Abstract
Abstract. The South Kanto gas field contains natural gas dissolved in water. In the past, large-scale land subsidence has occurred due to the extraction of this natural gas. Therefore, continuous and accurate monitoring for subsidence using satellite remote sensing is essential to prevent any extreme subsidence events, particularly in urban areas, and ensure the safety of residences. In this study, we adopted the small baseline subset (SBAS) method to understand the subsidence trend. We used Advanced Land Observing Satellite (ALOS)-2 Phased Array type L-band Synthetic Aperture Radar (PALSAR-2) data from 2015 to 2019 for this purpose. The results show that the maximum displacement around the Kujyukuri area is more than 10 mm/year and the mean displacement rate for 2015 to 2019 is -1.4 ± 3.2 mm/year; this value is not as large as some obtained with past PALSAR observations. Comparison of our results with PALSAR observations shows that the number of distributed targets is fewer and the root mean square error of each time-series displacement value is larger. Further quantitative analysis is required to discuss the reliability of the SBAS-derived displacement rates by PALSAR-2.
Highlights
In the Kanto region of Japan, a large quantity of natural gas can be found dissolved in brine water, distributed widely across the region
Almost no displacement was observed around the coast of the Tokyo Bay, while obvious displacement was observed around the Kujyukuri area (Figure 5)
The displacement rates for this area, derived from Phased Array type L-band Synthetic Aperture Radar (PALSAR) data for 2006 to 2010, were -3.3 ± 5.8 mm/year. This implies that recent displacement has been less than half that of ten years ago, and the deviation from the mean value is less, more than -10 mm/year of displacement velocity is seen around cities of Yachimata and Oamishirasato from PALSAR-2
Summary
In the Kanto region of Japan, a large quantity of natural gas can be found dissolved in brine water, distributed widely across the region. The extraction of this water has caused land subsidence in the past. Since the 1930s, gas production activities have been undertaken by private companies. The large-scale production of gas and iodine began in the mid-1950s in the Kujyukuri area of Kanto region. As a consequence, began to occur in the 1960s and serious land subsidence surveys was initiated at the end of the 1960s. For sustainability with respect to development, in urban areas, understand land deformation trends as a consequence of human action is vital
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