SATREPS project
(2014~2020)
Application of state of the art technologies to strengthen research and response to seismic, volcanic and tsunami events, and enhance risk management
Earthquake rupture and slip scenarios for Ecuador-Colombia subduction zone
(v1.0 May 13/2019)
by
Esteban
Poveda1
and Nelson Pulido 2
1Servicio Geológico Colombiano (SGC)
2National Research Institute for Earth Science and Disaster Resilience (NIED)
Introduction
In the frameworks of the SATREPS project “Application of state of the art technologies to strengthen research and response to seismic, volcanic and tsunami events, and enhance risk management” we have developed a set of finite fault slip models for possible scenario earthquakes in the Pacific margin of Ecuador and Colombia. The models are appropriate for deterministic estimations of seismic hazard in Colombia (simulations of strong ground motions) as well as tsunami hazard assessment in the Pacific coast of Colombia.
Source models for North Andes
For the estimation of slip models from megathrust earthquakes in the Ecuador and Colombia Pacific coasts we apply the methodology based on a model of inter-seismic coupling distribution in subduction margins obtained from geodetic data, as well as information of recurrence and size of historical earthquakes (Pulido et al. 2015). Slip deficit from coupling represents the long wavelength asperities at the plate interface. These slip models are enhanced with short wavelength slip heterogeneities to make them suitable for strong motion simulations and tsunami hazard estimations (Pulido et. al. 2015). This methodology has been largely applied to the seismic and tsunami hazard in subduction margins in Central and South Peru as well as in the Guerrero gap in Mexico. (Pulido et al, 2015, Pulido et. al. 2014, Villafuerte et al., AGU, 2018).
Estimation of slip deficit
The slip deficit is obtained from interseismic coupling model of Sagiya and Mora-Paez (2019) obtained by inverting the GNSS data of GEORED in Colombia (Mora-Paez et al., 2018), as well as published velocity vectors in Ecuador (Chlieh et al., 2014). In figure 1 we show the slip deficit distributions for three scenarios considered in this study (Pulido et al., AGU 2018);
1906 earthquake type scenario (~Mw 8.5 for 200 years of slip deficit)
It approximately corresponds to the source area of 1906 earthquake. It mainly involves the ruptures of the Northern Esmeraldas, Manglares and Southern Tumaco segments. The moment magnitude of 8.5 assumed for this scenario corresponds to the value obtained from a source model of the 1906 earthquake obtained from tsunami waveforms and observed intensity data of this event (Pulido et al, 2019). (Figure 2a).
1979 Tumaco type earthquake scenario (~Mw 8.3 for 200 years of slip deficit)
It approximately corresponds to the source area of 1979 earthquake. It mainly involves the ruptures of the Manglares and Tumaco segments. The moment magnitude of 8.3 assumed for this scenario corresponds to the value obtained from a source model of the 1979 earthquake obtained from teleseismic waveform data of this event (Yoshimoto et al, 2019). (Figure 2a).
Worse scenario (Mw 8.8~8.9 for 500 years of slip deficit)
It would involve the combined rupture of the Northern Esmeraldas, Manglares and Tumaco segments. Although there is no historical information for such an event, we conjecture this is the largest possible event along the Ecuador-Colombia subduction margin. The selection of this earthquake scenario is motivated by the characteristics of paleo-tsunami deposits sampled in the delta of San Juan river near Buenaventura city (Colombia) (Gonzalez and Correa, 2001), as well as the patterns of paleo-turbidites sampled in a marine borehole at the Esmeraldas canyon off-shore of Esmeraldas province (Ecuador) (Migneon et al, 2016), which may suggest the occurrence of a very large megathrust event along the Ecuador–Colombia subduction margin about 500 to 600 years BP (Figure 2a).
In figure 2a we show the source regions considered for the three earthquake scenarios considered in this study.
a)
b)
Broadband slip models
We obtained a set of 24 broadband-wavelength slip models for the aforementioned source regions and slip deficit scenarios. Slip distributions have been obtained for a subfault size of 10 km a fault strike of 30 and fault dip of 15 degrees. To calculate seismic moment of scenarios we used an average rigidity value of 36.5 GPa, obtained from a crustal velocity model of the southern Pacific region of Colombia (Ocola et al. 1975). The 24 broadband slip models for the 1906 scenario are shown in Figures 3 and 4, for the 1979 earthquake scenario are shown in Figures 5 and 6, and for the worse scenario the realizations are shown in Figures 7 and 8.
