international project.
Service to the Ecuadorian
permanent network
(RENSIG).
−82˚
1˚
ECU
UK
FRA
USA
−81˚
−80˚
Esmeraldas
−79˚
1˚
60+ stations to
complement the national
network.
0˚
2016 Mw7.8
Pedernales
0˚
OBS installed along the
trench.
Station spacing ∼ 20 km.
−1˚
Manta
−1˚
Deployment fully operative
for 1 year (May 2016 -
June 2017).
−82˚
−81˚
−80˚
−79˚
Context 2D 3D Discussion Conclusion
Sergio Leon-Rios et al. – GPI 26.09.2019 3/16

Problem
−82˚
−81˚
−80˚
−79˚
profile A − A’
0 25 50 75 100 125 150
IG catalogue, all magnitudes
Period: May - August, 2016
Events selected, Ml > 3.5
Coseismic slip contour
−10
−20
−30
−40
0
2000
0
−2000
−4000
1˚
A
1˚
2016 Mw7.8
A’
Depth (km)
25
50
75
0 25 50 75 100 125 150
0˚
B
−10
−20
−30
−40
−50
0˚
profile B − B’
0 25 50 75 100 125 150
2000
0
−2000
0
−4000
B’
−1˚
−1˚
Depth (km)
25
50
IG catalogue, all magnitudes
Period: May - August, 2016
Events selected, Ml > 3.5
75
−82˚
−81˚
−80˚
−79˚
0 25 50 75 100 125 150
Distance from trench (km)
There is still no consensus about the velocity structure of the area.
Current models are usually focused in small areas or have limited
resolution.
This leads to problems in the seismicity localization.
Context 2D 3D Discussion Conclusion
Sergio Leon-Rios et al. – GPI 26.09.2019 4/16

Opportunity
The high rate of aftershock seismicity.
An unprecedented seismic coverage.
High quality data.
→ Unique opportunity to better resolve the velocity structure of the
region.
Context 2D 3D Discussion Conclusion
Sergio Leon-Rios et al. – GPI 26.09.2019 5/16

Increasing complexity 1D → 2D
Minimum 1D model as a start for the 2D inversion.
More events added for a better resolution (∼ 500 in total).
Inversion performed using SIMUL (travel times and ray tracing
inversion).
Context 2D 3D Discussion Conclusion
Sergio Leon-Rios et al. – GPI 26.09.2019 6/16

2D modelling strategy
Min 1D
- Velocity model
- Aftershock location
Damping curve Vp
Smoothing
technique
- Shift nodes and
average the results
- Average Vp
- Refined locations
- Check resolution
Separate areas
North & South
- To see the contribution
from each section
2D
- Average Vp/Vs
- Refined locations
- Check resolution
Damping curve Vp/Vs
Context 2D 3D Discussion Conclusion
Sergio Leon-Rios et al. – GPI 26.09.2019 7/16

2D velocity model
Vp
Vp/Vs
Depth (km)
0
0
20
20
40
40
North
60
60
−100 −50 0 50 100 −100 −50 0 50 100
6.5
5
5.56
7
7.5
8
6
4.5
4.5
6.5
6
1.95
1.8
1.9
1.85
1.75
1.85
1.8
1.8
1.85
1.8
1.8
1.85
1.9
1.85
0
4.5
5.56
5
0
2
1.9
1.95
1.85
1.8
1.85
1.75
1.8
2
1.95
1.9
Depth (km)
20
40
8
6.5
7
7.5
6.5
6
8.5
20
40
1.8
1.8
1.85
1.9
1.8
1.8
1.85
South
4 5 6 7 8
8
60
60
−100 −100 −50 0 50 100
−50 0 50 100
Distance (km)
Distance (km)
P−wave velocity (km/s)
1.6 1.8 2.0
Vp/Vs ratio
Context 2D 3D Discussion Conclusion
Sergio Leon-Rios et al. – GPI 26.09.2019 8/16

