Jean-Philippe Avouac on the Creative Power of Earthquakes

Interview From the Special Topic of Earthquakes, July 2010

Jean-Philippe AvouacIn our Special Topics analysis of earthquakes research over the past decade, the work of Dr. Jean-Philippe Avouac ranks at #6 by total cites, based on 47 papers cited a total of 1,106 times. Three of his papers are featured in the accompanying Research Front Map titled, " 2004 Sumatra-Andaman Earthquake."

His record in Essential Science IndicatorsSM from Thomson Reuters from Clarivate Analytics includes 68 papers, the majority of which are classified in the field of Geosciences, cited a total of 1,628 times between January 1, 2000 and February 28, 2010.

Avouac is Professor of Geology and Director of the Tectonics Observatory at Caltech in Pasadena, California.

 
ScienceWatch.com talks with him about his highly cited earthquakes research.

SW: Please tell us about your educational background and early research experiences.

I graduated from the Ecole Polytechnique (France) in 1987, where I received a general education in science with a strong emphasis on mathematics, physics, mechanics, and chemistry. For my Ph.D. I chose to move to earth sciences, attracted by the possibility of combining outdoor activities and grounding my quite theoretical background to real earth problems.

My Ph.D. project at the Institut de Physique du Globe de Paris was very much field-oriented and gave me the opportunity to acquire some field skills in geology and geomorphology. My advisor, Paul Tapponnier, was a superb mentor in guiding my first steps in the field.

After my Ph.D., I took a position at the Laboratoire de Detection et de Geophysique (LDG), a seismological laboratory with the Commissariat a l’Energie Atomique (CEA). I was interested at the time in acquiring some expertise in seismology and taking advantage of my background in hardcore science and engineering to develop research activities tying together field geology, geophysical and geodetic techniques, and mechanical modeling.

SW: What first drew your interest to earthquakes?

I came to study earthquakes very indirectly. The primary goal of my Ph.D. was to describe how central Asia (the area north of the Himalaya) is deforming as a result of the northward indentation of India into Eurasia. I then studied some of the major faults, trying to establish their slip rate from geomorphic and geological techniques. These faults slip as a result of earthquakes.


Photo taken during a field trip in the Dzoungar basin (Western China) led by Jean-Philippe Avouac and John Suppe. Here Avouac is commenting on the fold-and-thrust belt which forms the northern piedmont of the Tian Shan range. This is an active fault system which has produced a M8.0 earthquake in 1906. See tab below for a larger view.

After my Ph.D. I got interested in describing in more detail how these faults work. I wanted, in particular, to better understand how faults generate earthquakes and how earthquakes, accumulated over thousands to millions of years, create mountain ranges such as the Himalaya.

These have remained my main research goals during my years at CEA and after I moved to Caltech in early 2003 to join the then-nascent Tectonics Observatory.

SW: Your most-cited paper in our analysis is the 2000 Journal of Geophysical Research-Solid Earth paper that you wrote with Jerome Lave, "Active folding of fluvial terraces across the Siwaliks Hills, Himalayas of central Nepal." Would you tell us about this paper and why you think it is so highly cited?

The Himalaya was a natural target given my research objective, and the fact that the LDG had some well-established collaboration with the Department of Mines and Geology of Nepal. After joining the LDG, I thus started a multidisciplinary project involving seismic monitoring, geodesy, and morphotectonics.

This paper came out as a result of the Ph.D. research of one of my graduate students, Jerome Lave, who focused on the morphotectonic aspect the research project. The objective of Jerome's work was to identify the most active faults in the Himalaya and determine their slip rate by looking at the deformation of river terraces.

Jerome's Ph.D. work demonstrated that a single fault at the front of the range takes up nearly all of the shortening across the Himalaya, which we estimated to 20 mm/yr. This result implies that this particular fault must be the one that generates the largest earthquakes in the Himalaya, and has fundamental implications with regard to mountain-building processes.

One reason for the success of this paper is that in addition to yielding those specific results, the study led to the development of a new methodology, combining geomorphology and structural geology, which has now been applied in a number of other settings.

SW: Several of your papers examine the Sumatra Megathrust. What exactly is this, and what does it mean for earthquake activity in that region?

After focusing for many years on the Himalayan system, where deformation is the result of a major continental collision, I started to get interested in investigating another, somewhat different, setting. I chose to focus on the subduction zone offshore Sumatra.

Offshore Sumatra, the oceanic crust of Indian plate is thrust along the plate interface (the "Megathrust" in our jargon) beneath the Sumatra mainland. I picked this area to take advantage of the unique dataset that my colleague Kerry Sieh was assembling with his students, based on the coral reefs fringing most of the islands along the trench.