Format of slip models
In this dataset we include a total of 75 slip models (24 broadband slip realizations and the original slip deficit model for each of the 3 aforementioned scenarios). Slip information of sub-faults is organized in 9 columns as follows;
longitude, latitude, depth (at the center of sub-faults, degrees and km), X size of sub-fault, Y size of sub-fault (km), strike, dip, rake (of sub-faults, in degrees), slip value (m).
Slip models can be downloaded below;
-1906 type slip models; slip_1906.tar
-1979 type slip models; slip_1979.tar
-Worse type slip models; slip_worse.tar
The
25 slip models for the 1906 scenario are a named as follows;
slip_1906_x.txt (where x corresponds to 1 to 24 slip realizations)
and slip_deficit_1906.txt (original slip deficit model). The name of
slip models for the other two scenarios changes accordingly to the
scenario names.
References
Gonzalez, J. L. and I. D. Correa, 2001. Late Holocene Evidence of Coseismic Subsidence on the San Juan Delta, Pacific Coast of Colombia, Journal of Coastal Research, 17, 2, 459-467.
Mora-Páez, H., J. N. Kellogg, J.T., Freymueller, D. Mencin, R.M.S Fernandes, H. Diederix, H., et al., 2018. Crustal deformation in the northern Andes – A new GPS velocity field, Journal of South American Earth Sciences, https://doi.org/10.1016/j.jsames.2018.11.002.
Migneon, S. et al., 2016. Earthquake-triggered deposits in the subduction trench of the North Ecuador/South Colombia margin and their implication for paleo seismology. Mar. Geol., http://dx.doi.org/10.1016/j.margeo.2016.09.008.
Ocola L.C., L. T. Aldrich, J. F. Gettrust, R. P. Meyer, and J. E. Ramirez, 1975. Project Nariño I: Crustal structure under southern Colombian-Northern Ecuador Andes from refraction data, Bulletin of the Seismological Society of America, 65(6), 1681–1695.
Pulido, N., Z. Aguilar, H. Tavera, M. Chlieh, D. Calderon, T. Sekiguchi, S. Nakai, and F. Yamazaki, 2015. Scenario source models and strong ground motion for future mega-earthquakes: application to Lima, central Peru. Bulletin of the Seismological Society of America, 105, 368–386. https://doi.org/10.1785/0120140098.
Pulido, N., Nakai, S., Yamanaka, H., Calderon, D., Aguilar, Z., and Sekiguchi, T., 2014. Estimation of a Source Model and Strong Motion Simulation for Tacna City, South Peru. Journal of Disaster Research 9, No.6, 925-930.
Pulido, N., Yoshimoto, M., Sarabia, A.M., Sagiya T., Mora H., and Arcila, M. 2018. Source model of the 1906 Ecuador-Colombia earthquake (Mw8.4) based on tsunami waveforms and seismic intensity data; Implications for megathrust earthquake potential in Northern South-America, Fall Meeting of the American Geophysical Union, T43E-3650.
Pulido N., M. Yoshimoto, and A. M., Sarabia, Broadband wavelength slip model of the 1906 Ecuador-Colombia megathrust-earthquake based on seismic intensity and tsunami data, submitted, 2019.
Sagiya, T., and Mora- Páez, H. (2019). Interplate coupling along the Nazca subduction zone on the 471 Pacific coast of Colombia deduced from GeoRED GPS observation data, Geology of Colombia, Servicio Geologico Colombiano.
Villafuerte C. D., V. Cruz-Atienza, J. Diaz-Mojica, J. Tago, and N. Pulido, 2018. Towards Ground Motions Prediction for Hazard Assessment Associated with large Subduction Earthquakes in the Guerrero Seismic Gap Mexico, Fall Meeting of the American Geophysical Union, S41D-1477.
Yoshimoto, M., Kumagai, H., Acero, W., Ponce, G., Vásconez, F., Arrais, S., M. Ruiz, A. Alvarado, P. Pedraza, V. Dionicio, O. Chamorro, Y. Maeda, and M. Nakano, 2017. Depth-dependent rupture mode along the Ecuador-Colombia subduction zone, Geophysical Research Letters, 44, 2203–2210. https://doi.org/10.1002/2016GL071929.
Yoshimoto, M.,H. Kumagai, T. Sagiya, H. Mora-Páez, and N. Pulido, Large earthquake ruptures and plate coupling in the Colombia-Ecuador subduction zone, submitted, 2019.
An maximum slip of 10.1 m (realization 22) is obtained for the set of random realizations, a minimum value of 7.2 m (realization 23).
A maximum slip of 5.7 m (realization 20) is obtained for the set of random realizations, and a minimum value of 4.2 m (realization 8).
A maximum slip of 23.2 m (realization 2) is obtained for the set of random realizations, and a minimum value of 17.0 m (realization 3).