Increasing complexity 2D → 3D
North and south models were merged to perform the 3D inversion.
More events were incorporated to the process. (604 in total).
Profiles along strike were included to increase resolution.
Same strategy used to build the 2D model was followed in this stage.
Context 2D 3D Discussion Conclusion
Sergio Leon-Rios et al. – GPI 26.09.2019 9/16

Resolution test
0
0
Depth (km)
20
40
Lat 1°N
60
−100 −50 0 50 100
Depth (km)
20
40
Lat 0.5°S
60
−100 −50 0 50 100
0
0
Depth (km)
20
40
Lat 0.5°N
60
−100 −50 0 50 100
Depth (km)
20
40
Lat 1°S
60
−100 −50 0 50 100
0
0
Depth (km)
20
40
Lat 0°
60
−100 −50 0 50 100
Depth (km)
20
40
Lat 1.5°S
60
−100 −50 0 50 100
0 1 2 3 4 5
spread function
Context 2D 3D Discussion Conclusion
Sergio Leon-Rios et al. – GPI 26.09.2019 10/16

Main geological features
Manta-Jama basin
Piñon
Manabi basin
Manabi basin
Reyes & Micheaud (2013)
Context 2D 3D Discussion Conclusion
Sergio Leon-Rios et al. – GPI 26.09.2019 11/16

3D velocity model: cross sections
Context 2D 3D Discussion Conclusion
Sergio Leon-Rios et al. – GPI 26.09.2019 12/16

3D velocity model: cross sections
Context 2D 3D Discussion Conclusion
Sergio Leon-Rios et al. – GPI 26.09.2019 13/16

−3000
−3000
−3000
0
500
1
1
0
0
1
2
3
5
2
500
3
2
0
1
0
0
3D velocity model: slice along slab
−81˚
−80˚
−79˚
1˚
Average Vp/Vs: 1.82
Interface range: 10 km
Data range: May - Nov 2016
Afterslip / SSE patches
−3000
−3500
−3500
−3000
−3500
−2500
−2000
−1000
−1500
−1000
−500
1˚
−3000
−3000
−2500
1.85
−3500
−2500
1.85
−2000
−1500
−1000
−2500
−3000
−3500
−3500
1.95
−3000
−2500
1.9
−1500
−2000
−1000
−500
2016 Mw7.8
1.85
1.9
−3500
1.85
−500
1.85
0˚
−2000
−2500
−2000
−2500
−3000
−1500
−1000
−500
1.85
3
1.85
1.8
4
1
1.85
0˚
1.85
1.85
−3000
1.9
−2000
1.9
−2500
−3000
−2500
−2000
−1500
−1000
−500
1.8
−1˚
−1˚
1.85
1.8
1.8
500
500
500
1.7 1.8 1.9
Vp/Vs ratio
−81˚
−80˚
−79˚
Context 2D 3D Discussion Conclusion
Sergio Leon-Rios et al. – GPI 26.09.2019 14/16

Conclusions
We were able to resolve the 3D velocity structure of the Ecuadorian
margin.
Main geological features at surface can be observed.
Seismicity is clustered.
High Vp anomaly offshore can be colocated with the Atacames
seamounts and the CR.
Low Vp/Vs areas coincide with coseismic slip.
Areas of high Vp/Vs colocate with afterslip and SSE patches.
Trench location and slab interface have to be studied in detail to allow
better interpretation.
Context 2D 3D Discussion Conclusion
Sergio Leon-Rios et al. – GPI 26.09.2019 15/16

3D seismic tomography and seismotectonics of the Ecuadorian margin
inferred from the 2016 Mw 7.8 Pedernales aftershock sequence
Sergio Leon-Rios et al. | 26.09.2019
GEOPHYISICAL INSTITUTE (GPI)
KIT – University of the State of Baden-Wuerttemberg and
National Laboratory of the Helmholtz Association
www.kit.edu