4:15 PM - 4:30 PM
[SSS02-10] An Encouragement of Ocean Bottom Observational Seismology
★Invited Papers
Keywords:ocean bottom seismometer, ocean bottom pressure gauge, slow earthquake
Field observations have been essential for earthquake seismology since the development of instruments to record seismic waves in the late 19th century. However, field observations in the ocean still remain a challenge. Advances in ocean bottom seismic measurements have led us to study megathrust earthquakes, especially in Japan. The pioneers of ocean bottom seismology in Japan started developing ocean bottom seismometers in the 1970s and succeeded in obtaining data for several weeks or months in the 1990s.
The circumstances surrounding field observations in earthquake seismology have sometimes been forced to change due to destructive earthquakes and social demands after disasters. The 2011 Tohoku-Oki earthquake was one of the most important era-defining events in the last decade; specifically, ocean bottom seismology in subduction zones has accelerated with the establishment of both online and offline ocean bottom seismic networks after the 2011 Tohoku-Oki earthquake. Some cabled ocean bottom seismic networks, such as DONET and S-net, have enabled us to obtain plentiful and high-quality data that can be readily distributed. Data from cabled networks are widely used by seismologists worldwide to calculate the source properties of earthquakes, determine the physical properties of the interior of the Earth, and conduct seismic and tsunami hazard analyses.
However, cabled networks may not be sufficient to test a working hypothesis, generally, which would be raised by individual seismologists; this perspective should be kept as the most important concept in observational seismology. An observation network should be designed to test a working hypothesis from individual seismologists, customizing the specifications of the ocean bottom system based on their specifications. After designing the networks based on ideas from the seismologists, we should deploy them and process data from the network. Finally, we need to distribute all of the data to general users in seismology because the great progress across the past century has been primarily due to abundant and high-quality data that can be readily distributed. In short, the main task of an observational seismologist is to design a seismic network, deploy it, process data, and distribute all of the data to test a working hypothesis.
Autonomous or off-line ocean bottom seismometers, hydrophones, and pressure gauges are still available to test a working hypothesis from individual researchers, even when cabled systems are established in Japan. Off-line networks with autonomous sensors are easily designed and customized based on specifications from researchers to measure seismic waves, crustal deformation just above the source area of the megathrust earthquakes, and related phenomena, such as slow earthquakes.
In the last decade, we have deployed seismic and geodetic networks around the world, including the Japan Trench, New Zealand, and Mexico, based on the ideas above. In the Japan Trench, we deployed an array of dense arrays composed of ocean bottom seismometers to detect shallow tectonic tremors. We have continued an ocean bottom pressure gauge array in the Hikurangi subduction margin to capture slow slip events since 2013. Recently, we established a seismo-geodetic amphibious network in the Guerrero seismic gap and captured tremor activities near the trench. We will introduce our recent results from autonomous networks, which were designed based on individual purposes or working hypotheses, and the data we processed.
The circumstances surrounding field observations in earthquake seismology have sometimes been forced to change due to destructive earthquakes and social demands after disasters. The 2011 Tohoku-Oki earthquake was one of the most important era-defining events in the last decade; specifically, ocean bottom seismology in subduction zones has accelerated with the establishment of both online and offline ocean bottom seismic networks after the 2011 Tohoku-Oki earthquake. Some cabled ocean bottom seismic networks, such as DONET and S-net, have enabled us to obtain plentiful and high-quality data that can be readily distributed. Data from cabled networks are widely used by seismologists worldwide to calculate the source properties of earthquakes, determine the physical properties of the interior of the Earth, and conduct seismic and tsunami hazard analyses.
However, cabled networks may not be sufficient to test a working hypothesis, generally, which would be raised by individual seismologists; this perspective should be kept as the most important concept in observational seismology. An observation network should be designed to test a working hypothesis from individual seismologists, customizing the specifications of the ocean bottom system based on their specifications. After designing the networks based on ideas from the seismologists, we should deploy them and process data from the network. Finally, we need to distribute all of the data to general users in seismology because the great progress across the past century has been primarily due to abundant and high-quality data that can be readily distributed. In short, the main task of an observational seismologist is to design a seismic network, deploy it, process data, and distribute all of the data to test a working hypothesis.
Autonomous or off-line ocean bottom seismometers, hydrophones, and pressure gauges are still available to test a working hypothesis from individual researchers, even when cabled systems are established in Japan. Off-line networks with autonomous sensors are easily designed and customized based on specifications from researchers to measure seismic waves, crustal deformation just above the source area of the megathrust earthquakes, and related phenomena, such as slow earthquakes.
In the last decade, we have deployed seismic and geodetic networks around the world, including the Japan Trench, New Zealand, and Mexico, based on the ideas above. In the Japan Trench, we deployed an array of dense arrays composed of ocean bottom seismometers to detect shallow tectonic tremors. We have continued an ocean bottom pressure gauge array in the Hikurangi subduction margin to capture slow slip events since 2013. Recently, we established a seismo-geodetic amphibious network in the Guerrero seismic gap and captured tremor activities near the trench. We will introduce our recent results from autonomous networks, which were designed based on individual purposes or working hypotheses, and the data we processed.