AIST Stories No1
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Impact in the following fields! Community lifeIndustry◦Living◦‌‌Disaster prevention◦‌‌Safety and security◦‌‌‌Environment, resources, energyAIST supporting livelihoods! 29The target is “slow slip” Real-time observation with underground sensorsIn preparing for the coming mega-earthquake, AIST continues to monitor the Nankai Trough. Mega-earthquakes in the Nankai Trough have occurred repeatedly in the past. In the Nankai Trough, the Philippine Sea Plate is being subducted under the Eurasian Plate at rates of 3–6 cm annually. At the plate boundaries (depths of 10–30 km), which is presumed to the hypocentral region, the bedrock in the upper layer adheres to the subducting plate and normally does not move, but at deeper locations (depths of 30–40 km), a slow slip phenomenon can be observed once every 3–6 months.This slow slip phenomenon has been known since around 2005 but more recently, it has come to be known that changes may occur prior to major earthquakes, such as increases in frequency, duration, and a mount of slip. In addition, immediately prior to the Great East Japan Earthquake, slow slip over one month was verified to have occurred in the vicinity of the hypocentral region. It is only recently that the relationship between this phenomenon and earthquake occurrences has been pointed out based on computer simulation. Slow slip, which is the most promising telltale sign of a mega-earthquake, appears in a form that can be visualized through changes in groundwater levels and strain in the earth’s crust. On this account, the Tectono-Hydrology Research Team of the Active Fault and Earthquake Research Center has bored deep wells at 16 locations from the island of Shikoku to the Kii Peninsula from which it carries out measurements using sensors placed deep within the earth. This observation data is furnished in real time to the Meteorological Agency and other organizations, and then publicly released.Research into the prediction of mega-earthquakes is still incomplete, but what is supporting this persistent research is the strong feeling of the researchers that one day they will be able to predict earthquakes. Moving forward, Team Leader Norio Matsumoto says that more observation points will be added, while the measuring instruments will be improved so that they can precisely indicate earth crustal movements from measuring the slightest strain, among other activities. While thus striving to improve analytical capabilities, the data accumulated will be used to target prediction of the mega-earthquake in the Nankai Trough.“Preparing for a mega-earthquake and tsunami is a critical issue that will affect how Japan can recover from such as event. Exploiting the observation findings for the sake of people’s lives and corporate activity is a major obligation of AIST.”Observation network of AIST for the megathrust earthquakes in the Nanka Trough131˚132˚133˚134˚135˚136˚137˚138˚139˚140˚31˚32˚33˚34˚35˚36˚010020060 km50 km60 km50 kmDepth of oceanic Moho discontinuity(Shiomi et al., 2008)Nankai Trough Tonankai EarthquakeNankai Earthquake30 km40 kmTokai EarthquakeObservation stationDeep, low frequencytremorsAssumed hypocentral zone according toCentral Disaster Prevention Council (2003) Assumed hypocentral zone of a large class of earthquakesaccording toCabinet Office committee (2012)●Mega-earthquake in the Nankai Trough, observation network data disclosure destinations, etc.Besides reporting to the governmental Earthquake Research Committee, which collects and analyzes survey findings from various organizations, and to the Earthquake Assessment Committee for Areas under Intensified Measures against Earthquake Disaster at the Meteorological Agency, data is also available at the Groundwater, Strain and Seismograph Presentation System Well Web (www.gsj.jp/wellweb).▲AIST observation well (A photo during construction. Upon completion, the derrick will be dismantled) Leader, Tectono-Hydrology Research TeamNorio MatsumotoImpact in the following fields! Community lifeIndustry◦Living◦‌‌Disaster prevention◦‌‌Safety and security◦‌‌‌Environment, resources, energyAIST supporting livelihoods! 29The target is “slow slip” Real-time observation with underground sensorsIn preparing for the coming mega-earthquake, AIST continues to monitor the Nankai Trough. Mega-earthquakes in the Nankai Trough have occurred repeatedly in the past. In the Nankai Trough, the Philippine Sea Plate is being subducted under the Eurasian Plate at rates of 3–6 cm annually. At the plate boundaries (depths of 10–30 km), which is presumed to the hypocentral region, the bedrock in the upper layer adheres to the subducting plate and normally does not move, but at deeper locations (depths of 30–40 km), a slow slip phenomenon can be observed once every 3–6 months.This slow slip phenomenon has been known since around 2005 but more recently, it has come to be known that changes may occur prior to major earthquakes, such as increases in frequency, duration, and a mount of slip. In addition, immediately prior to the Great East Japan Earthquake, slow slip over one month was verified to have occurred in the vicinity of the hypocentral region. It is only recently that the relationship between this phenomenon and earthquake occurrences has been pointed out based on computer simulation. Slow slip, which is the most promising telltale sign of a mega-earthquake, appears in a form that can be visualized through changes in groundwater levels and strain in the earth’s crust. On this account, the Tectono-Hydrology Research Team of the Active Fault and Earthquake Research Center has bored deep wells at 16 locations from the island of Shikoku to the Kii Peninsula from which it carries out measurements using sensors placed deep within the earth. This observation data is furnished in real time to the Meteorological Agency and other organizations, and then publicly released.Research into the prediction of mega-earthquakes is still incomplete, but what is supporting this persistent research is the strong feeling of the researchers that one day they will be able to predict earthquakes. Moving forward, Team Leader Norio Matsumoto says that more observation points will be added, while the measuring instruments will be improved so that they can precisely indicate earth crustal movements from measuring the slightest strain, among other activities. While thus striving to improve analytical capabilities, the data accumulated will be used to target prediction of the mega-earthquake in the Nankai Trough.“Preparing for a mega-earthquake and tsunami is a critical issue that will affect how Japan can recover from such as event. Exploiting the observation findings for the sake of people’s lives and corporate activity is a major obligation of AIST.”Observation network of AIST for the megathrust earthquakes in the Nanka Trough131˚132˚133˚134˚135˚136˚137˚138˚139˚140˚31˚32˚33˚34˚35˚36˚010020060 km50 km60 km50 kmDepth of oceanic Moho discontinuity(Shiomi et al., 2008)Nankai Trough Tonankai EarthquakeNankai Earthquake30 km40 kmTokai EarthquakeObservation stationDeep, low frequencytremorsAssumed hypocentral zone according toCentral Disaster Prevention Council (2003) Assumed hypocentral zone of a large class of earthquakesaccording toCabinet Office committee (2012)●Mega-earthquake in the Nankai Trough, observation network data disclosure destinations, etc.Besides reporting to the governmental Earthquake Research Committee, which collects and analyzes survey findings from various organizations, and to the Earthquake Assessment Committee for Areas under Intensified Measures against Earthquake Disaster at the Meteorological Agency, data is also available at the Groundwater, Strain and Seismograph Presentation System Well Web (www.gsj.jp/wellweb).▲AIST observation well (A photo during construction. Upon completion, the derrick will be dismantled) Leader, Tectono-Hydrology Research TeamNorio Matsumoto

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