F1b: Subduction in the past & today
A full understanding of the subduction process and of its role in the Earth’s evolution requires studying the interplay between different involved physical and chemical processes with complementary contributions from different geosciences disciplines (seismology, geodynamics, tectonics, volcanology, geochemistry…).
While many of Solid Earth geoscientists are dealing with some aspects of the subduction, most of existing studies are carried out in a frame of a single discipline and complex approaches to subduction are rare.
A unique example of such a complex approach is the NSF-funded program Geo-PRISMS (Geodynamic Processes at Rifting and Subducting Margins), while similar initiatives do not exist in Europe or in France. At the same time, the institutions involved in the LabeEx UnivEarthS and in particular the IPGP regroup specialists from a large spectrum of disciplines working on the subduction, providing us with a unique opportunity to take a leadership role in this area.
Therefore, the main goal of the proposed workpackage is to develop an interaction between these different disciplinary teams and to create a group focusing on complex studies of the subduction processes.
Active deformation and earthquake activity along the Andean subduction zone in Chile
Coordinators: R. Armijo (IPG Paris, France), R. Lacassin (IPG Paris), N. Shapiro (IPG Paris), J.P. Vilotte (IPG Paris)
International collaborations: Universidad de Chile (J. Campos and G. Vargas), Universidad Católica del Norte (G. Gonzalez), GeoForschungsZentrum (GFZ) Potsdam (O. Oncken), University Potsdam (M. Strecker)
The Andean subduction zone in Chile, associated with the fast convergence of the Nazca plate beneath the South American plate, is one of the most active in the world as attested by the Andes, the largest mountain belt – and high plateau – systems of our living planet, and by the associated seismic activity with four mega earthquakes and tsunamis in the last 120 years. Scientific questions today are related to the understanding of the transient and permanent deformation processes, their variations and interactions, along the Chilean subduction zone, that lead to the occurrence of large subduction earthquakes and tsunamis, and to the building of the Andes. A critical step, of important augmented economic and societal implications, is to integrate these different spatial and temporal scales within a geodynamic model.
The Andean subduction zone in Chile and the associated large subduction earthquakes: the earthquakes rupture area is indicated by the size of the ellipses; and the mean rate and direction of the convergence between the Nazca and the South American plate is indicated by the arrow. The main barriers associated to the segmentation the subduction zone are pointed in this map
To address these questions, innovative data analysis and data modelling methods are required to exploit the massive data generated by the detailed tectonic and paleo-seismology field studies, the high-resolution observation systems integrating geodesy and seismology monitoring networks operated by the International Associated Laboratory Montessus de Ballore (https://www.lia-mb.net), the French-Chilean initiative between the CNRS-INSU and the Universidad de Chile (Santiago), in which IPGP is one of the main partners, and by the spatial observation systems (InSAR).
The objectives are :
- Detailed analysis of the February 27, 2010 offshore Maule (Mw 8.6, Central Chile) earthquake, in terms of the rupture process, associated crustal deformation and crustal property changes, of its implication in term of the seismic hazard in the northern part of Central Chile – in particular the Valparaiso region. This analysis exploits the extensive seismological (at regional and global scales), geodetic and geological data that are today available with unprecedented accuracy, before, during and after the event. Lessons to be learned from the offshore Maule earthquake will have important implication and applications for further study of the seismic hazard in northern Chile.
- Study of the permanent deformation, associated to the growth of the Andean orogeny by tectonic shortening, measured over the 103-107 yr time scale, which is barely longer than the seismic cycle for subduction earthquakes. We want to characterise the evolution of the west-vergent geological structures in relation with the subduction processes and to construct a mechanical model involving tectonic accretion at the subduction interface consistent with the tectonic and morphological evolution of the Central Andes and the Altiplano. This implies new field observations to be collected during this project.
This project is supporting a postdoc, and a number of tectonic field studies, sampling and dating.
