Geodesists from 16 countries met in July to discuss the role of geodesy in earthquake and volcanic studies, natural hazard assessment, and disaster mitigation. The GENAH 2014 international symposium took place in Matsushima, Japan, a town that suffered greatly from the tsunami of 11 March 2011. The symposium featured sessions on seven topics: subduction zone earthquakes, the earthquake deformation cycle, near real-time warning, the interaction between earthquakes and volcanoes, the impact of great earthquakes on reference frame, geodetic techniques in volcanological research, and natural hazards.
One of the most studied topics at the meeting was the 2011 Tohoku-oki earthquake. Participants had extensive discussions on the results of research using several geodetic techniques, addressing the coseismic and postseismic deformation of the earthquake, the earthquake source, the causes of postseismic deformation, and the effect of the earthquake on seismic activity in and around Japan.
The earthquake cycle was another important subject. Several groups presented data and models of interseismic strain buildup in subduction zones and active fault zones. The detection of slow slip events and their role in the earthquake cycle were also discussed.
The impact of major earthquakes on the reference frame is a great concern from the viewpoint of geodesy. Zuheir Altamimi, from the Institut National de l’Information Géographique et Forestière, showed that major earthquakes have not biased the datum definition behind the reference frame and that logarithmic or exponential decaying provides a proper treatment of postseismic transients. However, the reestablishment of precise coordinates for sites displaced by earthquakes still takes a long time, because of long-lasting postseismic deformation. How to reconcile practical use and the long-term stability of the network remains a serious problem.
Several reports on monitoring volcanic activity in Japan, Indonesia, etc., were presented. Some reports emphasized that extensometers and tiltmeters are effective for the detection of precursory deformation before eruption. Participants also heard about case studies on volcanic activity triggered by large earthquakes.
Rapid detection of deformation was a popular topic at the symposium and is important for real-time monitoring. Speakers discussed methods to detect the very early part of the coseismic deformation and to estimate the size of earthquakes. Other presentations focused on the application of geodesy to monitoring various kinds of natural hazards, as well as the results of earthquake hazard estimates based on geodetic work in some countries. Coseismic ionospheric disturbances are clearly detectable, and controversy remains over whether any precursory signals exist.
Michinori Hatayama, from the Disaster Prevention Research Institute, Kyoto University, showed results of the application of geodesy to emergency response. He also emphasized that the content and accuracy requirements of the information needed may change depending on the stage of emergency response and disaster recovery.
A total of 130 scientists attended the symposium, and 83 oral and 50 poster presentations were given. On the whole, participants provided a complete description of the state of the art geodesy applied to natural hazards. They left with questions to focus on concerning scientific, technical and social issues.
—Manabu Hashimoto, Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan; email: [email protected]; Richard Gross, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, Calif., and Jeffrey Todd Freymueller, Geophysical Institute, University of Alaska, Fairbanks