Project COHERSiS

funded by the ANR "Chaires d'Excellences 2006" program

Brief description

Modern seismological networks provide new insight and information to address fundamental and applied problems including multidisciplinary research of the Earth dynamics and interior and mitigation of risks from geological hazards. Fully and efficiently exploring this large amount of new information is one of the main challenges for Earth scientists these days. Being successful in this direction requires creation of new theoretical approaches and methods and developing modern data-processing infrastructures in seismological laboratories.

The principal goal of this project is to create at the IPG Paris a research group working on development and application of innovative methods of processing, inversion, and interpretation of seismological data. We will focus on three main research axes. First, we will develop methods based on random seismic wavefields. This is a completely new and very promising research direction (e.g., Campillo and Paul, 2003; Shapiro et al., 2005) that may potentially revolutionize seismic imaging and monitoring in context of modern seismic networks. Second, we will continue the research in the area of the surface-wave tomography concentrating on improvement of the measurement and the inversion procedures and on creation of new tomographic models of the crust and upper mantle at global and regional scales. Third, we will work on development of methods for a near real time monitoring of large earthquakes required to improve the global seismic monitoring and tsunami warning systems.

The project is constructed around the arrival of Nikolai Shapiro at the IPG Paris. During last years, he worked in leading geophysical groups in Mexico and United States and acquired an expertise in a broad area of seismological research. When staying in UNAM, Mexico, Nikolai worked on regional-scale seismic imaging and on studies of large subduction-zone earthquakes. After moving to United States, Nikolai worked during five years in the seismic tomography group in the University of Colorado at Boulder where he developed several new methods that helped to bridge the gap between global and regional length scales and resulted in a new global high-resolution seismic tomographic model. His most recent research area is the development of high-resolution seismic imaging from the ambient seismic noise. The expertise brought by Nikolai will be complementary to the IPGP research on the global seismic tomography, on seismic inversion and modeling and on physics of the earthquake source and seismogenic processes. IPGP is also among leading institutions in the field of seismological observations maintaining a global network of broadband seismographs GEOSCOPE, seismic stations in many seismically active regions such as Chile and Greece, and volcanological observatories in French Antilles and in la Reunion Island. These observational facilities will form an experimental base for different research directions outlined in this proposal. The new research group will also strongly benefit from more broad collaborations with French geophysical and interdisciplinary communities, in particular, with researchers from LGIT, Grenoble, from Laboratoire Ondes et Acoustique de l'ESPCI, Paris, and from Géosciences Azur, Nice.

Group-speed maps constructed by Shapiro et al. (2005) by cross-correlating 30 days of ambient noise between USArray stations. (a) 7.5-s-period Rayleigh waves. (a) 15-s-period Rayleigh waves. Black solid lines show known active faults. White triangles show locations of USArray stations used in this study.		Examples of modern continental-scale seismological networks. (a) Transportable array component of USArray. (b) Virtual European Broadband Seismological Network (VEBSN).
First results of the noise-based monitoring of the Piton de la Fournaise volcano. (a) Map of the monitoring network. (b) Examples of signals extracted from correlations of one-day noise records between stations BORY and Soufriere during the beginning of 2005. A clear time shift can be seen between the signal computed before the eruption (black line) and after the eruption (red line). (c) Relative travel times estimated from day-long noise cross-correlations between stations BORY and Soufriere during first 110 days of 2005. A time shift between results before and after the eruption can be clearly seen. It corresponds to ~3% media velocity increase after the eruption.		Comparison between the location of sources of the 10-20 s seismic noise and significant wave heights estimated by TOPEX/POSEIDONE (Stehly et al., 2006). Both fields maximize in the southern oceans during the summer and in the northern oceans during the winter.