Position Name Laboratory Grade, employer WP leader Nikolai Shapiro IPGP DR CNRS WP member Anne Le Friant IPGP DR CNRS, WP member Nathalie Feuillet IPGP Physicienne , IPGP WP member Guyard Hervé IPGP Post-Doc WP member Seibert Chloé IPGP PhD/IPGP WP member Pierre Agrinier IPGP Professor, IPGP WP member Alberto Roman IPGP Post-Doc WP member William Frank IPGP Post-Doc WP member Jean Soubestre IPGP Post-Doc WP member Léonard Seydoux IPGP PhD/IPGP WP member Kairly Jaxybulatov IPGP PhD/IPGP WP member Sergey Abramenkov IPGP PhD/IPGP
During three years of the WP F1b, we followed the proposed plan and worked in the two target regions: the Lesser Antilles and the Kamchatka subduction zones. We analyzed and interpreted of previously collected data and performed new field experiments. We also worked on the analysis of geophysical data from other subduction zones (Mexico, Indonesia) that contribute to understanding of active seismogenic and volcanic processes.
This work resulted in several publications and presentations at international scientific meetings. The support from Labex also helped us to obtain other funding are used to extend our studies of the subduction zone dynamics in the two target regions. The expertise developed by our team in the Lesser Antilles thanks to the support of the Labex program WP F1b allows for developing a new research program on the Ryukyu subduction zone in Japan in collaboration with colleagues of the TOKYO University and the Earthquake Research Institute. The program began in January 2016. It was funded by INSU in 2017.
Thanks to the expertise acquired during the Labex program on subaqueaous paleoseismology and volcanology, two young researchers (who get their PhD at IPGP) were selected to participate to to Expedition IODP 372 in 2017 (Morgane Brunet) and IODP expedition 381 in 2018 (Gino de Gelder).
A – Lesser Antilles
To constrain a wide range of volcanic, tectonic and erosion processes in the Lesser Antilles to characterize an integrated volcanic system, allowing the assessment of mass flows at the scale of the entire arc, we focused on deep offshore sediments as a continuous record of extreme volcanic events, earthquakes, mass losses and erosion processes as drivers of the long-term evolution (construction and destruction) of a volcanic arc with converging margins. This has required the creation of a new multidisciplinary team (volcanology, tectonics, marine geophysics and sedimentology) to work towards a better understanding of the evolution of the volcanic arc at a scale that bridges the gap between conventional local volcanological studies on land and geodynamic studies at the plate scale.
The database was enriched with 42 cores for a total of 510 m of sediment and new geophysical data during the CASEIS campaign between May 27 and July 5, 2016 on the French research vessel “Pourquoi Pas?
The data set available in the Lesser Antilles is now exceptional, covering time and space scales never reached in other volcanic arcs in the world. We will have the potential to access the history of 4 million years of extreme events that impacted the entire arc over distances of several hundred kilometres.
B – Kamchatka
B-1 Geochemical sampling of water sources for C and Cl streams
In 2017, we continued the construction of a model for the carbon injection of surface reservoirs into the mantle via subduction zones and for the return flow to the surface via arc magmatism.
B-2 Seismological studies of active volcanoes
We continued the analysis of data from permanent seismic stations operated by the Kamchatka branch of the Russian Geophysical Service (these data were obtained through a collaboration established within the framework of the labex project). First, we developed a new method to detect and locate volcanic earthquakes (Shapiro et al., 2014, 2015; Droznin et al., 2015). Next, we conducted a long-term study of volcanic seismicity and established its relationship with the preparation of volcanic eruptions (Shapiro et al., 2016).
B-3 Geodetic studies of the seismotectonic cycle in the Kamchatka subduction zone.
Thanks to our collaboration with the Kamchatka branch of Russian Geophysical Studies, we have obtained the records of the permanent GPS stations operating in the peninsula since 2005. Initial analysis of these time series revealed some episodes of transient deformation prior to the deep Okhotsk Sea earthquake of 2013 (Walpersdorf et al., 2016).
C – Other Subduction Zones
In addition to studies in the Lesser Antilles and Kamchatka, we worked with data from other subduction zones. The seismological data set from Mexico was used to study the role of slow earthquakes in the seismotectonic cycle (Frank et al., 2016). In Indonesia, we conducted a series of seismic tomography studies of active volcanoes (Kulakov et al., 2016b,c; Jaxybulatov et al., 2016). We have also developed a new research program on the Ryukyu subduction zone in Japan in collaboration with TOKYO University and the Earthquake Research Institute. The program began in January 2016. It was financed in 2017 by the CNRS-INSU and we have already made 3 field trips to analyze coral microatolls in order to better constrain the seismic cycle of the Ryukyu trench. Preliminary results have been presented at several international meetings.