Takuya Nishimura (Associate Professor, Disaster Prevention Research Institute, Kyoto University)

Tracking the Earth's tremors

An interview with
Takuya Nishimura
Associate Professor
Disaster Prevention Research Institute

The challenges of monitoring earthquakes

Dr Nishimura with his earthquake detection equipment and geodetic antenna

Established in 1951, the Disaster Prevention Research Institute (DPRI) at Kyoto University has built a reputation for exceptional research focused on global issues such as climate change, earthquakes, and volcanic eruptions, as well as for implementing disaster risk management and recovery and restoration activities. Using the latest technologies available, Takuya Nishimura, Associate Professor at the DPRI, conducts research on earthquakes from the small-scale to the large. Here he discusses some of the challenges involved in earthquake science and prediction.

To begin with, what first led to your research on earthquakes? Did you always plan to specialize in this field?

Nishimura: I grew up in Hokkaido, northern Japan, where many earthquakes occurred. So I often felt the ground shaking from my childhood and wondered why the Earth vibrated. That was my first interest in earthquakes. I had always been interested in earth science but did not decide to specialize in solid earth until third grade in university. When the time came to choose a laboratory, I was very impressed with a tour of an earthquake observatory. It looked like a secret facility in a movie! That was the final reason why I started studying earthquakes.

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Distribution of interplate coupling in northeastern Japan from October 1997 to October 1999 (modified from Nishimura (2012)), estimated using global positioning system (GPS) data. Red and blue regions represent back-slip and forward slip, respectively. Back-slip is slip-deficit relative to rigid interplate motion. The contour interval is 2 cm per year.

Compared to 50 years ago, seismologists now have access to a wide variety of technologies and applications using geographic information systems (GIS) and the global positioning system (GPS). Could you please describe some of the ways in which you use these technologies in your research?

Nishimura: GPS is one of the main tools for my research. It can measure how the Earth deforms with very high accuracy. GPS has the advantage of being able to capture slow movements, which seismometers cannot detect. A tectonic plate moves as fast as a nail grows. We can now observe how fast the Japanese islands move. It can also provide insights about processes on fault movements that cause an earthquake. GIS is now an indispensable tool for earth science. It is a first step towards conducting research to plot archived data and compare various kinds of data using GIS. I plot my GPS data on a topographic and geologic map to gain various inferences.

What are some of the greatest challenges involved in your research?

Nishimura: It is earthquake prediction. It may be impossible to predict all earthquakes. However, I think some large earthquakes are predictable.

Could you please explain a little more about your current work on the links between short-term slow slip events and earthquakes along the Ryukyu Trench and Nankai Trough?

Nishimura: Both earthquakes and slow slip events (SSEs) are slips on a fault. The only difference is whether they radiate seismic waves or not. Earthquakes are fast slip events causing ground shaking. SSEs are slow slip, which only geodetic measurements including GPS can detect. I detected many SSEs along the Nankai Trough and Ryukyu Trench using GPS data. SSEs along the Nankai Trough concentrate in a narrow band at a depth of 30–45 km. However, those along the Ryukyu Trench are distributed over a depth of 10–60 km. Historical great earthquakes along the Nankai Trough rupture a shallow plate interface where no SSEs have been detected. Therefore, SSEs and earthquakes distribute in a complementary manner. I speculate that the scattered distribution of SSEs may suggest low potential of giant earthquakes along the Ryukyu Trench.

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A slow slip event (SSE) in central Shikoku around 10 May 2007. SSEs on the plate interface along the Nankai Trough occur several times per year. After Nishimura et al (2013).

Japan is known for its frequency of earthquakes. Following the Great East Japan Earthquake in 2011, many people wonder what more can be done to implement effective early-warning systems. How far is it possible to improve these early-warning systems?

Nishimura: Japan has the most advanced early-warning systems for earthquakes and tsunamis in the world. However, the systems did not prepare for a giant earthquake like the 2011 Tohoku-Oki (East Japan) Earthquake and caused underestimation of tsunami height on the Pacific coast. Several methods and algorithms have been proposed to improve accuracy. Real-time GPS can also contribute to estimate the magnitude of an earthquake accurately. Combining different sensors and methods can improve the redundancy and accuracy of the systems. However, we need to be aware of the situation that we cannot receive an alarm from these systems. Training and education are important to save people's lives from disasters.

I understand that you also have experience as a visiting researcher at the US Geological Survey. Could you please talk about some of your work during this time?

Monitoring earthquakes is a daily activity at the DPRI. Here Dr Nishimura points to a graph of GPS coordinates depicting the 2011 Tohoku-Oki (East Japan) Earthquake

Nishimura: I studied deformation associated with the Hebgen Lake earthquake that occurred in 1959 in southwestern Montana, western US. Broad uplift in the epicentral area continued for several decades after the earthquake. We found this uplift was caused by viscoelastic relaxation in the Earth's mantle. It was quite interesting to study a US earthquake because tectonic backgrounds in US and Japan are very different.

Since April 2013, you have been Associate Professor at the Disaster Prevention Research Institute (DPRI) at Kyoto University. Could you please describe some of the unique features of the Institute?

Nishimura: The DPRI has an interdisciplinary atmosphere. Experts in natural science, social science, and engineering are working together to mitigate earthquake hazards.

And finally, what would be your message to young scientists both in Japan and overseas who are interested in pursuing research on earthquakes?

Nishimura: Earthquake science is not only interesting as pure science but also useful to support hazard mitigation as applied science. I am interested in both fields. Abundant data from dense observation networks is one of the advantages of studying earthquakes in Japan. Kyoto University is one of the best places for earthquake research. I am happy to work together with anyone interested in earthquakes.

Thank you very much for your time.

 

 

Published: 11 November 2014

Profile

After gaining his doctoral degree at the Graduate School of Science, Tohoku University, in 2000, Dr Takuya Nishimura has conducted various geodetic surveys and researches, including work with the US Geological Survey, funded by the Ministry of Education, Culture, Sports, Science and Technology in Japan. He was appointed Chief Researcher at the Geography and Crustal Dynamics Research Center, Geographical Survey Institute in 2005. Since April 2013, he has been based in Kyoto as Associate Professor at the Disaster Prevention Research Institute, Kyoto University.

Additional information

For further information about Dr Nishimura's research, click here.

Interviews by Rieko Kawabata
 
Contact:
kawabata.rieko.7u * kyoto-u.ac.jp (Please replace * with @ when sending your e-mail.)
Kyoto University Research Administration Office (KURA)