Associate Professor Mako Ohzono
Affiliation: Faculty of Science (School of Science Department of Earth and Planetary Sciences)
Specialized fields: geodesy, seismology, volcanology
Research keywords: crustal movement, earthquake, volcano, numerical calculation, disaster prevention
Alma mater: Kinkowan High School (Kagoshima Prefecture)
Final academic background: Graduate School of Science, Tohoku University
HP address: https://www2.sci.hokudai.ac.jp/faculty/researcher/mako-ohzono
*This article was originally published in the 4th issue of "Frontiers of Knowledge" and has been re-edited for the web.
What kind of research are you doing?
We precisely measure the movements of the Earth's ground, so-called crustal movements, and investigate their causes and mechanisms. Japan is located in a plate subduction zone and is one of the most seismically and volcanically active regions in the world. I mainly use a precision surveying method using artificial satellites called GNSS (Global Navigation Satellite System) to observe crustal deformation that occurs during and after an earthquake, as well as crustal deformation accompanying volcanic activity. doing. In addition, by reproducing the changes obtained from actual observations by numerical calculation, we are trying to understand the underground dynamics that cause such crustal deformation. Earthquakes and volcanic activity have a great impact on human life. I am conducting research with the hope that I can provide information so that these research results can contribute to disaster prevention. I am currently working on two main research topics:
1. Elucidation of the postseismic deformation mechanism after the 2011 off the Pacific coast of Tohoku Earthquake:
Predicted values of postseismic deformation caused by the 2011 off the Pacific coast of Tohoku earthquake. The direction and magnitude of horizontal crustal movement in each region in 2020 are shown.
Postseismic deformation is slow crustal deformation caused by changes in the stress applied to the mantle, etc., by an earthquake, and is a phenomenon that continues for several years to several decades after a major earthquake. By analyzing GNSS data not only in Japan but also in Russia and China, we can grasp the postseismic turbulence field of the entire Northeast Asian region, predict the future of this turbulence by numerical calculation, and determine when the postseismic turmoil will end and when it will be. I am investigating how is related to repeated megaquakes in subduction zones.
2. Relationship between inland earthquakes and underground mechanical structure:
Inland earthquakes such as the 2016 Kumamoto earthquake often cause damage to human life. There are several places in Hokkaido where many inland earthquakes occur. The crust, which is the epicenter of an inland earthquake, has a heterogeneous structure, with areas that are easily deformed by surrounding forces and areas that are not easily deformed. leads to the evaluation of Currently, we are conducting GNSS observations in the eastern and northern parts of Hokkaido, and are trying to capture the characteristics of deformation in this area. In addition, we are working to comprehensively understand the mechanical structure that causes such deformation, together with various research results.
A shot of gravity and GNSS observations at Tokachidake.
Predicted values of postseismic deformation caused by the 2011 off the Pacific coast of Tohoku earthquake. The direction and magnitude of horizontal crustal movement in each region in 2020 are shown. In addition to Hokkaido and Japan, we have also traveled overseas to observe volcanic areas in the Far East of Russia and plate collision zones in Nepal. Crustal deformation data such as GNSS is an important tool for understanding earthquakes and volcanic activity. When we collect data from a place of interest and reproduce it through numerical calculations, we feel like we know a little more about the real, complex Earth that is actually moving.
GNSS observation at Kussharo Caldera.
What made you start your current research?
GNSS station installed on the flank of Klyuchevskoy Volcano, Kamchatka, Russia.
I became interested in measuring crustal deformation when I was thinking about my graduation research at university, but the trigger for my current research was the 2011 Tohoku earthquake. The steady state before an earthquake occurs, the momentary period before the earthquake occurs, and the three periods after the occurrence of the earthquake each generate different subsurface stress states, resulting in different crustal deformations. It can be said that the 2011 great earthquake provided important observational data for understanding these. I am working on my current research with the hope that I can make full use of this valuable data to understand the phenomena before and after an earthquake, and also to provide information for disaster prevention from a social perspective. . We also decided to conduct observations and research in various places, thinking that it would be very important to understand the state before phenomena such as earthquakes and volcanic activity occurred.
A new GNSS observation point in southern Nepal.
What kind of results can we expect in the future?
The crustal deformation data from the 2011 big earthquake provided us with a lot of information. Of all the mega-earthquakes that have occurred in the world so far, there is no example in which crustal deformation was captured by a dense observation network like this earthquake. By analyzing these and other observed data in detail and combining them with other research results, we will be able to understand the mechanisms of earthquakes and volcanic activity, as well as the cycle of past, present, and future earthquakes and the dynamics of the underground. You can expect a better understanding of the state. There must be many unknown systems that we have not seen yet in the phenomena captured by crustal movements. I believe that by answering the questions one by one, "Why is this happening?", we will be able to advance our understanding.