Luis RIVERA

Ten years of using W-phase for rapid analysis of large earthquakes: An unexpected application of long-period seismology

The research subjects of some earth scientists are naturally well suited for immediate societal applications. Examples are geothermal research, applied geodesy (GNSS) and, of course, geophysical prospecting (mining, oil, water, etc). However, this is not common at all in case of
the solid earth science community and, in particular, seismology where I personally develop my research. Simply put, the longer is the period of the used seismic waves, the lower is the probability for immediate application. For example, short period surface waves are sometimes used for civil engineering or shallow depth applications while long period normal-mode studies remain mostly a “pure research”. What I would like to describe here is in fact a remarkable counter-example of such a statement. Namely, the use of W-phase for fast analysis of large earthquakes. 

In 1960 and 1964 we had the two largest earthquakes of the twenty century: Valdivia (Chile), May 1960 and Anchorage (Alaska), March 1964. The global scale instrumentation that recorded the long-period waves generated by these two events was very limited and so are the models we have for them. This is particularly true for the 1960 event. No comparably large event occurred for forty years since then until the Mw 9.2, Sumatra earthquake occurred on December 26, 2004. The data quality and quantity, our understanding of seismic phenomena and computational capabilities had enormously advanced in the meantime. As a result, the 2004 event has been studied in great detail in thousands of publications with very diverse kind of data and techniques. A problem however was identified in the aftermath: seismologists were not capable of providing quick information concerning the event. More precisely, in 2004 it was necessary to wait several hours (in fact two days for this specific event), before having a robust evaluation of the size (magnitude) and the focal mechanism for such a large event. Large events are difficult to deal with because very long-period waves are necessary to obtain a complete view of the source, but such long-period waves are difficult to observe and analyze quickly. Realizing such a limitation was the starting point of our work on W-phase. The W-phase is a very long period (~ 200-1000 s) seismic phase that was observationally identified after the 1992 Nicaragua earthquake (Kanamori, 1993). It was visible globally in the time interval between the P and the surface waves. However, it remained a rare and exotic stone for fifteen years. Only a couple of publications were dedicated to it during this time period. In 2008 H. Kanamori and myself set to test the potential of W-phase to determine the focal mechanism and the magnitude of major earthquakes (say, Mw >= 8). We quickly started to obtain very promising results. Z. Duputel joined us in 2009 to work on this subject as his PhD dissertation. In a couple of years the algorithm was already operating at the Pacific Tsunami Warning Center (Hawaii, PTWC, NOAA) and at the National Earthquake Information Center (NEIC, USGS). Nowadays it routinely operates in a number of regional, national and international agencies to provide fast and reliable information to authorities, scientists, civil defense, etc. At global scale, it provides in less than half an hour a moment tensor solution for events with Mw as low as 6.0. At regional scale the delay is reduced to less than 15 min and the minimum Mw to 5.5. This information can be used, for example, for tsunami modeling or for humanitarian or civil defense decision making, etc. On the other hand several colleagues around the world also use the algorithm in “manual mode” to perform long-period source studies. The success of the practical application of such an exotic object like W-phase came as a complete surprise to us. It is an encouraging example of the power of scientific research and it prompts us to develop and cultivate interaction with applied scientific communities. 

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Degrees

  • 2001 Habilitation Geophysics Université Louis Pasteur, Strasbourg, France
  • 1989 Ph D. Geophysics Université Louis Pasteur, Strasbourg, France

Employments

  • February 2005 Present : Professor of Seismology, Université Louis Pasteur, Université de Strasbourg, Ecole et Observatoire des Sciences de La Terre.
  • October 1990 January 2005 : EOST, Associate Professor (Physicien Adjoint, CNAP, ULP)

Visiting

  • October. 1999-March 2001 : Seismological Laboratory, Caltech, Sabbatical
  • July 2004 : Seismological Laboratory, Caltech, Research Visit
  • Sep.-Nov. 2008 : Earthquake Research Institute, U. of Tokyo, Research Visit
  • June 2009 : Earthquake Research Institute, U. of Tokyo, Research Visit
  • August 2011 : Seismological Laboratory, Caltech, Research Visit
  • June-July 2012 : Earthquake Research Institute, U. of Tokyo, Research Visit
  • August 2013-June 2014 : Seismological Laboratory, Caltech, Sabbatical.

University Teaching

  • 2005-2019 : Seismic Source (M. Sc.), Mathematics (B. Sc.), Inverse Problem. Geophysics Engineer
  • School, Geophysics M.Sc., ULP, UdS, Strasbourg
  • 2015 : Long period source inversion and Inverse problems. EAFIT, Medellin, Colombia.
  • 2014 : Introduction to Long Period Seismiology, Ge-162, Seismological Laboratory, Caltech.
  • 2013-1015 : Introduction to the Inverse Problem in Geophysics, ENSG (National School of Geology), Nancy, France
  • 2001-2004 : Seismic Source, Geophysics B. Sc. and M. Sc. Geophysics Engineer School, EOST, ULP, Strasbourg
  • 1992-1999 : Seismic Risk and Structural Dynamics, Geophysics Engineer School, EOST, ULP, Strasbourg, France
  • 1992-1999 : Mathematical Physics, Geophysics B. Sc. and M. Sc. Geophysics Engineer School, EOST, ULP, Strasbourg
  • 1990-1993 : TA, Seismic Source, M. Sc., IPGS, Strasbourg
  • July 1998 Summer School in Seismology, EAFIT University, Medellín, Colombia
  • July 1997 Workshop : Introduction to Seismology, Los Andes University, Bogotá, Colombia
  • July 1993 International Workshop on Seismology. Ceresis, Uniandes, Onad, Ingeominas et Colciencias. Bogotá, Colombia

Supervisor or related

  • 1995-present : Ph.D. Advisor or co-advisor (ULP, UdS) (19)
  • 1995-present : Ph.D. committees, ULP, UdS and others (30)
  • 1993-present : Last year Engineer project (Geophysics School Engineer), EOST (34)
  • 1990-present : M.Sc., EOST, ULP or UdS, Strasbourg (21)
  • 1986-present : Workshops, Summer Schools, Invited Speaker (Organizer or Speaker) (21)

Community related activities

  • 2015-present : Leader of the Seismology team of the Institut de Physique du Globe de Strasbourg, Université de Strasbourg, CNRS (IPGS).
  • 2005-2012 : Deputy Director of the IPGS.
  • 2003-2014 : Associate Editor, Journal of Seismology.
  • 2004-2013 : Elected member of the council of the Ecole et Observatoire des Sciences de La Terre de Strasbourg (EOST)
  • 1999-present : Member of the American Geophysical Union (AGU).
  • 1996-2005 : In charge of the Global seismological observatory service (EOST). This service is responsible for the operation, maintenance and data treatment of part of the Geoscope network.
  • 1992-present : Reviewer for di erent journals of the Geophysical international comunity : Geophys. Res. Lett., Geophys. Journ. Int., Journ. Geophys. Res., Bull. Seism. Soc. Am., etc.
  • 1992-1999 : Elected member of the council of the Seismological Laboratory (IPGS)
  • 1990-present : Member of the French national committee for Geodesy and Geophysics (CNFGG)

Bibliometry as per January 2019

  • 115 peer-reviewd articles
  • > 200 communications in international meetings
  • > 2800 citations, h-index : 32 (Web of Science)