Abstract
In the Kanto region of Japan, a large quantity of natural gas is dissolved in brine. The large-scale production of gas and iodine in the region has caused large-scale land subsidence in the past. Therefore, continuous and accurate monitoring for subsidence using satellite remote sensing is essential to prevent extreme subsidence and ensure the safety of residences. This study focused on the small baseline subset (SBAS) method to assess ground deformation trends around the Kanto region. Data for the SBAS method was acquired by the Advanced Land Observing Satellite (ALOS)-2 Phased Array type L-band Synthetic Aperture Radar (PALSAR)-2 from 2015 to 2019. A comparison of our results with reference levelling data shows that the SBAS method underestimates displacement. We corrected our results using linear regression and determined the maximum displacement around the Kujyukuri area to be approximately 20 mm/year; the mean displacement rate for 2015–2019 was −7.9 ± 2.9 mm/year. These values exceed those obtained using past PALSAR observations owing to the horizontal displacement after the Great East Japan Earthquake of 2011. Moreover, fewer points were acquired, and the root mean-squared error of each time-series displacement value was larger in our results. Further analysis is needed to address these bias errors.
Highlights
The south Kanto gas field contains a large quantity of natural gas in the water, which distributed widely across the Kanto region of Japan [1]
To monitor the temporal changes in land subsidence caused by the extraction of natural gas, study estimated the land displacement within the Chiba Prefecture from 2015 to 2019 using time-series this study estimated the land displacement within the Chiba Prefecture from 2015 to 2019 using satellite SAR data
The estimated displacement had a similar spatial trend to that derived from Phased Array type L-band Synthetic Aperture Radar (PALSAR)
Summary
The south Kanto gas field contains a large quantity of natural gas in the water, which distributed widely across the Kanto region of Japan [1]. The natural gas produced in the South Kanto gas field accounts for more than 90% of the total Japanese production of natural gas dissolved in water. Since the 1930s, gas-production activities have been undertaken by private companies [2]. Large-scale production of gas and iodine began in the mid-1950s in Mobara-shi (the Kujyukuri area) of the Kanto region. This production involved the withdrawal of groundwater from depths of 500 to 2400 m [1]. It was reported that the trend of land subsidence has reduced in recent years owing to the efforts of administrations and companies [4].
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