These data revealed an exceptional record of the history of uplift and subsidence associated with stress accumulation and release due to the earthquake cycle on the Megathrust. We then worked on modeling these data and comparing it with the information collected from geodetic and seismological monitoring of the recent flurry of earthquakes which occurred there.

The activity started with the 2004 Mw 9.2 giant earthquake only about a year after the first stations had been deployed by the Caltech Tectonics Observatory in collaboration with our Indonesian partners from LIPI.

"...this particular fault must be the one that generates the largest earthquakes in the Himalaya, and has fundamental implications with regard to mountain-building processes."

Thanks to these data we now have a quite detailed view of how the Megathrust works: some patches of the plate interface remain locked during the interseismic period, leading to slow stress build up, until they rupture during large earthquakes. The rupture area of these large earthquakes can therefore be inferred from detecting those locked patches with geodetic or remote-sensing techniques. 

SW: You also have projects going in Taiwan and Tian Shan, and you did extensive work in France before coming to Caltech. Please tell us about this aspect of your work—is there a particular phenomenon or motif that ties together this far-flung research?

A common and generally most fruitful approach in geology consists in comparing similar processes occurring in settings with different characteristics. This is offers a way to identify the key factors involved in some particular phenomenon, and to develop and test models.

Taiwan and the Tian Shan are active mountain ranges similar to the Himalaya but with somewhat different characteristics (different climate in particular, leading to a different erosion rates). By studying those we try to understand the factors determining their respective seismic activities.

There is also a lot to learn by comparing the seismic activity of very active systems (like the Himalaya or the Sumatra Megathrust) with the seismicity of more stable areas like France.

SW: How much have we learned about earthquakes in the past decade? What advances would you like to see in the future of earthquake research?

We have made progress in many different directions. One is observational. Over the last decade new techniques have emerged to monitor crustal deformation and earthquakes. We have made progress in morphotectonics and know better how to identify and characterize active faults.

The development of networks of GPS stations and remote-sensing techniques allows us to monitor where and how fast stresses build up on faults and get released during earthquakes. In parallel we have better understanding of the mechanics of faulting and seismic ruptures thanks to laboratory experiments and numerical modeling.

I can foresee that in the hopefully not-too-distant future we will be able to develop models that will allow us to simulate earthquakes based on well-established mechanical principles and with proper accounts of the main factors determining fault seismic activity (fault geometries and mechanical properties, driving forces, etc.). This would revolutionize the current practice in seismic hazard assessment.

We could then envision assimilating observations (coming from seismology, geodesy, and remote sensing) in near real time to anticipate seismic activity, like the current approach in meteorology. This is not for tomorrow, but this is certainly the kind of dream that motivates most of my research on earthquakes.End

Jean-Philippe Avouac
Geological and Planetary Sciences
California Institute of Technology
Pasadena, CA, USA


JEAN-PHILIPPE AVOUAC'S CURRENT MOST-CITED PAPER IN ESSENTIAL SCIENCE INDICATORS:

Lave J, Avouac JP, "Active folding of fluvial terraces across the Siwaliks Hills, Himalayas od central Nepal," J. Geophys. Res-Solid Earth 105(B3): 5735-70, 10 March 2000, with 197 cites. Source: Essential Science IndicatorsSM from Clarivate Analytics.

KEYWORDS: EARTHQUAKES, GEOMORPHOLOGY, FAULTS, SLIP RATE, HIMALAYA, MOUNTAIN BUILDING PROCESSES, GEOLOGICAL STRUCTURES, GEODESY, MORPHOTECTONICS, STRUCTURAL GEOLOGY, SUBDUCTION ZONE, SUMATRA MEGATHRUST, TAIWAN, TIEN SHAN, COMPARATIVE SEISMIC ACTIVITY, CRUSTAL DEFORMATION, GPS, REMOTE SENSING, SIMULATION MODELS, SEISMIC HAZARD ASSESSMENT.

Citing URL: http://sciencewatch.com/ana/st/earthquakes2/10juleqAvou/

                     

 
Click tab above to view larger image and description.

Figure 1:

Photo taken during a field trip in the Dzoungar basin (Western 
        China) led by Jean-Philippe Avouac and John Suppe. Here Avouac is 
        commenting on the fold-and-thrust belt which forms the northern piedmont
        of the Tian Shan range. This is an active fault system which has 
        produced a M8.0 earthquake in 1906.

Figure 1:

Photo taken during a field trip in the Dzoungar basin (Western China) led by Jean-Philippe Avouac and John Suppe. Here Avouac is commenting on the fold-and-thrust belt which forms the northern piedmont of the Tian Shan range. This is an active fault system which has produced a M8.0 earthquake in 1906.

 

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